Postponing Insect Resistance to Biopesticides

Postponing Insect Resistance Biopesticides

The so-called treadmill effect has long been a problem with synthetic pesticides, with researchers trying to develop new classes of chemicals before insect pests develop resistance to the current ones.

Biopesticides have provided a less toxic alternative. Originally, the hope was that pests would also take longer to develop resistance to biopesticides than to their synthetic counterparts. Lately, though, researchers are sounding the alarm that pests are developing resistance to biopesticides as well.

Now, a new study suggests ways to slow that process down.

In some ways, it shouldn’t surprise anyone that insect resistance to biopesticides has emerged. Insect pests can develop resistance to synthetic pesticides because the chemical formula of any given pesticide is fixed, unchanging. A mutation in a single gene can be enough to confer resistance. When you’re spraying the same chemical over millions of acres, such a mutation is bound to occur – or even exist already.

So far, most biopesticides aren’t all that different. Take Bt as an example. In nature, the bacterium Bacillus thuringiensis makes a substance that’s harmful to insect pests. Commercial Bt producers brew that same substance up in a lab, package it, and sell it to farmers to put on their crops. But, produced and marketed in that way, it’s just as fixed and unchanging as a synthetic pesticide – and thus just as easy for resistance to evolve.

In fact, insect pests have developed resistance to Bt, but so far there are no known cases of resistance to living populations of B. thuringiensis.  Because it’s a living organism, adapting from one generation to the next, it can co-evolve with the pests, and prevent – or at least delay – their development of resistance.

With that key difference in mind, a team of researchers recently put forth a new strategy for delaying the development of resistance to biopesticides. They argue for using diversity in many aspects of cropping systems: changing up the mix of crops planted in both space and time via rotations, as well as alternating which biopesticides are used. They also promote living beneficials, with their capacity to adapt and change, over static biopesticides.

In the figure, Panel A shows a monoculture of a single crop – corn – grown in all the same fields, every year. Resistance grows quickly. In Panel B, the crop is still a monoculture, but now three different pesticides are used, a different one each year.

In Panel C, a rotation of three crops has been established, but the same pesticide is used in all fields year after year. In Panel D, both crops and pesticides are rotated, leading to the slowest possible development of resistance.

The study was published in the journal Trends in Ecology & Evolution.

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