Impact of recombinant baculovirus field applications on a nontarget heliothine parasitoid, Microplitis croceipes (Hymenoptera: Braconidae).
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abstract
The kill times of two viruses infectious to the heliothine pest complex indigenous to Texas cotton have been significantly reduced by expressing a scorpion toxin gene. Autographa californica nucleopolyhedrovirus (NPV) and Helicoverpa zea NPV express the toxin only in permissive lepidopteran hosts. The toxin, however, could indirectly harm members of upper trophic levels that feed upon and parasitize infected larvae producing the toxin. In this study, the effects of recombinant and wild-type viruses on Microplitis croceipes (Cresson) were studied in cotton using Heliothis virescens (F.) (Lepidoptera: Noctuidae) as hosts. Two recombinant viruses, their two wild-type progenitor viruses, and untreated cotton served as the five treatments of study. Larvae were previously parasitized 2 and 4 d before being confined for 72 h to cotton terminals treated with field rates of virus or left untreated. The sexes of adult M. croceipes that emerged from the recovered H. virescens larvae were determined and their head capsule widths were measured. Polymerase chain reaction (PCR) searched their extracts for virus DNA. There were no differences in percentage emergence and sex ratios of parasitoids among recombinant, wild-type, and control treatments. Significantly more wasps emerged from the 4-d cohort, but these wasps were significantly smaller than wasps from the 2-d cohort regardless of treatment. Finally, PCR found only 15-25% of the recovered H. virescens larvae and none of the emergent M. croceipes had detectable levels of viral DNA. Recombinant and wild-type viruses had a similar, minimal impact on emergent wasps, and the probability of virus dispersal via parasitoids is low in the system tested.
