Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/1999
Publication Date: N/A
Interpretive Summary: A question of basic interest is how various insects avoid predation by birds and other vertebrates. Scientists at the Department of Biology, Illinois State University, and the ARS laboratory (NCAUR) at Peoria, Illinois, collaborated to define the chemical secretion from a brightly colored "stink bug" and how this secretion deters feeding by three bird species and one kind of lizard. The sensitive equipment and new techniques in use at NCAUR allowed rapid identification of the defensive chemicals. One compound, a very unusual "trans" alkene, was found only from males and only at certain times of the year. It may be involved in reproduction and mate-finding (as a pheromone) rather than in insect defense. The study produced a carefully documented example of how natural chemicals can affect the interactions of insects and their predators, and it revealed new chemical information that will contribute to scientists' better understanding of chemical communication among stink bugs, some species of which are important agricultural pests but which are still poorly understood with respect to pheromones.
Technical Abstract: Adult Cosmopepla bimaculata (Thomas) discharge a volatile secretion from paired ventral metathoracic glands (MTG) when disturbed. Collected volatiles were similar in both sexes and consisted of n-tridecane (68%), (E)-2-decenal (12%), (E)-2- decenyl acetate (12%), (E)-2-hexenal (4%), (E)-2-hexenyl acetate (2%), n-docecane (2%), and n-undecane, n-tetradecane, and 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 glands or from 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 vociferus L.), starlings (Sturnus vulgaris L.), robins (Turdus migratorius L.), and anole lizards (Anolis carolinensis Voigt) 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.