The ability to sense toxins through their legs helps some malaria-carrying mosquitoes develop a resistance to insecticide, according to a new study.

Scientists found insecticide resistant populations of Anopheles gambiae and Anopheles coluzzii mosquitoes, two common malaria-carrying species in West Africa, featured higher concentrations of a unique group of binding proteins in their legs.

Lab tests showed the mosquitoes further boosted the production of the binding protein SAP2 when exposed to pyrethroids, the class of insecticides used on bed netting.

"We have found a completely new insecticide resistance mechanism that we think is contributing to the lower than expected efficacy of bed nets," Victoria Ingham, researcher at the Liverpool School of Tropical Medicine, said in a news release. "The protein, which is based in the legs, comes into direct contact with the insecticide as the insect lands on the net, making it an excellent potential target for future additives to nets to overcome this potent resistance mechanism."

When researchers silenced or quelled the genes related to SAP2 production, the mosquitoes became once again vulnerable to pyrethroids. Researchers also effectively inoculated previously susceptible mosquitoes by ramping up their SAP2 production.

As pesticide resistance has increased in mosquito populations, scientists have developed new bed nets with both pyrethroids and a chemical called synergist piperonyl butoxide, or PBO, which helps to weaken insect resistance to pyrethroids.

The latest research, published this week in the journal Nature, suggests mosquitoes have a variety of mechanisms for developing and evolving new resistances, thus necessitating the development of new mosquito control techniques.

"Long-lasting insecticide treated bed nets remain one of the key interventions in malaria control. It is vital that we understand and mitigate for resistance within mosquito populations in order to ensure that the dramatic reductions in disease rates in previous decades are not reversed," said LSTM professor Hilary Ranson, senior author of the new paper. "This newly discovered resistance mechanism could provide us with an important target for both the monitoring of insecticide resistance and the development of novel compounds able to block pyrethroid resistance and prevent the spread of malaria."

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