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

Morphological and behavioural studies were performed on male antennal tyloids of Pimpla turionellae (L.) (Hymenoptera: Ichneumonidae). SEM and TEM investigations revealed that tyloids located on 7th and 8th male antennomeres are release structures of integumentary glands rather than sensory organs. These are bicellular secretory units consisting of one secretory cell, with a well developed receiving canal, and a canal cell. The latter forms the evacuating canal, which connects the receiving canal to the external pore on the tyloids. Observations of mating behaviour showed that during the precopulatory phase, males typically perform antennal strokes during which the secretion containing tyloids comes in direct contact with the female antennae. Stroking intensity seemed to be correlated with female receptiveness, being more prolonged when females are initially unreceptive. When encountering receptive females, male stroking is usually limited or even omitted entirely. Results from behavioural comparisons between unmanipulated pairs and pairs in which male tyloids had been coated with glue, clearly indicate that the secretion mediates mate acceptance in females.