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EFFECTS OF THE AGGREGATION NYMPHAL
PHEROMONE BLEND (NPB) ON THE GREGARIOUS
ADULTS OF Schistocerca gregaria (Forskal).
(ACRIDIDAE: ORTHOPTERA)
By
TAGHREED ABDEL SALAM FAGEER
B. SC (AGRIC) HONOURS
UNIVERSITY OF KHARTOUM
SUDAN 1996
A thesis submitted in partial fulfillment of the requirements
For the degree of Master of Science in agriculture
FACULTY OF AGRICULTURE
UNIVERSITY OF KHARTOUM
2004
DEDICATION
To the soul of my beloved father
, may ALLAH Put Mercy on him,
I dedicate this study.
AKNOWLEDGEMENT
My sincere thanks and deep gratitude's goes to my patient
supervisor, Dr. Magzoub Omar Bashir, for his keen interest, critical
supervision and great technical and moral support.
Thanks are due to ICIPE and particularly to Portsudan field station
staff for their great practical support and friendly company during the
course of this study. Special thank are due to Dr. Sidi Ould Ely
I am indebted to my family especially to my uncle, Mr. Sharafal deen
Abbadi, and to my dear husband, Dr. Osama SidAhmed, for the support
and encouragement they provide was the driving force to initiate and
accomplish this study.
Thanks are also extended to all colleagues at Portsudan, for their
different helpful and valuable support during the practical stages,
statistical analysis and typing of the manuscripts and the final copies.
Above all, I render my thanks and praise to almighty ALLAH for the
mercy and giving's which enabled me to come out with this study.
ABSTRACT
This study was carried out to examine the effects of the nymphal
pheromone blend (NPB) on some biological activities of the adults' gregarious
desert locust Schistocerca gregaria. 0.01% synthetic nymphal aggregation
pheromone blend + anti-oxidant were used. Two control groups were
conducted, one with carrier (shell oil+ anti-oxidant), the other without any
treatment. The experiments were carried out under laboratory conditions (Max
temp 35.2oC, Min. 25.9oC, Rh 37 %).
Fully mature adults of mixed sexes were treated to reveal if there are any
differences in the insects circadian rhythm (feeding- moving- roosting), in
presence of the NPB. The result shows that there is no significant difference
between control and treated groups.
The effect of the NPB on feeding rates was also examined. The
gregarious adult insects were fed on a weighted amount of fresh millet; the
consumed and assimilated dry and wet food was calculated at the end. No
significant differences between treated and control groups were found.
Maturation of newly moulted gregarious immature males and females was
investigated by monitoring colour change, sexual activities and oviposition.
Onset of pairing was significantly delayed in adults treated with NPB.
Regarding colour change there was significant difference between the
untreated control and oil control and between the untreated control and the
pheromone treated groups. There was no significant difference between the
two sexes in the oil treated and pheromone treated groups.
Pre oviposition period, Fecundity and oviposition behaviour were
examined. It is clear that the NPB had an effect on fecundity. Females exposed
to the pheromone produced significantly few egg pods compared to the
untreated control; also the oil control produced few egg pods which mean that
the oil has an effect. A significantly high number of egg pods were scattered
by the treated females.
The NPB seemed to have no significant effect on the longevity and life span of
adult males and females.
Accordingly it was clear that the NPB has just affected the reproductive
physiology of the gregarious desert locust Schistocerca gregaria, so the
pheromone can be utilized in the control of desert locust through affecting the
synchronization of maturation of adults and increasing the number of scattered
egg pods.
LIST OF CONTENTS
Pa
ge
DEDICATION …………………………………………….........................I
ACKNOWLEDGMENT …………………………………………………
II
ABSTRACT (ENGLISH)…………………………………………..
……III ABSTRACT
(ARABIC)…………………………………………………..V
LIST OF CONTENTS
…………………………………………………...VI
LIST OF TABLES ……………………………………………………..
..X
LIST OF FIGURES
…………………………………………………….XI
INTRODUCTION
………………………………………………….…....1
LITERATURE
REVIEW…………………………………………...…...6
1 The desert locust distribution
…………………………………….……...6
2 Phase transformation
…………………………………………………….7
3 Life cycle
……………………………………………………….…...….10
3.1 Nymphal stages
……………………………………………..…11
3.2 Immature adults
……………………………………………….12
3.3 Mature adults
……………………………………….………....12
4 Swarms formation
…………………………………………….……......15
5 Importance of the desert locust
………………………………….…......16
6 Communications in the desert locust
…………………………….….....17
6.1 Insect communication
………………………………………...17
6.2 Pheromone in the desert locust
………………………...….….19
6.2.1 Aggregation pheromone in Schistocerca
gregaria…...20
6.2.2 Maturation synchronization pheromone
……….…….…24
6.2.3 Communal oviposition pheromone
…………………......26
6.2.4 Sex pheromone
……………………………….………....27
7 Locust control
………………………………………………….….….…..28
7.1 Traditional methods
…………………………………….……..…28
7.2 Chemical control …………………………………………
.…...29
7.3 Biological control
…………………………………………….….32
7.3.1 Parasitoids and predators
…………………………….….32
7.3.2 Viruses
……………………………………………….….32
7.3.3 Bacteria
…………………………………………….…....33
7.3.4 Protozoa
…………………………………………….…...33
7.3.5 Nematodes
……………………………………..………..34
7.3.6 Fungi
……………………………………………….…...34
7.4 Botanical control
………………………………………….……..36
7.5 Insect growth regulators
………………………………………....37
7.6 Juvenile pheromone analogues
……………………………….….38
7.7 Semiochemicals
………………………………………….………39
MATERIAL AND
METHODS……………………………….…………...42
1 The experimental insects
……………………………………….…….…...42
2 The experimental cages
………………………………………….…….….42
3 The pheromone and the oil carrier
………………………………….….…43
4 The experiments
………………………………………………………..…43
4.1 The effect of the NPB on circadian rhythm
…………………..….43
4.2 The effect of the NPB on feeding rates
………………….………44
4.3 The effect of the NPB on the onset of maturation
………….……45
4.4 The effect of the NPB on fecundity and oviposition behaviour.
...46
4.5 The effect of the NPB on male and female longevity
……….…..47
5 Data analysis
……………………………………………….……………47
RESULTS
……………………………………………………….………..48
1 Effect of NPB on circadian rhythm
……………………………………48
2 Effect of NPB on the feeding rates
……………………………….……..51
3 Effect of NPB on the maturation
…………………………………….….54
4 The effect of NPB on fecundity and oviposition behaviour
…………….57
5 The effect of NPB on longevity
…………………………………………57
DISCUSSION
…………………………………………………..………..62
REFFERANCES
………………………………………….………..…....66
SUMMARY…………………………………………………...….
……....87
Appendices
……………………………………………………..……92
LIST OF TABLES
Page
Table
1-A. Activity of the DL gregarious adults exposed to the nymphal
pheromone blend(NPB) during 6 : 00 am to 10 : 00 am. ……………..49
1-B. Activity of the DL gregarious adults exposed to the nymphal
pheromone blend (NPB) during 11 : 00 am to 3 : 00 pm. …………… .49
1-C. Activity of the DL gregarious adults exposed to the nymphal
pheromone blend (NPB) during 3 : 00 pm to 6 : 00 pm………………49
2.
Effect of the nymphal pheromone blend (NPB) on the feeding
rates of DL fledglings. ………………………………………………..52
3.
Effect of the nymphal pheromone blend (NPB) on the
maturation of DL fledglings. ……………………………………..….55
4.
Effect of the nymphal pheromone blend (NPB) on the
fecundity and oviposition behavior of DL female. …………..….…...58
5.
Effect of the nymphal pheromone blend (NPB) on the
longivity of DL fledglings. ………………………………….………60
LIST OF FIGURES
Figure
Page
1.A Activity of the DL gregarious adults during 6 : 00 am
to 10 : 00 am exposed to the nymphal pheromone blend
(NPB). ………………………………………………………………….50
1.B
Activity of the DL gregarious adults during 11 : 00 am
to 3 : 00 pm exposed to the nymphal pheromone blend
(NPB) …………………………………………………………………50.
1.C
Activity of the DL gregarious adults during 3 : 00 pm
to 6 : 00 pm exposed to the nymphal pheromone blend
(NPB) …………………………………………………………………50.
2
Food consumption and assimilation rates of DL gregarious
fledglings exposed to NPB……………………………………………53
3.A
Effect of the NPB on the maturation colour change of the
gregarious fledglings of the DL. ………………………………………56
3.B Effect of the NPB on the onset of mating of the gregarious
fledglings of DL. ………………………………………………………56
3.C
Effect of the NPB on the preoviposition period of the
gregarious females of the DL………………………………………….56
4.
Effect of the NPB on the fecundity and oviposition
behaviour of gregarious fledglings of the DL. ………………………..59
5.
Effect of the NPB on the longevity of the DL fledglings. ……….……61
INTRODUCTION
The desert locust Schistocerca gregaria (Forskal), is a
short horned grasshopper, belonging to the family Acrididae,
order Orthoptera. It is an important agricultural pest due to its
polyphagus feeding behaviour and its mobility, which enables
it to migrate long distances .The individual of this insects can
consume food equivalent to its own weight (1.5-3g of
vegetation daily). (Meinzingen, 1993).
The desert locust has a vast invasion area covering
about 20% of the total land surface of the world, affecting 57
countries in Africa and Asia.
Sudan is an important breeding area of the desert locust.
Breeding in Sudan takes place in summer, winter and spring.
From Sudan invasion spread to the inner parts of the country
and also to the neighboring countries.
Locusts are hemimetabolic insects that exhibit phase polymorphism and are
able to transform reversibly between two extreme phases. These two phases are
solitaria and gregaria that differ in physiology, biochemistry, behavior, pigmentation
and morphology (Uvarov, 1966).
Gregarization is predicated on locusts density which may be promoted by a
variety of environmental and biotic factors, including convergent winds, habitat
topologies, improved rains, distribution of food plants and oviposition sites (Kennedy,
1939; Roffey and Popov , 1968 ; Uvarov , 1977) .
Several mediating factors have been implicated in the phase dynamics of S.
gregaria including visual (Ellis and Pearce, 1962), tactile (Ellis, 1962), chemical
(Nolte, 1963; Gillette. 1968), auditory (Culmsee, 1997) and the previous phase history
of the locusts (Michel, 1980).
The gregarious phase is characterized by a highly cohesive behavior, long
distance migratory aptitude, polyphagy, synchronous and accelerated maturation of
males and females and mass egg laying by gravid females in common sites
(Steedman, 1988). It is this remarkable set of characters of gregarious phase that make
the desert locust such a devastating pest of agricultural crops, pastural land and other
natural vegetation. Accordingly the control strategy directed towards the gregarious
phase and in the same time keeping the population in the solitary phase down,
preventing population builds up and swarms formation.
The control strategy against the desert locust on regional and
international basis is a preventive strategy, which depends mainly on
application of chemical pesticides. This strategy proved to be highly
effective, however it affects a wide range of non-target organisms. These
include insects, birds, livestock and wild life. The pesticides also
constitute a risk to human and life environment integrity (Evert, 1990).
The current preventive control strategy needs to be revised. There is a strong drive to move from an emergency control,
when the locust has already become a problematic swarm to a long – term management within the known pillars of an IPM
approach which is environment friendly and biorational.
The new alternative methods are based on adequate knowledge and understanding of factors associated with gregarization of
solitarious locusts (physiology, behavior and chemical ecology). These alternative methods are meant to overcome largely
the shortcoming of the orthodox approaches. Of the alternative approach semiochemicals play an important role in regulating
the behaviour of the insect and its communication systems. They can provide information about the location of food, hosts,
mates or ovipositor sites. They may control behavior such as mating, aggregation, feeding and alarm. They can initiate
specific physiological and behavioral shifts in the gregarious phase.
Insect pheromones are the most widely researched group of semiochemicals.
The pheromone system of the gregarious desert locust is a complex of volatiles
emitted by different developmental stages, sexes of the insect and their waste products
(Ofori et al., 1993, 1994 a, b). These were first recognized by Nolte (1963) and later
confirmed by Gillette (1968,).
The pheromone system is crucial for initiating gregarization and sustaining
cohision, in nymphs and adults. It also accelerates; synchronizes sexual maturation;
stimulates and concentrates egg- laying within a common area. (Ofori et al., 1993,
1994 a,b; Torto et al.,1994; 1996; 1999 Njagi et al.,1996; Mahamat et al.,1993; Assad
et al.,1997b; Saini et al.,1995; Bashir et al.,2000).
