Pesticides generally take something of a shotgun approach to eliminating critters, but the problem is not all of them are bad news. Scientists have now discovered a way the recipe of these substances might be tweaked, so that they better take out the bad guys and leave the good ones to go about their business.

Because bees contribute to the vast majority of food that we eat by pollinating crops and plants, dwindling numbers are a real concern for the global population. Habitat loss is one reason for this, and another is the use of pesticides. In fact, earlier this month, the UK followed the lead of Europe in supporting a total ban on a type of pesticide that is particularly harmful to pollinating insects, called neonicotinoids.

So coming up with new pesticides that these critically important insects are resistant to would be a massive breakthrough, and scientists from Michigan State University (MSU) are reporting a promising advance in this area.

The work involves the pesticide pyrethroid, which works by targeting the sodium channels in the nerve and muscle cells that insects use for rapid electric signaling. The pyrethroids work by binding to the voltage gate of these channels and holding them open, which sends the bug's nervous system into overdrive and causes them to die.

Bees are highly sensitive to most pyrethroids, but the scientists looked to take some lessons from one type of pyrethroid insecticide called tau-fluvalinate, which they have actually shown a natural resistance to. Tau-fluvalinate is already used to control agricultural pests and varroa mites, and the hope is that this trait can be leveraged in the development of other more advanced, and selective, pesticides.

This meant examining other bugs that are sensitive to pyrethroids, such as mosquitoes, fruit flies and ticks, along with bugs that had developed resistance to them. Through this, the team was able to identify mutations that make wild mosquitoes resistant, along with molecular differences in insects and mammals that bring about different reactions.

All of this lead to the discovery of specific amino acid residues in the sodium channels of bees that make them resistant to tau-flauvinate. The researchers say this could lay the foundation for a new generation of selective pesticides.

"For the first time we are showing that unique structural features in bee sodium channels interfere with the binding of tau-fluvalinate to bumble bee sodium channels," says Ke Dong, MSU insect toxicologist and neurobiologist and co-author of the paper. "This opens the possibility of designing new chemicals that target sodium channels of pests but spare bees."

The research was published in the journal Proceedings of the National Academy of Sciences.