Immunosuppressive action of pyriproxyfen, a juvenile hormone analog, enhances pathogenicity of Bacillus thuringiensis subsp. kurstaki against diamondback moth, Plutella xylostella (Lepidoptera: Yponomeutidae)

Two developmental hormones, juvenile hormone (JH) and 20-hydroxyecdysone (20E), could modulate hemocyte behavior of diamondback moth, Plutella xylostella. JH inhibited hemocyte-spreading of P. xylostella but 20E antagonized the JH inhibitory action. Pyriproxyfen, a JH analog, mimicked the JH inhibitory effect on hemocyte behavior. When pyriproxyfen was treated with Bacillus thuringiensis subsp. kurstaki against final instar larvae of P. xylostella, it significantly enhanced the bacterial pathogenicity. These results demonstrate that immunosuppression enhances entomopathogenicity of B. thuringiensis.