The researchers also studied data about how often patients visited doctors for allergy treatments, and they incorporated “patient hay fever diaries,” in which people reported data like the severity of their symptoms, which medications they were taking, and how much work they were missing.
Finally, they modeled where you might expect the beetle to be able to thrive in Europe, based on variables like rainfall and temperature. Introduce the beetle in these areas, they calculated, and you could reduce common ragweed pollen so much that the number of affected patients would fall by 2.3 million, and medical costs by over 1 billion Euros per year.
But you can’t just import a bunch of leaf beetles and set them loose. Intentionally introducing an invasive species might be good at controlling common ragweed, but the beetles might also be good at devouring native species. You have to test the insect’s appetite for other plants, because while it specializes in common ragweed in its natural habitats, there’s no telling if it might take to an important crop if dropped into a new environment. And you have to determine how it might interact with other animal species, or else you could make a mess you can’t undo.
“Then comes 10 years of research,” says Müller-Schärer. “You have to find out: Does it really feed on [common ragweed]? How much does it? And then you have to do that across generations.”
But given the amount of money that the control of common ragweed could save European economies, he thinks it’s an option worth exploring. “The results of our interdisciplinary study justify a comprehensive risk-benefit assessment of O. communa,” he and his colleagues write in their paper, “also regarding a possible deliberate distribution of this leaf beetle across the climatically suitable areas in Europe.”
Species interact with each other in an ecosystem in incredibly complex ways, which requires equally complex research to predict how a newly-introduced organism will interact with the intended target. Even then, that interaction can spring surprises on scientists. In the western US, for example, researchers introduced a boring moth (the verb boring, not the adjective) to control the invasive Russian thistle, which produces tumbleweeds.
“It actually made the situation worse because, yes, it bored into the little tips of the branches, but that made it easier for the plant when it started rolling to break off the seed heads,” says University of California, Davis entomologist Lynn Kimsey, who wasn’t involved in this new work. “And so that was a little oopsie, that it actually ended up helping the plant as opposed to hurting it. Things like this just happen. Biology’s a tricky damn thing to work with.”
We might also worry that if European countries were to introduce this leaf beetle to control ragweed, then the beetle might evolve over time to generalize and begin eating other plants. But worry not, says entomologist and biological control specialist Mark Hoddle of the University of California, Riverside, who wasn’t involved in this work. Generalists can become specialists, but it doesn’t work the other way around.
“It’s well accepted in ecology that specialists have evolved from generalists, and they have done so by removing or highly refining certain characteristics that would allow them to eat a whole variety of different plants,” Hoddle says. “And it’s extremely difficult if not impossible for them to re-evolve all of those traits they would need to become generalists.” Those traits include their physiology, behavior, and the biochemistry allowing them to be able to eat different plants at different times of the year.
Now, if the beetle happens to spread from elsewhere in Europe without the assistance of humans, that’s a different story. The insect has now invaded France, says Müller-Schärer, but the country has decided to let the beetles be.
Not a decision to sneeze at, that’s for sure.
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