Morphology and ultrastructure of antennal sensilla of Macrocentrus cingulum Brischke (Hymenoptera: Braconidae) and their probable functions.

Macrocentrus cingulum Brischke (Hymenoptera: Braconidae) is a polyembryonic endoparasitoid of the Asian corn borer, Ostrinia furnacalis and the European corn borer, Ostrinia nubilalis. To better understand the host location mechanism, we examined the external morphology and ultrastructure of the antennal sensilla of this parasitoid by using scanning and transmission electron microscopy. Antennae of male and female of the M. cingulum are filiform in shape, 5.90-6.64mm in length and consist of scape, pedicel, and flagellum with 39 and 40 flagellomeres, respectively. Cuticular pore and nine types of morphologically distinct sensilla were identified in both sexes, including two types of sensilla chaetica (nonporous), s. trichodea (nonporous), s. basiconica I (nonporous blunt tip), s. basiconica II (porous wall) and basiconica III (nonporous wall) with branched blunt tip, s. coeloconica with finger-like projections, protruded s. campaniform with central tip pore, and plate-like s. placodea (porous). We compared number, morphology, and distribution of sensilla between sexes. S. campaniform and non-porous basiconica type I may play a role in gustatory functions whereas type II, and s. placodea may play a function in detecting odor stimuli due to their pores wall. The sensilla chaetica and s. trichodea may be involved in mechnosensation. S. coeloconica probably plays a role as thermo-hygro receptor, whilst cuticular pores may detect odor stimuli. No differences in antenna shape and basic structure in the males and females, but male antennae length and width were significantly greater than those of females. Furthermore, males had more placodea than females. The sensilla types, morphology, and structure of both sexes were compared to those found in other parasitic hymenoptera, especially braconid wasps.