Enhanced Bioactivity of Recombinant Baculoviruses Expressing Insect-Specific Spider Toxins in Lepidopteran Crop Pests

Abstract

Two genetically enhanced isolates of theAutographa californicanuclear polyhedrosis virus (AcMNPV) expressing insect-specific neurotoxin genes from the spidersDiguetia canitiesandTegenaria agrestiswere evaluated for their commercial potential. Since prevention of feeding damage is of primary importance in assessing agronomic efficacy, a method for estimating the median time to cessation of feeding (FT50) was developed. Neonate droplet feeding assays with preoccluded virus samples were conducted to compare the FT50s and median survival times (ST50s) of larvae infected by the toxin-expressing recombinant viruses with those of larvae infected by wild-type AcMNPV and the appropriate polyhedrin-minus control viruses. Low dosages were used to minimize the effect of dosage on the response times, and the time to molting of noninfected larvae was used to audit variability among batches of larvae within and between tests. Appropriate statistics are discussed. To evaluate host spectrum, response times were compared in three lepidopteran insect pests,Trichoplusia niHubner,Spodoptera exigua(Hubner), andHeliothis virescens(Fabricius). The recombinant viruses expressing insect-specific toxin genes fromT. agrestisandD. canities,designated vAcTalTX-1 and vAcDTX9.2, respectively, significantly reduced both FT50and ST50in all three lepidopteran pests. Reductions in feeding times compared to the wild-type virus ranged from 16 to 39% with vAcTalTX-1 and 30 to 40% with vAcDTX9.2. Reductions in survi val time were lower, ranging from 18 to 33% with vAcTalTX-1 and 9 to 24% with vAcDTX9.2. While vAcTalTX-1 tended to kill faster than vAcDTX9.2, vAcDTX9.2 stopped feeding faster than vAcTalTX-1, suggesting that it would be more effective in reducing crop damage. © 1997 Academic Press.