Functional morphology of antennal chemoreceptors of the parasitoid Microplitis croceipes (Hymenoptera : Braconidae)

The specialist parasitoid, Microplitis croceipes (Cresson) (Hymenoptera: Br aconidae), uses chemical cues from plants damaged by herbivore-feeding and also plant by-products in host location and acceptance. These chemicals are detected by the wasp's antennae. We conducted scanning and transmission el ectron microscopy studies of male and female M. croceipes antennae and dete cted no distinct morphological differences in the chemoreceptors between th e sexes. Male antennae are approximately twice as long as female antennae. We found five morphological sensillar types in both sexes: sensilla (s) tri chodea were the most abundant and distributed over the whole antenna; s. ch aetica were present in low numbers only on the scape and pedicel; and a. ba siconica, s. coeloconica and elongated s. placodea were found only on the f lagellum. Ultrastructural investigations revealed pore systems on s. basico nica and s. placodea. In s. placodea, sensory neurons run parallel to the l ongitudinal axis of the sensilla with terminal pores. We recorded responses from single olfactory receptor neurons in s. placodea to two plant-emitted volatiles, cis-3-hexenol and ocimene, and two anthropogenic compounds, cyc lohexanone and 2- diisopropylaminoethanol. Male receptor neurons were more sensitive than those of females with significantly higher spike frequency b eing registered from neurons in males. (C) 2001 Elsevier Science Ltd. All r ights reserved.