Effect of deltamethrin treatment on lepidopteran larvae infected with baculoviruses expressing insect-selective toxins micro-Aga-IV, As II, of Sh 1

Modification of sodium channels by pyrethroids is promoted by channel opening. The insect-specific neurotoxins mu-Aga-IV from the spider Agelenopsis aperta, As II from the sea anemone Anemonia sulcata, and Sh I from the sea anemone Stichadactyla helianthus all increase sodium channel opening and so we tested each of them in combination with deltamethrin for synergistic insecticidal activity. We found that As II increased the insecticidal activity of deltamethrin against the blowfly Lucilia sericata. We also examined the effect of deltamethrin on the infectivity and virulence of Autographa californica nuclear polyhedrosis virus (AcMNPV) and recombinant toxin-expressing viruses in both dose-dependent and time-mortality studies. The recombinant viruses expressed chimeric synthetic genes for mu-Aga-IV, As II, or Sh I (genes mag4, sat2, and ssh1, respectively). When Trichoplusia ni larvae were infected with a LC20 of the recombinant viruses and treated with a LC20 of deltamethrin in diet incorporation bioassays, the doses were strictly additive. A cooperative decrease in mortality rate was observed in droplet feeding bioassays when a low dose (LC20) of deltamethrin and high doses of toxin-expressing viruses were fed to larvae but this effect was host-dependent. In T. ni, only wild-type AcMNPV and a recombinant expressing mag4 under very late viral promoter control exhibited reduced times in controlling host feeding and mortality in the presence of deltamethrin. For Heliothis virescens, larvae infected with sat2-expressing viruses displayed shorter feeding times in the presence of deltamethrin than those infected with virus alone but only at very high virus doses. H. virescens larvae infected with wild-type AcMNPV and a mag4-expressing recombinant had shorter feeding times and also shorter effective and lethal times in the presence of deltamethrin. Our results indicate that coapplication of this pyrethroid will confer little or no advantage in field applications of recombinant baculovirus pesticides and that application of pyrethroids will probably have no adverse affect on recombinant virus efficacy unless it deters larval feeding and virus acquisition.