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Reported declines in insect populations have sparked global concern, with artificial light at night (ALAN) identified as a potential contributing factor. Despite strong evidence that lighting disrupts a range of insect behaviors, the empirical evidence that ALAN diminishes wild insect abundance is limited. Using a matched-pairs design, we found that street lighting strongly reduced moth caterpillar abundance compared with unlit sites (47% reduction in hedgerows and 33% reduction in grass margins) and affected caterpillar development. A separate experiment in habitats with no history of lighting revealed that ALAN disrupted the feeding behavior of nocturnal caterpillars. Negative impacts were more pronounced under white light-emitting diode (LED) street lights compared to conventional yellow sodium lamps. This indicates that ALAN and the ongoing shift toward white LEDs (i.e., narrow- to broad-spectrum lighting) will have substantial consequences for insect populations and ecosystem processes.

1. The night‐time environment is increasingly being lit, often by broad‐spectrum lighting, and there is growing evidence that artificial light at night (ALAN) has consequences for ecosystems, potentially contributing to declines in insect populations. 2. Moths are species‐rich, sensitive to ALAN, and have undergone declines in Europe, making them the ideal group for investigating the impacts of light pollution on nocturnal insects more broadly. Here, we take a life cycle approach to review the impacts of ALAN on moths, drawing on a range of disciplines including ecology, physiology, and applied entomology. 3. We find evidence of diverse impacts across most life stages and key behaviours. Many studies have examined flight‐to‐light behaviour in adults and our meta‐analysis found that mercury vapour, metal halide, and compact fluorescent bulbs induce this more than LED and sodium lamps. However, we found that ALAN can also disrupt reproduction, larval development, and pupal diapause, with likely negative impacts on individual fitness, and that moths can be indirectly affected via hostplants and predators. These findings indicate that ALAN could also affect day‐flying insects through impacts on earlier life stages. 4. Overall, we found strong evidence for effects of artificial light on moth behaviour and physiology, but little rigorous, direct evidence that this scales up to impacts on populations. Crucially, there is a need to determine the potential contribution of ALAN to insect declines, relative to other drivers of change. In the meantime, we recommend precautionary strategies to mitigate possible negative effects of ALAN on insect populations.

Although intensive forestry practices have greatly reduced the biodiversity of native woodland, sympathetic management offers much potential to reverse these negative trends. We tested, using a species-rich group, whether woodland conservation management practices could be of overall benefit, for threatened generalists and specialists alike. Our landscape-scale light-trap experiment compared presence/absence, abundance and species richness of macro-moths at 36 repeatedly sampled sites from six experimental ‘woodland management’ treatments. We recorded 11,670 individuals from 265 species. Our results show that the sheltered, dark, humid, late-successional, high deciduous forest biotope is characterised by high numbers of both individuals and species of moth, and is especially important for some scarce and specialist species of conservation concern. Coppicing and ride widening, which open up dense forest structures, are also valuable woodland conservation tools for macro-moths. Specifically, we show that the mechanism behind the pattern of increased species richness at the woodland-scale involved an increased structural and hence increased micro-climatic and resource diversity for species with an affinity for more open biotopes. This benefits generalist species of conservation concern. Additionally, we show that woodland area is an important factor affecting both moth abundance and species richness in coppiced plots, especially so for nationally declining and severely declining species, suggesting that larger woodlands offer the best opportunities to increase biodiversity through active coppice management. Based on these complementary findings we recommend zoning woodland conservation management practices to take into account the differential value of successional stages for different ecological groups of Lepidoptera.

Sweet Chestnut is a non-native tree in Britain and is considered to have a low biodiversity value. However, over seventy species of Lepidoptera have now been recorded utilizing Sweet Chestnut as a foodplant, demonstrating it to be an under-valued and important hostplant.