Recombinant, Catalytically Inactive Juvenile Hormone Esterase Enhances Efficacy of Baculovirus Insecticides

The insecticidal efficacy of baculoviruses can be enhanced by engineering the viral genome to express proteins that disrupt the physiology of the host insect. Here we describe the development of a genetically engineered Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV) which expresses a modified form of juvenile hormone esterase (JHE). Previously, two viruses expressing different modified JHEs were found to have a greater insecticidal effect on larvae of Trichoplusia ni and Heliothis virescens than a virus expressing wild-type JHE. To study a possible synergistic effect, the distinct mutations in the modified JHEs were combined in a new JHE construct. Two lysine residues were replaced with arginine residues to reduce the efficiency of lysosomal targeting (JHE-KK) and the catalytic serine was replaced with glycine, which eliminated catalytic activity (JHE-SG). The modified JHE, JHE-KSK, was expressed in a recombinant baculovirus, AcJHE-KSK. Larvae of H. virescens infected with this recombinant virus caused 44% less feeding damage to lettuce than larvae infected with the wild-type AcMNPV. However, AcJHE-KSK did not have significantly improved insecticidal properties over the parent viruses AcJHE-KK and AcJHE-SG, suggesting that the separate mutations have no major synergistic effect. Infection with a control recombinant baculovirus expressing JHE with the same lysine to arginine conversions and in which a catalytic histidine was converted to lysine (AcJHE-KHK) did not reduce feeding damage compared with that caused by larvae infected with AcMNPV.