BETA-GLUCOSIDASE - AN ELICITOR OF HERBIVORE-INDUCED PLANT ODOR THAT ATTRACTS HOST-SEARCHING PARASITIC WASPS

Cabbage plants respond to caterpillar (Pieris brassicae) herbivory by releasing a mixture of volatiles that makes them highly attractive to parasitic wasps (Cotesia glomerata) that attack the herbivores. Cabbag e leaves that are artificially damaged and subsequently treated with g ut regurgitant of P. brassicae caterpillars release a volatile blend s imilar to that of herbivore-damaged plants. We demonstrate the presenc e of beta-glucosidase in P. brassicae regurgitant. Leaves treated with commercial beta-glucosidase (from almonds) release a volatile blend s imilar to that of leaves treated with P. brassicae regurgitant. In a f light bioassay, leaves treated with almond beta-glucosidase are highly attractive to the parasitic wasp C. glomerata. Furthermore, the wasps do not discriminate between cabbage leaves treated with almond beta-g lucosidase and leaves treated with larval regurgitant. beta-Glucosidas e was also recorded in cabbage leaf extract, but this is not as effect ive as caterpillar beta-glucosidase in eliciting the volatile producti on. Caterpillars that feed on a beta-glucosidase-free diet secrete the enzyme, and their regurgitant is an effective elicitor of the plant r esponse. These findings strow that beta-glucosidase is a P. brassicae- secreted elicitor of the defense response of cabbage plants to herbivo re injury, inducing the emission of volatiles that are used by parasit oids of the herbivore to locate their victims.