Reducing yellow fever mosquitoes with genetically modified mosquitoes.

Now that the cabinet is relaxing the corona measures, holidays abroad are slowly becoming possible again. Holidaymakers who want to stay in a tropical area in Asia, Africa, South or Central America should not only remain alert to the corona virus, but also watch out for the yellow fever mosquito. These mosquitoes carry infectious diseases such as Zika fever, yellow fever, dengue and heartworms. They pass them on to people as soon as they insert their tiny snout needles into human flesh.

Kill the messenger

The yellow fever mosquito (Aedes aegypti)

One way to combat such infectious diseases is to kill the messenger – the yellow fever mosquito. This used to be done with chemical means, but now researchers are looking for a green alternative. The British company Oxitec hopes to have found such a way: yellow fever mosquitoes with a built-in self-destruct button. Last month, the company released nearly 150 thousand such mosquitoes on islands in the American Florida.

Female mosquitoes are the culprits. Only they transmit and transmit diseases. That is why the British scientists modified the DNA of a number of mosquitoes in such a way that only females die. They did this by giving the mosquitoes an extra gene that causes their daughters to die at an early stage. Next, the researchers let those mosquitoes reproduce in the lab to breed and release large quantities of genetically modified (GMO) mosquitoes in Florida.

Due to the suicide gene, the female mosquitoes do not have a chance to infect humans. All the sons who give birth to the genetically GMO mosquitoes will survive. Half of them inherit the suicide gene, so their daughters also die. Ultimately, only five of every 100 yellow fever mosquitoes remain in Florida, Oxitec says. Over time, once the numbers grow again, the technique must be repeated.

A major advantage over pesticides and chemicals is that the British company’s GMO method is highly selective. Male yellow fever mosquitoes mate exclusively with female yellow fever mosquitoes. Other insects and even other mosquito species do not suffer from it.

On off switch

Nevertheless, there is a lot of objection to the experiment from the population and some scientists are also questioning it. “Releasing GMO animals into nature is a lot riskier than, for example, growing crops with modified DNA,” says medical entomologist Bart Knols. “GMO crops can be removed from a field relatively easily and completely after an experiment, but GMO mosquitoes fly away and you can’t get them back in their cage.”

In nature, the GMO mosquitoes must eventually disappear, because only half of the male offspring are carriers of the suicide gene. In the laboratory, the researchers use a trick that allows the female mosquitoes to survive, because that is where the females have to reproduce. The biotechnologists do this with a kind of on/off switch for the suicide gene. When female mosquitoes are exposed to the antibiotic tetracycline, the suicide button is turned off. But without this substance, the switch will turn and the females will die.

Using the antibiotic is a pitfall, Knols thinks. “In various countries such as the United States, Brazil and also in the Netherlands, livestock farmers use antibiotics, including tetracycline,” explains Knols. “Such substances end up in the surface water, where mosquitoes lay their eggs.” Then there is a chance that the suicide gene will not work and the daughters will survive.

There is also the possibility that the GMO mosquitoes will spread. Although the animals only move 200 meters in their lifetime, it is not impossible for them to travel in cars or ships and thus end up in new places. That can also happen in Florida, because the islands where the mosquitoes fly around are connected by roads to each other and to the mainland.

The company will monitor the mosquitoes in the near future by catching them with traps. To distinguish between the GMO mosquitoes and the natural variant, the scientists also built in a piece of DNA that makes the mosquitoes glow under ultraviolet light. They determine how far the mosquitoes fly, but also how long they live and whether the female mosquitoes do indeed die at an early stage.

Invasive Species

The ecosystem shouldn’t be upset if the yellow fever mosquito disappears in a state like Florida. The animal does not occur naturally in the western hemisphere, but traveled with the slave trade from Africa about four hundred years ago. “From an ecological point of view, you can then easily remove this invasive species, because it does not belong in Florida,” says Helen Esser, ecologist at Wageningen University. Perhaps the mosquitoes now serve as food for other animals, but that void can be filled by other mosquito species.

The yellow fever mosquito likes to lay its eggs in enclosed spaces such as this cup of water.

“In addition, yellow fever mosquitoes lay their eggs in small, enclosed spaces where no other animals live,” adds mosquito expert Knols. “You can think of tree cavities, empty beer cans, buckets, or in the gutter. That way, the eggs and larvae are not eaten quickly.”

Thus, eradicating invasive species poses few risks. In other countries, where the yellow fever mosquito originates, more research will first be needed into the ecological consequences before the yellow fever mosquito can be eradicated there, Esser thinks.

Considerations

Although Knols believes that every method of combating infectious diseases deserves a chance, he is not very enthusiastic about the GMO mosquitoes. “With methods I’m working on, such as attractants and traps, we can also kill mosquitoes. We don’t have to tinker with the DNA or use chemicals for that. In addition, I personally find it disadvantageous that new GMO mosquitoes have to be released over time to keep the population in check. As a result, a country remains dependent on a company like Oxitec,” says Knols.

“Of course you have to be careful that you don’t become dependent on such a company”, responds ecologist Esser, “but that’s another discussion”. She herself calls the technology developed by the company beautiful and promising. “There will always be risks that scientists should be aware of, but now it’s about balancing the pros and cons. At the moment, people are still fighting mosquitoes with pesticides, which has greater consequences for humans and nature than genetically modified mosquitoes.”


Source: Kennislink by www.nemokennislink.nl.

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