The alternation of light and dark periods on a daily or seasonal time scale is of utmost importance for the synchronization of physiological and behavioral processes in the environment. For the last 2 decades, artificial light at night (ALAN) has strongly increased worldwide, disrupting the photoperiod and its related physiological processes, and impacting the survival and reproduction of wild animals. ALAN is now considered as a major concern for biodiversity and human health. Here, we present why insects are relevant biological models to investigate the impact of ALAN. First the phenotypic responses to ALAN and their underpinning mechanisms are reviewed. The consequences for population dynamics, and the community composition and functioning are described in the second part. Because ALAN provides new and widespread selective pressure, we inventory evolutionary changes in response to this anthropogenic change. Finally, we identify promising future avenues, focusing on the necessity of understanding evolutionary processes that could help stakeholders consider darkness as a resource to preserve biodiversity as well as numerous ecosystem services in which insects are involved.

1. Light pollution is a widespread phenomenon with major consequences on nocturnal organisms from individual to community. However, its effects on diurnal organisms are still scarcely studied.2. We exposed diurnal parasitoid wasps (Venturia canescens) to low (0.7 lux) or high (20 lux) artificial light for two to eight consecutive nights, and quantified its consequences on their physiology and daytime behaviour compared to a control group (0 lux). We next considered potential trans-generational effects on offspring whose mothers were exposed to light pollution.3. While in the dark night the wasps showed no activity, exposure to artificial light triggered nocturnal activity and altered diurnal behaviours related to foraging. Wasps exposed to light at night had a greater propensity to choose hosts rather than food compared to controls. They also spent more time feeding when exposed to 0.7 lux of light at night. However, these behavioural modifications were not related to changes in individual energy reserves.4. Light pollution effects persisted at trans-generational level: offspring development time and latency before feeding increased when mothers were exposed to 0.7 lux light at night.5. Even at low intensity, light pollution alters foraging behaviour of a diurnal insect. Searching for hosts or food being essential for fitness, light pollution is likely to have long-term repercussions on insect populations.6. Light pollution caused behavioural modifications potentially beneficial for V. canescens in the short term. However, longer term studies (e.g. on lifetime reproductive success) are needed to fully understand its consequences on insects.

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The increasing use of artificial light at night (ALAN) is currently a major anthropogenic disturbance, with largely unappreciated eco-evolutionary consequences for nocturnal but also diurnal organisms. It has been hypothesized that light pollution could create new opportunities for the latter to forage and reproduce at night, which is called the ‘night-light’ niche, with fitness consequences still scarcely explored.We exposed diurnal parasitoid wasps (Venturia canescens) to one of three light-at-night conditions: control (0 lux), low intensity (0.7 lux) or high intensity (20 lux) throughout their lives. We then monitored changes in both behavioural and life-history traits, namely daytime and nighttime feeding and egg-laying activity, reproductive senescence, lifespan and lifetime reproductive success.Light pollution influenced the nighttime activity of wasps. The proportion of wasps feeding and laying eggs at night increased, and we also detected a tendency for a higher nighttime reproductive success under a high intensity of light pollution. Surprisingly, high intensity of light pollution also increased the wasps’ lifespan. Such changes did not affect the lifetime reproductive success of the wasps, but influenced the distribution of ovipositions between day and night.Reproductive senescence occurs inV. canescens, evidenced by the linear decline in daily reproductive success with age regardless of the light condition. ALAN conditions, in interaction with mother age, affected developmental time in offspring, highlighting an effect on reproductive senescence.We demonstrated that light pollution induced the use of the ‘night-light’ niche in a diurnal insect, with a shift in the distribution of egg-laying events between day and night. While we did not observe strong consequences on individual fitness, such changes in the dynamics of parasitism behaviour may nevertheless have major consequences for population dynamics, especially in natural conditions.