Survival Times and Lethal Doses for Wild and RecombinantAutographa californicaNuclear Polyhedrosis Viruses in Different Instars ofPseudoplusia includens,

Survival times and lethal doses were determined inPseudoplusia includens(Walker) for three viruses: wild-typeAutographa californicanuclear polyhedrosis virus (AcMNPV.WT), recombinant AcMNPV encoding juvenile hormone esterase (AcMNPV.JHEKK), and recombinant AcMNPV encoding a scorpion toxin (AcMNPV.AaIT). Survival time was reduced significantly in insects treated with AcMNPV.AaIT compared to AcMNPV.WT, but >80% of insects treated with AcMNPV.AaIT in instars 2–5 were still alive after 6 days. For all three viruses, second instars had the longest survival times and fourth instars had the shortest, and survival time decreased with increasing viral concentration except at the highest concentrations. Median lethal doses (LD50) of all three viruses, based on units of polyhedral occlusion bodies (POB) per insect, increased significantly (based on lack of overlap of 95% C.L.) in every larval instar, except that LD50s in fourth instars were not significantly different from those in second instars. LD50s calculated in units of POB per insect body weight were significantly lower in fourth instars than in first, second, third, or fifth instars for all three viruses. The only significant difference in LD50among viruses was in fifth instars, in which AcMNPV.JHEKK had a higher LD50than AcMNPV.WT. The results indicate that AcMNPV.AaIT is likely to be more efficacious than AcMNPV.JHEKK for control ofP. includens.However, even AcMNPV.AaIT did not kill quickly enough to be competitive with many commercial insecticides.