Antennal sensilla and electrophysiological response of male and female Spodoptera frugiperda (Lepidoptera: Noctuidae) to conspecific sex pheromone and plant odors

The olfactory system of male and female Spodoptera frugiperda (J.E. Smith) was studied by examining the morphology and distribution of antennal sensilla and determining the responses of both sexes to conspecific female sex pheromone components and plant volatiles using electroantennography (EAG). Seven types of sensilla were observed on the flagellum of the antennae: trichodea, chaetica, coeloconica, styloconica, auricilica, squamiformia, and basiconica. Only one type of trichodea sensilla was found on the antennae of both sexes, but these sensilla were more abundant on male than on female. EAG records of both sexes to 10-μg stimulus loads of six pheromone components showed that (Z)-7-dodecenyl acetate (Z7-12: Ac) and (Z)-9-dodecenyl acetate (Z9-12: Ac) elicited larger responses than those evoked by (Z)-11-hexadecenyl acetate (Z11-16: Ac), (Z, E)-9,11-tetradecadienyl acetate (Z9, E11-14: Ac), (Z, E)-9,12-tetradecadienyl acetate (Z9, E12-14: Ac), and hexane in female antennae. In the case of male antennae, (Z)-9-tetradecenyl acetate (Z9-14: Ac) and Z9, E12-14: Ac evoked larger EAG responses than those elicited by Z7-12: Ac, Z11-16: Ac, Z9, E11-14: Ac, and hexane. The compounds that selectively evoked larger EAG responses from males than females were Z9, E12-14: Ac, and Z9-14: Ac. Dose-response experiments showed that, at the lowest dose tested, Z9-14: Ac and Z9, E12-14: Ac elicited larger EAG responses than Z9-12: Ac and Z7-12: Ac in male antennae. At the highest doses tested, the diene elicited the largest EAG responses. In the case of female antennae, the dose, but not the pheromone component, had a significant effect. Male and female responses to 10-μg stimulus loads of 16 plant volatiles showed that hexan-1-ol evoked larger EAG responses in comparison with those elicited by hexanal, (E)-3-hexenol, 2-carene, phellandrene, limonene, β-pinene, and hexane. The response of male antennae was significantly stronger than the female. Dose-response experiments showed that both sexes appeared to be most sensitive to alcohols, particularly at the highest dose tested.