European corn borer: Pheromonal catabolism and behavioral response to sex pheromone

Abstract

When physiologically excessive amounts of the female sex pheromone of the European corn borer (ECB) or esters analogous to the pheromone were applied to the antennae of males, their behavioral responsiveness to pheromone in a flight tunnel was significantly impaired for 2 hr. Concurrent quantitative analyses of heptane extracts of the male antennae by gasliquid chromatography showed that the compounds applied to antennae were hydrolyzed and, at 2 and 4 hr posttreatment, little or none of the compound applied or hydrolysis product was detectable in the antennal extracts. After 4 hr of in vivo incubation, male responsiveness to pheromone was restored among moths treated with the analogs but not among moths treated with pheromone. Esterase activity on the antennae was moderately inhibited in vivo by a pheromone analog that is a so-called transition-state esterase inhibitor, 1,1, 1-trifluoro-14-heptadecen-2-one. However, the analog did not inhibit male behavior when it was coevaporated with pheromone in a flight-tunnel assay. Therefore, in the presence of pheromone, the analog did not compete well for esterase or the pheromone receptor. Treating the antennae of intact males with tetrahydrofuran obliterated sex pheromone response capability in males, but the treatment did not significantly attenuate esterase and other catabolic activity of the antennae. Indications are that degradation of esters on the ECB antennae involves substrate-nonspecific esterase activity and other metabolic processes that in turn remove hydrolysis products from the antennae. Maintenance of a male's ability to respond to pheromone is linked to these processes.