Reduction in Damage to Cotton Plants by a Recombinant Baculovirus That Knocks Moribund Larvae of Heliothis virescens Off the Plant

Genetically engineered viral insecticides have considerable potential as biological control agents. Through genetic manipulation, the wild-type baculovirus Autographa californica nuclear polyhedrosis virus (WT AcNPV) has been modified to encode for an insect-selective toxin derived from the venom of the scorpion Androctonus australis to produce the recombinant virus AcAaIT. Larvae of tobacco budworm (Heliothis virescens) infected with the baculovirus AcAaIT fell off the plant 5-11 h before death and were unable to climb back on the plant to continue feeding. These larvae were capable of feeding if placed oil diet or confined to a leaf with a clip cage. Larvae infected with WT AcNPV died on the plant. Larvae infected with AcAaIT consumed significantly less foliage than larvae infected with WT AcNPV or uninfected controls. Thus, because larvae infected with the recombinant AcAaIT fall off the plant prior to cessation of feeding, there is a greater reduction in feeding damage than expected from lethal times. In addition, because AcAaIT causes a knock-off effect, the absence of liquefied cadavers on plants following treatment with AcAaIT may be more desirable to growers and consumers relative to treatment with wild-type virus. The relevance of our results to field use of recombinant viruses in pest control is discussed.