Diel Periodicity in Males of the Navel Orangeworm (Lepidoptera: Pyralidae) as Revealed by Automated Camera Traps

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 h 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 2-3 h 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 differ in important ways from the environmental effects on female release of sex pheromone.

Keywords: camera trap; pheromone lure; protandrous response; remote sensing.

Fig. 1.

(A) Trapview camera trap setup in the field. Including Trapview camera, sticky trap, and cleaning unit in the green and white unit, and solar panel with battery box and weather station. (B) and (C) demonstrate training of machine learning algorithm. (B) Photo of the sticky card in the trap where yellow boxes indicate provisional positive results as determined by the manufacturer’s propriety machine learning software. (C) The green boxes indicated confirmed of the target pests; as confirmed or entered by the user.

Fig. 2.

Daily total capture (left) of navel orangeworm and hourly temperature (right) at five research locations in 2019.

Fig. 3.

Daily total capture (left) of navel orangeworm and hourly temperature (right) at five research location in 2020.

Fig. 4.

Box plot showing hourly capture (0 = 18:00) by month for all navel orangeworm captured in five camera traps in 2019 and 2020. The distribution of capture times was significantly different between the months (Kruskal–Wallis, experiment-wise P < 0.05). Mean capture times were significantly different for month with different letters (Dunn test, P < 0.05, with Bonferonni adjustment for multiple comparisons).

Fig. 5.

Hour of median daily capture by month for all navel orangeworm captured in five camera traps in 2019 and 2020. There low association between temperature at the time of median capture and the time of day of the median capture for all months (Spearman’s rho ≤ 0.35).