Climate change may impact mosquitoes and midges regarding the size and location of their habitats. This can affect both animal and public health, because these insects can transmit diseases. In a review article in the April issue of the scientific journal of the World Organisation of Animal Health, Armin Elbers of the Central Veterinary Institute of Wageningen UR, Sander Koenraadt of Wageningen UR, and Rudy Meiswinkel (independent consultant) from Italy discuss the scientific evidence for the effects of climate change on the spread of mosquitoes and midges.
Vector-borne animal diseases are a continuing threat to global agriculture. Moreover, some of these infectious diseases can also be transmitted to humans. Increasing international transport, globalisation of trade and climate change are all contributing to the introduction, establishment and spread of diseases transmitted by midges and mosquitoes. Analyses by the Intergovernmental Panel on Climate Change (IPCC) of the United Nations have shown that the earth's surface has become steadily warmer in the past 30 years, particularly in the northern hemisphere. Rainfall has increased since 1901 in Europe, and the number of extreme weather events has increased since 1950. It is likely that fewer cold days and nights are occurring, while the frequency of heat waves in many parts of Europe, Asia and Australia is expected to increase in the future.
The literature review showed that many variables, such as temperature, humidity, wind and extreme weather conditions, can have both a negative and positive impact on the spread, and thus the habitat, of midges and mosquitoes. For example, higher temperatures may result in more insects emerging during a short period, leading to a higher risk of disease transmission. But in combination with low humidity, higher temperatures may also lead to increased insect mortality.
Seeking food and procreation, midges can travel up to 5 km in a few days within their habitats (short-range dispersion). However, due to air currents and wind (especially over the sea) midges can also spread across distances of tens to hundreds of kilometres (long-range dispersion).
Research into the impact of climate change on the dispersion of insects is still in its infancy. Data on the midge species Culicoides imicola – the primary vector of bluetongue disease in Africa, the Middle East and Southern Europe – has been collected for decades. As a result, a possible long-term relationship between habitat and climate change can be studied. No indications yet were found of a shift in the habitat of C. imicola due to climate change. For other midge species, no long-term data are known.However, the dissemination of mosquitoes has been studied for years. In recent decades many mosquito species – primarily from Asia – have been introduced into Europe and have become established. Such processes are likely to be driven by the interplay of world trade, such as unintentional import of mosquito eggs in old car tires, and climate change. Besides the impact of temperature, it is essential to gain better understanding of the effects of other changes, such as more extreme rainfall or drought, on the proliferation potential of mosquitoes. Models can be used to determine the interaction between mosquitoes that expand their habitats and local wild fauna and flora. Determining the ultimate impact of mosquitoes on animal and public health requires a large-scale and integrated approach involving various disciplines, in line with the One Health concept.