Adult Diel Locomotor Behaviour in the Agricultural Pest Plutella xylostella Reflects Temperature-Driven and Light-Repressed Regulation Rather than Coupling to Circadian Clock Gene Rhythms.

The diamondback moth, Plutella xylostella, is arguably the most economically impactful and widespread lepidopteran pest. Though the larval P. xylostella life stage is responsible for most of this cost through the consumption of crops, it is the adult form that spreads the pest to fresh crops all around the world, seeking them out in a seasonally expanding range. It is therefore important to understand the activity rhythms of adult P. xylostella in response to environmental cues such as light and temperature. We analysed diel rhythms in both adult clock gene expression and locomotor behaviour for the ROTH P. xylostella strain. Real-time quantitative PCR analyses of P. xylostella demonstrated diel rhythms for transcripts of the clock genes period and timeless under both entrained and free-running conditions indicating the presence of a functional daily timekeeping mechanism. However, adult locomotor rhythms exhibited temperature-driven and light-repressed regulation rather than circadian control. Thus, our analyses show a lack of coupling between the P. xylostella circadian clock and adult locomotor behaviour, which may be relevant in predicting the activity patterns of this agricultural pest.