Fine Structure and Distribution of Antennal Sensilla of the Predatory Clerid Beetle, Thanasimus lewisi (Coleoptera: Cleridae)

Abstract

The predatory clerid beetle Thanasimus lewisi (Jacobson) (Coleoptera: Cleridae) is an important predator of bark beetles (Scolytidae) and has been used in China for the biological control of the larch bark beetle Ips subelongatus Motschulsky and the spruce bark beetle Ips typographus Linnaeus. In this study, the number, external morphology and distribution of antennal sensilla of T. lewisi were determined using scanning electron microscopy. The filiform antennae of both sexes of both species consist of the scape, pedicel, and nine flagellomeres. Two types of sensilla chaetica (SC1 and SC2), four types of sensilla basiconica (SB1, SB2, SB3 and SB4), two types of sensilla trichodea (ST1 and ST2), and Böhm's bristles (BB) were identified according to the morphology and fine structure of each type of sensilla in both sexes. No difference in shape, structure, sensilla distribution and typology was observed between the sexes. The density of sensilla was greater on the last 3 than on the first 8 segments. SC1, SC2, ST1 and ST2 occurred on all antennal segments in both sexes. SB1, SB2 and SB3 were absent on the first 4 segments of the antennae in both sexes. SB4 were found only on the last 2 segments of the antennae. BB only occurred on the scape and pedicel. The distal antennal sensilla of T. lewisi had notably more sensilla than proximal ones in type and number, indicating this is the main area to detect environmental stimuli for feeding or oviposition. These structures likely have roles in the host locating and habitat searching behavior of adult T. lewisi and suggest future studies on the olfaction and host location behavior of T. lewisi and other coleopteran predators.