Increasing Temperatures and Decreasing Insect Populations

Halsch, C. A., Shapiro, A. M., Fordyce, J. A., Nice, C. C., Thorne, J. H., Waetjen, D. P., & Forister, M. L. (2021). Insects and recent climate change. Proceedings of the National Academy of Sciences118(2). DOI: 10.1073

Insects are often a relatively unseen and ignored part of life, but they actually provide us with many services that we may not think about on a daily basis. For example, plants often require pollinating insects to grow. Without pollinators, many of our plant food sources would no longer exist and we would be missing a vital part of our diets. Some insects are be considered pests and damage our crops, while other insects are actually predators and help to control the population of those pests. Insects also help keep freshwater and terrestrial ecosystems functioning. There are many more ways that insects are beneficial to us and to other living organisms.

The butterfly and bee shown above are pollinators. These insects carry pollen from male flowers to female flowers, which allows seeds to be produced. Without pollinators, we wouldn’t have many of the food plants that we rely on. Sources: WikiCommons, Pixabay

Despite the benefits they provide, insects are increasingly threatened by things like pesticide use, pollution, and habitat loss, but perhaps the biggest threat they face is climate change. Climate change can alter ecosystem function and lead to habitat loss, both of which can be harmful to insects. In order to better understand how insects respond to climate change, a group of researchers from the United States examined the impact of climate change on insect populations by conducting a literature review. They searched for studies that focused on long-term monitoring of insect populations (10+ years), examined ten or more species, and analyzed climate data. From analyzing these studies, the authors were able to get a clearer understanding of how insects universally respond to climate change.

The first question the authors investigated was how the impacts of climate change on insects compare with impacts from other threats they face. Historically, habitat loss has been the primary threat to insect populations, but climate change may be just as bad. For example, in a study that occurred in Great Britain, land use change and climate change caused the populations of 260 species of macro moths to decline and the populations of 160 species to increase. While habitat loss played a widespread role in the population declines, climate change played a larger role in the declines of the species that live in the northern, colder parts of the country. It also led to the increase in southern, warm-adapted species’ populations. In a study from a protected forest in New Hampshire, beetle populations declined by 83% because of warmer temperatures. Overall, many studies the authors read indicated that temperature plays a large role in determining the population sizes of insects, with cold-adapted species experiencing population declines and warm-adapted species experiencing increasing populations with changing temperatures.

The authors then wanted to examine the potential effects of changing daily maximum and minimum temperatures and changing seasonal average temperatures on insect populations. Nighttime temperatures have been warming faster than daytime temperatures, and in a study from California, this had a large negative impact on insects, especially during drier years. However, in other places, such as central Europe, warmer average winter temperatures resulted in increasing insect populations. Extreme weather events are likely to increase due to climate change, which can also negatively impact insect populations. For example, flooding in Costa Rica led to the population declines of parasitoids and Lepidoptera (moths and butterflies), including the loss of an entire genus of moths.

This is the Manduca dilucida, a moth species that is drastically declining in Costa Rica due to climate change. Source: WikiCommons

The authors also found that insect populations may be able to move to more suitable habitat as climate change occurs. Since temperature decreases as elevation increases, insect species that live in areas with varying elevations, like mountains, may be able to move up in elevation to cooler temperatures. This process has also been observed in many other species. Places at higher latitudes experience climate change on a more rapid scale than those close to the equator. Due to the varying global climate, some species may be able to migrate with the changing climate to suitable habitat. Since the plant is warming the fastest at the poles, insect species living closer to the poles are likely to be impacted sooner that those at the equator, but they are more adapted to varying climates. Since climate at the equator is historically more stable and those insect species have adapted to that stable climate, even small changes in climate can drastically impact them.

The figure above shows how global temperatures have changed over time. Note that the northern latitudes in particular have experienced greater warming. Source: Wikipedia

Overall, the studies that the authors examined indicated that climate change generally results in insect population declines. The combination of these studies can be used to help predict the impacts of climate change on certain species, which can help us prepare for how declines in those species may impact us. For example, some studies found that predatory insects are likely to experience large population declines, which would mean that we would likely begin to have issues with insects we consider to be pests eating crops. Continued monitoring of insects will help us to get a better understanding of the expected impacts of climate change and help us to come up with solutions to ensure that we don’t lose insect species and the services they provide.

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Elisabeth Lang

Elisabeth Lang

I recently graduated from Johns Hopkins University with a Masters degree in Environmental Science and Policy. My undergraduate education was at McDaniel College, where I majored in Environmental Studies and Biology. My undergraduate research focused on land use change and its impacts on biodiversity in Central America using GIS-based research. My graduate research examined potential sea level rise impacts on National Wildlife Refuges in the Mid-Atlantic region using GIS. I am currently working at the US Army Public Health Center where I analyze environmental samples. In my spare time, I enjoy traveling, reading, and running.

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