While insecticide-treated bed nets do help protect people from malaria-carrying mosquitos, the chemicals are becoming less effective as the insects develop a resistance to them. It now appears that microwaving one such insecticide, however, makes it "good" again.
The discovery was made by a team of scientists at New York University, led by Prof. Bart Kahr.
They were initially studying the obsolete insecticide DDT (dichloro-diphenyl-trichloroethane) and noted that it has two crystal forms, one of which is better at killing mosquitos than the other.
This knowledge prompted the scientists to examine deltamethrin, an insecticide which is still widely used on bed nets and other surfaces. When mosquitos land on those surfaces and come into physical contact with the deltamethrin micro-crystals, the effect on the insects is usually lethal – but not as much so as it used to be. Unfortunately, an increasing number of mosquitos are developing an immunity to the chemical.
Drawing on a previous study conducted by Kahr and colleagues, the scientists experimented with simply heating flasks of deltamethrin in a regular microwave oven. Doing so reduced the thermodynamic stability of the insecticide's crystals, making it approximately 12 times more effective against malaria-spreading Anopheles mosquitos that had developed a resistance to the chemical in its traditional form.
"We have found that lethality of a crystal is inversely correlated with thermodynamic stability," Kahr told us. "In other words, more stable crystals are more reluctant to give up their molecules. Molecules on surfaces of less stable crystal with transport themselves across the epicuticle of the mosquito leg faster."
The experiments have so far been conducted using chalk as a substrate, but it is hoped that laboratory-heated deltamethrin will be equally effective on bed netting material.
"At the moment, the World Health Organization recognizes that bed nets are not working as they were intended, largely because of the development of insecticide resistance," said Kahr. "We have a method that can overcome resistant mosquitos."
And it should probably go without saying, but we'll say it anyway, don't try this at home with a can of bug spray.
Source: New York University