Identification of the gland secreting oviposition-deterring pheromone in the cabbage seed weevil, Ceutorhynchus assimilis, and the mechanism of pheromone deposition

After laying an egg into a pod of Brassica napus, the female cabbage seed w eevil, Ceutorhynchus assimilis, brushes the caudal setae of the eighth abdo minal tergite (VIII UT) on the host pod as she walks along it, depositing o viposition-deterring pheromone (ODP). The VIII UT is periodically extended and withdrawn, thus repeatedly rubbing against the posterior fold of the se venth urotergite (VII UT) which bears the individual outlets of glandular e pidermal cells. In post-diapause, sexually mature, gravid (i.e. oviferous) females (virgin or mated) the cells of this VII UT gland were hypertrophic, showing intense secretory activity. Extracts of VIT UT from these individu als elicited strong electrophysiological responses from antennal club gusta tory sensilla and deterred oviposition. In pre-diapause (sexually immature) females, the cells of the VII UT gland were neither hypertrophic nor activ e and an extract of their VII UT elicited no significant electrophysiologic al or behavioural response. Extract of female rectum was a less potent ovip osition deterrent than VII UT extract and elicited an electrophysiological response similar to male rectum extract. An extract of ovarian calyces and ovaries elicited no behavioural response. We conclude that ODP is secreted by the epidermal cells of the VII UT posterior fold. (C) 1999 Elsevier Scie nce Ltd. All rights reserved.