Comparison of navel orangeworm (Amyelois transitella) trap activity and damage in almonds using egg and pheromone traps

Studies to compare the currently-used egg traps and pheromone traps (wing traps baited with unmated females) as methods for monitoring the navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae) were compared from 2006 to 2008 in 41 16-ha plots in Kern County, CA; and in 2008 over 320 ha in western Fresno County, CA. In 2007 damage in Nonpareil almonds in the 41 Kern County plots was approximately 20% of 2006 damage. Overall the number of males captured in the 41 plots in pheromone traps in the first and second flights was similar between the two years, whereas the overall number of eggs in egg traps was greatly reduced in 2006 v. 2007. However, on a per-plot basis, there was significant correlation of males in traps in second flight with almond damage, whereas there was no association of eggs in egg traps with damage in individual plots. The discrepancy between the results on a regional and per-plot basis is apparently because the frequency distribution of eggs on egg traps is far more right-skewed compared to that of male on pheromone traps, thus more traps per plot are needed to detect meaningful association of egg trap numbers with damage.