Evolution-Proof Insecticides

The title of this article in PLOS-Biology was at first a little scary. Insect resistance to insecticides is the bane of malaria control programs, but I jumped to the conclusion this was talking about making the Anophales mosquito extinct. Wouldn't there be unintended consequences?

Turns out that was an error on my part. The authors put forward an intriguing idea that shows the problem-solving abilities of evolutionary theory (could ID ever come up with something like this? I wonder). Insecticides used in malaria control kill lots of mosquitos, which imposes intense selection pressure for resistance. The females bite and feed on blood, make eggs and lay them in water, every few days. They go through this cycle only a few times before they die. The development cycle of the malaria parasites is longer, so that there will be some biting/feeding/egg laying cycles where the female mosquito is not yet capable of infecting someone with malaria. The authors draw the conclusion from this:

These facts together lead to one of the great ironies of malaria: most mosquitos do not live long enough to transmit the disease.

The strategy then is to only kill mosquitos after they've reproduced, but before the malaria parasites become infective. The goal is to find insecticides that minimize selection pressures by killing only older mosquitos who have had some opportunity to breed. While noone is actually doing this yet, the authors discuss the modes of action of "late-life acting" (or LLA) insecticides and identify the kinds of research needed to test this concept.

Let's hope someone gives it a try.