POINT-SOURCE DISTRIBUTION AFFECTS PHEROMONE SPIKE FREQUENCY AND COMMUNICATION DISRUPTION OF EPIPHYAS-POSTVITTANA (LEPIDOPTERA, TORTRICIDAE)

To determine impact of point source distribution on communication disr uption in Epiphyas postvittana (Walker), 100 dispensers releasing pher omone and inhibitor were deployed in replicated 0.5-ha New Zealand app le orchard blocks at 3 point source densities (1, 9, or 100 points), a long with untreated control. Weekly inspections of pheromone-baited st icky traps were compared with field electroantennogram (EAG) recording s, of 3-min duration, which were made at 2 locations in the 4 treatmen ts with the same antenna. EAG recordings were later normalized to the calibration pulses, and the mean squared error of the signal (MSE) was calculated. Assessment of spike size and frequency was also made. Sig nificantly increased disruption of trap catches resulted from increase d number of point sources. In pheromone-treated plots, 4 inner traps w ere more disrupted than were 12 outer traps. EAG signals in treated pl ots showed significantly higher numbers of spikes that exceeded a give n signal-to-noise ratio (as defined from untreated sites). Spike size and spike frequency both increased with increasing numbers of point so urces. The MSE signal from the EAG was also higher in the more dense o f the pheromone treatments. The inverse relationship between spike fre quency and catch suggests that aerial environments with higher spike f requencies are more effective at communication disruption. There appea rs to be value in using both the MSE and spike frequency recorded by E AG to characterize fluctuations in pheromone concentrations in treated orchards.