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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.

In the hymenopteran parasitoid Venturia canescens, asexual (obligate thelytoky not induced by Wolbachia bacteria) and sexual (arrhenotokous) wasps coexist in field conditions despite the demographic cost incurred due to the production of males by sexual females. Arrhenotoky predominates in field conditions, whereas populations in indoor conditions (mills, granaries) are exclusively thelytokous. These differences in the relative abundance of the two modes of reproduction between environments suggest that the individuals of each reproductive mode may have developed strategies adapted to the conditions prevailing in each kind of habitat. The two environments contrast in temperature variability and in the spatial heterogeneity of host availability. In this study, we considered the combined effect of temperature and host availability on host patch exploitation by thelytokous and arrhenotokous V. canescens. As expected, arrhenotokous females were more sensitive to temperature changes. If the temperature decreased before foraging, they remained longer and exploited patches more thoroughly. This is consistent with the expected behaviour of parasitoids in response to signs of unfavourable conditions that entail increasing risk of time limitation or a reduced probability of attaining further patches. Both arrhenotokous and thelytokous females increased patch exploitation with host availability. However, unexpectedly, we found no difference in the way the two types of wasp responded to differences in host availability. Differences in the strategies adopted under different environmental conditions may indicate divergence of niche-specific life history traits between the two modes of reproduction. Niche displacement may partly account for the coexistence of these two modes of reproduction at a geographical scale.

1. Flight is an energy-demanding behaviour in insects. In parasitic wasps, strategies of nutrient acquisition and allocation, resulting life-history trade-offs and relationships with foraging strategies and resource availability have received much attention. However, despite the ecological importance of dispersal between host and food patches, and the great impact energy diverted to flight should have on lifetime reproductive success, the eco-physiology of flight in parasitoids is poorly understood.2. The objective of this study is to (i) identify the energetic resources used to fuel flight, and (ii) relate nutrient type and rate of utilisation to selective pressures in terms of resource availability posed by the environment.3. Using a flight mill and biochemical assays, we compared flight performance and nutrient dynamics during flight between two reproductive modes of the parasitoid Venturia canescens Gravenhorst, which is known to thrive preferentially in contrasted environments (i.e. natural vs. anthropogenic habitat), differing notably in host and food distribution. 4. Biochemical analyses of different nutrient types showed that glycogen is the flight fuel used by this species, yet no significant differences in its dynamics in flight were found between the two reproductive modes.5. Results suggest that both glycogen quantity and flight performance are related to the diverging ecological conditions experienced by thelytokous and arrhenotokous strains.

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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.

The ability to adjust resource allocation to the quality of the environment has broad implications for animal reproductive success. Organisms with complex life cycles that may experience various selection pressures during their lifetime are expected to evolve mechanisms to modulate the resource allocation strategies adopted during ontogeny to the conditions encountered by the adult. In the parasitoid Venturia canescens Gravenhorst (Hymenoptera: Ichneumonidae), thelytoky appears to have been selected for in anthropogenic habitats, where hosts are relatively numerous and food is absent, and arrhenotoky in natural habitats where hosts are more scarce and food is present. A previous study postulated that during their juvenile stage, females of both reproductive modes adopt strategies of energy allocation in accordance with these conditions, possibly providing a direct short‐term advantage to arrhenotokous forms, which partially co‐occur with thelytokous forms under natural conditions. To test this assumption, we provided daily adult thelytokous and arrhenotokous females with a small number of hosts together with food. To compare their lifetime resource allocation strategies, we recorded wasp longevities, egg loads, and carbohydrate reserves in wasps of different ages. Our analysis indicates that thelytokous females are able, to a certain extent, to cope with these conditions, because they reached the same longevity as arrhenotokous females. Nevertheless, thelytokous females suffered from a higher degree of time limitation compared with arrhenotokous ones, and arrhenotokous wasps appeared to maintain their energetic advantage over the adult stage. These results provide new insights, and point to the consideration of other activities, such as flight performance and/or ability to reach food and hosts, in the understanding of the role of resource allocation strategies in the maintenance of sex in this species.

In sexual organisms, low population density can result in mating failures and subsequently yields a low population growth rate and high chance of extinction. For species that are in tight interaction, as in host-parasitoid systems, population dynamics are primarily constrained by demographic interdependences, so that mating failures may have much more intricate consequences. Our main objective is to study the demographic consequences of parasitoid mating failures at low density and its consequences on the success of biological control. For this, we developed a deterministic host-parasitoid model with a mate-finding Allee effect, allowing to tackle interactions between the Allee effect and key determinants of host-parasitoid demography such as the distribution of parasitoid attacks and host competition. Our study shows that parasitoid mating failures at low density result in an extinction threshold and increase the domain of parasitoid deterministic extinction. When proned to mate finding difficulties, parasitoids with cyclic dynamics or low searching efficiency go extinct; parasitoids with high searching efficiency may either persist or go extinct, depending on host intraspecific competition. We show that parasitoids suitable as biocontrol agents for their ability to reduce host populations are particularly likely to suffer from mate-finding Allee effects. This study highlights novel perspectives for understanding of the dynamics observed in natural host-parasitoid systems and improving the success of parasitoid introductions.