There are two sets of releaser pheromone systems; a juvenile aggregation
pheromone produced by nymphs and specific to nymphal stages and an adult
pheromone produced by older adult males and specific to the adult stage (Ofori et al. ,
1993 ).
This study is intended to examine the effect of the nymphal
pheromone blend on gregarious adults through monitoring sum selected
biological activities such as:
(1) Circadian rhythm.
(2) Feeding rate (food consumption).
(3) Effect on maturation rate
(4) Effect on fecundity and oviposition behaviour.
(5) Effect on male and female longevity.
The study is conducted at the premises of the International Centre
of Insect Physiology and Ecology (ICIPE), Port Sudan field station. It is
an integral part of the ICIPE project directed towards utilizing
semiochemical as a new approach for the management of the desert
locust. The over all objective of the study is to lay the foundations for the
use of the NPB in new control tactics against the adult stage of the DL.
This could be done by exposing the adult swarm to the pheromone so as
to cause behaviour shift, which are not to the advantages of the species in
general and to the gregarious phase in particular.
LITREATURE REVIEW
1.
The Desert Locust distribution
The desert locust Schistocerca gregaria (Forskal) is the most devastating of all
the major locust species. Of all Orthopteran species, Shistocerca gregaria has the
largest distribution area. This occurs mainly in semi desert and short grass Savannah.
It threatens agricultural crops in many parts in north and central Africa, the Near East
and Southwest Asia (Uvarov, 1977 and Steedman, 1988). These regions are
characterized by rain fall averaging between 80 and 400 mm annually, which can vary
dramatically from year to year with annual rain fall being up to 70% about or below
the average (Magor, 1994).
In the Sudan, the insect has been recorded from the Red Sea littoral and along
the central parts of the country (Maxwel-Darling, 1936; Karrar, 1972). The Sudan lies
at the heart of both the invasion and recession areas. It is mainly a summer breeding
area, though majour breeding may take place in winter at the Read Sea littoral.
◦
However, the country is subjected to infestation as far as latitude 12 N (MaxwellDarling, 1953; Karrar, 1972).
According to studies carried out by Walloff and Conners (1964) during the period
from 1937 to 1963 the desert locust swarms invaded the Sudan in 25 years and it was
the country with the highest frequency of swarms invasions.
Phase Transformation
2.
The desert locust can exist in two different phases, as scattered individuals with in the
recession area (solitary phase) or as swarms through out the invasion area (gregarious
phase) (Uvarov, 1921 and Roffey, 1982). Uvarov (1966 and 1977) blieves that by
passing through transient stages, the desert locust S. gregaria convert between these
two extreme phases.
Although phase dynamics is predicted on locust density (Roffey and Popov, 1968;
Pener, 1991) a number of mediating factors have also been implicated, including
visual (Ellis and Pearce, 1962); tactile (Ellis, 1962) and chemical stimuli (Gillette,
1968). Moreover, dietary factors (Culmsee, 1997); previous phase history (HunterJones, 1958; Michel, 1980) and interaction with other species (Gillette, 1968) have
also been shown to influence phase characters.
Phase transformation also depends on other environmental factors such as temperature
(Hussain and Mathur, 1943; Wilps, 1997);
humidity (Albrecht and Lauga, 1979); convergent wind (Rainey, 1989); level of
localized rain, (Carlisle and Ellis, 1965) and topologies (Chapman, 1976).
The phase status of the desert locust has commonly been characterized on the basis of
morphometrics, which are not good phase indicator since they change slowly over
several generations (Uvarov, 1921; Hunter Jones, 1958 and Deng et al., 1996).
Body colour pattern in locust can also be used to differentiate solitary from
gregarious, (Pener, 1967 and 1991; Norris, 1954; Steedman, 1988; Loher, 1990), Ellis
and Pearce, (1962); Roessingh et al (1993).
Roessingh and Simpson (1994) and Bouaichi et al (1995) suggested that hehaviour is
a good phase indicator and it is the first characteristic to alter when locusts experience
a variation in population density. Behavioural changes followed by a series of
associated physical and morphological changes, lead to irregular periods of mass- out
breaks separated by extended periods of recession (Uvarov, 1977).
The dynamics of behavioural phase change in individuals of the DL are subject to
periods of crowding or isolation (Roessingh and Simpson, 1994; Bouaichi et al.,
1995).
Typical green solitarious nymphs of S. gregaria behave like their gregarious
counter parts, after only a few hours of crowding, but revert quickly to soliarious
behaviour if removed from the crowd (Roessingh and Simpson, 1994). Kennedy
(1939) found swarming locust populations with typical solitarious morphometrics this
means that hehavioural transformation might occur rapidly.
Burnett (1951) said that the number of eye strips could be used as a phase marker.
Reproductive characteristics (Hunter-Jones, 1958); endocrine balance, (especially in
relation to juvenile hormone) (Ellis and Carlisle, 1961; Pener, 1991), lipid storage,
and strength of adipokinetic reaction (Scheneider et al., 1995), were also identified as
phase markers.
Mahamat et al (1991) demonstrated that the absorbency ratio of haemolymph pigment
could be used to differentiate solitary from gregarious locusts.
Solitary phase locusts live as sedentary, harmless individuals far apart from one
another (Roessingh et al., 1993) and show strong repulsive reactions to confrontation
between hoppers (Wiesel et al., 1996). The adult stages fly individually by night. In
contrast in the gregarious phase, hoppers actively aggregate forming large crowded
groups, termed as bands. Hoppers in bands have a higher locomoter activity in the
same direction (Uvarov, 1977). Likewise, adults fly together in swarms during the day
with a higher flight activity compared to solitarious one (Michel, 1980).
life cycle
3.
The desert locust like all other locusts and grasshoppers is hemimetabolous
insect, which develop gradually without under going a pupal stage and its life cycle
comprises mainly 3 stages (eggs, hoppers and adults). The time spent in each stage
varies considerably depending on the weather conditions (Steedman, 1988).
The number of eggs per pod of isolated females is higher than that of crowded
females. According to Anonymous (1982) a gregarious female usually lays 2-3 egg
pods each with about 60-80 eggs, whereas solitarious female mostly lays 3-4 egg pods
each pod containing 100-160 eggs, with egg pods laid at an interval of 7-10 days.
Also Ripper and George (1965) found that a female lays an average of 3 egg pods at
intervals of one week (minimum 3 days and maximum about 14 days).
According to Steedman (1988) the preferred oviposition sites are sandy soil, which
support the eggs to complete their development. The females find these sites by
probing with their ovipositor.
The incubation period of eggs varies according to the soil temperature. Bellow 15oC
there is no development; from 15oC to 35oC, as in the summer breeding areas, the
incubation period takes 10-14 days, but this is extended to 25-30 days in the cooler
spring and winter breeding sites (Steedman,1988). Hunter- Jones, (1964) said that
eggs need to absorb their own weight of moisture during development.
3.1. Nymphal stages
The entire hoppers from one egg pod normally start hatching on the same day.
They usually take three days for a complete hatching of
a whole egg field, but longer periods have been recorded (Uvarov, 1977 and
Anonymous, 1982).
According to Steedman (1988), the rate of instar development depends on
temperature. It varies from 22 days under hot conditions (approximately 37oC) to over
70 days under cool conditions when the temperture is about 22oC. He also mentioned
that under optimum conditions, gregarious nymphs develop faster than solitarious
ones.
Magor, (1994) clarified that hopper development varies between one to two months.
The colour of the gregarious instars is a heavy black pattern on yellow or orange back
ground and they develop through five instars, whereas the solitarious has six instars
with a uniform green colour in early instars, which may become white colour in the
last two instars (Pedgley, 1981; Anonymous, 1982; Steedman, 1988).
Immature adults
3.2.
The final moult from the last instar hopper results in the fledging adult which
dose not grow in size but gradually increases in weight (Anonymous, 1982 and
Steedman, 1988).
The immature adults of the gregarious phase are usually pinkish in colour during the
6-7 days after emerging. In both sexes the pink colour disappears and a beige or
brownish colour becomes apparent about 9-10 days after emerging (Pener, 1967). On
the other hand the immature adults of the solitarious counterparts are usually grayish
brown in both sexes (Anonymous, 1993).
Mature adults
3.3.
At this stage the sexually immature adults become mature and there is change in
their colour, behaviour and reproductive organs (Pedgley, 1981). The maturation
period of the individuals is variable, adults may become sexually mature in few weeks
or few months according to the environmental conditions. At law temperatures and
under drought conditions maturation may take as long as six months, whereas under
optimum food and weather conditions maturation occurs with in 3-4 weeks (Pener,
1967 and Steedman, 1988). Pedgley (1981) demonstrated that males usually mature
earlier than females and become bright yellow, where as females become only dull
yellow. He also confirmed that the first area to become yellow is normally the base of
the hind wings; next, the colour appears on the upper side of the near abdominal
segments, and at this stage males are usually ready to copulate. Also Steedman (1988)
mentioned that the beginning of the maturation processe can be recognized by the
disappearance of the pink colour from the hind tibiae, copuled with the deposition of
yolk in the eggs. Pener (1967) and Norris (1954) also distinguished between the
sexually immature and mature stage through colour changes. Pedgley (1981) said that
in solitarious populations the colour changes, which occur at maturation, are less
pronounced than in gregarious populations. But according to Amerasinghe (1978 a,b)
yellow colouration is not always a reliable guide to sexual maturity.
In attempt to find biochemical markers Mahamat et. al (1991) reported that the
haemolymph proteins of locusts showed distinguishable differences between
immature and mature gregarious individuals. Also the ovarian development in virgin
females was accelerated by the presence of mature males, but was unaffected by the
presence of immature adults (Richard and El Mangoury, 1968).
Mahamat et. al (1993) confirmed this observation by exposing immature females to
mature males or their abdominal extract.
Together with the appearance of the yellow colour, males start to show sexual
behaviour and the female ovaries can easily be seen when the abdomen is pulled away
from the thorax. At this time copulation take place, spermatozoa are passed into the
female’s genital organs and the eggs are fertilized. The time spent in copulation varies
from 3-14 hrs. One male can fertilize several females and the spermatozoa can be
stored inside the female’s body in the spermatheca and used to fertilized more than
one set of eggs (Pener, 1967; Uvarov, 1977; Steedman, 1988).
Once eggs are fully developed inside the female, the female can only keep them for
about three days then the eggs must be laid weather a suitable soil is available or not
(Uvarov, 1977). Within hours of the commencement of copulation the females start
searching for suitable egg laying sites (Pedgley, 1981).
The length of life of individual adults varies. Some have been kept alive in cages for
over a year, but in the field they probably live between 2.5 and 5 months. A part from
accidental death, the lifespan depends on how long they take to become sexually
mature. The quicker they mature the shorter the total length of life (Steedman, 1988).
Swarms formation
4.
Swarms formation takes place when environmental conditions are favourable
(Uvarov. 1977). Pedgley (1981) observed that swarms are so variable in structure,
density and size. The size of desert locust swarms range from less than one square
kilometer to several hundred square kilometers. A square kilometer of a medium
density swarm may contain up to 50 million insects (Steedman, 1988).
According to Pedgley (1981) gregarious Schistocerca gregaria can migrate up to
3000-4000 km.
The speed of swarm displacement depends on the wind speed and the food
availability (Pedgley, 1981 and Meinzingen, 1993). Steedman (1988) told that desert
locust swarms fly by day and settled on vegetation at night, although some times they
fly after dark.
Meinzingen (1993) said that because of their ability to migrate long distances, swarms
of desert locust could invade large areas with in a short time. Joffe (1995) mentioned
that out- breaks occur on average of one year in every six. But there is no regular
periodicity in the onset of plagues (COPR, 1982).
Importance of the desert locust
5.
Desert locust feed on a very wide range of host plants. The individual eats its
own weight of fresh vegetation every day. Locusts cause damage to host plants by
eating leaves, flowers, seeds and growing tips. They some times settle so density that
their weight break the branches of trees and plantation crops such as coffee, which
they do not eat. It has been found that 8% of the damage done is caused by hoppers,
69% by immature and maturing swarms and 23% by maturing swarms. The damage
inflected by hoppers is low because the breeding areas are mostly out side cropping
areas (Steedman, 1988).
Communication in the desert locust
6.
