- by Alison Booth

Controlling mosquito populations with toxic sugar

Image of the world's deadliest creature. The mosquito.

Images courtesy of Professor Gunter Müller

Controlling mosquito populations is becoming an ongoing battle in much of the world. Like any other living thing, mosquitoes need the energy to survive. They need it to fly, to reproduce … to live. Many people think that all mosquitoes bite humans and that our blood is their main source of food.

But did you know that it’s only female mosquitoes that bite us? And that she uses the protein in our blood to help her eggs develop – not as a source of energy? The main source of energy for mosquitoes – male and female alike – is actually sugars derived from plant nectar, fruit juices, and other natural juices.

So, what does this have to do with vector control?

More than a decade ago, Professor Gunter Müller and Professor Yosef Schlein from the Department of Microbiology and Molecular genetics, IMRIC, Kuvin Center for the Study of Infectious and tropical Diseases, Faculty of Medicine, Hebrew University of Jerusalem in Israel (HUJI) came up with an elegant vector control solution based on the simple fact that mosquitoes require sugar for survival.

Amy Junnila, an entomologist at HUJI, explains one of the key benefits of this approach: “While current insecticide-based vector control solutions use environmentally toxic materials to which mosquitos develop resistance, this solution overcomes resistance because there’s no repeated exposure.”

There are currently three teams working on the project: a team – including the principal investigator – from the Hebrew University, a group from the University of Miami and researchers at the University of Bamako in Mali.

The right formulation

The attractive toxic sugar bait, or ATSB as it is more widely known, has three main components: something attractive to entice the mosquito, an oral toxin to kill it and a feeding stimulant to compel the mosquito to eat and digest the toxin.

Finding a suitable attractant wasn’t easy. After all, it needed to be more enticing than the natural flowers and vegetation that mosquitoes would normally gravitate towards. Attractants suited different ecologies. “Local fruits and seedpods ripen in buckets worked very well in Mali,” says Amy.

The team tested various flower scents, fruit juices, wine and seed pods. Whilst many were similar in their effectiveness, they needed something that was commercially available. That way they would be able to scale the solution up for mass production. They settled on using nectarine juice.

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The oral insecticide chosen was garlic oil. Not only had it been used against other pests; it was a food additive and, as such, poses little risk and requires little regulation.

“We started out with Spinosad because it’s a good, low-risk insecticide with low toxicity to mammals,” says Amy. “But it would have been too expensive for many regions. We also looked at boric acid and Dinotefuran.”

For the feeding stimulant, the team chose sugar.

How the ATSB works

The ATSB is sprayed on non-flowering vegetation. It works by first attracting the mosquitoes then providing sugar to entice them to feed and the oral toxin to eliminate them.

“By not spraying it on the attractive blossoms that bees and other insects feed on for their sugar we have reduced its impact on those populations.”

Not poisonous to mammals or other animals, the ATSB can also be used within a portable bait station. The station looks like a water bottle with a sock around it. Mosquitoes are attracted to and feed on the ATSB-soaked sock.

“You could hang the bait station around the yard for the mosquitoes to come and feed on,” says Amy. “Putting a wire mesh around it ensures bees and butterflies can’t reach it.”

Image aof a mosquito trap intended at controlling mosquito populations.

Image courtesy of Professor Gunter Müller

Extensive testing

HUJI first tested the ATSB approach in Israel against a number of mosquito species. Since mosquitoes in Israel don’t carry disease, the testing focused on the ATSB’s effectiveness in eradicating mosquitoes. “We added different food dyes to the ATSB to allow us to see which mosquitoes had fed from which ATSB,” says Amy.

image of a mosquito.

Image courtesy of Professor Gunter Müller

Testing found the solution to be particularly effective against more mature insects, which, incidentally, are the age group most likely to carry and transmit disease.

Funding from the Bill and Melinda Gates Foundation allowed testing to move to Mali in Africa, where it focused on the ATSB’s effectiveness in eradicating disease-carrying mosquitoes. In Mali, the ATSB solution sprayed onto vegetation near breeding sites reduced local vector densities by 90%.

“We’re also testing the ATSB against different vectors,” says Amy. “We’re testing it against the Asian tiger mosquito because it’s such a nasty invasive mosquito species that’s so difficult to get rid of.” As well as dengue, the Asian tiger mosquito – Aedes albopictus – also transmits the chikungunya virus and heartworm in dogs.

More than that, the ATSB was also found to be effective against the sand fly, which also carries disease.

With the potential to help in the fight against a wide number of vectors and diseases, it certainly sounds like the ATSB will be a very welcome addition to the integrated vector management toolbox.