Antennal glands in male bees: structures for sexual communication by pheromones?

Morphological investigations were conducted on male antennae of three Apidae species, Apis mellifera, Bombus pascuorum and Xylocopa violacea. Male antennal glands were present in all species, with some differences regarding both external morphological characters and internal cytological features. There are externally obvious sites of pheromonal release (provided with evident pores) in B. pascuorum and X. violacea males, while pores are lacking in A. mellifera males. Internally A. mellifera presents a glandular complex composed of class 1 secretory cells, while the two other species possess two types of glands (with class 1 and class 3 secretory cells) associated with the same release sites. The functional hypothesis for the secretion of these glands is that they may act as a sex pheromone during courtship behaviour.