6.1. Insect Communication
Some members of the class insecta are characterized by different sensory modes of communication, i.e. chemical, auditory,
visual and tactile signals and combinations of them. Among all this tools the chemical communication is, no doubt, the
primary mode of information transfer in a number of species of the class insecta and exemplified in the insect world (Jutsum
and Gordon, 1989).
Karlson and Butenandt (1939) defined the pheromone as a designated
substance that is secreted by insects to the out side and cause specific
reaction in the receiving individuals of the same species.
The pheromone communication is ubiquitous and the insects pheromones
are important substances which mediate various behavioural and
biological processes in insects (Wall, 1985).
Insect pheromones have been classified in several ways by different
workers for example, Wilson (1963) classified them as releaser
substances and primer substances.
Karlson and Butenandt (1939) said that, pheromone secretion does not
need to occur in definite glands, a cuticular excretion may also be a
pheromone. Whereas Karlson and Luscher (1959) said that the
pheromone are produced in glands and transferred to individuals of the
same species at closed range or by contact.
The insects do not only synthesize the pheromone component to a high
degree of purity, by specific biosynthetic pathways, but they also
precisely control the geometrical and optical isomerism of the molecules
and ratio in which they are produced (Lofstedt and Odham, 1984).
Boppre (1978) confirmed that if the insects do not have access to a
particular type of
plants they are unable to synthesize the
pheromone.
Pheromones are perceived at extremely low concentrations through the
antennae (Slyfer et al., 1959). Some pheromones are perceived ascent by
olfactory receptors and affect the recipient via the central nervous system
(CNS). In other cases pheromones are ingested by the recipient, they may
be perceived by the sense of taste, exerting their effects via the CNS. The
ingested pheromone may be absorbed and play some parts in the
biochemical reaction with in the recipient, so discrimination between the
molecules must occur in the antennae and in certain nerves (Chapman,
1983).
Pheromones are species specific with varying response in different
species. They may exert no effect at all, or may produce different types of
behaviour in the recipient in different environmental conditions or in
different concentrations. They may also have adverse effect and may
serve to advertise the presence of an insect to their potential parasites and
predators. (Chapman, 1983).
Some times the pheromones also function as defensive substances, but in
most cases defensive substances and pheromones are quite different
(Chapman, 1983).
The sex attractants of insects are the most thoroughly investigated pheromones
(Karlson and Butenandet 1939).
6.2. Pheromones in the Desert Locust
Today there is clear evidence that a multitude of behaviour patterns and
physiological changes in locust are strongly influenced by pheromones (Francke and
Schulz, 1994). Accoding to Wilson classification (1963) two principal pheromonal
effects have been demonstrated: primer pheromones, which elicit either a
physiological or behavioural alteration, occurring after a time lag and releaser
pheromone which trigger an immediate and reversible behavioural response in the
receiver.
Two primer pheromones are implicated in gregarisation of locusts: a
primer signal that contributes to phase shift from solitary to gregarious
and another one responsible for transfer of gregarious characteristics from
parents to offspring (Heifetz.et al., 1996). The same authers also
demonstrated that chemotactile cues derived from the cuticle of
gregarious nymphs elicit significant gregarisation behaviour in isolated
nymphs. So primer pheromones effect long-term morphometric,
behavioural and genetic changes.
The mediators of phase transformation of S. gregaria are pheromones, of
which four types have been identified (gregarisation pheromone,
maturation acceleration pheromone, oviposition pheromone and sex
pheromone in solitaria). Each of these pheromones induce gregarisation
differently at different stages of the locust development (Loher, 1990 ;
Byer, 1991).
6.2.1. Aggregation Pheromone in S. gregaria
The mediation of a gregarizing pheromone was first recognized by
Nolte (1963) and later confirmed by Gillette (1968). Gillette (1968)
demonstrated that the grouping behaviour of nymphs and adults of
s.gregaria reared in visual and tactile isolation was influenced
significantly by the action of an airborne factor. Obeng-Ofori et al., 1993,
1994a,b) confirmed that agregation behaviour in the desert locust S.
gregari is mediated by a complex pheromone system released in the
volatile emissions of
Obeng-Ofori et al
different locust stages, sexes and their feces.
(1993) found that volatiles emitted by locusts
stimulate grouping behaviour in receptive individuals.
In Acrididae aggregation constitutes a highly specialized behavior
that leads to redistribution of the insect population, recolonization of old
habitats and at times, colonization of new ones (Kennedy, 1939). Torto et
al., 1994 and Obeng-Ofori et al., 1993 confirmed the existence of stage
differentiation in pheromone mediated aggregation behaviour of the
desert locust and the existence of sex differentiation in the biosynthesis of
the adult pheromone. Obeng-Ofori et al., 1993 confirmed significant
qualitative and quantitative differences in the composition of nymphal
and adult emission. They also demonstrated that the aggregation
behaviour of S. gregaria is mediated by two sets of releaser pheromone
systems, and that the nymphal stages of the locust respond only to
nymphal, volatiles, while the adults respond only to adult volatiles. The
production of the pheromone in the adult is confined predominantly to the
male (Obeng-Ofori et al., 1994a). Volatiles from solitarious and
gregarious
adult
male
D.L
S.gregaria
were
qualitatively
and
quantitatively different (Njagi et al., 1996). The adult male pheromone
could release an immediate behavioural response in the solitarious
individuals and in a prolonged encounter it could contribute towards
priming physiological transformation into the gregarious phase (Njagi et
al., 1996). Chang in emission of aggregation pheromone by adult D.L
occur rapidly in response to shift from crowded to solitary rearing
conditions or the reverse, concluding that pheromone titers are amore
sensitive measures than morphometrics to determine the onset of phase
change in the D L (Deng et al., 1996). Njagi et al (1996) suggested that
the gregarious adult male aggregation pheromone may play a role in the
arrestment and subsequent recruitment of solitarious individuals into
gregarious or gregarizing groups during the early stages of a locust
outbreak. Young adults and females of all ages produce none or trace
quantitative of the components of adult male’s pheromone and their
emission lack of any aggregation stimulus. The young adults represent an
interesting stage because they do not emit any significant pheromone
themselves and are thus not induced to aggregate significantly by their
own volatile emission. They response only to the older males pheromone
(Obeng-Ofori et al., 1993; 1994b, Torto et al., 1994). In the absence of
older males, young adults aggregate in response to guaiacol and phenol
present in their fecal volatile and those of nymphal stages with which
they associated during fledging (Oben-Ofori et al., 1994b). The chemical
emissions of the fledglings’ fecal droppings and those of the hopper
stages are compositionally similar (Hassanali and Bashir, 1999). In the
2nd, 3rd, 4th and 5th instars the nymphal stages response to one another’s
volatile and that no sexual differentiation occur either in the production of
or response to nymphal volatiles (Obeng-Ofori et al., 1993, 1994a). Thus,
the aggregation behaviour of nymphal DL appear to be modulated by
three sets of pheromonal compounds: short chain aldehydes and acids
produce by gregarious nymphs and guaiacol and phenol associated with
their fecal volatile, which act synergistically (Torto et al., 1996). Some of
the aldehydes and acids detected in the volatile of the nymphs have been
reported as plant constituents (Visser, 1986).
The nymph may synthesize the components de novo or obtaine them from
plants. Significantly, solitary nymphs reared on the same food as their
gregarious counterparts emit trace amounts of this compound, but they
are not always detectable in their volatile emissions. (Torto et al., 1996).
Previous study by (Nolte et al., 1973), had implicated nympal feces as the
source of locust gregarizing pheromone. Fecal volatile appears to be part
of the releaser pheromone complex of the D.L. It has an augmentative
role in aggregating the hoppers and older adults with an important
function of keeping young adults cohesive during the critical period when
they are transient from fledglings to full mature adults at which time they
do not produce any other aggregation factors (Obeng-Ofori et al., 1994b).
The nymphs aggregate in response not only to volatile of their own feces
but also to those of the young adults. The young and older adults were not
only responsive to their own fecal volatile but also cross responsive to
each others and that of the nymphs (Obeng-Ofori et al., 1994). (Uvarov,
1966; Steedman, 1988) suggested that fecal volatile may augment the
nymphal pheromone system in modulating cohesion in this stage of the
insect. Gillett and Philips, (1977) concluded that adult feces had the effect
of making nymphs less gregarious. This confirmed by (Gillett, 1983) who
found that solitarizing stimulus was produced by gregarious adults. Of
special interest is the finding that exposure of groups of insect of either
stages to the aggregation pheromone of the other resulted in a loss of
aggregation behaviour. In olfactometric assay similar cross-stage effects
were found between the 1st instar nymphs and the rest (Hassanali and
Bashir, 1999).
6.2.2. Maturation Synchronization Pheromone
The synchronization of maturation could lead to simultaneous
mating and facilitate communal oviposition critical for spatial and
temporal cohesiveness of the progeny (Popov, 1958; Stower et al., 1958).
Synchrony in a breeding area probably starts with the onset of
reproductive activity of scattered solitarious adults stimulated by volatile
emission of desert plants, just before the onset of seasonal rains (Carlisle
et al., 1965; Assad et al., 1997a). Richard and El Mangoury (1968)
suggested that in nature sequential retarding and acceleration promote a
high degree of maturation synchrony. Loher (1960) found that solvent
extract of mature males accelerate the maturation of the young adult
insects and he also showed that accelerated maturation in the insect could
also be induced without actual contact with the stimulant, suggesting that
a volatile pheromone was involved.
Mahamet et al., (1993) confirmed the mediation of maturation
acceleration pheromone and demonstrated conclusively that it is
associated with volatile emissions of older males, which also plays an
aggregation role in the adult stages. So two primer pheromone systems
have been implicated in the regulation of maturation in the gregarious DL
S. gregaria. These are maturation-accelerating pheromone associated
with mature adult males (Norris, 1954; Amerasinghe, 1978 a,b; Mahamet
et al., 1993), and a maturation-retarding pheromone associated with
young nymphal stages (Richard and El Mangoury, 1968; Assad et al.,
1997b). It has been suggested that the two effects operating sequentially
facilitate synchronous maturation of the entire fledgling population
(Popov, 1958; Uvarov, 1966; Richard and El Mangoury, 1968; Assad et
al., 1997b; Hassanali and Torto, 1999). Amerasingh,(1978 a,b),
confirmed the presence of a maturation acceleration pheromone in mature
male extracts. He concluded that the signal did not appear to be very
effective in inducing yellowing, nor to be consistent in initiating the
vibration reaction in immature males.
Mahamat et al., (1993) confirmed that yellowing represent a convenient
indicator of maturation, and showed that casual contact with mature
males or exposure for short period would not elicit a similar response.
6.2.3. Communal Oviposition Pheromone
Norris, (1963) found that both visual and chemical cues were
important in aggregating females to common egg-laying sites. He
reported that exuviae from Locusta migratoria were attractive to
ovipositing females of S. gregaria but also to a lesser extent than those
from conspecific locusts. So the oviposition aggregation pheromone was
at least partially species specific. (Lauga and Hatle, 1978) showed that
females of L. migratoria were strongly attracted over a distance of 0.5 m
to sand into which gregarious females had laid egg-pods.
Group egg laying behaviour is mediated by several sets of pheromones,
first a signal emitted by ovipositing female that have found suitable egglaying sites, a second associated with the egg froth of gregarious females
(Saini et al., 1995) and a third signal present in the sand into which
oviposition by gregarious females took place (Torto et.al.,1999).
Thus, gregarious phase of S. gregaria females invest heavily in ensuring
that the eggs that are laid and hoppers that emerge are within close
proximity of one another.
An unidentified primer signal is also associated with the gregarious
oviposition sites, which predisposes the off-spring including those from
solitarious
eggs
to
emerge
more
gregarious,
thus
affecting
transgenerational transfer and accumulation of phase characters (Lauga
and Hatle, 1978; Bouachi, et al 1995). Bashir, et al (2000) found that a
releaser kairomone from specific desert plants is preferred for egg laying.
Clustered eggs lying by solitarious females promote forced togetherness
of hoppers. They also found that pods originating from gregarious
females are most attractive to solitarious females to lay near.
