Simple Summary
Light is a critical environmental factor for insects like the harlequin ladybird (Harmonia axyridis), a beneficial predator used in pest control. This study investigated how different light intensities and colors affect the behavior and predation efficiency of ladybirds with varying color patterns (melanic/dark vs. non-melanic/yellow morphs). We found that darker elytra ladybirds are generally more active and consume more aphids under all tested light intensities compared to yellow ladybirds, suggesting their high mobility is genetically determined, not just due to faster heating from the light. Increasing light intensity increased activity for all morphs. Furthermore, while silencing a specific ultraviolet-sensitive visual gene (HaUVSop-2) reduced movement in well-fed ladybirds, adding blue light increased their activity. These findings are valuable because they suggest that by adjusting the light environment in places like greenhouses, we can optimize the effectiveness of these natural enemy ladybirds for pest management.
Abstract
Light is a fundamental ecological cue for insects, influencing physiological rhythms and behavior. We investigated how varying light intensities affect locomotion and foraging in H. axyridis color morphs, and examined the role of visual opsins. Three adult female morphs were assayed under white light at 1000, 5000, and 10,000 lx. Higher light intensity significantly elevated body temperature and locomotor activity across morphs, with the inherently dark f. conspicua morph exhibiting the greatest increases. Predation rates on pea aphids trended upward with intensity but differed significantly by morph: f. conspicua beetles consistently consumed more prey than f. succinea. RNAi knockdown of the UV-sensitive opsin HaUVSop-2 significantly reduced the crawling distance of satiated beetles under 5000 lux white light. Correspondingly, supplementation of white light with blue light (short wave) enhanced movement, whereas red supplementation increased aphid consumption. These results suggest that Short-wavelength light has the potential to stimulate the dispersal of ladybirds, whereas long-wavelength light may enhance predation on prey by increasing microenvironment temperature or improving prey recognition. We conclude that light intensity and spectrum jointly modulate H. axyridis behavior in a morph-dependent manner, mediated in part by visual opsins. Melanic morphs leverage thermal melanism to gain higher activity under bright light, implying an evolved trade-off between dispersal and stress tolerance. Our findings have practical implications: tailored lighting (e.g., blue-enhanced illumination to stimulate predation and dispersal of H. axyridis) could improve biological control efficacy in agroecosystems.