Climate warming is considered to be among the most serious of anthropogenic stresses to the environment, because it not only has direct effects on biodiversity, but it also exacerbates the harmful effects of other human‐mediated threats. The associated consequences are potentially severe, particularly in terms of threats to species preservation, as well as in the preservation of an array of ecosystem services provided by biodiversity. Among the most affected groups of animals are insects—central components of many ecosystems—for which climate change has pervasive effects from individuals to communities. In this contribution to the scientists' warning series, we summarize the effect of the gradual global surface temperature increase on insects, in terms of physiology, behavior, phenology, distribution, and species interactions, as well as the effect of increased frequency and duration of extreme events such as hot and cold spells, fires, droughts, and floods on these parameters. We warn that, if no action is taken to better understand and reduce the action of climate change on insects, we will drastically reduce our ability to build a sustainable future based on healthy, functional ecosystems. We discuss perspectives on relevant ways to conserve insects in the face of climate change, and we offer several key recommendations on management approaches that can be adopted, on policies that should be pursued, and on the involvement of the general public in the protection effort.

Disruptive effects of climate change include range shifts, phenological mismatches among consumers and producers, and population declines. While these biological alterations have been widely documented, studies identifying specific mechanisms linking climate change to population declines are scarce. Extreme events, such as heatwaves can have devastating effects on living organisms and are increasing in frequency as Earth warms. Hence, understanding the effects of heatwaves on insects is necessary to inform conservation efforts and to develop predictions of population dynamics under future climate scenarios. Here, we experimentally evaluated the effects of heatwaves on the survival and phenology of the Baltimore Checkerspot (Euphydryas phaeton phaeton), a wetland butterfly with imperiled populations that has incorporated a novel host. We performed laboratory manipulations (implementing realistic temperature regimes) to assess the effect of heatwaves during summer and winter on the survival and phenology of E. p. phaeton. In addition, we analyzed historical temperature records to quantify the incidence of heatwaves within E. p. phaeton's range to assess their potential role in the decline of southeastern populations. We found that winter heatwaves with maximum temperatures of 20°C can have more devastating effects on survival than summer heatwaves (up to 41°C). Eggs endured acute heat stress during summer with no significant effects on phenology and survival; similarly, pre-overwintering larvae were robust to heatwave exposure, as only the most intense heatwave treatment reduced their survival (37% reduction compared to control conditions). By contrast, dormant larvae were the most vulnerable stage, as they lost from 2 to 6% of their body mass after a three-day summer heatwave. Furthermore, their exposure to winter heatwaves resulted in 75 to 100% mortality. Feeding on the native host provided higher resilience under thermal stress than feeding on the invasive, recently acquired host. Finally, both heatwave incidence and severity have increased in the southern range of E. p. phaeton in the period from 1894 to 2011. We show that warm winter days induced severe mortality, providing a mechanistic explanation of how climate change can trigger population declines in E. p. phaeton and other insects.

Organisms from temperate ecosystems experience a cyclic alternation of favorable seasons, when they can grow and develop, and unfavorable periods, characterized by low temperatures and reduced resource availability. A common adaptation to these changing conditions is to undergo a state of metabolic arrest triggered by environmental cues (e.g. diapause) during the unfavorable periods. Altered environmental conditions resulting from global change can expose organisms to contradictory cues, potentially triggering maladaptive responses. Here, I compared the performance of an oligophagous butterfly when experiencing consistent vs contradictory environmental cues by manipulating temperature, daylength, and host plant in the laboratory. I implemented a fully factorial design with realistic temperature and photoperiodic regimes to resemble environmental conditions during mid-summer and the summer-autumn transition within the focal species’ range. To assess the role of host plant at mediating the effects of abiotic factors, larvae were fed foliage of either a high or a low-quality host species. Decreasing daylength was the primary cue inducing diapause; however, feeding on a low-quality host at low temperatures also induced diapause in larvae growing under constant summer daylength. Conversely, exposure to high temperatures while feeding on a high-quality host occasionally overruled the diapause-inducing effect of decreasing daylength. Feeding on a high-quality host mitigated the lethal effects of cold, but not of hot temperatures. In addition, exposure to cold temperatures resulted in a significant reduction of pupal mass only under decreasing daylength. These results indicate that responses to environmental stressors in this multivoltine butterfly differ across the growing season according to the eco-physiological state of individuals (whether they undergo direct development or diapause). Traits related to oligophagy, such as sensitivity to multiple cues for diapause induction, as well as some of its consequences, such as the occurrence of overlapping generations, are likely to mitigate some of the detrimental effects of global change.