6.2.4. Sex Pheromone
Mate finding, recognition and copulation are essential steps in
successful reproduction. Mate finding in high- density populations of
gregarious locusts is probably accomplished by random encounters. The
bright yellow body colour of the males and females and release of
aggregation pheromone by the adults serve as effective means of bringing
the mates together and assist in their mutual recognition (Obeng-Ofori, et
al., 1993; 1994). In contrast, males and female of solitarious desert locust
are similar in colour and their population densities can be extremely law
(<5/ha) (Uvarov, 1977
The attraction of the solitarious males toward the females in the absence
of visual and acoustic cues affirms the presence of a volatile sex
pheromone released by the females (Inayatullah et al., 1994). Sex
pheromone have been reported in other Orthopteroids (Jacopson, 1972)
and in several acridids ( Otte, 1970).
7.
Locust control
Steedman (1988), mentioned that locusts can be controlled at all stages of their life cycle through a variety of methods
and equipment, both from the ground and from the air. The choice between these methods will depend upon several factors such
as environment, farming system, locust population, national technical capabilities and availability of equipments.
7.1. Traditional methods
Many traditional methods of locust control have been applied in the past such as, heating, burning, trenching, harrowing and
tilling. (Duranton et al., 1987)
Chemical control
7.2.
The current methods to control locust are mainly based on application of toxic chemicals. However chemical control of
locusts and grasshoppers plagues is expensive and environmentally damaging (Raina, 1992 and Bateman et al 1993). Showler
(1995), said that, basically there are three approaches to locust control, preventive, proactive and reactive.
Chara (1997) mentioned that control measures against the desert locust can be based on two possible strategies, preventive and
reactive. The current locust control is claimed to be a preventive one, which during upsurges changes into a plague containment
and eventually to a crop protection or plague elimination efforts (Symmons, 1992).
Chara (1997) explained that preventive control entails permanent monitoring of the potential gregarization areas and the rapid
destruction of primary target if possible before gregarization begins. Lecoq et al (1997) said that one could reasonably assume
that preventive control has played positive role in preventing the return of major invasion of locusts, since it was first put into
practice in the 1960s. Lecoq et al (1997) and van Huis (1992) demonstrated that the preventive strategies relied to a great extent
on the use of chlorinated hydrocarbons and it was considered appropriate when used in conjunction with the dieldrin, the
persistence of which, permitted successful barrier treatment.
Since 1958, Dieldrin has been progressively withdrawn from the market for locust control because of its possible risk to
the environment, persistence and bioaccumulation (Launois and Rachadi, 1997).
With dieldrin no longer available replacement acridicides such as Organophosphates (Malathion and Diazinon), Carbamates
(Bendiocarb) and synthetic pyrethroids (Deltamethrin or Decis and Cybermethrin) or combination of these have been used for the
control of locusts (Menzingen, 1997; van Huis, 1997).
Chemical control of locust in South Africa today became pyrethroid driven with Deltamethrin and playing a leading role (Brawn
and Kisser, 1997).
These conventional chemicals are actually applied or offered to the locust control in one of three forms, baits, dust or spraying.
The most common locust control technique is drift spraying. This technique requires the use of specialized equipment and the use
of ultra law volume (ULV) formulation that can be applied either by air craft or by ground spray equipment (Menzingen, 1993
and Symmons, 1992).
Symmons (1992, 1997) observed that swarm spraying has been argued to be more efficient than hopper control and van Huis
(1997) claimed that swarm spraying is the only feasible method to achieving general population reduction. Steedman (1988) said
that most experts agree that the early hopper stage is the most vulnerable, whereas adult swarms are very mobile and they are
successfully controlled only by spraying from aircraft.
According to Food and Agriculture Organization of the United Nations (FAO) sources, in 1986-1989, 26 million hectares of
locust infestation areas were treated approximately by 16 million liters of liquid and 14 million kilograms of dust pesticides
(Meinzingen, 1997). Krall (1994); Joffee (1995) pointed out that millions of dollars are spent on preventive control measures
every year.
Recent concerns over possible human health problems and environmental damage resulting from the large scale application of
chemical pesticides for locust and grasshopper control, as well as doubts about their efficacy (Anon, 1990; Joffee, 1995), have
lead to proposal for alternative strategies (Rowley and Bennet, 1993). The proposed alternative strategy is preventive,
environmentally friendly and sustainable one; its focus is on pregregarious locust, and its goal is to keep locusts permanently
solitarious, through implementation of integrated pest management tactics (El Bashir, 1997).
Biological control
Parasitoids and predators
7.3.1.
7.3.
Locusts are attacked by natural enemies during all their developmental stages (COPR, 1982; Steedman, 1990). Various
authors have reviewed the potential of these natural enemies for use in biological control of locusts (Prior and Greathead, 1989;
Greathead, 1992, van Huis, 1992 and Greathead et al, 1994). They have generally agreed that parasitoids and predators are not
able to prevent locust outbreaks even those, which are specialized to some extent on locusts.
Mass production and releasing even the smallest parasitoids is too costly
and often nightmare (Kooyman, 1999).
Viruses 7.3.2.
A number of viruses have been isolated from locusts and
grasshoppers; the majority of which belong to the group of Entomopox
Viruses (EPV) (Greathead et al., 1994). These viruses seem to be safe for
wide spread application, they are not highly virulent and debilitate rather
than kill their host (Kooyman.1999). Acording to Greathead (1992)
another virus group known as crystalline array viruses (CAV), created
some interest as a biological control agent but as it was found to be too
close to Picornaviruses of vertebrates therefore research on it was
terminated.
Bacteria 7.3.3.
Serratia marcescens and Pseudomonas aeruginosa are the two
species of bacteria that infect locust, especially in breeding colonies
(Kooyman, 1999). Attempt to control locust by applying these bacteria
have failed (Zelazny et al., 1997) due to the low pH of the locust that
prevents dissolution of the toxin crystals (Prior and Greathead, 1989).
Protozoa 7.3.4.
Protozoa infecting locusts and grasshoppers are known from the
phyla Rhizopoda, Apicomplexa, Ciliophora and Microspora (Kooyman,
1999). The most virulent species, with potential for use in biological
control belongs to the genera Nosema and Johenrea (Microspora),
(Johnson, 1997).
Nosema locustae was found in the population of S.gregaria in Red Sea
coastal area of Sudan( Tokar Delta ) ( El Bashir et al., 1992)
Nematodes 7.3.5.
Under natural conditions it is not uncommon to find grasshoppers infected by nematodes of the family Mermithidae
(Enoplida), although rates of infection in Africa seem to be much lower than other countries (Kooyman, 1999). Finny (1981)
reported that the prospects of using mermethoids for biological control were limited, because no mass rearing technique had
been developed. He showed that Nematodes in biological control usually belong to the families Heterorhabditidae and
Steinernematidae (Rhabditida).
Nematodes can be integrated with an insect hormonal treatment or another pathogen
to debilitate the host and favour parasitism, and also with insecticides having no
adverse effects on the nematodes (Finny, 1981).
Fungi 7.3.6.
At the moment entomopathogenic fungi are the most interesting and important
pathogen of locusts and grasshoppers receiving considerable attention for biological
control of these insects Prior and Greathead (1989)
The species Metarhizium flavoviride(Gam and Rozsypal), Metarhizium anaisopliae (Metschnikoff, Sorokin) and Beauveria
bassiana are studied intensively with respect to the development of biopreparation (Zimmermann et al., 1994). Fungi of these
genera are commonly found infecting locusts and grasshoppers in nature (Kooyman, 1999).
High (>90%) insect mortality has been demonstrated in the field following the application of oil-based formulation, with ultra
law volume spraying equipment normally used for acridid conrtrol (Bateman, 1997), and he also said that like many other
pathogenic fungi Metarhizium-conidia infect by attaching to the insect cuticle (exocuticle).
Bateman et al., (1996) said that LUBILOSA program, (Lutte Biologique contre les Locustes et les sauteriaux) has know
identified more than 30 highly virulent isolates of Metarhizium from Acridoidae hosts.
Bateman (1997) said that an African fungal isolate of Metarhizium was developed and ready for commercial use any where in
Africa and Middle East.
Amore comprehensive description of the fungus Sorosporella is given by Welling et al., 1995. Although the bioassay in the
laboratory did not reveal clear results, the fungus seem to have a high virulence to locusts in its nature habitat (Welling and
Zimmerman, 1997).
Botanical control 7.4.
In search of a soft chemistry for desert locust control, botanical
insecticides have been shown to be highly effective on locusts and are
non- toxic to mammals and birds (Rembold, 1997) and epigeal arthropods
(Peveling et al., 1994).
Biologically interesting limonoids (Terpenoids) have been identified in
tropical Meliaceae, like Azadirachta indica (Neem) and Melia volkensii
(Mwangi et al., 1997;Rembold, 1997)
Wilps and Nasseh (1994) and Peveling et al.(1994)
indicated that
Meliaccea extract is even found to be more effective than Azadirachtin.
According to Wilps et al
(1993) meliaccea extract exhibits a dose
dependent effect against S. gregaria.
The above-mentioned extracts give repellent effect and act as an antifeedant agent (Rembold, 1997).
Indications of reduced physical fitness in desert locusts were reported
(Nasseh et al., 1993, Rembold, 1997); retarded development and growth
inhibiting in nymphs of S. gregaria and shifting phase to solitary status
was also noticed by (Rembold, 1997); delay in attainment of sexual
maturity (Nasseh et al,1993; Rembold,1997); reduced fecundity (Wilps
and Nasseh,1994) and malformation and morphogenetic defects (Wilps
and Nasseh,1994) were observed when the insect was exposed to the
previously mentioned products .
Up to now natural products have not entered the commercial pesticide
market (Rembold, 1997).
Insect growth regulators 7.5.
Recent research has confirmed the potential of insect growth
regulators such as teflubenzuron, triflumuron and diflubenzuron which
belong to the chemical class of benzoyl phenylureas (BPUS)
(Meinzingen, 1997; Peveling et al., 1997).
The benzoyl phenylureas (BPUS) discovered in 1970s were initially classified as
chitin synthesis inhibitors (Meinzingen, 1997; Peveling et al., 1997) and then later as
insect growth regulators (Wilps and Nasseh, 1994; Scherer and Celestin, 1997). The
products have been tested with good results for the control of hopper bands (Scherer
and Celestin, 1997). IGRs are suitable products for the prevention of locust outbreak.
However they are not suitable for direct crop protection because of their slaw action
(Meinzengen, 1997). IGRs also have great persistence and are suitable for barrier
spraying (Peveling et al., 1997;Wilps and Nasseh, 1994), and their mode of action is
through ingestion and contact (Meinzengen, 1997).
Reduced fecundity was noticed when female adults were fed on treated diet of both
chlorfluazuron and teflubenzuron (Metwally et al., 1991)
This agent entered the control of desert locust in the 1990s, although little
knowledge existed about side effects on non-targets in semi-arid and arid ecosystems
(Peveling et al., 1997), and its mode of action is still unknown (Wilps and Nasseh,
1994).
Juvenile hormone analoges
7.6.
Juvenile hormone analoges (JHAs) are a group of highly selective substances.
They occur naturally in certain plants (Toong et al., 1988), and probably serving as
defense chemical substances against insects, but are also accessible to chemical
synthesis (Dorn, et al., 1997)
Laboratory tests have shown that a variety of JHAs including Fenoxycarb applied to
the last instar larvae increased mortality, induced morphogenetic defects during
metamorphosis, reduced fertility and provoked solitarization of gregarious hoppers
(Pener, 1991 and Dorn et al., 1997). Dorn et al., 1997, confirmed that field trials were
quite comparable to those obtained in the laboratory, and said that Fenoxycarb has
already gained commercial importance.
Semiochemicals 7.7.
Semiochemicals are a non- toxic, behaviour modifying compounds, which are
not known to have significant negative environmental impact (El Bashir, 1997). These
play an important role in regulating behaviour of insects and their communication
systems. They provide information about the location of food, host, mates or
oviposition sites. They may control behaviour such as mating, aggregation, feeding
and alarm; or they can initiate specific physiological and behavioural transformations
in certain organisms (Saini, 1991).
Semiochemicals open up new avenues for innovative tactics to be integrated with
other environment friendly methods. These tactics would be based on a good
understanding of locust biology, behaviour and ecology as well as the application of
the IPM (El Bashir, 1997).
Although semiochemicals have been successfully used in the field for the
management of some pests, they are not generally considered to be sufficiently robust
in their action to be used alone (Smart et al., 1994). They are less persistent than most
pest control chemicals hence they have to be repeatedly applied to achieve
satisfactory pest control (Griffiths, 1990).
