Tyloids in Pimpla turionellae (L.) are release structures of male antennalglands involved in courtship behaviour (Hymenoptera : Ichneumonidae)

Morphological and behavioural studies were performed on male antennal tyloi ds of Pimpla turionellae (L.) (Hymenoptera: Ichneumonidae). S.E.M. and T.E. M. investigations revealed that tyloids, located on 8th and 9th male antenn omeres, are release structures of integumentary glands rather than sensory organs. These are bicellular secretory units consisting of one secretory ce ll, with a well-developed receiving canal, and a canal cell. The latter for ms the evacuating canal, which connects the receiving canal to the external pore on the tyloids. Observations of mating behaviour showed that during t he precopulatory phase, males typically perform antennal strokes during whi ch the secretion containing tyloids comes in direct contact with the female antennae. Stroking intensity seemed to be correlated with female receptive ness, being more prolonged when females are initially unreceptive. When enc ountering receptive females, male stroking is usually limited or even omitt ed entirely. Results from behavioural comparisons between unmanipulated pai rs and pairs in which male tyloids had been coated with glue, clearly indic ate that the secretion mediates mate acceptance in females. (C) 1999 Elsevi er Science Ltd. All rights reserved.