Insects comprise herbivorous, predatory, parasitoid, pollinating, decomposing and detritivorous species found in all types of bioclimatic regions, from tropical to polar. This functional and ecological diversity makes them very useful as bioindicators of the effects of climate change. However, it also complicates the task of studying changes in their populations.
The list of ways in which climate change affects insects is long. Below, we summarise the main effects of both gradual climate change and increased extreme events.
Effects of gradual climate change
Species distribution
The range of a species is highly dependent on climate. It may therefore contract or expand depending on long-term changes. In response to warming, it has been observed that some species are moving towards the poles or to higher altitudes. However, not all can do so, as there are factors that may limit their movement, such as their ability to disperse, the availability of suitable habitats or the need to maintain ecological interactions.
Phenology
Higher temperatures increase the activity time and accelerate the development of some species. This may result in more generations per year or smaller individuals. In addition, temperatures that are too warm can alter the diapause (hibernation), preventing full development or forcing some insects to remain active in the low temperatures of the cold months.
Interactions with other species
Plants, herbivores, predators, parasites and pathogens interact with each other, and climate change can disrupt these interactions. For example, plants under water stress may lose nutritional value to herbivores, which in turn affects their predators. Alterations in distribution and periods of activity may also lead to some species no longer overlapping in time and space, while others might start overlapping for the first time.. For example, the activity period of pollinators may become out of sync with the flowering period of plants, and insects in cold bioclimatic regions may encounter new competing species that move into these areas due to warming. Also, many insects harbour beneficial or harmful micro-organisms, the growth of which is also climate-dependent.
Extreme weather events
Extreme temperatures
Temperature extremes are becoming more frequent and intense. The intensification is of particular concern because insects are exposed to temperatures that may be new to them and to which they are not evolutionarily adapted. Even when not lethal, prolonged exposure to extreme temperatures can cause cumulative damage. For example, it has been observed that heat can cause sterility in many different insect species.
Droughts
They particularly affect herbivores and pollinators of small plants as these are very vulnerable to water shortages. In addition to reducing plant abundance, drought can reduce the concentration of nutrients and other compounds, such as defence substances, that insects obtain from plants. It also harms aquatic insects, such as dragonfly nymphs, which inhabit ponds that may dry up.
Floods and very heavy rains
They can drown insects, displace them or dislodge them from plants. Floods can also alter soil conditionsaffecting both the insects that live there and the plants consumed by herbivores. In addition, heavy rainfall, together with the associated low temperatures, can impede foraging.
Fires
Although some species benefit from or even depend on fires, when fires become too frequent they can be negative even for these species. It has been shown that frequent fires can favour generalist species and disadvantage more specialised species,although studies that analyse these effects in depth are still lacking.
Although in this review we have focused on the negative effects of climate change, there are also positive effects on some species. However, the overall trend is negative, and climate change is still considered to be the most important fastest growing global threat.
References
Descamps, C., Quinet, M., & Jacquemart, A. L. (2021). The effects of drought on plant-pollinator interactions: What to expect. Environmental and Experimental Botany, 182, 104297.
Harvey, J. A., Tougeron, K., Gols, R., Heinen, R., Abarca, M., Abram, P. K., ... & Chown, S. L. (2023). Scientists' warning on climate change and insects. Ecological monographs, 93(1), e1553.
Van Dyck, H., Bonte, D., Puls, R., Gotthard, K., & Maes, D. (2015). The lost generation hypothesis: could climate change drive ectotherms into a developmental trap?. Oikos, 124(1), 54-61.
Wilson, R. J., & Fox, R. (2021). Insect responses to global change offer signposts for biodiversity and conservation. Ecological Entomology, 46(4), 699-717.
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