POLYETHYLENE DISPENSERS GENERATE LARGE-SCALE TEMPORAL FLUCTUATIONS INPHEROMONE 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. T hree replicate matched pairs of blocks were pheromone-treated with 700 dispensers per hectare or left as untreated controls. An array of 9 d elta traps was installed in the center of each block Male catch in the traps baited with rubber septa containing pheromone was recorded dail y, and the following weekly cycle was operated: disruptant pheromone d ispensers were present in the field for 2 d, but were then removed fro m 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 pul ses as fluctuations in pheromone concentration in the treated area. No comparable pulses were measured in the untreated control blocks or fr om 5 min to 1 h after the removal of the dispensers from the heated ar ea. The frequency of the pheromone pulses in treated plots was positiv ely correlated with wind speed. After removal of the dispensers from t he treated plots, the mean EAG signal declined linearly, indicating a log-linear rate of drop in mean pheromone concentration. Our results s how 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.