New Zealand Entomologist, 1992, Vol. 15 81 A simple sample separation system based on flotation for small samples of insects contaminated with soil B. H. ROHITHA Ruakura Agricultural Centre, Private Bag, Hamilton, New Zealand ABSTRACT An apparatus for separating insects and soft bodied organisms in small samples contaminated with soil is described. The sample to be separated is placed on a detachable sieve at the bottom of a separator cone. The unit is lowered into a saturated magnesium sulphate bath and the detachable sieve (containingthe heavier fraction) is exchanged with an identical sieve. The unit then contains the separated insect sample. Keywords: Insect sampling techniques, quantitative sampling, suction samples, Berlese funnel, Tullgren funnel. INTRODUCTION Separation of insects and other soft bodied organisms in routine sampling operations is often time consuming. In insect extractions from suction samples (e.g. Dietric 1961), Berlese (1905) funnel and Tullgren (1917) funnel samples often get contaminated with soil and this can pose problems in sorting. The problems are greater with smaller insects such as free living springtails in soil (e.g. from Berlese funnel extractions). Southwood (1978) reviewed techniques for separating insects and other invertebrates from soil. Ladell (1936), Salt & Hollick (1944), and Dondale et al. (1971) described extraction of organisms from soil. They described methods based on flotation and finally isolated the insect samples from the soil using saturated magnesium sulphate in water. These methods are suitable for bulky samples, but with smaller samples contaminated with soil, such apparatus can be cumbersome and time consuming. The aim of this paper is to describe a simpler sample separation technique suitable for the isolation of insects and other soft bodied organisms from small samples contaminated with soil or sand. MATERIALS AND METHODS The apparatus used a salt bath which consisted of one outer and one inner plastic vessel (Fig. 1). The outer vessel (17 cm x 17 cm square top, 15 cm x 15 cm bottom, 19 cm tall; ex Plastic Wholesalers, Hamilton) contained a saturated magnesium sulphate solution (specific gravity: 1.22 at 20°C). The inner vessel (15.5 cm diameter top, 13 cm diameter bottom, 11.5 cm tall) was a plastic flower pot with the bottom removed and a nylon organdie mesh (140 mm diameter) attached with ADOS contact adhesive (Eastern Hutt Road, Lower Hutt) in place. The inner vessel floated in the salt solution and the bottom mesh kept the salt' solution clean during separations. The other parts of the apparatus were cut from three 120 ml conical polyethylene specimen canisters (Medic D.D.C. Ltd, Hamilton, item No. 500/1000/500). One canister (C) was cut off 35 mm from the top and the bottom removed to form an open cone (58 mm top and 52 mm bottom diameter). From the other 2 canister (S), two 10 mm rings (between 12 mm and 22 mm from top) were taken, and an organdie mesh (56 mm diameter) glued onto the narrower end ( = sieve-rings). The narrower end of the open cone fitted snugly inside a sieve ring (this collectively is the separator-unit; SU) (Fig. 1). The sample to be separated was transferred into the SU. Large plant parts, debris and dung particles were removed under a gently flowing tap. The SU was then lowered into the salt solution. The insects floated to the surface and the soil and other heavy matter stayed in the sieve-ring. While holding the open cone (C) with one hand, the sieve-ring (S) was carefully detached, and removed out of the solution. With the insect sample still 82 New Zealand Entomologist, 1992, Vol. 15 suspended inside the open cone, the second sieve-ring was fitted to the SU and then the SU was lifted out. The separated insect sample was collected on the second sieve ring by washing down under a gently flowing tap and was then ready for examination. Salt bath Separator unit Fig 1: Schematic diagram of sample separator assembly (top) and its itemised components (bottom). RESULTS AND DISCUSSION The recovery efficiency of insects belonging to 5 families is shown in Table 1. A known number of insects were stained overnight with Picro sireus red (Flint & Firth 1983) mixed with 5 g of soil and extracted with the apparatus. The time taken to separate a small (< 10 g total matter) suction sample was 42 see/sample. Soil dwelling springtails from Tullgren (1917) funnel extractions were successfully separated by this method. The organdie sieve mesh size was sometimes a limitation as some springtails were smaller than the mesh size. New Zealand Entomologist, 1992, Vol. 15 83 Table 1: Recovery efficiency of the sample separating system with some common pasture and soil dwelling insects. Percentage recovery of stained1 insects Insect species/family Acyrthosiphon kondoi (Aphididae) Coccinella undecimpunctata (Coccinellidae) Micromus tasmaniae (Hemerobiidae) Melanostoma fasciatum (Syrphidae) Free living springtails (Poduridae) Number of insects used in assessment. REFERENCES Berlese, A,, 1905: Apparecchio per raccogliere presto ed in gram numero piccoli artropodi. Redia 2 : 85-89. Dietrick, E.J., 1961: An improved backpack motor fan for suction sampling of insect populations. Journal of economic entomology 54 : 394-395. Dondale, C.D.; Nicholls, C.F.; Redner, J.H.; Seemple, R.B.; Turnbull, A.L., 1971: An improved Berlese-Tullgren funnel and floatation separation for extracting grassland arthropods. Canadian entomologist 103: 1549-1552. Flint, F.O.; Firth, B.M., 1983: Histochemical demonstration of collagen in communited meat products. The analyst 108: 757-759. Ladell, W.R.S., 1936: A new apparatus for separating insects and other arthropods from the soil. Annals of applied biology 23: 862-879. Salt, G.; Hollick, F.S.J., 1944: Studies of wireworm populations. 1. A census of wireworms in pasture. Annals of applied biology 31 : 53-64. Southwood, T.R.E., 1978: (2nd ed). Ecological Methods. London, Chapman and Hall. 524 pp. Tullgren, A., 1917: An enkel apparat for automatiskt vittjande av sallgods. Entomologisk Tidskrift 27: 91-100. Freeze-dried artificial diets for three species of Chilocow Ladybirds R. C. HENDERSON, M. G. HILLAND P. J. WIGLEY DSIR Plant Protection, Private Bag, AucMand, New Zealand ABSTRACT Artificial diets were developed for coccinellid beetles of the genus Chilocorus, which prey on armoured scale insects. Comparisons were made between 3 insect diet bases; bee brood, wasp brood and pupae of light brown apple moth, Epiphyas postvittana, with various additives. A freeze-dried wasp brood-based diet was found to be the most successful for rearing the larvae of these ladybirds. Adults of C. infernalis reared through the larval stages on scale insects, were able to oviposit normally when fed the artificial wasp brood diet, but C . bipustulatus and C . cacti did not oviposit readily unless fed the natural host scale insects. Keywords: Freeze-dried artificial diet, Chilocow, armoured scale, wasp brood, bee brood, Epiphyas postvittana.