Compatibility of LED greenhouse lighting and parasitoid biocontrol for aphid management in pepper

Artificial light in protected agriculture provides benefits to crops, but it might also affect insects in these systems. Biological control is widely used in protected agriculture, so it would be beneficial to optimize the combination of these management approaches. Our research tested the hypothesis that extending the day with short-wavelength-enriched light could improve parasitoid biocontrol efficacy, while benefiting crop growth. To examine the impacts of lighting on the insects individually, we studied the effects of 14- to 20-hour photoperiods and day extensions of three spectral qualities on the locomotor activity of the parasitoid Aphidius matricariae and the peak fecundity of the aphid Myzus persicae in growth chambers. To determine how lighting affects the insects and plants in a tri-trophic context, we grew pepper seedlings in a greenhouse under supplemental LED illumination of two spectral qualities, and exposed them to aphids, aphids and parasitoids, or no insects. We assessed how plant dry mass, aphid density, and parasitoid mummification rate responded. Aphid populations were not affected by any of the light treatments. In growth chambers, parasitoids adjusted their activity timing in response to lighting without changing their total amount of daily movement. In the greenhouse, plants grew 78% larger on average under extended days than under the control, while parasitoids reduced aphid densities by 173% on average, regardless of LED treatment. This indicates that insects can be resilient to major changes in their light environments, and that it is possible to manipulate LED illumination for plant productivity without compromising greenhouse biocontrol.