Chemical defense in the stink bug Cosmopepla bimaculata

Adult Cosmopepla bimaculata discharge a volatile secretion from paired Vent ral metathoracic glands (MTG) when disturbed. Collected Volatiles were simi lar 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-dode cane (2%), a tridecene isomer (1%), and n-undecane, n-tetradecane, and n-pe ntadecane (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 proj ection and a pleural scent area consisting of specialized rough cuticle sur rounding the gland opening. Insects can selectively discharge from either t he right or left gland or both glands simultaneously, can control the amoun t of fluid ejected, and can resorb the ejected secretion droplet back into the gland reservoir. In feeding trials, killdeer (Charadrius vociferus), st arlings (Sturnus vulgaris), robins (Turdus migratorius), and anole lizards (Anolis carolinensis) rejected or demonstrated aversion to feeding on the b ugs. Furthermore, bugs that lacked the secretion were more susceptible to p redation than bugs with secretion, suggesting that the secretion functions in defense against predators.