The flight pattern of navel orangeworm (Amyelois transitella Walker) 2008-2023 in California pistachio

Authors: Siegel, Joel

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/19/2024
Publication Date: 11/25/2024
Citation: Siegel, J.P. 2024. The flight pattern of navel orangeworm (Amyelois transitella Walker) 2008-2023 in California pistachio. Insects. 15(12). Article 919. https://doi.org/10.3390/insects15120919.
DOI: https://doi.org/10.3390/insects15120919

Interpretive Summary: The navel orangeworm, Amyelois transitella, is the principal pest of pistachios and almond in California. The timing of insecticide application is challenging because there is no model to predict when pistachios are vulnerable to infestation, therefore it is difficult to decide when to intensify scouting orchards in order to make application decisions. Sixteen years of flight data were analyzed (541,892 adults) to determine if there was a predictable pattern in flight activity, using degree days, a measure of heat accumulation during the growing season that determines navel orangeworm generation time. The goal is to be able to scout orchards to identify pistachio vulnerability before peak insect pressure. A common starting point was identified that occurred 944.4 degree days° C from January 1 each year. This starting point, also known as a biofix, remained consistent despite the changes in trap lures and the expansion of almond and pistachio hectarage that occurred over the 16 year period. This information can be used to predict flights each year, thereby increasing scouting efficiency because pistachio vulnerability can be determined before peak pressure.

Technical Abstract: The navel orangeworm, Amyelois transitella, is the principal pest of pistachios and almond in California. The timing of insecticide application is challenging because there is no model that predicts when pistachios are vulnerable to infestation. Sixteen years of pistachio flight data from Madera and Fresno counties (541,892 adults) were analyzed to determine if there was a consistent starting point each year for the flights that overlap pistachio vulnerability. This effort was complicated by changes in trap lures over this time period as unmated females were replaced by a combination lure consisting of the synthetic pheromone and phenyl propionate, which is needed because mating disruption suppresses pheromone lure trap capture. There were two additional complications, the increased degree day accumulation during the growing season and the hectarage expansion of pistachio. A biofix at 944.4 degree days° C was identified from the dataset that was consistent across all years in both counties. Using the biofix, subsequent flight peaks occurred at 277.78 degree day° C intervals (generation time on new crop pistachios), corresponding to three weeks in the field. This biofix can be used to improve the timing of field scouting which in turn will improve the timing of insecticide application.