Disease-spreading mosquitoes may be more likely to occupy areas affected by human activities such as pesticide use and habitat destruction than areas less disturbed by humans. This was the finding of a recent study by Oregon State University.
While working in a national park in South Africa, researchers found a significant difference in the incidence and species composition of mosquitoes in the park compared to densely populated areas outside the park, with species known to spread diseases such as malaria and the Zika virus to humans Areas outside the park.
People care a lot about the environment in which a Leo must succeed. We have studied this extensively. But people don’t do that to mosquitos. We do not understand them as a group of species and how their ecology differs between species. “
Dr. Brianna Beechler, study co-author, disease ecologist, assistant professor of research, Carlson College of Veterinary Medicine, Oregon State University
To find disease mitigation strategies for vector-borne diseases, which are diseases that spread through parasites like mosquitoes and ticks, mosquitoes are an obvious target, Beechler said. But scientists still don’t understand mosquitoes well enough to target the species that cause disease.
“All we can do is reduce mosquitoes overall. What can be more effective, however, is to reduce certain species by changing their habitats,” she said.
To compare how mosquitoes fared in Kruger National Park compared to densely populated areas, the researchers looked at five “pressures” caused by human presence: frequency of organophosphate pesticides; Eutrophication, ie over-mineralization of water, which leads to widespread algae growth; Population density; Ungulate biomass, which includes domestic animals such as cattle and wildlife such as impala and buffalo; and loss of vegetation.
Human populations influence the habitat and breeding patterns of mosquitoes in a kind of domino effect. For example, pesticide use is spreading in ponds and other small bodies of water, killing the fish and removing the natural predators that would otherwise eat mosquito larvae and keep insect populations low.
During South Africa’s rainy season in 2016-17, researchers caught 3,918 female mosquitoes from 39 different species both inside and outside the national park.
The mosquito incidence outside the park – in human-dominated areas – was almost three times higher than inside the park. And there was a significant difference in mosquito species composition, with the species known to spread diseases (such as dengue, West Nile virus, chikungunya, yellow fever, and Zika virus) more often outside the park than inside.
“It seems to suggest that disease-causing mosquito species certainly do better in human-altered environments,” Beechler said, although she found that at this stage it is difficult to determine why it is. Further studies are needed to understand the environmental requirements of different mosquito species.
There are some success stories with current mosquito control strategies. Beechler cited a technique in the Caribbean that asked residents to introduce fish into nearby stagnant water so the fish can eat mosquito larvae before they have time to hatch.
And several countries have experimented with releasing groups of sterile mosquitoes into the wild so that they can eat and ingest resources but not reproduce.
“But none of these target disease-carrying mosquitoes, unlike non-disease-carrying mosquitoes,” she said. “It’s just that all mosquitoes are the same.”
Vector-borne diseases are not a pressing problem in Oregon right now, although there are several different types of mosquitoes in the state and some are known to spread the West Nile virus.
However, mosquitos with malaria, zika and chikungunya have all broken new ground in recent years.
“With climate change, the distribution of mosquitoes and the distribution of diseases will likely change,” said Beechler. “So it would be nice to know how to attack these species before that happens.”
M. Schrama et al. (2020) Human practices promote the presence and frequency of disease-transmitting mosquito species. Scientific reports. doi.org/10.1038/s41598-020-69858-3.