Male european corn borer, Ostrinia nubilalis (Hübner), antennal responses to analogs of its sex pheromone - Strain, electroantennogram, and behavior relationships

Experiments were conducted to (1) determine whether the electroantennogram (EAG) can detect differences among the responses of antennae from males derived from the three strains of Ostrinia nubilalis (Hübner), and (2) characterize the EAG responses of each strain to isomeric forms of the natural pheromone, (E)- and (Z)-11-tetradecen-1-ol acetate (TDA), and analogs possessing differences in the terminal alkyl group, cyclopropyl (CPA), or tert-butyl (TBA). EAG responses differed among the strains in two ways: (1) Antennae from ZZ males always produced an EAG to (Z)-TDA with an extended duration of response. This "signature" EAG response was found to be unique to the antennal response of ZZ males to (Z)-TDA, thus providing a relatively easy method of distinguishing live ZZ males from EE or ZE males. Correlated with this longer EAG response was a longer disadaptation time, i.e., the EAG response of ZZ antennae disadapted more slowly (ca. 10 min) than the response of EE antennae. (2) Strain differences in the relative EAG amplitudes to isomers and analogs were observed at the stimulus amounts eliciting the peak EAG amplitude as follows: TDA ≥ CPA > TBA for ZZ males and both isomers; TDA > CPA ≥ TBA and CPA ≥ TDA > TBA for EE males and the E and Z isomers, respectively; CPA > TBA ≥ TDA for ZE males and both isomers. Dose-response relationships were seen for all compounds if amplitude ("peak height") of the EAG was used as a measure of response. However, if width of the EAG at half the peak height ("peak width") was used, then only the ZZ antennal response to (Z)-TDA resulted in a meaningful dose-response relationship. For all strains, the EAG amplitudes elicited by the Z isomers of any of the tested compounds were greater than those elicited by the corresponding E isomers. Therefore, correlations between the relative EAG and upwind flight responses were observed in the ZZ (r = 0.86) and ZE (r = 0.80) strains but were not correlated in the EE strain (r = 0.18). Temporal studies showed that adaptation, not postexcision deterioration, was responsible for the observed decreases in the EAG amplitude after repetitive stimulation or after stimulation with amounts in a descending order. Disa-daptation required at least 20 min for a moderate dose (10 μg for 1 sec). Developmental studies showed that antennae from 2-day-old adults had the greatest EAG response.