Abstract
Analysis of female sex pheromone gland extracts of the turnip moth (or common cutworm), Agrotis segetum, from Zimbabwe revealed three compounds previously identified as sex pheromone components in the Swedish population, namely (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 the Zimbabwean population (1 :0.25:0.03) differ from those in the Swedish population(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 identified as a fourth sex pheromone component for the Swedish population. Single-sensillum recordings from both Zimbabwean and Swedish populations showed the presence of two types of antennal receptors responding to either Z5-10:OAc 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, while in Swedish males it was distributed along the entire antennal branch. Dose-response curves of Z5-10:OAc or Z7-12:OAc specific receptor neurons from males of both populations showed similar response profiles, but the neurons of the Zimbabwean population showed higher maximal responses. In Eight tunnel tests with Zimbabwean males, the three-component Zimbabwean blend of Z5-10: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 of gland extracts, exerted an antagonistic effect in the flight tunnel. In field tests conducted in Sweden, local males were preferentially attracted to local females, while in Zimbabwe preferential attraction to local females was less pronounced. Local response to the Swedish and Zimbabwean synthetic four-component blends mirrored the responses to the local females. Zimbabwean males are much more strongly attracted to Z5-10:OAc alone than are Swedish males and the high concentrations of Z7-12:OAc and/or Z9-14:OAc present in the Swedish blend reduced attraction of Zimbabwean males. This reduced attraction appears to be counteracted by the trace amounts of Z5-12:OAc found in the Swedish four-component blend. Addition of Z5-12:OAc to the three-component Zimbabwean blend did not. however. significantly increase the trap catches of Zimbabwean males.
