The Effects of <scp>LED</scp> Daylength Extensions on the Daily Activity Patterns of a Greenhouse Biological Control Agent, <i>Aphidius matricariae</i>

ABSTRACT Supplemental lighting, such as with LED lamps, allows greenhouse producers to maintain yields when natural light levels are low. Since both insect pests and their natural enemies are sensitive to light, both the duration and spectrum of LED daylength extensions could affect biological pest control in greenhouses. For example, they could extend periods of foraging activity for biological control agents. Insect responses to light can be species‐specific, so it would be useful to have a high‐throughput method to study the effects of novel light regimes on many different greenhouse biological control agents. It is unknown to what extent parasitoids change their daily activity patterns under longer days due to artificial illumination on multi‐day timescales. In growth chambers, we examined the locomotor activity of the parasitoid biocontrol agent Aphidius matricariae Haliday (Hymenoptera: Braconidae) over multiple days under different illumination regimes. We compared the effects of 14, 16, 18, and 20 h photoperiods, and 12 h days extended by 6 h with three different spectral qualities. The parasitoids adjusted how their activity was distributed throughout the lit period of the day (i.e., total activity duration and peak timing) without changing the total amount of daily activity, regardless of the photoperiod or the light spectrum used for daylength extension. Our results suggest that at least some behavioral traits of parasitoids can be resilient to changes in their light environment, and may help to mechanistically interpret subsequent experiments showing that their biological control effects are also resilient to different LED lighting regimes. This experimental approach may be useful in screening other biological control agents for strong responses to LED spectra or artificially‐extended photoperiods, which can then be confirmed through more in‐depth research in more realistic settings.