How notorious beetle pests can beat pesticides

The Colorado potato beetle is a notorious pest, but also a kind of unstoppable genius. It can overcome more than fifty different pesticides.

The modern pesticide era began in the 1860s when Midwest farmers started killing these beetles by spraying them with a paint color called Paris Green that contained copper arsenate. The beetles soon overcame that poison as well as lead arsenate, mercury DDT, and dieldrin, and over fifty other pesticides, writes a statement.

Scientists have a poor understanding of how this creature turns this trick. While the beetle shows a lot of genetic variation, new DNA mutations probably do not show up frequently enough to let them evolve resistance to so many types of pesticides. But now a first-of-its-kind study has moved dramatically closer to an explanation.

Ramping up DNA defence

A team of researchers, led by Prof. Yolanda Chen at the University of Vermont, shows that even small doses of the neonicotinoid pesticide, imidacloprid, can alter how the beetle manages its DNA.

To fend off the pesticides, the new research suggests, the beetle may not need to change its underlying genetic code. Instead, the team found that beetles respond by altering the regulation of their DNA, turning certain genes on or off in a process called “DNA methylation.”

These so-called epigenetic changes allow beetles to quickly ramp up biological defense mechanisms–perhaps putting into overdrive already-existing genes that allow the beetle to tolerate a broad range of toxins found in potato plants. Most important, the new study shows that these changes – triggered by even small doses of the pesticide – can be passed on to descendants across at least two generations.

Rapid evolution and pesticide resistance

Over the last half-century, agricultural researchers and chemical companies have spent millions developing innovative chemical compounds to try to kill off this beetle that causes hundreds of millions of dollars of damage – and almost all eventually fail.

It’s well known that many insects in agricultural areas develop pesticide resistance; it’s not just Colorado potato beetles. More than six hundred species have developed resistance to over three hundred pesticides, with tens of thousands of reports from around the world. A growing body of research shows that many of these involve epigenetic mechanisms.

In the case of the Colorado potato beetles studied at UVM, the research suggests that pesticides may flip a whole raft of epigenetic switches some of which can ramp up production of existing defenses against the toxins – while changes in DNA methylation can unleash portions of the DNA called transposable elements.

In short, the dynamic interplay between epigenetics and genetics points toward an explanation for the largely unexplained reality of rapid evolution and pesticide resistance.

Photo: Natural England/ Flickr Creative Commons

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