A Bug’s Life: the stress climate change is placing on insects

by Alice Melvin

Whilst often dismissed as inconvenient when they make their way into our homes, the humble insect is the glue that holds our ecosystems together. They pollinate plants, disperse seeds, maintain soil fertility, provide food for other animals, and unlock the nutrients which entire ecosystems use to survive. But due to the short generational time periods of insect populations and their strong sensitivity to temperature changes, small changes to the climate can have big impacts on insect populations, leading to even larger impacts on the rest of the ecosystems that rely so heavily on insect activity.

However, despite an acute awareness of the importance of insects to biodiversity, the biggest issue researchers have is a lack of information. Expanded study into the effect of climate change on an increased variety of insect species is desperately needed to be able to predict how ecosystems will change and develop. Insects are affected by CO₂ levels, droughts and rising temperatures, amongst many other factors. This can result in both expansion and decline in various insect populations. There is so much uncertainty in the predictions currently being made that it is very difficult to adapt to the potential changes we are facing. The possibility of insect outbreaks for certain species or extinction for others mean that ecosystems will be forced to adapt to the huge shift in species populations. If we do not know how each of the insect species will be impacted, and therefore how the ecosystem will be affected, how can one plan appropriately?

Extinction for some…

There are many cases of insect species facing extinction due to climate change. One of the earliest observations of this was seen from the Californian butterfly Euphydryas editha. The change in the local populations of this butterfly perfectly demonstrated how changes in the climate affected the numbers of butterflies observed. The southern and low elevation populations were much more likely to go extinct than those at more northern and higher elevations, showing how subtle changes to the climate of an area could wipe out a species in an ecosystem.

…and outbreaks for others.

The other side of the impacts of climate change on insect populations is a very different picture. Conjuring up images of truly biblical plagues, the unprecedentedly large swarms of locusts seen in Kenya this year ravaged the produce grown in the area, devasting the local economy. Further swarms are extremely likely and risk placing millions of people into severe food shortages. The swarms in 2020 have been the worst seen in the last 70 years.

Another example of a devasting insect outbreak, as a result of climate change, is the case of the mountain pine beetle in North America. These are bark beetles which infest and attack trees, in particular pine trees. Changes to the suitability of the climate is causing these beetles to expand their range outside of where they have been historically observed. There is a risk that they could become so widespread as to be deemed an infestation through the boreal forests. The introduction of new insect species into an area can cause deep disturbances to the carefully balanced ecosystem, especially when insects such as these are so destructive to the forest. In the past, outbreaks of these beetles have caused hundreds of millions of trees to die over large areas. It is therefore vital to the health of these forests that the causes behind the outbreaks of insects, such as the pine beetle, are understood and appropriate adaptation plans are put in place.

So, what now?

Vast differences in insect responses to changes in local climates make it extremely difficult for those responsible for the conservation of natural habitats and the biodiversity of local ecosystems to adapt. With insects being one of the most diverse set of species on Earth, the complexity in predicting how ecosystems will change is huge. The most important issue to tackle is therefore the information gap in what we know about insect populations and their responses to climate change. A much larger variety of species must be researched and in much greater depth if we are to really understand the gravity of the challenges being faced by each of the delicate ecosystems around the world.

References

1. G.G.E Scudder, “The Importance of Insects”, Insect Biodiversity: Science and Society, chapter 2, 2017
2. D.S Pureswaran, A Roques, and A Battisti, “Forest Insects and Climate Change”, Current Forestry Reports: Topical Collection on Forest Entomology, pp. 35-50, 2018
3. H Jactel, J Koricheva, and B Castagneyrol, “Responses of forest insect pests to climate change, not so simple”, Current Opinion on Insect Science, volume 35, pp. 103-108, 2019
4. C.L Boggs, “The fingerprints of global climate change on insect populations”, Current Opinion in Insect Science, volume 17, pp. 69-73, 2016
5. D Njagi, “The Biblical locust plagues of 2020”, BBC Future Planet Africa, 2020
6. L Safranyik, A.L Carroll, J Régnière, and D.W Langor, “Potential for range expansion of mountain pine beetle into the boreal forest of North America”, The Canadian Entomologist, volume 142, issue 5, pp. 415-442, 2010
7. M Montgomery, “Researching a new tool against the devasting mountain pine beetle”, Radio Canada International, 2019
8. J Harvey, R Heinen, R Gols, and M.P Thakur, “Climate change-mediated temperature extremes and insects: From outbreaks to breakdowns”, Global Change Biology, 2020