Point Source Distribution Affects Pheromone Spike Frequency and Communication Disruption of Epiphyas postvittana (Lepidoptera: Tortricidae)

Abstract

To determine impact of point source distribution on communication disruption in Epiphyas postvittana (Walker), 100 dispensers releasing pheromone and inhibitor were deployed in replicated 0.5-ha New Zealand apple orchard blocks at 3 point source densities (1, 9, or 100 points), along with untreated control. Weekly inspections of pheromone-baited sticky traps were compared with field electroantennogram (EAG) recordings, of 3-min duration, which were made at 2 locations in the 4 treatments 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. Significantly increased disruption of trap catches resulted from increased number of point sources. In pheromone-treated plots, 4 inner traps were more disrupted than were 12 outer traps. EAG signals in treated plots showed significantly higher numbers of spikes that exceeded a given signal-to-noise ratio (as defined from untreated sites). Spike size and spike frequency both increased with increasing numbers of point sources. The MSE signal from the EAG was also higher in the more dense of the pheromone treatments. The inverse relationship between spike frequency and catch suggests that aerial environments with higher spike frequencies are more effective at communication disruption. There appears to be value in using both the MSE and spike frequency recorded by EAG to characterize fluctuations in pheromone concentrations in treated orchards.