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Researchers Refine Pesticides
November 22, 2017

In the battle to keep insects at bay, modern pesticides, specifically pyrethroids, have become more and more effective, but based on new research, maybe too effective. Because their killing power is non-selective, many beneficial insects, such as pollinators like bees, also fall victim.

According to information provided by Michigan State University (MSU), researchers at MSU’s entomology department have unlocked a key to maintain the insecticide’s effectiveness in eliminating pests without killing beneficial insects. Funded in part by the National Institutes of Health and MSU AgBioResearch, the study, published in Proceedings of the National Academy of Sciences, shows that molecular tweaks can make the difference.

Pyrethroids target the voltage-gated sodium channel, a protein found in nerve and muscle cells used for rapid electrical signaling. Pyrethroids basically work by binding to the voltage gate of the sodium channel and prevent it from closing. The nervous system becomes over-stimulated and the insect is killed. These pesticides, however, don’t have the same effect on humans, or other mammals for that matter.

Ke Dong, MSU insect toxicologist and neurobiologist and co-author of the paper, “Molecular basis of selective resistance of the bumblebee BiNav1 sodium channel to tau-fluvalinate,” honed in on a single protein that could afford bumble bees the same resistance as humans – tau-fluvalinate, a pyrethroid insecticide. Prof. Dong worked with Shaoying Wu, lead author from Henan Agricultural University (China), who conducted the research in Dong’s lab as a visiting scholar.

“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,” said Prof. Dong. “This opens the possibility of designing new chemicals that target sodium channels of pests but spare bees.”

Sodium channels are large transmembrane proteins of more than 2,000 amino acid residues. Prof. Dong’s lab spent many years unraveling this groundbreaking advance. The scientists initially started with sodium channels from other bugs, such as mosquitoes, fruit flies, cockroaches, mites and ticks, to find where pyrethroids bind on insect sodium channels to effectively kill them.

“By examining wild mosquitoes that have become resistant to pyrethroids, we were able to help narrow down the potential sites on which to focus,” Prof. Dong said.

In the new study, the team focused on a longstanding enigma that bumble bees and honey bees are highly sensitive to most pyrethroids, but they were resistant to tau-fluvalinate. Currently, tau-fluvalinate is widely used to control agricultural pests and also varroa mites, which are one of the biggest threats to bees worldwide.

Eventually, the team discovered that the channel is resistant to tau-fluvalinate but sensitive to other pyrethroids. Further mutational analysis and computer modeling revealed that specific amino acid residues in bumble bee sodium channels are responsible for the selective toxicity.

Future research will examine sodium channels from various pest and beneficial insects to explore the features of pyrethroid binding sites, which could lay the groundwork for designing new and selective pesticides. It also will shed light on how pests develop resistance to insecticides over time and how beneficial insects respond to them in the field.

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