Aggregation of the scarab beetle Holotrichia consanguinea in response to female-released pheromone suggests secondary function hypothesis for semiochemical

The pheromone system of the scarab beetle H. consanguinea, an agricultural pest native to India, was investigated by extracting abdominal glands of females with dichloromethane and ether and analyzing them by GC-MS. Indoor bioassays with the natural product separated on a silica gel column showed that males responded to the hexane-ether (80:20) fraction by displaying a clear sexual behavior. Although the indoor bioassay-oriented approach did not lead to the identification of the active compound(s), field tests of candidate chemicals-anisole, indole, and phenol-showed that beetles responded strongly to anisole. Males and females were captured in anisole-baited traps in a ratio close to 1 : 1. Nearly the same sex ratio was also observed in beetles captured over the time during the flight activity of the beetles in the field. Because no clear evolutionary basis exists for why competing females are attracted to the semiochemical, it was simply referred to as a ''female-released pheromone.''