The uncontrolled population growth of mosquitoes is a threat to the world. These insects spread dangerous diseases such as malaria, dengue, chikungunya, etc. Their population is rapidly increasing as they have become resistant to insecticides. But researchers at New York University have found a new way to tackle this problem. They discovered that microwaving an insecticide can rejuvenate its power and kill highly resistant mosquitoes.
Insecticides Versus Mosquitoes’ Population
Insecticides are chemical substances that are used to kill insects. These are widely used in various industries, such as agriculture and medicine. Insecticides are also used in homes to prevent the transmission of mosquito-borne diseases by killing mosquitoes. These come in the form of ready-to-use sprays, coils, bed nets and bed nets. All these formats of insecticides are used to control the population of mosquitoes. But increased urbanisation and climatic changes have contributed to the rise of the mosquito population. This puts people at a higher risk of suffering from mosquito-borne diseases. Also, due to genetic mutations, these insects have become resistant to the insecticides that are used today. However, scientists have found a solution to this problem. Insecticides with new chemical properties can reduce the mosquito population.
The research ‘microwaving an insecticide to restore its power’ is an accidental discovery. Researchers were working on crystal growth experiments. For this, they were using DDT which is an old and notorious insecticide. When they heated this insecticide, they found that the crystal structures were rearranged and its power to kill insects was renewed. As DDT has two crystal forms, out of which one works better compared to the other, researchers decided to use deltamethrin instead of DDT crystals. “We didn’t set out to revive insecticides,” said Bart Kahr, a crystallographer at New York University.
Deltamethrin is a commonly used insecticide that kills malaria-carrying mosquitoes. This insecticide is incorporated in sprays and bed nets which are used in homes. Researchers observed that heating this insecticide changes its crystal structure allowing it to work faster. According to Kahr, altering the crystal structure is a tried-and-true way of providing drugs with different and new properties. “We just were surprised at how relevant it really was, and a little surprised that nobody has looked at this before,” said Kahr. “Different communities of scientists just have different urgencies. And sometimes when you come from the outside, you look at things from a completely different way.”
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Then, they tested this new deltamethrin on mosquitoes and found that they were sensitive to this insecticide. Like deltamethrin, researchers experimented with the chalk formulation of this insecticide called D-Fense Dust. They heated it in the microwave so that they could control the temperature. This experiment also worked well. So, they decided to test it on the mosquitoes. For this, researchers teamed up with entomologists and tested this heated D-Fense Dust on Anopheles mosquitoes which were resistant to deltamethrin. This heated insecticide with rearranged crystals killed the mosquitoes.
“That’s important because insecticide resistance is a growing problem and is impairing the ability to control mosquito populations to tamp down malaria spread, ” said Janet Hemingway, a geneticist at the Liverpool School of Tropical Medicine, England, who was not involved in the discovery. Though this discovery helps control the mosquito population, one cannot apply this principle immediately to mosquito repellents like bed nets and spray.
Kahr and his team are working on including these heat-treated insecticide crystals in bed nets. According to them, sprays are not a good option as the rearranged crystals will lose their properties when mixed with water. They said people can also use insecticide chalks on their walls.
To seek more information regarding the study, we interviewed Dr. Bart Kahr.
Dr. Bart Kahr
What led to the discovery that microwaving can rejuvenate the effectiveness of an insecticide? What exactly were you trying to discover but ended up with this discovery?
A microwave is just a convenient way to heat something, whether in your kitchen or in a lab. There is nothing special about microwave heating. A regular oven works as well. Why heat? Heating can transform one crystal form or polymorph with a particular structure into another structure with a different energy. If the transformed material is higher in energy, it tends to liberate molecules more readily to mosquitoes that are in contact with it. Based on previous work in our lab on the crystal forms of the malaria insecticide deltamethrin, we were aiming to achieve increased activity by heating.
Can you tell us more about crystal growth experiments? What is its significance?
As mentioned above, different crystals of the same molecule have different structures, energies and consequent activities. If we can control crystal polymorphism (the range of structures in which a molecule may present itself in the solid state) we can rationally control the activities of contact insecticides.
Why did you use deltamethrin instead of DDT for the microwave experiment?
Deltamethrin is a synthetic pyrethroid insecticide (derived from pyrethrum that is found in chrysanthemum flowers). Pyrethroids have been doing the lion’s share of malaria prophylaxis in the past 50 years. DDT is a relic. It has a long and unfortunate history. It carries a lot of baggage. Some malariologists think that it has legitimate public health applications, but the political obstacles are too great.
Can this method be applied to all types of insecticides, or are there specific insecticides that respond better to microwaving?
It can’t be applied universally – it depends on the behaviour of each compound which is a universe in itself – but the correlation between crystal energy and activity in general. So the method may be applicable to other compounds. One has to look at it case by case.
In practical applications, how would this microwaving process be implemented on a larger scale, such as in mosquito control programs?
As I said, there is nothing special about microwaves. This is a comparatively expensive way to heat things in resource-poor countries. Any heat source, if controlled, works well and should be scalable. Unfortunately, dust isn’t a mainline application in fighting the Anopheles mosquito. We have to transfer this phenomenon to insecticides that present themselves on bed nets or are used in indoor residual spraying. Working on it.
The detailed research has been published in Malaria Journal.