Olfactory basis of cannibalism in grasshoppers (Orthoptera: Acididae): I. laboratory assessment of attractants.

Two laboratory-reared and five field-collected species of grass-hoppers were assayed for behavioral responses to volatile chemicals emitted from grasshopper cadavers using a two-choice olfactometer with no stimulus as a control. Necrophilic and necrophobic responses to the stimuli were dependent upon species, sex, development, starvation, crowding, and attractant. Laboratory-rearedMelanoplus differentialis (Thomas) and field-collectedHadrotettix trifasciatus (Say) andAulocara elliotti Thomas exhibited significant responses to the cadavers. Females of these three species showed significant movement towards the cadavers, but males were not significantly necrophilic. All tested developmental stages ofH. trifasciatus (fourth-instar nymphs through adults) showed significant attraction to cadavers. FedM. differentialis adults andH. trifasciatus adults and nymphs were significantly attracted to cadavers, but starved individuals were either repelled or exhibited no significant response. Although femaleA. elliotti from an uncrowded population were significantly attracted to cadavers, females from a crowded population were significantly repelled from cadavers. Contraspecific cadavers more frequently elicited a measurable response in adultM. sanguinipes andH. trifasciatus than did conspecific cadavers, and only contraspecific cadavers yielded a significant (necrophilic) response. AlthoughM. differentialis was necrophilic, neither males nor females were significantly attracted to water.