In case of DL, semiochemicals are chemical signals which stimulate and synchronize
various vital process associated with changes of phase status
(El Bashir, 1991).
Recent studies on the chemical ecology of the DL S. gregaria have unraveled a rich
and
complex
system
of
pheromonal
and
other
semiochemical
mediated
communication in this insect (Hassanali and Bashir, 1999 and Saini, 1991). The
pheromone associated with such behavioural processes are better understood (Obeng-
Ofori et al., 1993, 1994a,b Saini et al., 1995; El Bashir, 1997; Torto et al., 1999;
Bashir et al., 2000).
The main objective of this new alternative strategy is to keep locust permanently
solitarious since solitary locust are harmless and may even have a beneficial role in
the ecosystem. Its also envisages that, development of the locust into the gregarious
phase may be prevented by the disruption of the processes of multiplication or
gregarisation (El Bashir, 1991; Hassanali and Mahamat, 1991).
Previous experiments on the applications of locust pheromones have considered the
possibility of disrupting gregarisation at critical stages of population build up and
phase transformations (Byer, 1991; Hassanali and Torto, 1999). Electrophysiological
studies have shown that the adult pheromone inhibits perception by nymphs of their
own aggregation pheromone (Ochieng, 1997). Hassanali and Bashir (1999) confirmed
that exposure of gregarious hoppers to very low concentration of the adult pheromone
in experimental cages or in the field elicit a series of abnormal behaviour in the
individuals. In cages exposure to the adult pheromone led to hyperactivity, abnormal
circadian rhythm, reduced feeding rate and increased cannibalism. Field trials based
on very large hopper bands (>100,000 insects) at two different locations in the Red
Sea breeding area have shown that the treated gregarious nymphs exhibit an
immediate arrestment of their marching behaviour. Random movement, significant
longer roosting period of the individual on vegetation and disbanding were also
noticed. The exposed insects have also shown to be susceptible to predators and to
chemical and biopesticides, even at very low doses. The most exiting finding
demonstrates that it is possible to disrupt the process of gregarization by the insects’
own communication signals and effect levels of control with this environmentally
benign agents which are comparable to conventional pesticides (Hassanali and Bashir,
1999). Those studies provide a model for other important locust species and the
frequent co- out break of some of these species suggests some overlap in their
chemical communication system (Niassy et al., 1999).
MATERIALS AND METHODS
1.
The experimental insects
The experimental insects were obtained from ICIPE, Port Sudan
field station. Both sexes of the insect were bred under crowded conditions
in standard aluminum cages (50 x 50 x 50cm). The individuals used for
the experiments were fully mature adults and newly moulted fledglings (2
– 3 days old). Fresh shoots of millet, alfa alfa and wheat bran, were
provided daily as food plants. The food provided was inserted in a cup
half filled with water to keep the plants fresh.
2.
The experimental cages
Tow types of cages were used: A wire mesh cages (50 x 50 x
50cm), and acubical cages (25x 25x 25cm) having one cardboard side
with an opening fitted with a sleeve to use for feeding and handling. The
other five sides were made of mosquito wire net. This type was used only
in experiment (8). Cages were cleaned daily and fresh food was supplied.
3.
The pheromone and the oil carrier
Synthetic nymphal agregation pheromone blend (NPB) + anti
oxidant was supplied by Dr. B.Torto. Torto et al., (1996) analyzed and
identified the component of the blend.
The required concentration of the pheromone was 0.01%. This was prepared by adding
1m of the concentrated blend to 99 ml of shell oil (shell sol – t oil 50% + ondina oil
50%) which was the carrier end solvent used in the experiment. The concentration of
the oil when used as a carrier was 0.01% prepared by adding 1ml of the shell oil +
antioxidant to 99 ml of the pure shell oil.
4.
The experiments:
4.1.
The effect of the (NPB) on circadian rhythm
The objectives of conducting this experiment was to reveal any
difference in the insects daily rhythm in the presence of (NPB).
Sixty fully mature adults of mixed sexes were divided into 3 cages one was treated
with NPB. The two others were control cages one with carrier
(oil + anti oxidant)
and the other without any treatment. 24 h r after treatment the observations and
records were carried out repeatedly every hour from 6.00 am. to 6.00 pm, i.e. 12
readings.
Careful observations were made by sitting near the cage and the number of insects, actively moving, those feeding and those
roosting (i.e. static one), were recorded. Dead insects were counted and removed from the cage. Each set of this experiment was
replicated three times (using a new groups in each replicate).
The daily mean of each activity was calculated from the observation and
analyzed. Analysis of variance was used to show if there was any
significant difference between the treatment and the controls.
4.2.
The effects of the NPB on feeding rates
This experiment was conducted to determine if there is any change
in the
feedings rate elicited by NPB on adult locusts. The tested insects were 90 newly moulted fledglings (2-3-days old) divided into 9
cages, 10 individual in each cage. The insects were fed for four days on weighed amounts of fresh millet.
The food plant was inserted in a small glass half filled with water to keep
the food fresh. A large number of weighted millet samples were dried for
24 hours at 80Cº to determine the average dry weight per gram of this
plant so that the dry weight of wet food supplied could be calculated.
The faeces, spill and the remaining uneaten plant were collected
daily and oven dried separately at 80Cº for 24 hours.
Data obtained on food intake described above were used to calculate the
utilization of the food consumed by using the following formula :
Asdry food = Condry food – dry feces
Aswet food = Asdry food / dw/G
or
Aswet food = Conwet food – wet feces
Condry food =Indry food – (Remdry food+ dry spill )
Conwet food = Condry food / dw/G
Indryfood = Inwet food xdw/ G
as dw/G was the dry weight per one gram of millet
Assdry food was the assimilated dry food
Asswet food was the assimilated wet food
Condry food was the consumed dry food
Conwet food was the consumed wet food
Indry food was the input dry food
Inwet food was the input wet food
4.3.
The effects of the NPB on the onset of maturation
Twenty newly moulted immature adult males and females (2 – 3 day old),
from the gregarious colony were exposed to NPB pheromone 0.01%. The
recipient insects were monitored daily for visual signals of maturation in
accordance with colour classification of Norris (1954). Observations were
taken daily and the date of the external colour change of each individual
was recorded. Two control cages were conducted, one with carrier (oil +
anti oxidant), and the other without any treatment. Each treatment was
replicated 3 times.
4.4.
The effect of the (NPB) on the fecundity and oviposition behaviour
Investigation of fecundity and pre-oviposition period was
carried out in the laboratory. A cage containing 20 individual
(10males + 10females) was treated with N.P.B. Two control cages
were conducted, the same as in (4-3). Each cage was provided with 5
standard aluminum oviposition tubes (12x 1x 4cm). These tubes were
filled with sieved sand.
The soil was moistened with water to give approximate moisture content
of about 10% as mentioned by Norris (1968).
The tubes were placed in holes at the front of the false floor of the
cages. Daily observation was made to determine the age of the tested
females at the oviposition of the first egg - pod. The number of egg –
pods per female was recorded. The dead females were removed daily and
the date of death was recorded. This test was replicated 3 times.
4.5.
The effects of the NPB on male and female longevity
Twenty newly fledglings, males and females (2-3-days old) were exposed to NPB.
The insects were daily inspected. The Number and percentage of dead individuals
was recorded with any observed cases of cannibalism. The observation was
extended till all individuals died. This experiment was replicated 3 times. In each
replication there was two control cages, one with the oil carrier and the other
without any treatment
5.
Data Analysis
Student t-test was used to analyze data throw statistical package of Microsoft® Excel 97.
.
RESULTS
1
Effect of NPB on circadian rhythm of mature desert locust
The effect of the N.P.B. on the activity and circadian rhythm of the
gregarious DL is summarized in tables 1-A, B,C, which represent
different times during the day.
Table 1-A and figure 1-A, reflect the result obtained at the period from 6.00 to 10.00 am and it shows that in the control group
the mean number of roosting individuals was 91.23±8.20, feeding individuals was 3.51±5.96 and moving individuals was
5.25±7.05. In the treated group 92.71±7.00 where roosting, 3.85±6.99 feeding and 3.10±4.10 moving. In the oil control group
94.67±5.70 were roosting, 2.24±4.04 feeding and 3.09±3.28 moving.
At the second period from 11.00 to 3.00 pm, the mean number of roosting
individuals in the control group was 83.88±10.37 compared to
93.78±6.50 in the treated group, the mean number of feeding individuals
was 2.73±4.26 in the control group while it was 0.64±2.16 in the treated
group and the moving
individuals was 13.39±9.67 in control group while it was 5.59±6.41 in the treated group Table 1B and Figure 1B. In the oil
control group 91.48±5.30 were roosting, 1.12±2.48 feeding and 7.40±4.30 moving.
Table 1-A. Activity of the DL gregarious adults exposed to the nymphal
pheromone blend (NPB) during 6:00 to 10:00 am.
Percent engaged in
Roosting
Feeding
Moving
91.23+(8.20)a
3.51+(5.96)a
5.25+(7.05)a
Control
Oil
94.67+(5.70)a
2.24+(4.04)a
3.09+(3.28)a
Oil +NPB
92.71+(7.00)a
3.85+(6.99)a
3.10+(4.10)a
Means with the same letter are not significantly different (P>0.05)
Treatment
Table 1-B. Activity of the DL gregarious adults exposed to the nymphal
pheromone blend (NPB) during 11:00 am to 3:00 pm.
Treatment
Control
Oil
Oil +NPB
Roosting
83.88+ (10.37)a
91.84+5.30)a
93.78+ (6.50)a
Percent engaged in
Feeding
2.73+ (4.26)a
1.12+ (2.48)a
0.64+2.16)a
Moving
13.39+ (9.67)a
7.40+ (4.30)a
5.59+ (6.41)a
Means with the same letter are not significantly different (P>0.05)
Table 1-C. Activity of the DL gregarious adults exposed to the nymphal
pheromone blend (NPB) during 3:00 to 6:00 pm.
Treatment
Percent engaged in
Roosting
Feeding
Moving
87.21+ (8.49)a
5.05+ (5.36)a 7.74+ (6.63)a
Control
Oil
95.90+ (5.24)a
2.20+ (4.30)a 1.89+ (2.77)a
Oil +NPB
92.87+ (8.71)a
1.80+ (4.33)a 5.33+ (6.88)a
Means with the same letter are not significantly different (P>0.05)
In the third period from 3.oo to 6.00 pm, as shown in Table 1C and
Figure 1C, 87.21±8.49 were roosting, 5.05±5.36 feeding and 7.74±6.63
moving in the control cages compared to 92.87±8.71 roosting, 1.80±4.33
feeding and 5.33±6.88 moving in the pheromone treated cages while in
the oil control 95.90±5.24 were roosting, 2.20±4.30 feeding and
1.89±2.77 moving.
2.
Effect of NPB on the feeding rates of the desert locust
fledglings
Table 2 and Figure 2 reflect the effect of the NPB on the feeding rates of
the fledglings D.L.
The mean weight of consumed dry food in the control group was
2.95±0.09 grams per 10 individuals while it was 2.94±0.06 grams for the
oil control and 2.94±0.07 for the treated group.
The consumed wet food was 9.45±1.28 grams per 10 individuals for the
control group and 8.83±1.49 grams for the oil control group whereas it
was 9.59±1.42 grams per 10 individuals for the pheromone treated group.
The means of the assimilated wet food was 7.91±1.18 grams per 10
individuals for the control group, 7.37±1.45 grams for the oil control
group while it was 8.07±1.29 grams for the treated group.
Table 2. Effect of the nymphal pheromone blend (NPB) on the feeding
rates of the DL fledglings.
Treatment
Control
Oil
Oil +NPB
Condryfood
2.95+(0.09)a
2.94+(0.06)a
2.94+(0.07)a
Grams per 10 individuals
Conwetfood
Asdryfood
9.45+(1.28)a
0.59+(0.24)a
8.83+(1.49)a
0.48+(0.32)a
9.59+(1.42)a
0.59+(0.26)a
Aswetfood
7.91+(1.18)a
7.37+(1.45)a
8.07+(1.29)a
Means with the same letter are not significantly different (P>0.05)
Accordingly the means of assimilated dry food was 0.59±0.24 grams per
10 individuals for the control group, 0.48±0.32 grams for the oil control
group and 0.59±0.26 grams per 10 individuals for the treated group.
3.
Effect of NPB on the maturation of the gregarious desert locust
fledglings
The effect of the NPB on the maturation time of the immature males and females
as reflected by colour change, copulation and preoviposition periods is summarized
in Table 3 and Figure 3-A, 3-B and 3-C.
