Comparative study of pheromone production and response in Swedish and Zimbabwean populations of turnip moth, Agrotis segetum

Analysis of female sex pheromone gland extracts of the turnip moth (or comm on cutworm), Agrotis segetum, from Zimbabwe revealed three compounds previo usly identified as sex pheromone components in the Swedish population, name ly (Z)-5-decenyl acetate (Z5-10:OAc), (Z)-7-dodecenyl acetate (Z7-12:OAc), and (Z)-9-tetradecenyl acetate (Z9-14:OAc). However, the proportions from t he Zimbabwean population (1 :0.25:0.03) differ from those in the Swedish po pulation(1 :5 :2.5). In addition, gas chromatography-mass spectrometric (GC -MS) analysis of the Zimbabwean female gland extracts revealed a trace of ( Z)-5-dodecenyl acetate (Z5-12:OAc). This compound has recently been identif ied as a fourth sex pheromone component for the Swedish population. Single- sensillum recordings from both Zimbabwean and Swedish populations showed th e presence of two types of antennal receptors responding to either Z5-10:OA c or Z7-12:OAc. In Zimbabwean males the Z7-12:OAc receptor neuron appeared to be confined to the basal and medial thirds of the antennal branches, whi le in Swedish males it was distributed along the entire antennal branch. Do se-response curves of Z5-10:OAc or Z7-12:OAc specific receptor neurons from males of both populations showed similar response profiles, but the neuron s of the Zimbabwean population showed higher maximal responses. In Eight tu nnel tests with Zimbabwean males, the three-component Zimbabwean blend of Z 5-10:OAc, Z7-12:OAc and Z9-14:OAc elicited significantly greater responses than the Swedish blend, but not significantly greater than pheromone glands from calling Zimbabwean females. (Z)-5-decenol (Z5-10:OH), a constituent o f gland extracts, exerted an antagonistic effect in the flight tunnel. In f ield tests conducted in Sweden, local males were preferentially attracted t o local females, while in Zimbabwe preferential attraction to local females was less pronounced. Local response to the Swedish and Zimbabwean syntheti c four-component blends mirrored the responses to the local females. Zimbab wean males are much more strongly attracted to Z5-10:OAc alone than are Swe dish males and the high concentrations of Z7-12:OAc and/or Z9-14:OAc presen t in the Swedish blend reduced attraction of Zimbabwean males. This reduced attraction appears to be counteracted by the trace amounts of Z5-12:OAc fo und in the Swedish four-component blend. Addition of Z5-12:OAc to the three -component Zimbabwean blend did not. however. significantly increase the tr ap catches of Zimbabwean males.