Sampling and pheromone trapping for comparison of abundance of Amyelois transitella in almonds and pistachios

The navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae), is the primary insect pest of almonds, Prunus amygdalus Batsch (Rosaceae), and pistachios, Pistacia vera L. (Anacardiaceae), in California, USA. Abundance of A. transitella was compared between these crops by examining total and infested mummy nuts collected in trees and on the ground between January and March in 2003 and 2004, and by examining the number of males captured in sticky traps baited with virgin females as a pheromone source during the subsequent growing seasons. There was an 8-9-fold greater density of total mummies (potential hosts) in pistachios compared to almonds. The proportion of mummies infested was not significantly different between the crops in 2003, but significantly more almond than pistachio mummies were infested in 2004. In 2003, the average density of infested mummies per hectare was greater in pistachios than in almonds, but in 2004 the converse was true. Examination of meteorological data did not suggest an explanation for more live A. transitella per infested mummy in almonds in 2004. The number of males captured in pistachios was consistently greater than the number captured in almonds, particularly during the second flight in June and July. The number of males captured in sticky traps in the summer was more strongly associated with the total mummy density in the sanitation survey of the previous winter than with the density of infested mummies. We conclude that the overall density of mummy nuts serving as potential oviposition sites prior to the next year's crop has a greater impact on the abundance of A. transitella during the growing season and subsequent harvest than does the density of infested mummies. The implications for the ecology and management of this pest species are discussed.