The mean maturation time of males and females as assessed by colour in
the control cages was found to be 19.20±6.46 days for males and
20.69±5.66 days for females respectively. In the oil control cages it was
24.39±5.55 days for males and 25.81±6.26 for females while in the
treated group it took 27.20±12.59 days for males and 29.23±10.54 days
for females to change colour.
The onset of copulation time was 33.84±10.37 days in case of control
cages, 42.40±6.47 days in the oil control cages and 58.53±16.95 days in
the pheromone treated cages.
The mean pre-oviposition periods registered was 38.25±9.26 days in
control cages, 55.73±3.49 days in oil control cages while it was
70.40±15.99 days in the pheromone treated cages
.
Table3. Effect of the nymphal pheromone blend (NPB) on the maturation
of the DL fledglings.
Treatment
Colour change
Onset of
Preoviposition
period
Mating
Control
Male
19.20+(6.46)a
Female
20.69+(5.66)a
33.84+(10.37)a
38.25+(9.26)a
Oil
24.39+(5.55)b
25.81+(6.26)b
42.40+(6.47)a
55.73+(3.49)a
Oil +NPB
27.20+(12.59)b
29.23+(10.54)b
58.53+(16.95)b
70.40+(15.99)b
Means with the same letter are not significantly different (P>0.05)
4.
The effect of NPB on fecundity and oviposition behaviour of the gregarious
desert locust
Table 4 and Figure 4 show the effect of NPB on the fecundity and oviposition behavioure of the gregarious desert locust females.
The mean number of total egg pods in the pheromone treated cages was
1.48±0.90 pods/female compared to 3.19±1.26 pods/female in the control
cages and 1.91±0.28 pods/female in the oil control cages.
The percentage of normal pods was 69.43±30.71 % in case of the
pheromone treated group where as in the control group it was
98.89±2.46% and 95.56±9.94% in the oil control group.
The percentage of scattered egg pods in the treated group was 30.57±30.71%
compared to 1.11±2.46% in control group and 4.44±9.94% in oil control group.
5.
The effect of NPB on longevity of gregarious desert locust fledglings
Table 5 and Figure 5 show the effect of NPB on longevity of the
fledglings of gregarious DL. In the pheromone treated group the mean
survival Period of the females was 68.12±38.86 days and 73.35±35.90
days for males, whereas in the control group the females lived about
54.87±21.96 days and the males about 49.69±17.41 days. In case of the
oil control group the females survived for 67.09±26.49 days and the
males' 80.04±34.65 days.
Table 4. Effect of the nymphal pheromone blend (NPB) on the
fecundity
and oviposition behaviour of gregarious DL female.
Treatment
Control
Oil
Oil+NPB
Fecundity & state of pods
Pods/Female
%Normal pods
3.19+(1.26)a
1.91+(0.28)b
1.48+(0.90)b
98.89+(2.46)a
95.56+(9.94)a
69.43+(30.71)b
%Scattered
Eggs
1.11+(2.16)a
4.44+(9.94)a
30.57+(30.71)b
Means with the same letter are not significantly different (P>0.05)
120
% Engaged
100
80
60
Roosting
Feeding
Moving
40
20
0
-20
Control
Oil
Oil+NPB
Treatment
Figure 1 A. Activity of the DL gregarious adults during 6:00
to 10:00 am
exposed to the nymph pheromone blend (NPB)
120
% Engaged
100
80
Roosting
Feeding
Moving
60
40
20
0
-20
Control
Oil
Oil+NPB
Treatment
Figure 1 B. Activity of the DL gregarious adults during
11:00 am to
3:00 pm exposed to the nymph pheromone blend
(NPB)
100
% Engaged
80
Roosting
Feeding
Moving
60
40
20
0
-20
Control
Oil
Treatment
Oil+NPB
Figure 1 C. Activity of the DL gregarious adults during 3:00
to 6:00 pm
exposed to the nymph pheromone blend (NPB)
50
12
Gram per 10 adults
10
Cndryfood
8
Cnwetfood
6
Asdryfood
Aswetfood
4
2
0
Control
Oil
NPB
Treatment
Figure 2. Food consumption and assimilation rates of DL
gregarious
fledglings exposed to NPB
Days from fledging
53
45
40
35
30
25
20
Male
Female
15
10
5
0
Control
Oil
NPB
Treatment
Figure 3 A. Effect of the NPB on the maturation colour change of
gregarious fledglings of the DL
80
Days from fledging
70
60
50
40
AVR
30
20
10
0
Control
Oil
NPB
Treatment
Figure 3-B. Effect of the NPB on the onset of mating of the gregarious
fledglings of the DL
Days from fledging
100
90
80
70
60
50
40
30
20
10
0
AVR
Control
Oil
NPB
Treatment
Figure 3-C. Effect of the NPB on the preoviposition period of the
gregarious females of the DL
56
Pod/female
%Scattered pods
%Normal Pods
5.00
120.00
100.00
80.00
3.00
60.00
2.00
Percent
Pods per female
4.00
40.00
1.00
20.00
0.00
0.00
Control
Oil
Oil+NPB
Treatment
Figure 4. Effect of the NPB on the fecundity and oviposition behaviour of
gregarious fledglings of the DL
59
140
120
Gram per 10 adults
100
80
female
male
60
40
20
0
Control
Oil
Oil+NPB
Treatment
Figure 5. Effect of the NPB on the longevity of the DL fledglings
61
Table 5. Effect of the nymphal pheromone blend on the Longevity of the
DL fledglings.
Treatment
Mean longevity
Female
Male
Control
54.87+(21.96)a
49.69+(17.40)a
Oil
67.08+(26.49)a
80.04+(34.65)a
Oil +NPB
68.12+(38.86)a
73.35+(35.90)a
Means with the same letter are not significantly different (P>0.05)
DISCUSSION
This study is directed towards investigations that could lead to utilizing
semiochemicals as a new approach for the management of the Desert Locust and
establishing their respective roles in phase transformation through the effect of the
nymph pheromone blend (NPB) on different activities of the adult gregarious phase.
The study confirmed the maturation-retarding effect of the NPB on the
immature adults (Norris 1954, 1964; Richard and El Mangoury, 1968;
Assad et.al., 1997).
Taking the colour change as a parameter of onset of maturation, there was no
significant difference between sexes. However, there was a significant difference in
the onset of colour change between those treated with NPB and the control group at
p> 0.05. Also there was a significant difference between the control group and the oil
control group where the individuals in the control group changed colour earlier, so it
appears that the oil has some effect (Table 3 and Figure 3-A, 3-B and 3-C). This
confirms that the pheromone signal is not very effective in inducing yellowing and
that yellowing is not always a reliable guide to sexual maturity (Amerasingh, 1978 a,
b).
However, it differs from the result obtained by Mohamat et.al (1993) who
distinquished between sexualy mature and immature stages through colour change.
The onset of mating time and preoviposition period were
significantly prolonged on exposure to the NPB. Delay in maturation of
the males is a delay in the production of the adult phormone (Mahamat
et.al 1993 and Obeng-Ofori, 1994b), and since the adult phormone is both
an aggregating signal in the adult and maturation accelerant for 0the
immature males and females (Mahamat et.al., 1993), a delay in it`s
production means a further delay in the maturation of the earlier fledges.
This affects the synchronization of maturation of adults and group
oviposition at common egg laying fields (Richard and El Mangoury 1968,
Stower et.al., 1958). There for the gregarious integrity of locust
population is not achieved or reached if exposed to the NPB.
It is also noticed that the NPB has an effect on reducing the number of egg pods
per female compared to the control group; also there was a significant difference
between the control group and the oil control group so it appears that the oil has an
effect. The NPB significantly increased the number of scattered egg pods, (Table 4,
Figure 4). This finding is of great significance in control strategies. It opens new
avenues for the utilization of this pheromone to disrupt the reproductive physiology of
the desert locust. It remains for further field trials to determine the proper delivery
method and application rates under field conditions.
The NPB seem to have no effect on the DL circadian rhythm. The result
shows that the rhythm of caged mature adults differs from that of the
nymphs reported by Steedman (1988). Caged adults do not seem to have
a defined rhythm.
The NPB has no effect on the food consumption and assimilation and this
is reverse of the effect of the adult pheromone (PAN) on the hoppers,
which led to hyper activity, abnormal circadian rhythm, disbanding,
reduced feeding rates and increased cannibalism (Hassanali and Bashir
1999).
This study showed no significant difference or effect on longivity of
DL males and females in presence of the NPB, (Table 5, Figure 5).
According to previous studies semiochemicals have been implicated in
locust control, they are not generally considered to be strongly sufficient
to be used alone (Smart et.al., 1994), becouse they are less persistant
(Griffiths, 1990). Accordingly Hassanali and Bashir (1999) the adult
pheromone made the hopper bands more susceptible to chemical and
biopesticide even at very low doses. The level of control with this at low
dosages of biopesticides and sub lethal dosages in conjunction with these
environment benign agents are comparable to recommended dosages of
conventional pesticides. It will be more rational to examine the effect of
the NPB with sub-lethal doses of conventional pesticides and low dosages
biopesticides on the fully mature adults.
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SUMMARY
This study was carried out under laboratory conditions, (max.
temp. 35.2°C, Min. 25.9°C, Rh 37 %), to examine the effect of the
aggregation Nymph Pheromone Blend (NPB) on the gregarious adults of
the desert locust Schistocereca gregaria.
Synthetic aggregation NPB + antioxidant were dissolved in Shell
oil to give a concentration of 0.01%. Two control groups were conducted
in each experiment, one with carrier (shell oil + antioxidant) while the
other without any treatment.
The effect of the NPB on activity and circadian rhythm of the
mature gregarious adults of mixed sexes were tested. Observation and
records were carried out repeatedly every hour from 6.00 am to 6.00 pm
(i.e. 12 readings). At the period from 6.00 to 10.00 am the mean number
of roosting individuals was 91.23±8.20 in the control group and
92.71±7.00 in the pheromone treated group and 94.67±5.70 in the oil
control group. Whereas the mean number of feeding individuals was
3.51±5.96 in the control group and 3.85±6.99 in the pheromone treated
group and 2.24±4.04 in the oil control group. The mean number of
moving individuals was 5.25±7.05 in the control group and 3.10±4.10 in
the pheromone treated group and 3.09±3.28 in the oil control group.
The period from 11.00 to 3.00 pm showed that the mean number of
roosting individuals was 83.88±10.37 in the control group and
93.78±6.50 in the pheromone treated group, while it was 91.84±5.30 in
the oil control group. The mean number of the feeding individuals was
2.73±4.26 in the control group and 0.64±2.16 in the pheromone treated
group, while it was 1.12±2.48 in the oil control group. The mean number
of moving individuals was 13.39±9.67 in the control group and 5.59±6.41
in the pheromone treated group, while it was 7.40±4.30 in the oil control
group.
At the period from 3.00 to 6.00 pm the mean number of roosting
individuals was 87.21±8.49 in the control group and 92.87±8.71 in the
pheromone treated group, in the oil control group it was 95.90±5.24. The
mean number of feeding individuals was 5.05±5.36 in the control group
and 1.80±4.33 in the pheromone treated group, while it was 2.20±4.30 in
the oil control group. The mean number of moving individuals was
7.74±6.63 in the control group and 5.33±6.88 in the pheromone treated
group, while 1.89±2.77 in the oil control group. Analysis of this data
clarified that the NPB elicit no significant different in the circadian
rhythm of the DL.
10 mature adult males and females were fed for four days on a
weighted amount of fresh millet to examine the effect of the NPB on the
feeding rates. In the control group the consumed dry food was found to be
2.95±0.09 gram. The consumed wet food was 9.45±1.28 gram. The
assimilated dry food was 0.59±0.24 gram and the assimilated wet food
was 7.91±1.18 gram.
In the pheromone treated group the consumed dry food was 2.94±0.07
gram, the consumed wet food was 9.59±1.42 gram. The assimilated dry
food was 0.59±0.26 gram and the assimilated wet food was 8.07±1.29
gram. In the oil control group the consumed dry food was 2.94±0.06
grams while the consumed wet food was 8.83±1.49 grams and the
assimilated dry food was 0.48±0.32 grams, the assimilated wet food was
7.37±1.45 grams. These results revealed that there are no significant
differences between pheromone treated and the control groups.
