Differences among sibling speciesRhagoletis mendax andR. pomonella (diptera: ephritidae) in their antennal sensitivity to host fruit compounds.

Prior electrophoretic and morphological studies have identified two closely related, economically important tephritid flies,R. mendax (Curran) andR. pomonella (Walsh), which infest the fruits of ericaceous and rosaceous plants, respectively. Further studies also have shown consistent differences among these species in their ovipositional preferences for apples and highbush blueberries and have determined that their ovipositional behavior is elicited by extracts obtained from these fruits. In this paper we report the results of an experiment that tested whether these species show distinct electroantennogram (EAG) responses to a large array of compounds present in gas chromatograph-fractionated pentane extracts of apples and highbush blueberries.R. mendax andR. pomonella flies were found to have significant differences in their antennal sensitivity to 11 blueberry and nine apple extract peaks, which correspond to 24.4% of all blueberry and 25.0% of all apple peaks that elicited a measurable EAG response from either species. Interspecific differences in peripheral sensitivity were more pronounced for blueberry than apple extract;R. pomonella flies were most sensitive to blueberry compounds with low retention times, whereasR. mendax flies responded to blueberry compounds with a broader range of retention times. Both species were most sensitive to apple peaks with high retention times. The retention times of most apple and blueberry peaks that elicited EAG responses fromR. mendax andR. pomonella flies were different from the retention times of seven attractant fruit esters that were previously identified by Fein et al. (1982). The identification of these unknown apple and blueberry compounds could lead to the discovery of new chemical cues that mediate the host-plant preferences of these sibling species.