Field and laboratory electroantennographic measurements of pheromone plume structure correlated with oriental fruit moth behaviour

Peak-to-trough electroantennogram amplitudes (bursts), caused by the individual filaments of a plume of female pheromone, diminish as high-emission-rate sources are approached by male Grapholita molesta, and this reduction is correlated with in-flight arrestment (ceasing to advance upwind) These findings are consistent with the hypothesis that one cause of in-flight arrestment in response to high-concentration point sources is the attenuation of the peak-totrough amplitudes close to the source High burst frequency, high pheromone flux, or low levels of continuous neuronal activity all are less well correlated with arrestment Rather, arrestment appears due to a reduction of chemosensory input to the CNS during flight up the plume, even though the actual molecular concentration continues to increase In a laboratory wind tunnel, upwind flight initiation by more than 20% of males was elicited only by pheromone source concentrations evoking significant fluctuations in EAG amplitudes at downwind release points The burst frequencies that evoked high levels of upwind flight initiation ranged from a mean of 0 4-2 2 burstsls Because a previous study revealed that flying male G molesta change their course angle within 0 15 s of losing or contacting pheromone, these EAG burst frequencies indicate that during flight in a pheromone plume, many manoeuvres are probably made in response to contact with individual plume filaments Thus, upwind flight tracks may be shaped by hundreds of steering reactions in response to encounters with individual pheromone filaments and pockets of clean air Field-recorded EAGs reveal that burst amplitudes diminish from 3 to 30 m downwind of the source, whereas burst frequencies do not, averaging c 11s at 3, 10 and 30 m downwind