Research Finds Killing Off Malaria-Carrying Mosquitoes Unlikely To Cause Ecological Damage

A recent study done on the effect of removing malaria-carrying mosquitoes from a region found that it is unlikely to negatively affect ecosystems. The study was carried out by researchers from Imperial College London , and it suggests that mosquitoes that carry malaria could be reduced or even eliminated in a region without harming the ecosystem of that region.

Combating Malaria Through Genetic Engineering

Researchers at Imperial College London (ICL) combined multiple studies done on one species of mosquito that carries malaria. The meta-analysis found that while locally eliminating this single species of mosquito would drastically reduce cases of malaria, it wouldn’t leave much of an impact on the surrounding ecosystem. However, the researchers do note that more research in the field will be needed to test this hypothesis and determine that an ecosystem won’t be negatively affected by the elimination.

Malaria is one of the most prolific killer diseases in the world, and the World Health Organization believes that approximately half of the world’s entire population is at risk of developing malaria. 2016 saw around 216 million cases of malaria and around 450,000 of all these cases resulted in deaths. Most of these deaths were in children who were under five years of age. Cases of malaria had fallen dramatically between 2000 and 2015, but the disease seems to be seeing a resurgence in certain parts of the world.

Many different strategies are being used by world governments and health organizations to combat malaria, and one notable possible solution is to genetically modify mosquitoes to kill off local populations of mosquitoes. There are several different methods being investigated to accomplish this. One method involves modifying mosquitoes with a defective gene that will cause them to die over time, but not before they can breed with other mosquitoes and pass this fatal gene onto the next generation. Since only the female mosquitoes bite people, another project involves the sterilization of female mosquitoes who carry malaria. The creation of a gene drive would be used to spread the sterilization gene throughout an entire population. Those who work on genetic engineering of mosquitoes like this refer to these projects as “friendly mosquitoes.”

Photo: nuzree via Pixabay, CC0

One of the primary worries about genetic engineering is that it might have unintended consequences, such as damaging populations of frogs and fish that rely on mosquitoes for food.

Researching The Impacts Of Suppressing Mosquito Populations

Most cases of malaria occur in sub-Saharan Africa, and within this geographical region there are actually only a few species of mosquitoes that spread malaria, out of the hundreds of species that are present in the region. The Target Malaria project is working with researchers to determine the possibility of suppressing one of the species, Anopheles gambiae, with genetic modification. The team wanted to predict the possible ecological impact of this suppression before they set out to do so, hence the need for the study that was recently published in Medical and Veterinary Entomology.

The report found that while there are species of animals that eat An. gambiae, those that do don’t rely on the mosquito for their survival. They also subsist on other species of mosquitoes as well as other insects generally, and since they don’t need An. gambiae to survive the suppression of it in the region is unlikely to have a notable effect.

Tilly Collins, a researcher at the Centre for Environmental Policy at ICL and lead author on the study, explains that there’s little evidence to suggest that An. gambiae is a necessary part of the diet of insect predators. Collins explains:

As adults, An. gambiae mosquitoes are small, hard to catch, most mobile at night and not very juicy, so they are not a rewarding prey for both insect and vertebrate predators. Many do eat them — sometimes accidentally — but there is no evidence that they are a big or vital part of the diet of any other animal.

Collins notes that there is a species of spider known as the “vampire spider” which is found in homes around the Lake Victoria region. The vampire spider does seem to have a preference for the female An. gambiae mosquitoes, as the females are those that subsist on blood. When a blood-fed female An. gambiae is resting, it is nutritious and easy prey for the spider, but the spider will also eat any other readily available species of mosquito as it is an opportunistic predator.

The ICL research team also examined larval mosquito habitats, as the creatures which prey on adult mosquitoes are often different to those which prey on mosquito larva. The female mosquitoes will usually lay their eggs in ephemeral puddles and small ponds that are away from the main aquatic predators. When the eggs are laid in larger ponds, the predators which feed on the larvae also subsist on many other larvae and small aquatic creatures.

The research team didn’t just examine what preys upon An. gambiae, it also researched the species that competed with the mosquito in that ecological niche. This is important because if one competitor for a niche suddenly disappears, the other competitors can suddenly become dominant in that niche and grow. If the competitors for that niche have their own problems (for example, they carry a different human disease), one problem may have simply been traded for another.

Future Research

Future research will focus on the effects of mosquito suppression in Ghana, where many who live in rural villages are at risk of developing malaria. Photo: lapping via Pixabay, CC0

The researchers found that other mosquito species were likely to compensate for the suppression of An. gambiae, and that there was unlikely to be any major problems associated with the other species. However, lab studies and field studies don’t always find the same results, and neither does the past suppressing of mosquitoes populations always agree with lab studies.

In order to improve the base of research and derive better conclusions, the Target Malaria project will be partnering with the University of Ghana, and the University of Oxford to do a four-year-long study. The study will examine populations of An. gambiae in Ghana’s local environment much like other studies on An. gambiae.