SURVIVAL TIMES AND LETHAL DOSES FOR WILD AND RECOMBINANT AUTOGRAPHA-CALIFORNICA NUCLEAR POLYHEDROSIS VIRUSES IN DIFFERENT INSTARS OF PSEUDOPLUSIA-INCLUDENS

Survival times and lethal doses were determined in Pseudoplusia includ ens (Walker) for three viruses: wild-type Autographa californica nucle ar polyhedrosis virus (AcMNPV.WT), recombinant AcMNPV encoding juvenil e hormone esterase (AcMNPV.JHEKK), and recombinant AcMNPV encoding a s corpion toxin (AcMNPV.AaIT). Survival time was reduced significantly i n 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 surviva l times and fourth instars had the shortest, and survival time decreas ed with increasing viral concentration except at the highest concentra tions, Median lethal doses (LD50) Of all three viruses, based on units of polyhedral occlusion bodies (POB) per insect, increased significan tly (based on lack of overlap of 95% C.L.) in every larval instar, exc ept that LD(50)s in fourth instars were not significantly different fr om those in second instars. LD(50)s calculated in units of POB per ins ect body weight were significantly lower in fourth instars than in fir st, second, third, or fifth instars for all three viruses, The only si gnificant difference in LD50 among viruses was in fifth instars, in wh ich AcMNPV.JHEKK had a higher LD50 than AcMNPV.WT. The results indicat e that AcMNPV.AaIT is likely to be more efficacious than AcMNPV.JHEKK for control of P. includens. However, even AcMNPV.AaIT did not kill qu ickly enough to be competitive with many commercial insecticides. (C) 1997 Academic Press.