PERCEPTION OF VOLATILES ASSOCIATED WITH SEX AND FOOD BY DIFFERENT ADULT FORMS OF THE BLACK-BEAN APHID, APHIS-FABAE

Electroantennograms (EAGs) were recorded from adult male and asexual forms (winged and wingless virginoparae and gynoparae) of the black bean aphid, Aphis fabae, during stimulation with two sex pheromone components, (+)-(4aS,7S,7aR)-nepetalactone and (-)-(1R,4aS,7S,7aR)-nepetalactol, as well as six plant volatiles, i.e. (E)-2-hexenal, (E)-2-hexenol-1, (Z)-3-hexenol-1, (Z)-3-hexenyl acetate, hexanal and allyl isothiocyanate. The male antennae are 1000-10,000 times more sensitive to nepetalactol and nepetalactone than to the plant compound (E)-2-hexenal. Besides this marked difference of EAG peak responses in males, the EAG rise and decay are slower for the sex pheromone components. Males are also much more sensitive to the sex pheromone components than asexual females. This high sensitivity correlates with a predominance of antennal secondary rhinaria, the major sites of pheromone perception in the male. However, it is the primary rhinaria on the antennae of the wingless asexual females that are responsible for pheromone perception. Male antennae are as responsive as the asexual female antennae to the plant volatiles. The specialization of the male for mate location is discussed.