Australian Journal of Entomology (2004) 43, 83–87 Blackwell Science, LtdOxford, UKAENAustralian Journal of Entomology1326-67562004 Australian Entomological SocietyMarch 20044318387Original ArticleRearing parasitoids Netelia and HeteropelmaCV Johns and MEA Whitehouse *Author to whom correspondence should be addressed (email: mary.whitehouse@csiro.au). Mass rearing of two larval parasitoids of Helicoverpa spp. (Lepidoptera: Noctuidae): Netelia producta (Brullé) and Heteropelma scaposum (Morley) (Hymenoptera: Ichneumonidae) for field release Caitlin V Johns and Mary E A Whitehouse* CSIRO Cotton Research Unit, Locked Bag 59, Narrabri, NSW 2390, Australia. Abstract Parasitoids are becoming an increasingly important part of our biological arsenal in Integrated Pest Management strategies against major insect pests like Helicoverpa armigera (Hübner). Inundative or supplementary releases of parasitoids have been successfully used in the past to help manage insect pests in the field. This paper reports attempts to mass rear two larval parasitoids of Helicoverpa spp., Heteropelma scaposum and Netelia producta. The results suggest that N. producta is the easier species to culture, although the parasitism rates for either wasp species were not high (29% for N. producta and 19% for H. scaposum). The authors suggest ways in which the parasitism rates could be increased and culturing made easier. It was found that culturing H. scaposum resulted in a male-biased sex ratio that was less suitable for mass release. Possible reasons for the bias are discussed, including single- locus complementary sex determination (CSD) that can result in a high proportion of homozygotic diploid males occurring in inbred populations. Although single-locus CSD is a plausible explanation for the male biased sex ratio, the authors caution that more work is needed to confirm that it can occur in H. scaposum. Key words complementary sex determination, heliothis, IPM, mass rearing, sex ratio. INTRODUCTION Helicoverpa armigera (Hübner) is an insect pest of major economic significance in Australian cotton. It has proven dif- ficult to manage, due to its rapid development of resistance to a range of pesticides (Pyke & Brown 1996). Considerable research into alternative control methods, including utilisation of natural enemy populations, is occurring in order to combat the growing resistance problem (Walker et al. 1996; Mensah 1999; Johnson et al. 2000) Parasitoids have been identified as potentially important biological control agents of Helicoverpa spp. The egg, larval and pupal stages of Helicoverpa spp. in field crops in Australia are parasitised by at least 45 different native wasp and tachinid fly species (Johnson et al. 2000). Hymenoptera reared from H. armigera or H. punctigera (Wallengren) in Australian cot- ton include species from the families: Ichneumonidae (Heteropelma scaposum (Morley), Ichneumon promissorius (Erichson), Lissopimpla excelsa (Costa) and Netelia producta (Brullé)); Braconidae (Microplitus spp. and Cardiochiles sp.); Trichogrammatidae (Trichogramma spp., Trichogramma- toidea spp. and Trichogrammatoides spp.); Scelionidae (Tele- nomus spp.); Chalcidae (Brachymeria spp.); and Pteromalidae (Zalucki et al. 1986; Johnson et al. 2000). Although the mass rearing of egg parasitoids, such as Tri- chogramma spp., is widely applied in the control lepidopteran pests, little attempt has been made to mass rear larval parasi- toids in cotton (other than the small larval parasitoids, Microplitis demolitor (Murray & Rynne 1991) and Cotesia kazak (Harrington 1983; D. Murray pers. comm. 2001)). Although the ichneumonids Heteropelma scaposum and Nete- lia producta are frequently encountered parasitoids of larval H. armigera (Pyke & Brown 1996; Johnson et al. 2000), rel- atively little is known of their biology or potential as biological control agents. The amenability of these species to mass rear- ing will, in part, determine their suitability for inundative, augmentative, or inoculative field releases to help control Heli- coverpa spp. A factor that may limit the culturing of large numbers of wasps is the presence of single-locus complementary sex determination (CSD) (Stouthamer et al. 1992; Cook 1993). In species with single-locus CSD, females result when the animal is diploid, while males normally result when the animal is haploid. However, diploid males can occur when the animal is homozygotic at the sex locus. Homozygotic diploid males either do not survive or are sterile, so, that if a female mates with these males only, all resulting offspring will be male. The chance of obtaining homozygotic males increases at a genetic bottleneck, such as that which occurs when a small sample of individuals are used to rear up large populations during cul- turing. It has been hypothesised that the relatively high rate of biocontrol failures with Ichneumonidae and Braconidae wasps