Polyethylene dispensers generate large-scale temporal fluctuations in pheromone concentration

The temporal distribution of pheromone of Epiphyas postvittana (Walker) and its possible effect on communication disruption was investigated using field electroantennogram (EAG) measurements and insect traps. Three replicate matched pairs of blocks were pheromone-treated with 700 dispensers per hectare or left as untreated controls. An array of 9 delta traps was installed in the center of each block Male catch in the traps baited with rubber septa containing pheromone was recorded daily, and the following weekly cycle was operated: disruptant pheromone dispensers were present in the field for 2 d, but were then removed from treated plots for 5 d. Significant disruption of trap catch occurred for the 2 d that dispensers were present, and for 1 additional night following their removal. Field EAG recordings of 3 min duration taken while the dispensers were present showed a high frequency of large pulses as fluctuations in pheromone concentration in the treated area. No comparable pulses were measured in the untreated control blocks or from 5 min to 1 h after the removal of the dispensers from the heated area. The frequency of the pheromone pulses in treated plots was positively correlated with wind speed. After removal of the dispensers from the treated plots, the mean EAG signal declined linearly, indicating a log-linear rate of drop in mean pheromone concentration. Our results show that the large fluctuations in pheromone concentration detected in EAG recordings arise from the dispensers. However, large fluctuations detectable by EAG do not seem to be required for mating disruption of E. postvittana.