Antennal sensilla of the click beetle, Melanotus villosus (Geoffroy) (Coleoptera : Elateridae)

The typology, number and placement of antennal sensilla of the click beetle Melanotus villosus (Geoffroy) (Coleoptera: Elateridae) were studied using scanning electron microscopy. On both the males and females the antennae ar e made up of the scape, pedicel and nine flagellomeres. Two types of basico nic sensilla, three types of trichoid sensilla, one type of styloconic sens illa, one type of chetoid sensilla, dome-shaped sensilla, grooved pegs, and Bohm sensilla all appear on the antennae of the beetles of both sexes, wit h the exception of trichoid sensilla type II, whose large number (average o f 1635 hairs per antenna) was found only in male beetles. Sensilla trichode a type II evidently respond to the sex pheromone produced by the female bee tle. Unlike the other two click beetles, studied up till now, Agriotes obsc urus and Limonius aeruginosus, the trichoid and basiconic sensilla of M. vi llosus, whose proven or assumed function is olfactory, are located predomin antly on the flagellomeres' ventral extensions. It is assumed that the plac ement of the olfactory sensilla, mainly on the ventral side of M. villosus' s antennae, and their more or less even distribution on the flagellomeres, can be seen as morphological adaptation of this species of insect, whose sp ecific behavioural reaction of olfactory searching is flying, both before a nd after contact with an odour plume. (C) 1999 Elsevier Science Ltd. All ri ghts reserved.