Antennal sensilla of some aphidophagous Syrphidae (Diptera): fine structure and electroantennogramme study
Antennal sensilla of Metasyrphus venablesi (Cn.) and Eupeodes volucris O.S. (Diptera: Syrphidae) were studied by scanning and transmission electron microscopy. Males and females both had four types of sensilla. Three of these, two multiporous pitted (mpp) sensilla (one round-tipped and one pointed) and a multiporous grooved peg sensillum, were also confirmed by scanning electron microscopy on the following species: Syrphus torvus O.S. (♂, ♀), Syrphus opinator O.S. (♂, ♀), Scaeva pyrastri (L.) (♂, ♀), Dasysyrphus amalopsis O.S. (♂), Xanthogramma flavipes Lw. (♀), Brachyopa perplexa Cn. (♀), Pipiza sp. (♂), and Xylota quadrimaculata Lw.(♀). The fourth mpp sensillum had thicker walls and fewer pores. All four types were located among dense noninnervated setae on the antennal bulb and are probably olfactory. Electroantennogramme (EAG) study revealed antennae of female M. venablesi to be sensitive to some components of the aphid–plant oviposition site complex, namely, some green plant volatile substances (6-carbon alcohols), crushed pea aphids, crushed carnation petals, methylsalicylate and amylacetate, and to be nonresponsive to honeydew and some of its components (tryptophan, indolealdehyde, and indoleacetaldehyde).