From Science Advisor (5/12/24)…
Roundup use may promote the evolution of insect-resistant superweeds
The herbicide glyphosate, best known by the brand name Roundup, is used to kill off unwanted flora. However, not all plants are equally susceptible to the stuff. And that doesn’t just mean farmers could end up with fields full of Roundup-resistant plants—it could also lead to insect-hardy superweeds, as some plants that are resistant to the herbicide are better able to fend off bugs, too.
Researchers studying common morning glory—a prevalent agricultural weed in the tropics—wondered if glyphosate treatment had any knock-on effects. Studies in other species had found that plants treated with Roundup were more susceptible to damaging insects. So maybe, the team thought, even though the herbicide doesn’t kill all the morning glories in an area, it might make the surviving plants weaker against other methods of control.
Except, that’s not quite what happened. While the herbicide made some of the flowery weeds more susceptible to insect damage, morning glories that were especially resistant to glyphosate turned out to be really resistant to insect herbivores as well. And as the team selected for Roundup resistance in experiments, they ended up with more insect-resistant plants, too. “This is really interesting because the implications are that there’s a causal relationship between glyphosate resistance and herbivory resistance ,” lead author Grace Zhang said in a statement. That may mean that using glyphosate shapes interactions between plants and bugs in big, unexpected, and potentially undesirable ways.