Do mosquitoes serve any useful purpose on Earth? Here in Canada and in most temperate climates, they are a nuisance with their bites, causing itchiness and sometimes skin infections. In subtropical and tropical environments, however, mosquitoes can be deadly.
There are 3,500 known species of mosquitoes and counting, found in almost every eco niche on Earth. Mosquitoes are incubators for parasites which they spread from species to species, in some cases, causing disease and death. Malaria, spread by mosquitoes, killed 619,000 people in 2021. Most of the victims were under the age of 5.
It seems, therefore, to be a legitimate question to ask,
“What would happen if we eradicated mosquitoes from the planet?”Â
A lot of unintended consequences.
Mosquitoes And Climate Change
As the planet warms, mosquito-borne diseases are spreading to areas where they have never been endemic in recent history. Climate change facilitates the spread of vector-borne diseases like West Nile, Malaria, Dengue, Zika, Chikungunya and Yellow Fever.
I asked Perplexity.ai to summarize the impact mosquito-borne diseases have on humanity. This is the chart it produced:
Among the above-mentioned diseases, Dengue is the fastest-growing over the last 60+ years and is endemic in over 120 countries today. The Aedes aegypti mosquito that hosts the Dengue virus lives in proximity to human populations. It likes the clutter of dense urban areas where standing water provides fast-breeding opportunities.
Malaria is the best-known mosquito-borne disease. It is endemic in Africa, with Nigeria reporting 31% of the continent’s cases. Anopheles mosquitoes spread the disease as hosts of the Plasmodium falciparum parasite. Insecticide overuse has led to growing mosquito population resistance. The need for alternative control strategies is, therefore, a global imperative.
Combatting Mosquitoes
Traditional approaches to fighting mosquito-borne diseases include eliminating stagnant water breeding grounds such as ponds, ditches, swamps, and standing water sources around homes and buildings. A few years ago, Toronto reported its first West Nile Virus cases caused by the spread of Aedes aegypti mosquitoes into Southern Ontario. Homeowners were asked to remove rainwater collection sites like old tires and pots, and to unblock eavestroughs and rain gutters, all potential breeding sites.
Using genetic engineering is a high-tech deterrent now being employed. A recent mosquito control program has introduced genetically modified sterile males to be released into the wild. The British company, Oxitec, has pioneered this technology in a series of test trials covering five countries. It has targeted Aedes aegypti populations responsible for spreading West Nile, Dengue, Zika, Chikungunya and Yellow Fever.
Crashing mosquito populations can produce negative ecosystem consequences. Why?
Mosquitoes are a food source for amphibians, reptiles, birds, bats, fish, spiders and other insects.
Mosquito larvae live in water where they play a significant role both as a food source and in maintaining freshwater environments. Freshwater today is a scarce commodity.
Eliminating breeding populations at the larval stage has negative impacts above the water, with adult winged populations crashing. Losing mosquito pollinators, therefore, has consequences for plants.
Fortunately, Oxitec and other sterilization experiments have been limited to date, with the vast majority of the 3,500 mosquito species unaffected.
Targeted Genetic Modifications That Don’t Kill Mosquitoes
What about other genetic modification strategies?
Previously, I wrote on this blog site about the World Mosquito Program (WMP). This Australian-founded research program has genetically modified Aedes aegypti mosquitoes. These modifications don’t sterilize. Instead, they create genetic changes that block intracellular disease-causing bacteria, viruses, and parasites that make the mosquito a carrier. (See the image appearing at the top of this posting.)
A paper published in the journal Annals of Medicine in 2024 describes additional research using gene drive technologies. A group of African universities and medical research institutions were involved in publishing work on gene-drive technology to control malaria-spreading mosquitoes. The research involves deploying the CRISPR gene-editing tool to modify mosquito DNA sequences to inhibit malaria. The desired outcome is to create inherited traits from generation to generation to produce a better than 50% reduction in the wild population’s disease transmission rates.
Altering mosquito genes without reducing their numbers is considered ideal.
Ethical Questions and Eco Considerations
Could a genetically altered mosquito spread through the natural environment and compete with other benign mosquito species, leading to their extinction? Could cross-breeding in the wild create unintended negative consequences, producing a super spreader, and could genetically modified mosquitoes cause irreversible negative impacts on biodiversity? Then there is the need to advise the public and get informed consent when deploying gene-drive technology experiments.
In the referenced paper, the authors express the hope that gene-drive technology is the tool to eradicate malaria, and by extension, other vector-borne diseases spread through mosquito bites.
For the millions who suffer from vector-borne diseases, this type of research with guardrails in place should turn gene-drive technologies into “a robust, cost-effective, and sustainable prospect” and ensure humans, animals and mosquitoes can find an ecological balance in the 21st century.