Newly moulted fledglings (2-3 days) of mixed sexes were treated
with NPB to inspect the effect of the NPB (in presence of visual, tactile
and olfactory cues) on the onset of maturation through monitoring the
colour change, copulation time and preoviposition period.
The mean onset of maturation time of the immature males and
females as assessed by colour change in the control cages was found to
be 19.20±6.49 days for males and 20.69±5.66 days for females while in
the pheromone treated group it was 27.20±12.59 days for males and
29.23±10.54 days for females. In the oil control group it was 24.39±5.55
days for males and 25.18±6.26 days for females. This result reflects that
there was no significant difference between males and females to change
their colour. But there was significant delay in the maturation time in the
pheromone treated group. Also the oil control group showed a significant
delay in the maturation time. This means that the oil also has an effect on
the maturation time.
The onset of copulation time was 33.84±10.37 days in case of
control and 58.53±16.95 days in the pheromone treated group, in case of
oil control group it was 42.40±6.47 days. The pre-oviposition period was
38.25±9.29 days in the control group and 70.40±15.99 days in the
pheromone treated group and 55.73±3.49 days in the oil control group.
This result confirms the maturation retarding effect of the NPB.
Investigation on fecundity and oviposition behavior was carried out
in the laboratory. 20 individual (10 males+ 10 females) were treated with
NPB. The mean number of total egg pods per female in the pheromone
treated group was 1.48±0.90 and 1.91±0.28 in the oil control group,
compared to 3.19±1.26 in the untreated control group. This result showed
that the NPB had an effect on fecundity. Females exposed to the
pheromone produced significantly few egg pods compared to the
untreated controls. However, oil control reflected a reduction in the
number of egg pods per female; this means that the oil also has an effect.
The mean percentage of scattered egg pods in the pheromone
treated group was found to be 30.57±30.71 and 1.11±2.46 in the control
group, while it was 4.44±9.94 in the oil control group. This result shows
that the NPB elicit a significant increase in the percentage of scattered
egg pods.
The effect of the NPB on the longevity of gregarious fledglings
was found to be 54.87±21.96 days for females and 49.69±17.40 days for
males in case of the untreated control group, and 68.12±38.86 days for
females and 73.35±35.90 days for males in the pheromone treated group.
While it was 67.08±26.49 for females and 80.04±34.65 days for males in
the oil control group. This result shows that there is no significant effect
of the NPB on the longevity and life span of the gregarious desert locust,
males and females.
Accordingly it was clear that the NPB has just affected the reproductive
physiology of the gregarious desert locust Shistocerca gregaria.
1. Effect on Circadian Rhythm
Data analysis
Means
Treatment
Time
rep
1
rep
2
rep
3
rep
4
1.
Period
6:00 to 10:00 AM
Control
Percent Engaged in
Roosting Feeding
Moving
Oil
Percent Engaged in
Roosting Feeding
Moving
Oil+NPB
Percent Engaged in
Roosting
Feeding
Moving
6:00
7:00
8:00
9:00
10:00
90.00
100.00
95.00
90.00
90.00
10.00
0.00
0.00
0.00
0.00
0.00
0.00
5.00
10.00
10.00
100.00
100.00
86.36
95.45
95.45
0.00
0.00
4.55
0.00
0.00
0.00
0.00
9.09
4.55
4.55
90.00
100.00
100.00
84.21
89.47
0.00
10.00
0.00
0.00
5.26
0.00
0.00
0.00
0.00
10.53
6:00
7:00
8:00
9:00
10:00
80.00
75.00
85.00
85.00
85.00
5.00
0.00
0.00
0.00
0.00
15.00
25.00
15.00
15.00
15.00
90.91
100.00
95.24
80.95
85.71
9.09
0.00
0.00
14.29
4.76
0.00
0.00
4.76
4.76
9.52
89.47
89.47
94.74
94.74
89.47368
0.00
0.00
0.00
0.00
0.00
10.53
10.53
5.26
5.26
10.53
6:00
7:00
8:00
9:00
10:00
100.00
100.00
90.48
90.48
90.48
0.00
0.00
4.76
9.52
4.76
0.00
0.00
4.76
0.00
4.76
100.00
100.00
86.36
95.45
95.45
0.00
0.00
4.55
0.00
0.00
0.00
0.00
9.09
4.55
4.55
100
100.00
85.00
85.00
85.00
0.00
0.00
10.00
15.00
15.00
0.00
0.00
5.00
0.00
0.00
6:00
7:00
100.00
100.00
0.00
0.00
0.00
0.00
90.91
100.00
9.09
0.00
0.00
0.00
100.00
100.00
0.00
0.00
0.00
0.00
rep
5
rep
6
8:00
9:00
10:00
95.24
90.48
100.00
0.00
9.52
0.00
4.76
0.00
0.00
95.24
80.95
85.71
0.00
14.29
4.76
4.76
4.76
9.52
100.00
89.47
89.47
0.00
10.53
0.00
0.00
0.00
10.53
6:00
7:00
8:00
9:00
10:00
92.00
92.00
100.00
87.50
70.83
8.00
8.00
0.00
0.00
25.00
0.00
0.00
0.00
12.50
4.17
96.00
96.00
96.00
92.00
100.00
0.00
0.00
0.00
8.00
0.00
4.00
4.00
4.00
0.00
0.00
96.00
96.00
96.00
91.30
88.00
0.00
0.00
0.00
0.00
8.00
4.00
4.00
4.00
8.70
4.00
6:00
7:00
8:00
9:00
10:00
AVG
SD
100.00
100.00
100.00
83.33
79.17
91.23
8.202579
0.00
0.00
0.00
16.67
4.17
3.51
5.958354
0.00
0.00
0.00
0.00
16.67
5.25
7.0498
100.00
100.00
100.00
95.83
87.50
94.12
6.006468
0.00
0.00
0.00
0.00
4.17
2.58
4.319563
0.00
0.00
0.00
4.17
8.33
3.30
3.365236
100.00
100.00
100.00
70.83
87.50
92.71
7.004386
0.00
0.00
0.00
29.17
12.50
3.85
6.985481
0.00
0.00
0.00
0.00
0.00
3.10
4.096424
Treatment
rep
1
Time
11:00
2.
Period
11:00 AM to 3:00 PM
Control
Oil
Percent Engaged in
Percent Engaged in
Roosting
85.00
Feeding
0.00
Moving
15.00
Roosting
100.00
Feeding
0.00
Oil+NPB
Percent Engaged in
Moving
0.00
Roosting
13.04
Feeding
86.96
Moving
0.00
rep
2
rep
3
rep
4
rep
5
rep
6
12:00
13:00
14:00
15:00
70.00
55.00
75.00
95.00
0.00
5.00
10.00
0.00
30.00
40.00
15.00
5.00
86.36
90.91
86.36
90.91
4.55
0.00
9.09
0.00
9.09
9.09
4.55
9.09
24.81
30.56
13.58
5.21
71.43
69.44
78.19
94.79
3.76
0.00
8.23
0.00
11:00
12:00
13:00
14:00
15:00
80.00
65.00
70.00
85.00
80.00
0.00
5.00
15.00
0.00
10.00
20.00
30.00
15.00
15.00
10.00
90.48
80.95
85.71
95.24
100.00
0.00
4.76
0.00
0.00
0.00
9.52
14.29
14.29
4.76
0.00
84.21
89.47
94.74
84.21
94.74
0.00
0.00
0.00
0.00
0.00
15.79
10.53
5.26
15.79
5.26
11:00
12:00
13:00
14:00
15:00
100.00
85.71
95.24
90.48
80.95
0.00
4.76
0.00
0.00
4.76
0.00
9.52
4.76
9.52
14.29
100.00
86.36
90.91
86.36
90.91
0.00
4.55
0.00
9.09
0.00
0.00
9.09
9.09
4.55
9.09
100.00
95.00
95.00
100.00
75.00
0.00
0.00
0.00
0.00
0.00
0.00
5.00
5.00
0.00
25.00
11:00
12:00
13:00
14:00
15:00
90.48
80.95
80.95
95.24
75.00
0.00
0.00
0.00
0.00
0.00
9.52
19.05
19.05
4.76
25.00
90.48
80.95
85.71
95.24
100.00
0.00
4.76
0.00
0.00
0.00
9.52
14.29
14.29
4.76
0.00
84.21
84.21
94.74
100.00
100.00
10.53
0.00
0.00
0.00
0.00
5.26
15.79
5.26
0.00
0.00
11:00
12:00
13:00
14:00
15:00
84.00
84.00
80.00
84.00
88.00
8.00
0.00
0.00
0.00
0.00
8.00
16.00
20.00
16.00
12.00
84.00
88.00
88.00
96.00
95.83
4.00
0.00
0.00
0.00
0.00
12.00
12.00
12.00
4.00
4.17
92.00
88.00
88.46
96.00
96.00
0.00
0.00
0.00
4.00
0.00
8.00
12.00
11.54
0.00
4.00
11:00
12:00
13:00
14:00
91.67
87.50
100.00
91.67
8.33
0.00
0.00
0.00
0.00
12.50
0.00
8.33
95.83
91.67
91.67
95.83
0.00
0.00
0.00
0.00
4.17
8.33
8.33
4.17
95.83
95.83
95.83
100.00
0.00
0.00
0.00
0.00
4.17
4.17
4.17
0.00
15:00
AVG
SD
Treatment
rep
1
rep
2
rep
3
91.67
83.88
10.36725
8.33
2.73
4.255226
0.00
13.39
9.670282
3.
Period
3:00 to 6:00 PM
Control
Percent Engaged in
95.83
90.91
5.376524
0.00
1.41
2.742336
4.17
7.68
4.337012
Oil
96.00
82.54
26.98871
4.00
11.46
27.61731
0.00
6.00
6.244751
Oil+NPB
Percent Engaged in
Percent Engaged in
Time
15:00
16:00
17:00
18:00
Roosting
95.00
80.00
90.00
80.00
Feeding
0.00
5.00
0.00
5.00
Moving
5.00
15.00
10.00
15.00
Roosting
90.91
86.36
86.36
100.00
Feeding
0.00
13.64
9.09
0.00
Moving
9.09
0.00
4.55
0.00
15:00
16:00
17:00
18:00
80.00
75.00
80.00
80.00
10.00
10.00
5.00
10.00
10.00
15.00
15.00
10.00
100.00
100.00
100.00
100.00
0.00
0.00
0.00
0.00
15:00
16:00
80.95
85.71
4.76
9.52
14.29
4.76
90.91
86.36
0.00
13.64
Roosting
100.00
89.47
84.21
84.21
Feeding
0.00
0.00
0.00
0.00
Moving
0.00
10.53
15.79
15.79
0.00
0.00
0.00
0.00
94.74
89.47
88.89
88.89
0.00
5.26
0.00
0.00
5.26
5.26
11.11
11.11
9.09
0.00
75.00
75.00
0.00
15.00
25.00
10.00
rep
4
rep
5
rep
6
17:00
18:00
76.19
100.00
14.29
0.00
9.52
0.00
86.36
100.00
9.09
0.00
4.55
0.00
75.00
100.00
15.00
0.00
10.00
0.00
15:00
16:00
17:00
18:00
75.00
100.00
76.19
100.00
0.00
0.00
19.05
0.00
25.00
0.00
4.76
0.00
100.00
100.00
100.00
100.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
100.00
100.00
100.00
100.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
15:00
16:00
17:00
18:00
88.00
92.00
92.00
92.00
0.00
0.00
4.00
8.00
12.00
8.00
4.00
0.00
95.83
87.50
100.00
100.00
0.00
8.33
0.00
0.00
4.17
4.17
0.00
0.00
96.00
92.00
100.00
100.00
0.00
4.00
0.00
0.00
4.00
4.00
0.00
0.00
15:00
16:00
17:00
18:00
AVG
SD
91.67
95.83
95.83
91.67
87.21
8.494161
8.33
0.00
0.00
8.33
5.05
5.361842
0.00
4.17
4.17
0.00
7.74
6.634955
95.83
100.00
95.83
95.83
95.75
5.525382
0.00
0.00
4.17
0.00
2.41
4.587547
4.17
0.00
0.00
4.17
1.83
2.916307
96.00
100.00
100.00
100.00
92.87
8.712295
4.00
0.00
0.00
0.00
1.80
4.332452
0.00
0.00
0.00
0.00
5.33
6.876632
Effect of the NPB on gregarious adults
1. Effect on feeding rates
Five cages in each treatment each contain 10 greg. adults
Duration of test 4 days i.e. 4 readings per cage
Dry weight per one gram of millet= 0.195407
1.1 Dry weight per gram Millet
Sample
No.
