Pest control groups prepare for mosquito boom in rich countries as planet warms

Pest control companies are developing ways to combat the growing number of mosquitoes carrying life-threatening diseases such as malaria and dengue fever into new areas of the world as a result of climate change.

The rise in temperatures has led to the spread of mosquito-borne diseases to higher altitudes and areas of the developed world where they had previously not been prevalent.

Local dengue transmission has been reported in multiple European countries including France, Spain, Croatia and Italy, as well as in parts of the US and Japan. 

Rentokil Initial, the world’s largest pest control provider, recently installed a “blood room” in its UK innovation centre to study the behaviour of mosquitoes and other insects, which would “add to our knowledge and expertise in years to come”, said chief executive Andy Ransom. 

Rentokil forecasts that the global market for mosquito control will expand from $1.6bn in 2021 to $2.1bn by 2026, an estimated compound annual growth rate of 5.8 per cent.

The blood room housed mosquitoes that had “taken nicely” to the set-up, “where we feed them on human blood sourced from a blood donation service”, Rentokil said.

“In Europe, the current trend is seeing Aedes albopictus [the Asian tiger mosquito] moving north, primarily in Italy, southern France and Spain,” said Ransom. The Asian tiger mosquito is a vector for the transmission of a number of pathogens, including dengue, yellow fever, Zika and chikungunya.

The pest control group uses mosquito larvicides to remove breeding sites from small bodies of water, and the targeted spraying of adulticides — a different type of insecticide — to exterminate mature mosquitoes from low-lying vegetation.

Rentokil’s vector control company, Vector Disease Control International, has warned that diseases spread by mosquitoes and ticks “are on the leading edge of increasing concerns about climate change”.

The Wellcome Trust, a healthcare research charitable foundation, has said it expected disease-carrying mosquitoes to reach up to 500mn more people than they do at present by 2050. It estimated that more than 1bn people would be newly at risk of malaria, dengue, Zika, chikungunya and many other diseases by 2080. The foundation said it was developing an open-source database to track these climate-sensitive infectious diseases.

Felipe Colón, the Wellcome Trust’s technology lead in data for science and health, said climate change had also increased the spread of other pests, such as termites.

Northern regions of the US were experiencing termites in places they had not been previously reported, according to Orkin, a subsidiary of US pest control group Rollins.

“There’s a termite called the Formosan subterranean termite and it is found in the south-eastern US. There’s also some in California and in Hawaii — it tends to be in warmer areas,” said Benjamin Hottel, technical service manager at Orkin. “There was a recent discovery of it up in the Norfolk area of Virginia . . . that’s the furthest north they’ve ever gotten.”

Last year was the sixth-warmest year on record since 1880, according to the US National Oceanic and Atmospheric Administration. Temperatures have risen by at least 1.1C in the industrial era.

Experts also cautioned that it was difficult to predict how the breeding cycles of insects such as mosquitoes would respond to changes in the climate.

“As you increase the temperature, you increase the suitability for that process to function and usually there’s some optimal range, but once it gets too hot the process can also break down,” said Kris Murray, professor of environmental change and health at the London School of Hygiene and Tropical Medicine’s medical research council unit in the Gambia.

“A warming climate can speed up the lifecycle of temperature-dependent species,” he added. “If you’re an organism that can complete more life cycles in, say, one year, due to more suitable temperatures brought on by climate change, then that could increase the likelihood that you’ll be able to establish in a new location if introduced or have bigger populations if already there.”

Murray noted that climate change was projected to have, on average, a greater impact on reducing species diversity and abundance. But it had also made conditions in some European countries more hospitable to invasive insects.

“There are parts of Europe that were previously too cold to really support the mosquito very well. Climate change is warming [them] up a little bit and it’s making it just that bit more suitable, [so] the mosquitoes may be better able to establish or survive there,” he said.

There are about 3,600 known species of mosquito. The native range of the Asian tiger mosquito is in south-east Asia, but it has been spreading since the 1960s and was discovered in Albania in 1979. It is now present in much of southern and central Europe.

“Last year, France recorded its worst ever number of dengue cases that were vectored by [the Asian tiger mosquito],” said Steven White, theoretical ecologist at the UK Centre for Ecology & Hydrology.

The presence of this mosquito in the UK was first discovered in 2017. “It was likely that the mosquitoes were introduced from across the channel on transportation, however, it is not believed that they were able to establish,” White said. “This may change in the near future under climate change.”

A separate species of concern is the common house mosquito or Culex pipiens. “This species is resident to the UK, our modelling work indicates that [it] is likely to increase in abundance,” said White.

“Culex pipiens is a vector of West Nile virus, which is currently absent in the UK, but could be introduced via migratory birds,” he added. “Our work suggests that increases in temperature may make the risk of West Nile virus outbreaks in the UK in the next few decades more likely.”