Sensilla on the Antennal Flagellum of Sirex noctilio (Hymenoptera: Siricidae)

The antennal receptors of Sirex noctilio F. (Hymenoptera: Siricidae) were examined using scanning and transmission electron microscopy. Male and female antennae share five sensillum types: Bohm bristles, sensilla chaetica, sensilla basiconica, sensilla ampullacea, and uniporous contact chemoreceptors. Contact chemoreceptors make up approximate to 85 and 78% of the total sensilla on male and female antennae, respectively. On the most proximal flagellomere of the antennae, contact chemoreceptors are located in a shallow depression on the ventral surface. The number of contact chemoreceptors increases toward the distal end, covering two thirds of the circumference of each flagellomere. Contact chemoreceptors seem to be innervated by two sensory dendrites that terminate near the tip. In longitudinal section, a single subterminal pore is seen to be associated with each sensillum. Males had significantly more uniporous sensory pegs than females on the proximal half of the antennae. These receptors may play an important role in male identification, suggesting that a female-released contact pheromone may be used by this insect. The putative function of these sensilla types is discussed.