Scanning electron microscopy studies of antennal sensilla of Pteromalus cerealellae (Hymenoptera: Pteromalidae).

Pteromalus cerealellae (Ashmead) (Hymenoptera: Pteromalidae) is an ectoparasitoid of several insect pests of stored products. In order to provide requisite background information to support our ongoing research on its host location mechanisms, we examined the external morphology of the antennal sensilla of this parasitoid using scanning electron microscopy. Antennae of male and female P. cerealellae are geniculate in shape, approximately 1300mum in length, and consist of 15 antennomeres. Eight morphological sensilla types were recorded in both sexes, including four types of the highly abundant and widely distributed sensilla trichodea (types I, II and IV are aporous while type III is multiporous), basiconic capitate peg sensilla, coeloconic sensilla, chaetica sensilla, and the most conspicuous plate-like placoid sensilla. Detailed examination of sensilla morphological features including pore presence and numbers suggest that the multiporous type III sensilla trichodea and the multiporous placoid sensilla may play a role in olfaction, whereas the uniporous chaetica sensilla may function as contact chemoreceptors. The types I and II sensilla trichodea are presumably mechanosensory, while the type IV sensilla trichodea may function as proprioceptors. The basiconic capitate peg sensilla and coeloconic sensilla probably function in thermo-hygro reception. Although the shape, structure, and size of antennae of males and female were basically similar, major differences were recorded between the sexes in the distribution of some sensilla types. The type II sensilla trichodea and the multiporous placoid sensilla are relatively more abundant in females, whereas males have greater number of the multiporous type III sensilla trichodea than females. These results are discussed in relation to the possible roles of the sensilla types in the host location behavior of P. cerealellae.