INFLUENCE OF SOIL TEXTURE AND MOISTURE ON THE INFECTIVITY OF HETERORHABDITIS SP. D1 AND STEINERNEMA GLASERI FOR LARVAE OF THE SHEEP BLOWFLY, LUCILIA CUPRINA BY A. S. MOLYNEUX1)*) and R. A. BEDDING2) 1) Department of Entomology, Waite Agricultural Research Institute, University of Adelaide, Glen Osmond, 5064 South Australia, Australia 2) Division of Entomology, CSIRO, Stowell Avenue, Hobart, 7000 Tasmania, Australia Lucilia cuprina larvae were exposed to infective juvenile nematodes of Heterorhabditis sp. D1 and Steinernema glaseri KG strain in sand, loamy sand and a clay loam at various moisture contents representing a range of moisture potentials. Parasitism was less in soils of high clay content, with the larger nematode, S. glaseri,having the lowest level of parasitism. Parasitism in loamy sand oc- curred at low moisture potentials equivalent to or below the permanent wilting point of plants. In sand only, both nematode species parasitised larvae at high moisture potentials close to satura- tion. Moisture potential was found to be more meaningful than moisture content per se for com- parisons of nematode parasitism in different soil types. Heterorhabditis and Steinernema species are potential control agents of post-feeding, 3rd instar L. cuprina larvae and other soil-dwelling insect pests in areas of low rainfall and suitable soil texture. Keywords: Moisture potential, soil structure, parasitism, entomophilic nematodes, biological control. Nematodes of the genera Heterorhabditis and Steinernema (syn. Neoaplectana, Wouts et al., 1982) are obligate parasites of insects in nature (Poinar, 1979). These nematodes are characterised by having a non-feeding, free-living, infective-stage juvenile (dauer stage) and a mutualistic association with specific bacteria, Xenorhabdus spp. (Poinar, 1979; Akhurst, 1980). The infective juvenile carries cells of its bacterial associate in its intestine (Poinar, 1979). In- fective juveniles are particularly abundant in soil habitats and are attracted to insects from a distance (Bedding & Akhurst, 1975). On encountering an insect they enter its mouth, anus or spiracles (Poinar, 1979) and Heterorhabditis spp. also enter via intersegmental membranes (Bedding & Molyneux, 1982). After penetration, the infective juvenile moves to the haemocoel where it voids its bacteria and secretes an inhibitor of the antibacterial enzymes of the insect host (Gotz et al., 1981). The bacteria kill the insect and provide nutrients for nematode development and reproduction while inhibiting the growth of other bacteria (Akhurst, 1982). *) This work was completed at the Division of Entomology, CSIRO, while on a fixed-term contract funded by the Australian Government.