ENHANCED BIOACTIVITY OF RECOMBINANT BACULOVIRUSES EXPRESSING INSECT-SPECIFIC SPIDER TOXINS IN LEPIDOPTERAN CROP PESTS

Two genetically enhanced isolates of the Autographa californica nuclea r polyhedrosis virus (AcMNPV) expressing insect-specific neurotoxin ge nes from the spiders Diguetia canities and Tegenaria agrestis were eva luated for their commercial potential, Since prevention of feeding dam age is of primary importance in assessing agronomic efficacy, a method for estimating the median time to cessation of feeding (ST(50)s) was developed. Neonate droplet feeding assays with preoccluded virus sampl es were conducted to compare the FT(50)s and median survival times (ST (50)s) 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 th e effect of dosage on the response times, and the time to molting of n oninfected larvae was used to audit variability among batches of larva e within and between tests. Appropriate statistics are discussed. To e valuate host spectrum, response times were compared in three lepidopte ran insect pests, Trichoplusia ni Hubner, Spodoptera exigua (Hubner), and Heliothis virescens (Fabricius). The recombinant viruses expressin g insect-specific toxin genes from T. agrestis and D. canities, design ated vAcTalTX-1 and vAcDTX9.2, respectively, significantly reduced bot h FT50 and ST50 in all three lepidopteran pests. Reductions in feeding times compared to the wild-type virus ranged from 16 to 39% with vAcT alTX-1 and 30 to 40% with VAcDTX9.2. Reductions in survival time were lower ranging from 18 to 33% with vAcTalTX-1 and 9 to 24% with VAcDTX9 .2. While vAcTaITX-1 tended to kill faster than vAcDTX9.2, vAcDTX9.2 s topped feeding faster than vAcTalTX-1, suggesting that it would be mor e effective in reducing crop damage. (C) 1997 Academic Press.