Scientists call it Ambrosia artemisiifolia, but you can call it the bane of your existence. Otherwise known as the common ragweed, this plant releases potent pollen in August and September, spreading hay fever—the sneezing, the mucus, the itchy eyes—throughout the land. Native to the Americas, the common ragweed has been unintentionally introduced all over the world, from Asia to Africa to Europe, bringing with it both facial misery and economic burdens in the form of missed work and health care costs.
A diverse group of researchers, including ecologists, entomologists, epidemiologists, and medical doctors, have now calculated that 13.5 million people across Europe suffer from ragweed allergies, resulting in 7.4 billion euros in health costs each year. But they also calculated a possible solution: In parts of Europe where the plant’s natural enemy, the leaf beetle Ophraella communa, has also been introduced, pollen counts have crashed 80 percent compared to areas without the beetle. They argue that if countries can safely introduce the tiny insect—just one eighth of an inch long—they could ease their people’s suffering and save money on health care. They are not arguing, though, that countries should release the beetles willy-nilly, as this kind of biocontrol requires years of careful experiments to avoid ecological chaos.
The common ragweed is a vegetative menace of the highest order. To keep the plant from producing pollen and seeds, you’d need to cut it three times a year across whole landscapes. “If you cut it two times at 5 centimeters above the soil, it will still produce the same amount of pollen as a control that you don’t cut,” says University of Fribourg biologist Heinz Müller-Schärer, coauthor on a new paper in the journal Nature Communications describing the findings. “So it has a huge regrowth capacity.”
But as much as the common ragweed loves to grow, Ophraella communa loves to devour it. “They eat and eat and eat,” says Müller-Schärer. “We had some plants that were one meter tall and close to producing flowers, and then they were hit by the beetle and you just see the stem left. In two days, the plant is dead.”
This antagonistic relationship has kept the common ragweed in check for millennia throughout the Americas, where the plant and beetle both naturally coexist. But when the plant was introduced to Europe without the beetle, ragweed ran riot. The higher the density of ragweed, and the longer it’s there, the larger percentage of the human population that develops an allergy to it. Hungary’s got it particularly bad, where 30 to 40 percent of the population may be allergic to ragweed. “The more you get exposed, the more you get sensitized,” says Müller-Schärer. “And the more you get sensitized, the more you get sick.”
To calculate just what an economic burden this is, Müller-Schärer and his colleagues pulled in a wide variety of data sources. For one, they looked at sales of allergy medications. Because common ragweed unloads its pollen in the late summer and early autumn, and it’s the most vicious allergen in the air, the researchers could be confident that its signal isn’t muddied by other pollinating flowers, which go wild in the spring. They found that in areas with the leaf beetles, sales of antihistamines were 80 percent lower than areas without the beetles.
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 such as 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 more than 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 whether 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 UC 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 UC 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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