Brightness Discrimination in the Crepuscular Moth Grapholita molesta (Busck, 1916) Under Dappled Light

The light environment in orchards is highly heterogeneous, characterized by dappled light caused by sunlight filtering through plant canopies, and poses a challenge for the color perception of insects. For the crepuscular moth Grapholita molesta, a global pest of fruit trees, females can visually discriminate between plants to locate young leaves with higher brightness or intensity for oviposition around dusk. However, whether dappled light affects this brightness discrimination performance remains unknown. In this study, we investigated the oviposition preference of G. molesta females between two brightness stimuli (light-green and dark-green), as well as among three different light intensities under uniform light, simulated dappled light, and complex dappled light conditions at three ecologically relevant illuminances (100, 1, and 0.01 lx). G. molesta females laid significantly more eggs on light-green than dark-green stimuli under all three light conditions at each illuminance. Similarly, females consistently preferred high-intensity over lower-intensity light areas across uniform, dappled, and complex dappled light conditions, with more than 66% oviposition frequency. Our findings show that the brightness and intensity discrimination ability of G. molesta is not affected by dappled light, which may enable moths to accurately locate suitable oviposition sites even when the orchard canopy creates a heterogeneous light distribution.