Wet weight
Dry Weight
dw/G
AVG dw/g
SD
1
5.41548
1.12048
0.206903
0.195407
0.014827
2
5.6401
1.14202
0.202482
3
5.55508
1.02651
0.184788
4
5.65273
1.09714
0.19409
5
5.64057
1.07351
0.190319
dry feces
1.27301
1.24507
1.42906
1.28257
0.77503
1.07406
1.19244
1.6735
1.17005
dry spill
0.07403
0.06046
0.09447
0.08877
0.04875
0.05608
0.06203
0.09457
0.14303
Feeding Rates Raw Data
1.
Controle
cage no.
1
2
3
4
5
6
7
8
9
inwetfood
15.012
15.9421
15.055
15.90075
15.419
15.927
15.3357
15.46608
15.479
rmdryfood
1.2675
0.86358
1.00807
0.92908
1.6487
1.02706
1.21276
0.83457
1.2223
wet
feces
1.42374
1.725
1.67557
1.82646
1.5821
1.335
1.39255
1.91246
1.0162
6
5.07754
0.84703
0.166819
7
5.43414
1.02619
0.188841
10
11
12
15.8207
15.6635
15.46512
1.2038
1.00607
0.97253
1.25219
1.66052
1.6478
1.02342
1.44205
1.48503
0.03547
0.09205
0.24709
AV
15.5405
1.099668
1.537466
1.255441
0.0914
SD
0.319206
0.226028
0.258618
0.237868
0.056607
inwetfood=
rmdryfood=
wet feces=
dry feces=
Weight of the provided fresh food
Dry weight of the remaining food after 24 hours
Weight of fresh feces
Weight of dried feces
dry spill=
Dry weight of spilled food
Feeding Rates Raw Data
2. Oil
treatment
cage no.
1
2
3
4
5
6
7
8
9
10
11
12
AV
SD
inwetfood=
rmdryfood=
wet feces=
dry feces=
dry spill=
inwetfood
15.276
15.4015
15.32004
15.64405
15.609
15.5604
15.328
15.65957
15.503
15.9316
15.546
15.14008
rmdryfood
1.09504
0.86805
1.57105
1.04357
1.01607
1.62106
1.412048
0.97201
1.04305
1.08408
1.76375
1.16356
wet
feces
1.59
1.6005
1.32959
1.44071
1.2934
1.56301
1.50902
1.6297
1.5151
1.44908
1.28908
1.36804
dry feces
1.20703
1.25658
1.15579
1.63241
0.95645
1.27153
1.32314
1.44102
1.14904
1.16901
1.10093
1.25406
dry spill
0.06601
0.06708
0.06348
0.13472
0.03753
0.05803
0.08902
0.1819
0.07506
0.04815
0.04772
0.09251
15.49327
0.213412
1.221112
0.292837
1.464769
0.122155
1.243083
0.171595
0.080101
0.041141
Weight of the provided fresh food
Dry weight of the remaining food after 24 hours
Weight of fresh feces
Weight of dried feces
Dry weight of spilled food
Feeding Rates Raw Data
3. NPB
Treatment
cage no.
1
2
3
4
5
6
7
8
9
10
11
12
AV
inwetfood
15.677
15.684
15.954
15.25108
15.572
15.668
15.535
15.93407
15.93
15.3375
15.587
15.48408
rmdryfood
0.96006
0.75976
0.83473
1.22571
0.80508
1.30057
1.60239
0.94255
1.37857
0.73656
1.48736
0.94377
wet
feces
1.59
1.624
1.9171
1.46307
0.9454
1.10344
1.09304
1.68753
1.4181
1.7387
1.45977
1.7077
dry feces
1.13313
1.32904
1.70248
1.35056
1.22703
1.0141
0.9601
1.55653
0.78908
1.45206
1.27439
1.57392
dry spill
0.12105
0.07308
0.15097
0.09952
0.12507
0.13306
0.02055
0.15098
0.02718
0.125
0.05185
0.21259
15.63448
1.081426
1.478988
1.280202
0.107575
SD
0.225314
15.63448
0.302402
1.081426
0.296584
1.478988
0.272494
1.280202
0.056111
0.107575
0.225314
0.302402
0.296584
0.272494
0.056111
inwetfood=
rmdryfood=
wet feces=
dry feces=
Weight of the provided fresh food
Dry weight of the remaining food after 24 hours
Weight of fresh feces
Weight of dried feces
dry spill=
Dry weight of spilled food
Feeding Rates Data Analysis
1. Control
Indryfood
2.93345
3.115198
2.941852
3.107118
3.012981
3.112247
2.996703
3.02218
3.024705
Cndryfood
2.85942
3.054738
2.847382
3.018348
2.964231
3.056167
2.934673
2.92761
2.881675
Cnwetfood
8.146688
11.2133
9.412725
10.69188
6.732259
10.38401
8.811932
10.71118
8.491891
Asdryfood
0.31891
0.946088
0.410252
0.806698
0.540501
0.955047
0.529473
0.41954
0.489325
Aswetfood
6.722948
9.488303
7.737155
8.865418
5.150159
9.049005
7.419382
8.798724
7.475691
3.091476
3.060758
3.056006
2.968708
9.478706
10.04384
0.828786
0.520588
8.226516
8.383325
AVG
3.021993
3.036722
2.774903
2.945322
9.223685
9.445175
0.317343
0.590213
7.575885
7.907709
SD
0.062375
0.092067
1.276718
0.232437
1.183671
Indryfood
2.985037
3.009561
2.993643
3.056957
3.050108
3.040611
2.995198
3.05999
3.029395
3.113146
3.037797
Cndryfood
2.919027
2.942481
2.930163
2.922237
3.012578
2.982581
2.906178
2.87809
2.954335
3.064996
2.990077
Cnwetfood
9.334299
10.61595
6.955294
9.614123
10.21718
6.967617
7.646249
9.754408
9.781045
10.13739
6.275759
Asdryfood
0.616957
0.817851
0.203323
0.246257
1.040058
0.089991
0.17099
0.46506
0.762245
0.811906
0.125397
Aswetfood
7.744299
9.01545
5.625704
8.173413
8.923777
5.404607
6.137229
8.124708
8.265945
8.688306
4.986679
2.958478
3.027493
0.041702
2.865968
2.947393
0.05727
8.712112
8.834285
1.488544
0.448348
0.483199
0.32221
7.344072
7.369516
1.449874
2. Oil Treatment
AVG
SD
3. NPB Treatment
Indryfood
3.063396
3.064763
3.117523
2.980168
3.042878
3.061637
3.035648
3.113629
3.112834
2.997055
3.045809
Cndryfood
2.942346
2.991683
2.966553
2.880648
2.917808
2.928577
3.015098
2.962649
3.085654
2.872055
2.993959
Cnwetfood
10.19133
11.47477
10.96014
8.508371
10.86196
8.369914
7.263018
10.38574
8.776463
10.97901
7.745731
Asdryfood
0.849156
0.902883
0.429343
0.304378
0.885698
0.613907
0.452608
0.463569
0.918004
0.683435
0.232209
Aswetfood
8.554394
9.797921
8.992557
7.006114
9.866535
7.227924
6.136526
8.650374
7.317941
9.189746
6.250286
AVG
3.025698
3.055086
2.813108
2.947511
9.610644
9.593925
0.295418
0.585884
7.85868
8.07075
SD
0.044028
0.072518
1.417696
0.256944
1.293007
Effect of the NPB on gregarious adults
RAW DATA
1. Effect on Maturation, mating and preoviposition
1.1 Maturation colour change
Colour
Indiv No.
Male
Female
1
14
11
2
14
14
3
14
14
4
15
18
5
15
18
6
15
18
7
15
18
8
18
18
9
18
21
10
18
33
11
18
26
12
24
22
13
33
26
14
24
26
15
33
24
16
18
24
1.2. Maiting
1.3. Preoviposition period
Pair No.
Pair No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
55
55
26
26
30
30
30
30
36
28
36
21
25
20
25
43
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
49
40
24
46
32
26
32
63
32
41
39
37
40
35
39
37
17
18
19
AVR
SD
42
43
42
AVR
SD
38.25
9.262829
33.84211
10.36695
1. Effect on Maturation, mating and preoviposition
1.1 Maturation colour change
Colour
Indiv No.
Male
1
15
2
21
3
16
4
31
5
17
6
24
7
31
8
20
9
16
10
26
11
26
12
26
13
26
14
32
15
28
16
28
17
28
18
28
24.38889
1.2. Maiting
Female
1.3. Preoviposition period
Pair No.
34
34
29
24
32
20
18
16
16
22
22
26
28
28
32
32
25.8125
Pair No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
AVR
SD
39
49
39
48
51
36
32
51
40
37
50
33
42
45
44
42.28571
6.467501
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
AVR
SD
54
60
56
54
60
56
55
53
54
55
53
49
55
59
63
55.73333
3.494213
Effect of the NPB on gregarious adults
RAW DATA
1. Effect on Maturation, mating and preoviposition
1.1 Maturation colour change
Colour
Indiv No.
Male
Female
13
19
21
21
22
37
15
37
17
11
47
19
47
28
47
14
47
14
47
14
31
18
31
11
13
12
13
47
26
47
28
27
11
27
14
33
15
33
15
33
14
33
14
32
1.2. Maiting
Pair No.
1
2
3
4
5
6
7
8
9
10
11
12
13
Mean
STD
81
31
16
59
64
62
62
64
59
66
72
59
66
58.53846
16.95393
1.3. Preoviposition period
Pair No.
1
76
2
84
3
81
4
73
5
55
6
40
7
58
8
37
9
73
10
76
11
84
12
80
13
85
14
87
15
67
Mean
70.4
STD
15.99464
Mean
STD
15
15
47
47
27
27
28
33
33
24
36
36
36
27.2
36
36
47
47
27
27
33
33
33
33
32
36
36
Effect of the NPB on gregarious adults
RAW DATA
A. Control
1. Effect on Fecundity and Oviposition Behaviour
Cage No.
1
2
3
Females
20
18
10
Tot Pods
Nor Pods
70
70
59
70
70
59
Scat Eggs
0
0
0
Pod/Fem
3.50
3.89
5.90
%NorPods
100.00
100.00
100.00
%ScatEggs
0.00
0.00
0.00
4
5
6
7
8
9
10
9
11
12
33
30
20
16
28
30
21
62
101
78
30
26
30
21
62
97
78
30
2
0
0
0
4
0
0
3.11
2.73
1.75
1.88
3.37
3.90
1.88
92.86
100.00
100.00
100.00
96.04
100.00
100.00
7.14
0.00
0.00
0.00
3.96
0.00
0.00
Effect of the NPB on gregarious adults
RAW DATA
B. Oil
1. Effect on Fecundity and Oviposition Behaviour
Cage No.
Females
1
2
3
4
5
6
7
8
9
10
4
6
11
6
6
11
7
12
6
6
Tot Pods
9
9
20
12
12
18
14
22
11
12
Nor Pods
7
9
20
12
12
17
14
20
9
12
Scat
Eggs
2
0
0
0
0
1
0
2
2
0
Pod/Fem
2.25
1.50
1.82
2.00
2.00
1.64
2.00
1.83
1.83
2.00
%NorPods
77.78
100.00
100.00
100.00
100.00
94.44
100.00
90.91
81.82
100.00
%ScatEggs
22.22
0.00
0.00
0.00
0.00
5.56
0.00
9.09
18.81
0.00
Effect of the NPB on gregarious adults
RAW DATA
C. Oil+NPB
1. Effect on Fecundity and Oviposition Behaviour
Cage No.
Females
1
2
3
4
5
6
7
8
9
10
2
8
2
9
12
10
11
11
2
9
Tot Pods
2
7
7
12
12
10
12
10
6
10
Nor Pods
1
3
3
7
12
4
6
2
2
10
Scat
Eggs
1
4
4
5
0
6
6
8
4
0
Pod/Fem
1.00
0.88
3.50
1.33
1.00
1.00
1.09
0.91
3.00
1.11
%NorPods
50.00
42.86
42.86
58.33
100.00
40.00
50.00
20.00
33.33
100.00
%ScatEggs
50.00
57.14
57.14
41.67
0.00
60.00
50.00
80.00
66.67
0.00