Consistent thrips biological control by Orius insidiosus on cucumber plants despite different LED lighting regimes

Artificial lighting, particularly light-emitting diodes (LEDs), is widely used in controlled- environment agriculture (CEA) to enhance crop productivity. Yet, light also acts as a sensory cue, directly and indirectly affecting insect pests and their natural enemies. Despite growing interest, the impacts of LEDs on multitrophic interactions remain poorly understood. This study assessed how spectral photoperiod extension modulates top-down effects (predator effects on pest densities, pest-related damage to plants, and plant defense-related gene expression) and bottom-up effects (plant morphology, light assimilation, and defense as well as growth hormone-related gene expression) in a tri-trophic system involving a plant, Cucumis sativus (greenhouse cucumber), a pest insect, Frankliniella occidentalis (western flower thrips), and a predator used for biological control, Orius insidiosus. Plants were exposed for two weeks to a 12-hour artificial sunlight simulating a cloudy winter day, with or without an 8-hour extension of blue, blue-red, or blue-green-red LEDs. Orius insidiosus reduced thrips populations by 96% {+/-} 9%, regardless of light treatment, and decreased foliar damage due to thrips by 46% on average. Predators produced offspring under all lighting conditions, although total numbers of O. insidiosus were lower under blue-green-red lighting. Pest densities remained similar across all light treatments, suggesting that light supplementation did not benefit F. occidentalis. Blue and blue-red spectra improved plant light assimilation, and photoperiod extension generally increased dry biomass (8% {+/-} 11%). Defense-related phytohormones were only marginally affected; surprisingly, some jasmonic acid pathway-related genes were upregulated in the presence of predators, suggesting additional plant-mediated effects. Our results underscore the potential of O. insidiosus to provide biological pest control services under artificial lighting regimes already used in crop production. Key MessageO_LILighting in agriculture alters dynamics of pest and beneficial insects C_LIO_LIWe asked how LED spectra influence net biological control outcomes in a tri-trophic system C_LIO_LIO. insidiosus reduced pest numbers by 96% and foliar damage by 46% C_LIO_LIPredators increased the expression of some jasmonic acid-related genes C_LIO_LIO. insidiosus showed potential for pest suppression under different lighting regimes C_LI