BIOLOGICAL AND MICROBIAL CONTROL Impact of Recombinant Baculovirus Field Applications on a Nontarget Heliothine Parasitoid, Microplitis croceipes (Hymenoptera: Braconidae) CHAD R. SMITH, KEVIN M. HEINZ, CHRISTOPHER G. SANSONE, 1 AND J. LINDSEY FLEXNER 2 Biological Control Laboratory, Department of Entomology, Texas A&M University, College Station, TX 77843Ð2475 J. Econ. Entomol. 93(4): 1109Ð1117 (2000) ABSTRACT The kill times of two viruses infectious to the heliothine pest complex indigenous to Texas cotton have been signiÞcantly reduced by expressing a scorpion toxin gene. Autographa californica nucleopolyhedrovirus (NPV) and Helicoverpa zea NPV express the toxin only in per- missive 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 Þve treatments of study. Larvae were previously parasitized 2 and 4 d before being conÞned for 72 h to cotton terminals treated with Þeld 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. SigniÞcantly more wasps emerged from the 4-d cohort, but these wasps were signiÞcantly smaller than wasps from the 2-d cohort regardless of treatment. Finally, PCR found only 15Ð25% 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. KEY WORDS Microplitis croceipes, Heliothis virescens, recombinant baculovirus, risk assessment, endoparasitoid, cotton RECOMBINANT DNA TECHNOLOGY and advances in genomic mapping have been combined to improve the insecticidal qualities of naturally occurring baculovi- ruses (reviewed by Bonning and Hammock 1996). Although the host speciÞcity of wild-type baculovi- ruses make them ideal components of integrated pest management (IPM) programs, their usage in pest sup- pression has been limited to plants able to tolerate moderate levels of feeding damage while viral infec- tion slowly kills the pests. Recently, the lengthy in- fection cycle has been signiÞcantly shortened by in- corporating insecticidal toxin genes into the viral genomes. Genes coding for diuretic hormone (Maeda 1989), juvenile hormone esterase (Hammock et al. 1990), maize mitochondrial protein (Korth and Lev- ings 1993), mite neurotoxin (Popham et al. 1997, Tomalski and Miller 1991), and insect-speciÞc scor- pion neurotoxins (Carbonell et al. 1988, Maeda et al. 1991, McCutchen et al. 1991, Stewart et al. 1991) have been successfully incorporated to produce recombi- nant baculoviruses able to cause lethal infections and terminate feeding in their respective host larvae more rapidly than their wild-type progenitor viruses. Recombinant viruses of Autographa californica nucleopolyhedrovirus (AcMNPV) and Helicoverpa zea NPV (HzSNPV) have been engineered to express the insect-selective toxin genes of the scorpion Leiurus quinquestriatus hebraeus (Birula) (Scorpiones: Buthi- dae) (abbreviated as LqhIT2). These viruses naturally infect Helicoverpa zea (Boddie) (Lepidoptera: Noc- tuidae) and Heliothis virescens (F.) (Lepidoptera: Noctuidae), key pests of cotton, Gossypium hirsutum (L.) (Gro ¨ ner 1986). Nontarget species, such as pred- ators and parasitoids of the heliothine pest complex, are not able to support viral replication; thus they should not be directly affected by these toxin-produc- ing viruses (Huang et al. 1997). However, if these scorpion toxin recombinants were applied to cotton, natural enemies would be likely to indirectly encoun- ter the expressed toxins by consuming infected he- liothines actively producing the toxins. Laboratory studies have examined both predator- host-virus and parasitoid-host-virus interactions. Predators apparently do not suffer deleterious effects from consuming wild-type or recombinant virus-in- 1 Texas Agricultural Extension Service, Texas A&M University, 7887 U.S. Highway 87 North, San Angelo, TX 76901Ð9782. 2 DuPont Agricultural Products, Stine-Haskell Research Center, P.O. Box 30, Elkton Road, Newark, DE 19714. 0022-0493/00/1109Ð1117$02.00/0  2000 Entomological Society of America Downloaded from https://academic.oup.com/jee/article/93/4/1109/2217237 by guest on 27 May 2022