Cantharidin-Secretion by Elytral Notches of Male Anthicid Species (Coleoptera: Anthicidae)

Within the beetle family Anthicidae or ant-like flower beetles the canthariphilous species N otoxus m onoceros shows a pair o f notch-like structures on the apices o f male elytra. A reser­ voir-like swelling at the apex o f each elytron contains a bilobed gland. Its glandular tubules run into the sclerotized notch. Gaschromatographic investigations o f elytral notches and the testes o f cantharidin-fed and unfed male N otoxus m onoceros revealed huge quantities o f can­ tharidin stored in these organs in fed specimens. Other body parts, such as legs, elytral parts or flight muscles, had low cantharidin-titres, both in cantharidin-fed and unfed beetles. The cantharidin-titres o f unfed individuals were very low compared with cantharidin-fed specimens, although cantharidin was present, mostly in notches. During sexual display the females bite several times into these notches and easily copulate, if the males had access to offered canthari­ din crystals. Thus, the elytral notches o f male N otoxus m onoceros seem to function as „testorgans“ for females which are able to select males with high cantharidin loads prior to copula­ tion. Even small quantities o f cantharidin stored in notches o f field caught specimens seem of advantage for males in competing for a female partner.