Pimpla turionellae; ANTENNAE-; Tyloids, function as glandular release structures & role in courtship, male; INTEGUMENTARY-GLANDS; Antennal glands; Role in courtship, males; COURTSHIP-; Male antennal gland secretion role; Tyloids function as release structures; PHEROMONES-; Male antennal gland secretion; Tyloids function as release structures & role in courtship Morphological and behavioural studies were performed on male antennal tyloids of Pimpla turionellae (L.) (Hymenoptera: Ichneumonidae). S.E.M. and T.E.M. investigations revealed that tyloids, located on 8th and 9th 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. none