Nocturnal Lepidoptera Larvae in Mega-Project: Habitat and Environmental Factors Over Construction Effects.

Mega-projects are large-scale developments that profoundly transform landscapes while delivering infrastructure and socio-economic benefits. However, they are also major drivers of biodiversity loss through multiple direct and indirect impacts. Among these, artificial light at night (ALAN) is increasingly recognised as a threat to biodiversity, including nocturnal Lepidoptera, which play crucial ecological roles. While ALAN effects on adult moths are well documented, its influence on preimaginal stages, critical for fitness and population persistence, remains poorly understood. This study examined construction-related factors, including ALAN effects, on Lepidoptera larvae in natural environments within mega-projects context using an After-Control-Impact (ACI) design. Focusing on larvae is essential, as this longest and least mobile life stage is particularly vulnerable to local environmental alterations such as artificial lighting, and environmental complexity can either buffer or amplify ALAN effects. However, our findings indicate that larval presence, species richness and biomass were not consistently associated with ALAN intensity. Instead, other environmental factors, including habitat characteristics, plant species, exposure and vegetation management, emerged as more important determinants of larval assemblages. In two sites, at least one control area showed higher larval abundance than the impacted site, but this pattern appears linked more to local environmental conditions than to lighting. Species richness showed no consistent pattern, and biomass analyses were limited by sample size and developmental variability. Overall, the results highlight that mega-project impacts on nocturnal Lepidoptera larvae are complex and context-dependent. ALAN was not retained as a significant predictor relative to other environmental factors, though this may reflect limited statistical power rather than a true absence of effect. These findings emphasise the need for standardised approaches to mitigate multiple construction-related impacts on nocturnal Lepidoptera.