Understanding sex differences in lifespan can provide valuable insights into lifespan evolution. Despite abundant published species-level data, comparative studies on the drivers of sex differences in lifespan in invertebrates remain scarce compared to vertebrates. Here, we present a comparative analysis of sex differences in adult lifespan (SDL) in insects, using literature-derived data for 395 species spanning 17 orders. Across this dataset, female adults outlived males in 65% of species, with their median lifespan 9% longer. Mean lifespan was consistently female-biased across orders and functional groups, although the magnitude of this bias varied considerably. Phylogeny explained a relatively modest 28% of the variation in SDL, with both male- and female-biased patterns observed within most orders and even among congeneric species. SDL was positively, albeit weakly, associated with sexual size dimorphism. Lifespan differences were generally more female-biased in functional groups where extended lifespan is expected to more strongly enhance female reproductive success, either because of time-consuming resource acquisition for egg production (e.g., predators), or prolonged search for oviposition substrates (e.g., parasitoids). Overall, our findings indicate that shared ancestry, sexual size dimorphism, and sex-specific reproductive strategies each contribute to variation in sex differences in adult lifespan, without any single factor clearly predominating.

Population density often modifies the phenotypes of the members of the population. Such density-dependent phenotypic plasticity can affect basic life-history traits of the organisms. In insects, a frequently observed expression of such plasticity is the crowding response (CR), where individuals growing at high densities develop faster and attain smaller final sizes compared to those at low densities. This plastic change qualitatively differs from the general stress response where smaller final sizes are associated with longer development periods. The adaptive significance of CR, as well as the nature of the cues that trigger CR remain poorly understood. We performed series of experiments to identify proximate signals leading to CR in the geometrid moth Hypomecis atomaria, a species in which larvae reared in groups consistently pupate earlier and at lower weights than those reared in isolation. Our findings reveal that CR is also induced in complete darkness, suggesting that visual cues of high population densities do not play a decisive role. CR was triggered when the larvae were separated by a mesh barrier, preventing tactile interaction between them. The presence of heterospecific lepidopteran larvae also triggered CR, though to varying degrees. By contrast, neither the presence of dipteran insects in the rearing environment nor human-inflicted tactile stimulation affected the growth schedules of H. atomaria larvae. We conclude that CR is likely induced either by chemical signals or substrate-borne vibrations caused by other larvae. In any case, CR is not merely a response to high densities of conspecifics, nor is it a general reaction to unspecific disturbances. This allows us to narrow down the set of potential adaptive explanations for the phenomenon.

Temperature has a profound effect on the growth and development of ectothermic animals. However, the extent to which ecologically-driven selection pressures can adjust thermal plastic responses in growth schedules is not well understood. Comparing such responses between sexes provides a promising but underexploited approach to evaluating the evolvability of thermal reaction norms: males and females share largely the same genes and immature environments but experience different ecological selection pressures. In this study, we performed a meta-analysis of sex-specific thermal responses in insect development times. We show that sex-specific responses of development times to temperature variation are broadly similar. Moreover, sex differences in thermal plasticity are considerably less pronounced than sex differences in plastic responses induced by variations in larval diet. Our results point at the existence of substantial constraints on the evolvability of thermal reaction norms in insects, an essential aspect to consider in predicting evolutionary responses to climate warming.

Current climate change is disrupting biotic interactions and eroding biodiversity worldwide. However, species sensitive to drought, high temperatures and climate variability might persist in microclimatic refuges, such as leaf shelters built by arthropods. We conducted a distributed experiment across an 11,790 km latitudinal gradient to explore how the importance of leaf shelters for terrestrial arthropods changes with latitude, elevation and underlying climate. Our analyses revealed leaf shelters to be key facilitative elements for the diversity of arthropods. Predator diversity and overall biomass within shelters increased with local drought and temperature variability, regardless of latitude and elevation. In contrast, shelter usage by herbivores increased with abundance of predators on those same plants and in wetter climates. Projected increase in climatic variability and drought in certain geographic regions is therefore likely to enhance the importance of biotic refuges, especially for predators, in mitigating the impact of climate change on species persistence.