Tanzanian Scientists Study Mosquitoes’ Mating Behaviour to Control Malaria
A resident of Ifakara tucked into a mosquito net.

IFAKARA, Tanzania – When you think of malaria, a swarm of mosquitoes flying against an orange sunset is a dangerous sight.

As part of their mating ritual, the dreaded bloodsuckers brazenly hover for 30 minutes, males adroitly flapping their slender wings to produce a sound that lures female partners to join them.

The mosquito proliferation that results from this harmonic mating song ensures a grim reality for farmers in Tanzania’s Mchombe Village, who struggle with bouts of malaria.

Locals in this impoverished village use all the ammunition at their disposal to fight the deadly insects, whose population keep rising. At dusk, they routinely shut down windows, burn piles of fresh eucalyptus leaves to produce scented smoke to chase away the mosquitoes and, most importantly, get under their bed nets to sleep.

“Malaria is a big problem here. The mosquitoes reproduce themselves in large numbers,” said Amina Jaka, a paddy farmer at Mchombe Village.

The 28-year-old mother of four children, says mosquitoes are ubiquitous due to the presence of stagnant ponds of water, and her children struggle to sleep through the night because of them.

Clever insects

Jaka, who has witnessed two malaria deaths in the village in the past few weeks, is increasingly worried about her children and makes sure they are tucked under mosquito nets even they sleep in the afternoon.

“Mosquitoes are very clever insects. You simply don’t know when they will bite you,” she said.

Msombwa villagers, who had considered themselves exempt from malaria after a mammoth government-led anti-malaria campaign in the village two years ago, are baffled by the rising number of mosquitoes in recent months.

Nestled on the lower echelons of the Kilombero River, the village is a hotspot for the Anopheles mosquito, which transmits the plasmodium parasite that causes malaria.

Although malaria infections have declined in most parts of Tanzania since 2000 thanks to multiple vector control interventions, including insecticide-treated bed nets, residual spraying and improved diagnostics, the struggle is far from over.

Constant innovation

Scientists in Tanzania are constantly devising new ways to control the mosquito population. At a research institute run by the Ifakara Health Institute dubbed ‘Mosquito City’ as it’s home to the world’s largest captive colony of mosquitoes, researchers are studying the mating behaviour of mosquitos.

Fedros Okumu, a senior entomologist and director of science at the centre, said his team uses cutting-edge approaches to trap, repel and kill mosquitoes when mating.

“One of the most interesting experiments we have done is to study the mating behaviour of malaria mosquitoes,” he told Health Policy Watch.

“Male mosquitoes usually fly to their favourite mating places to begin a ritualistic flight dance [at sunset], drawing in females,” Okumu said, adding that a male would then identify and pursue a flying female by detecting her flight sound.

 “If the male can’t properly hear the female then the chase fails and they don’t mate,” he said.

Although mosquitoes’ romances sound like a trivial matter, researchers say it is a rare opportunity to kill the malaria-causing insects.

A doctor at Ifakara district hospital treating a malaria patient

In 2021 there were approximately 247 million cases of malaria worldwide with about 619,000 deaths, according to World Health Organisation (WHO).

The  WHO Africa region carries the heaviest global malaria burden. In 2021 the continent was home to 95% of malaria cases and 96% of deaths, with children under five accounting for about 80% of the deaths.

At Mosquito City, scientists are studying the Anopheles funestus mosquito, which is responsible for 90% of malaria cases in the region.   

“This is a least understood species of mosquitoes because it is extremely difficult to raise in a laboratory environment,” Okumu said.

There are 3500 known species of mosquitoes of which 400 belong to Anopheles family, and only 50 to 70 of them can transmit malaria to humans, he said. In Africa, malaria parasites are transmitted by the Anopheles gambiae, funestus, arabiensis and colluzzi species.

“Effective malaria control can be achieved when we identify, understand and target just one or two anopheles species instead of trying to kill all mosquitoes,” he said.

Recent gains in the fight against malaria have been attributed particularly to the use of insecticide-treated bed nets . Since 2000, over two billion insecticide-treated nets have been delivered to malaria-endemic countries including Tanzania. This rapid scale-up has been by far the largest contributor to the impressive drops seen in malaria incidence since the turn of the century, according to WHO.

But in the last two decades, analysts say their effectiveness is increasingly being compromised by the emergence and spread of insecticide resistance and increasing outside exposure to mosquito bites.

Genetically modified mosquitos

Scientists globally are now working to better understand the overall ecology of mosquitoes as the malaria vector and how the changing landscape will affect the mosquito population in the future.

One such innovation is to create genetically modified mosquitoes under lab conditions, which, upon mating with wild mosquitoes, produce offspring that are incapable of further reproduction or transmitting malaria to humans.

However, malaria researcher Zul Premji said past efforts to ensure the genetic control of mosquitoes using the sterile-insect technique have been less successful than expected due to low competitiveness between sterile and wild males.

“Many mosquito species can be cultured in large numbers under controlled conditions, but due to genetic selection and loss of natural traits, such insects may behave differently from their wild siblings,” Premji told Health Policy Watch.

However, the seasoned researcher is confident that laboratory cultures and subsequent genetic transformation of target mosquito species may result in insects with widely different mating behaviours compared to their wild siblings.

But Jaka and fellow villagers are sceptical about whether a genetically modified species will make any difference.

To them, what matters to prevent malaria is the provision of free insecticide bed nets, and repellents, quality diagnostics at local hospitals and the availability of antimalarial drugs.

Image Credits: Peter Mgongo.

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