Chemical Defense in the Stink Bug Cosmopepla bimaculata

Abstract

Adult Cosmopepla bimaculata discharge a volatile secretion from paired ventral metathoracic glands (MTG) when disturbed. Collected volatiles were similar in both sexes and consisted of n-tridecane (67%), (E)-2-decenal (12%), (E)-2-decenyl acetate (12%), (E)-2-hexenal (3%), hexyl acetate (2%), n-dodecane (2%), a tridecene isomer (1%), and n-undecane, n-tetradecane, and n-pentadecane (all <1%). In addition, undisturbed males produced a novel insect compound, (E)-8-heneicosene, whose function is unknown. The MTG secretion emerges as an enlarging droplet, which is held in place by a cuticular projection and a pleural scent area consisting of specialized rough cuticle surrounding the gland opening. Insects can selectively discharge from either the right or left gland or both glands simultaneously, can control the amount of fluid ejected, and can resorb the ejected secretion droplet back into the gland reservoir. In feeding trials, killdeer (Charadrius vociferous), starlings (Sturnus vulgaris), robins (Turdus migratorius), and anole lizards (Anolis carolinensis) rejected or demonstrated aversion to feeding on the bugs. Furthermore, bugs that lacked the secretion were more susceptible to predation than bugs with secretion, suggesting that the secretion functions in defense against predators.