Artificial light at night increases top-down pressure on caterpillars: experimental evidence from a light-naive forest

Abstract

Artificial light at night (ALAN) is a globally widespread and expanding form of anthropogenic change that impacts arthropod biodiversity. ALAN alters interspecific interactions between arthropods, including predation and parasitism. Despite their ecological importance as prey and hosts, the impact of ALAN on larval arthropod stages, such as caterpillars, is poorly understood. We examined the hypothesis that ALAN increases top-down pressure on caterpillars from arthropod predators and parasitoids. We experimentally illuminated study plots with moderate levels (10–15 lux) of LED lighting at light-naive Hubbard Brook Experimental Forest, New Hampshire. We measured and compared between experimental and control plots: (i) predation on clay caterpillars, and (ii) abundance of arthropod predators and parasitoids. We found that predation rates on clay caterpillars and abundance of arthropod predators and parasitoids were significantly higher on ALAN treatment plots relative to control plots. These results suggest that moderate levels of ALAN increase top-down pressure on caterpillars. We did not test mechanisms, but sampling data indicates that increased abundance of predators near lights may play a role. This study highlights the importance of examining the effects of ALAN on both adult and larval life stages and suggests potential consequences of ALAN on arthropod populations and communities.

When Night Becomes Day: Artificial Light at Night Alters Insect Behavior under Semi-Natural Conditions

“…ALAN-induced changes in the timing of stridulation may make crickets more vulnerable to such predators. ALAN was suggested to induce both top-down and bottom-up changes in ecosystems and insect populations (Bennie et al, 2018; Deitsch et al, 2023). Further research is needed to fully elucidate these various and intricate effects.…”