Innovative biocontrol technique targets female insects to combat mosquito-borne diseases

Innovative biocontrol technique targets female insects to combat mosquito-borne diseases

A genetic biocontrol method that shortens the lifespan of female insects could work as quickly as pesticides to reduce populations of disease-carrying mosquitoes and destructive plant pests, researchers say.

Insect pests pose a huge threat to global health and agriculture, causing hundreds of thousands of deaths and millions of infections each year, and causing billions in health and crop damage.

Biocontrol is increasingly seen as a viable alternative to pesticides, which can harm non-target species and ecosystems and become less effective as resistance to them increases.

A new approach called Toxic Male Technique (TMT), developed by researchers at the ARC Center of Excellence in Synthetic Biology at Macquarie University in Australia, involves genetically engineering male insects to shorten the lifespan of the females they mate with.

Researchers say it can be used to quickly respond to outbreaks of agricultural pests and combat mosquito-borne diseases such as malaria, dengue and Zika.

“We believe our technology has the potential to work as quickly as pesticides, without the associated risks of harm to other species and the environment,” says Samuel Beach, an applied life sciences researcher at Macquarie University and lead author of the study published today in Nature Communication.

Beach says the approach is more efficient than existing methods such as the sterile insect technique or the release of insects with lethal genes, which work by releasing masses of sterilized or genetically modified males to mate with wild females.

With these techniques, the mated females give birth to no or only male offspring, but they continue to feed on blood and spread disease until they die naturally - meaning the population of biting females only declines as the next generation emerges.

“TMT is cheaper because you need fewer males to reduce the insect population or the spread of disease much faster,” Beach explains.

Poison proteins

The new technique involves genetically engineering male insects to produce insect-specific venom proteins in their sperm. When these males mate with females, the proteins are transferred, significantly shortening the females' lifespan and their ability to spread disease.

The researchers found that mating females with genetically modified males shortened their lifespan by 60 percent.

"Ideally, we're aiming for a 100 percent reduction in lifespan - that is, the females die as soon as they mate with the male," Beach told SciDev.Net. “But we want to achieve this in the long term, it will take some time.”

Even a 60 percent reduction could go a long way toward reducing the impact of mosquito-borne diseases, he adds.

Diseases such as malaria, dengue fever, Zika, chikungunya and yellow fever are transmitted by female mosquito species Aedes aegypti and Anopheles gambiae.

Beach explains that a female mosquito that feeds on a host's blood and becomes infected with the virus is not contagious for a few days. For a period of five to ten days, she cannot transmit the disease to another person.

"That means we don't have to get to 100 percent mortality, we just have to shorten their lifespan within that period of time where they can't transmit the disease to a second person, which we estimate to be about 60 to 80 percent per person. "The lifespan is shortened by one percent," says Beach.

The researchers say the technology could work even better for farmers because plant pests have a longer lifespan than mosquitoes - up to a year or two compared to three to four weeks.

“Because the generation time is so long, if we can kill the female earlier it will be of much greater benefit to agricultural pests,” adds Beach.

Operating costs

Tonny Owalla, a researcher at Med Biotech Laboratories Kampala, Uganda, who was not involved in the study, believes that developing male mosquitoes to reduce the population of female malaria carriers could be a useful approach.

But he warns that the cost of deployment could make the technology unusable for routine use in malaria-endemic countries.

“Take for example how many male mosquitoes you would release in the Democratic Republic of Congo, the most malaria endemic country in Africa, how many rounds of releases per year, infrastructure, mosquito supply source…” says Owalla.

Beach says the technology must go through rigorous safety testing before it is rolled out. In addition, regulatory frameworks for the use and infrastructure for breeding mosquitoes are also required.

However, we are sure that in a few years our technology will provide millions of people around the world with a sustainable solution to combat diseases and plant pests.”

Tonny Owalla, researcher at Med Biotech Laboratories Kampala, Uganda

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