Electroantennogram responses of western corn rootworm (Coleoptera: Chrysomelidae) adults in relation to maize silk morphology and phenology

Volatile maize, Zea mays L., silk semiochemicals are attractive to Diabrotica virgifera virgifera LeConte, western corn rootworm, adults and were evaluated using an electroantennogram (EAG) to determine the morphology and phenology of silk that is most EAG active. Senescing portions (the brown portion that protrudes from the tip of the ear) of silks 7-24 d after silk emergence elicited strong EAG responses from adults, significantly stronger than EAG responses to the green portion of silks (under the husks) or whole silks from die same phenology. When the EAG response of adults to the portion of silk that protrudes from the tip of the eat was evaluated at different phenologies, EAG response was significantly stronger to silks 7-24 d past silk emergence than to silks 1-4 d past silk emergence. Both males and females gave strong EAG responses to senescing portions of silks, but the response of female antennae to senescing silk was significantly greater than the response of males. Dichloromethane extracts of senescing brown silks elicited significantly higher EAG responses from the antennae of western corn rootworm and D. undecimpunctata howardi Barber, southern corn rootworm, adults than dichloromethane extracts of green portion of silks (under the husks) or husks.