DISTRIBUTION OF OLFACTORY AND SOME OTHER ANTENNAL SENSILLA IN THE MALE CLICK BEETLE AGRIOTES OBSCURUS L. (COLEOPTERA, ELATERIDAE)

The distribution of 5 types of sensilla was statistically analysed on the 4-10th antennal segments of the male click beetle Agr io res obscu rus (Coleoptera : Elateridae). The distribution pattern of the trichoi d pheromone receptors (T-2 sensilla) and the olfactory basiconic B1B2 sensilla on the antennae of male A. obscurus differs significantly fro m the distribution pattern of the contact chemoreceptors (T-1 sensilla ) and probably the non-olfactory B-7 and D sensilla. A significant pec uliarity of the distribution of olfactory sensilla is their location o n the antennal segments as 2 separate (dorsal and ventral) fields of s ensilla. The numbers of T-2 and B1B2 sensilla on dorsal fields of sens illa of the 4-10th segments increase towards the apex of the antenna n early linearly. On ventral fields of sensilla of the 4-10th antennal s egments, the number of B1B2 sensilla is nearly uniform; the number of T-2 sensilla in the proximal part of the antenna increases towards the apex, but on distal segments of the antenna their number stabilizes. It is characteristic of both the T-2 and to B1B2 sensilla that their n umbers are slightly greater on anterior than posterior sides of dorsal sensillar fields, and also greater on posterior than anterior sides o f ventral sensillar fields of all antennal segments investigated. We a ssume that the number of olfactory sensilla on the antennae of male be etles coincides with the distribution of strength of olfactory signal on the antennae of beetles orientating in an odour plume. The distribu tion patterns of T-2 and B1B2 sensilla of the male A. obscurus can be related to some behavioural peculiarities of olfactory orientation (wa lking or flying and vibrating of the antennae). (C) 1997 Elsevier Scie nce Ltd.