- Title: Stressed out mosquitoes die more easily, researchers find
- Date: 2nd November 2016
- Summary: RECIFE, BRAZIL (FILE - JANUARY 27, 2016) (REUTERS) VARIOUS OF AEDES AEGYPTI MOSQUITOES INSIDE LAB JAR CLOSE OF PETRI DISH WITH MOSQUITO VARIOUS OF SCIENTIST EXAMINING MOSQUITO UNDER MICROSCOPE CLOSE OF AEDES AEGYPTI MOSQUITO SEEN UNDER MICROSCOPE
- Embargoed: 17th November 2016 10:36
- Keywords: mosquitoes Zika malaria University of Leuven pesticide stress
- Location: LEUVEN, BELGIUM / RECIFE, BRAZIL
- City: LEUVEN, BELGIUM / RECIFE, BRAZIL
- Country: Belize
- Topics: Health/Medicine
- Reuters ID: LVA00256R52SB
- Aspect Ratio: 16:9
- Story Text: Mixing a small amount of a biological pesticide with a synthetic chemical substance emitted by one of the mosquito's natural enemies triggers a stress response that increases mortality, according to research carried out in Belgium. Scientists hope this cocktail of substances could one day be used to target specific regions blighted by mosquitoes, while at the same time reducing the amount of pesticide needed.
"(The) scent of a predator can have many negative effects on prey species... because prey then sense that there is a chance that they will get eaten by a predator, so this causes fear. And they react to this with a stress response," said researcher Lin Op de Beeck from the University of Leuven.
"I thought it would be very interesting to try to explore also this pathway for mosquito control especially since the chemicals of the scent of an important natural predator which is the backswimmer, from the genus Notonecta, they have been recently identified and they can be synthetically produced."
Mosquitoes transmit a number of deadly diseases, including Zika; a virus linked with a rare birth defect known as microcephaly. The virus has spread to around 60 countries and territories since the current outbreak was identified last year in Brazil.
Mosquitoes are building resistance to many existing pesticides. Some traditional pesticides are still effective but can be toxic to other wildlife, including bees. One such pesticide, from a class of pesticide called organophosophates, is banned in Europe, where the risk is seen as unacceptable. In the U.S. territory of Puerto Rico, where Zika is widespread, the governor prohibited its use amid protests over safety.
Scientists from the University of Leuven used the biological pesticide Bti (Bacillus thuringiensis israelensis), for which there is recent evidence of some environmental impact and development of resistance. However, they combined it with the synthetic chemicals heneicosane and tricosane, based on the chemical substances - known as predator cues - produced by the backswimmer insect.
"I found that when I used a cocktail of these two products, so the synthetic pheromones and the biological pesticide Bti, that when combined the mortality of the mosquitoes increased a lot. So when I used both substances separately there would be no mortality, but when combined together you would see a strong increase in mortality of the mosquitoes," Op de Beeck told Reuters.
Crucial to the cocktail's success is that a much lower dose of pesticide is needed to kill the mosquito once the synthetic predator cues is added, said Op de Beeck.
"Even though the BTI is in a low dose they cannot handle the stress from this biological pesticide anymore. So it's the extra stress of fear of being eaten that will make sure that they die more easily from this biological pesticide," she said.
Furthermore, this stress response also suppresses the mosquito's immune system. Op de Beeck said that mosquitoes not immediately killed will probably have a shorter lifespan, so that possibly the parasites they transmit don't have the time to complete their incubation period.
The initial research was conducted in a laboratory. The next step is to study the impact of the chemical cocktail in a more natural setting. Eventually, the team hopes it could offer a more effective and sustainable method for controlling mosquito-borne diseases.
However, Op de Beeck said mosquito killing has to be targeted to specific regions where they are spreading disease, as the tiny insect is still an important part of the eco-system.
"They are indeed food for different birds or bats, also their laval stages are food for different fish and other animals. So it cannot be the goal to kill every mosquito on our planet, that's for sure," she said.
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