Oviposition Response to Light With Different Spectra in the Crepuscular Moth <i>Grapholita molesta</i>

The light spectrum is a critical visual feature influencing insect behavior. The crepuscular moth <i>Grapholita molesta</i> (Busck), a significant pest of stone and pome fruits worldwide, has been shown to discriminate variations in brightness/intensity under dim-light conditions. However, the behavioral responses of <i>G. molesta</i> females to various light spectra remain unknown. In this study, we investigated the oviposition preference of <i>G. molesta</i> females by assessing eggs laid in light and dark conditions, as well as under two different types of light in two-choice experiments. Light in the upper canopy of <i>Prunus persica</i> is richer in UV light than lower parts characterized by a green light spectrum. When given the choice between light and dark, <i>G. molesta</i> females preferred to lay eggs in the illuminated areas over the dark ones. Further experiments revealed that when presented with colored light versus white light of the same intensity, or between two lights of different spectra, <i>G. molesta</i> females could discriminate between these light types. They exhibited a strong preference for ultraviolet (UV) light, followed by blue and green light. Notably, this preference for UV light was dependent on intensity, with higher intensity light attracting more female. In cases where spectrum and intensity cues conflicted (e.g., UV light was paired with lights that had 10-fold or 100-fold lower intensity), <i>G. molesta</i> females still showed a preference for UV light for oviposition. These results indicate that the crepuscular <i>G. molesta</i> can differentiate between various light spectra, and the preference for UV light likely aids females in selecting suitable oviposition sites during dusk.