Violet LED light enhances the recruitment of a thrip predator in open fields.

The predatory bug Orius sauteri is an indigenous natural enemy of thrips and whiteflies in Asian countries. To put these bugs to practical use in pest management, methods to attract and retain the bugs in agricultural fields are needed. We previously showed that violet light (405 nm) attracts O. sauteri selectively. Many thrips and whiteflies are attracted to UV or green light. In this study, we examined the effect of violet-LED illumination on O. sauteri in pesticide-free eggplant (Solanum melongena L.) cultivation. In three cultivation trials, the density of O. sauteri on eggplant leaves was consistently higher in the illuminated plots; at least twice that of the non-illuminated plots. Simultaneously, the density of thrips declined markedly to less than half that of the non-illuminated plots. We identified three positive effects of violet light including an "immediate-effect" on predator attraction, a "persistent-effect" on predator reproduction, and a "secondary-effect" on the food web structure. Our results showed that illumination with violet light provides a powerful tool for integrated pest management. This is the first report on the use of illumination to manipulate the behavior of natural enemies.