Artificial Light at Night Affects Larval Growth Without Altering Survival or Pupation in Spongy Moth (Lymantria...

Artificial light at night (ALAN) can disrupt circadian rhythms in nocturnal insects, but its effects on immature stages remain understudied. However, this knowledge is crucial, as a change in the development of insects can have ecological and economic consequences. For example, the spongy moth (Lymantria dispar dispar), native to Europe and Asia, has become an invasive species in North America, causing extensive defoliation of trees in forests and urban landscapes. Therefore, we investigated how LED light color influences larval development and pupation in the spongy moth. Larvae were reared under three light conditions simulating outdoor lighting: (1) neutral white LED (3700 K), (2) amber LED (2200 K), and (3) a dark control (no light). Results showed no significant differences in larval survival, growth patterns, or pupal stage outcomes between treatments. However, larvae exposed to 3700 K light reached significantly higher body masses at the eighth instar than those exposed to 2200 K and tended to be heavier than the control caterpillars. This is accompanied by a consistently higher weight gain at 3700 K in all larval stages. These results suggest that ALAN can influence larval growth-a crucial factor for fitness and population dynamics. Understanding the effects of ALAN on fitness-related traits-especially in pest species like the spongy moth-is critical given the increasing prevalence of nighttime illumination.