Getting wild mosquitoes back to the lab alive takes a custom backpack

This backpack isn’t typical hiking gear. Look inside and instead of water and snacks, you’ll see swarms of mosquitoes.

Molecular biologist Deogratius Kavishe designed the bag to transport these bloodsucking insects from deep in the Tanzanian wilderness to the lab. Made from locally available materials like PVC fiberglass netting (often used for window screens), a metal frame and Tanzanian kitenge cotton fabric, the backpack cost about $70 to produce and can hold enough mosquitoes to fill 18 paper cups. Because the backpack is ventilated and has a cover flap that can be soaked in water, the environment inside remains cool and moist, protecting mosquito passengers from the sun and heat.

Kavishe, a research scientist at Ifakara Health Institute in central Tanzania, and colleagues intend to test whether mosquitoes in the region are still susceptible to a common class of insecticide. Insect nets laced with pyrethroids have been used for decades to kill mosquitoes that harbor diseases like malaria. The extended exposure has led many mosquito populations to become resistant, no longer reliably killed by the chemicals (SN: 5/21/23). “We have a very big problem with resistance,” says Kavishe.

Resistant mosquitoes have been found across Africa, with some populations able to survive exposure to pyrethroid levels that are 1,000 times higher than the standard deadly dose. The World Health Organization warns that this growing problem could erase the progress made in the last decade against malaria, which kills about 600,000 people worldwide each year. There’s an idea that using pyrethroid in combination with another pesticide could help reverse the trend. For that strategy to work, though, there need to be some pyrethroid-susceptible mosquitoes still in the environment.  

Searching for those mosquitoes can entail long trips on foot through grasslands, forests and swamps. Once the insects are caught, they need to survive the journey to the lab to have their sensitivity tested. That’s where the backpack-turned-mosquito-hotel comes in.

Kavishe’s team brought mosquitoes from Ifakara to a nearby wildlife management area. From there, the researchers loaded up two backpacks with some of the insects and trekked into the wilderness. The rest of the mosquitoes stayed at the base camp to serve as controls.

Putting the backpacks to the test also tested the scientists. Once, Kavishe walked 25 kilometers (about 15.5 miles) in a day. He also waded through floodwaters and mud up to his thighs, and encountered wild animals like snakes and buffalo. “I wanted to quit several times,” Kavishe recalls with a laugh.  

Mosquitoes survived in the backpacks just as well as their less adventurous counterparts at base camp, the team reports in a study posted April 16 at bioRxiv.org. Their survival far exceeded the researchers’ original goal of keeping mosquitoes alive for three days in the field — after 10 days, about 70 percent were still alive. Of the mosquitoes that traveled the farthest, 143 kilometers over 25 days, around 30 percent survived. And more than half of wild-caught mosquitoes carried out of Nyerere National Park, some as far as 200 kilometers, survived the journey — although this time, they weren’t hauled all the way out on foot; the researchers could access areas in Nyerere by car or boat.

Now that he knows the backpack works, Kavishe hopes to soon begin looking for pyrethroid-susceptible mosquitoes in earnest. “Malaria is a big burden in our countries,” he says. “Whatever effort, whatever initiative, whatever success, which will maybe be able to eliminate malaria in four or five years — if I’ll be part of that, I’ll feel very good.”