Diel periodicity in males of the navel orangeworm (Lepidoptera: Pyralidae) as revealed by automated camera traps

Authors: Burks, Charles - Chuck; HENGST, FOSTER - University Of California; WILSON, HOUSTON - University Of California, Riverside; WENGER, JACOB - University Of California

Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/19/2022
Publication Date: 10/18/2022
Citation: Burks, C.S., Hengst, F.S., Wilson, H., Wenger, J.A. 2022. Diel periodicity in males of the navel orangeworm (Lepidoptera: Pyralidae) as revealed by automated camera traps. Journal of Insect Science. 22(5). Article 11. https://doi.org/10.1093/jisesa/ieac059.
DOI: https://doi.org/10.1093/jisesa/ieac059

Interpretive Summary: The impact of the biological clock and external temperature on the timing of sexual activity of moth pests like the navel orangeworm is important for optimization of pheromone mating disruption for their control. Remote automated camera traps offer a more efficient way to monitor such pests for treatment decisions and can also provide a research tool to improve understanding of biology of these pests. Two years of camera trap data found both similarities and differences from previous studies that relied primarily on field observations of laboratory-reared females. Like the females, the males exhibited the greatest sexual activity in the last few hours before sunrise in summer conditions and, like females, this activity began earlier in cooler times of the year. Unlike the previous studies, a small minority of wild males were captured at all hours of the day and night, and peak timing changed with season but not with transient temperature changes. Improved understanding of day-night patterns of male activity will enhance the understanding of monitoring data and optimization of mating disruption for the navel orangeworm. These trends will advance navel orangeworm control and reduce insecticide used to control this primary pest of almonds and pistachios, which are crops worth nearly $8.5 billion unprocessed and planted on approximately 1.25 million acres of land mostly in California.

Technical Abstract: Navel orangeworm, Amyelois transitella (Walker), is a key pest of walnuts, pistachio, and almonds in California. Pheromone mating disruption using timed aerosol dispensers is an increasingly common management technique. Dispenser efficiency may be increased by timing releases with the active mating period of navel orangeworm. Past work found that the peak time of sexual activity for navel orangeworm females is 2 hours before sunrise when temperatures are above 18° C. Inference of male responsiveness from data collected in that study was limited by the necessity of using laboratory-reared females as a source of sex pheromone emission to attract males and the inherent limitations of human observers for nocturnal events. Here we used camera traps baited with artificial pheromone to observe male navel orangeworm mating response in the field over two field seasons. Male response to synthetic pheromone exhibited diel patterns broadly similar to females, i.e., they were active for a brief period of 2 to 3 hours before dawn under summer conditions and began responding to pheromone earlier and over a longer period of time during spring and fall. But contrary to the previous findings with females, some males were captured at all hours of the day and night, and there was no evidence of short-term change of pheromone responsiveness in response to temperature. Environmental effects on the response of navel orangeworm males to an artificial pheromone source differs in important ways from the environmental effects on female release of sex pheromone.