Artificial Light at Night Alters Larval Activity in a Marine Insect: Intensity‐ and Spectrum‐Dependent Effects

ABSTRACT Artificial light at night (ALAN) is an emerging stressor whose effects on marine insects, particularly their larval stages, remain virtually unknown. We tested the influence of two key aspects of ALAN (light intensity and spectral composition) on the activity of larvae of the sandy beach beetle Phalerisida maculata . Larval activity was highest under darkness and declined markedly under very low (15 lx) and very high (75 lx) intensities, while intermediate levels produced slightly stronger but variable responses. Activity was also reduced when larvae were exposed to lights of distinct spectral composition: activity was lowest under violet, amber, and red lights, and significantly reduced compared to blue and green. These results show that P. maculata larvae are highly sensitive to ALAN, with various levels of activity suppression operating across multiple intensities and spectral ranges. The responses recorded highlight the importance of incorporating light characteristics to better understand the ALAN impacts.