Collateral damage: Japanese beetle traps snare nature’s helpers

The research team measured the abundance and diversity of pollinators and a less studied group, the carrion beetles that feed on insect carcasses and help recycle organic matter. 

Both categories of insects were accidentally captured in traps set on 20 farms in an agricultural region in southern Quebec. The researchers collected 360 samples from the traps between June and September and analyzed the bycatch—the capture of nontargeted species—by season, Japanese beetle abundance, landscape composition and weather.

They found that pollinators were most likely to be caught in the traps early in the season, particularly on days when the temperature was high and the humidity low, and on highly intensive farms or farms surrounded mainly by natural land cover. 

Carrion beetles were caught in greater numbers in late August, mostly in cooler, rainier weather and on medium-intensity farms.

“Pollinators are attracted to the floral scents emanating from the traps,” explained Brodeur, hoilder of a Canada Research Chair Emeritus in Biological Control. 

“Later, once the traps are full of Japanese beetle carcasses, the smell of decomposition attracts the carrion beetles. To give you an idea of the volume, a single trap can catch between 5,000 and 6,000 Japanese beetles per week.”

The research team doesn’t advocate abandoning pheromone traps, but in light of these results they believe their use should be more judicious and better controlled. Specifically, the authors recommend not setting traps in early summer, when pollinators are very active and the Japanese beetles haven’t appeared yet.

To make the traps less attractive to pollinators, which play such a critical role in ecosystems, they also suggest avoiding yellow or white traps and not using geraniol, a floral compound pollinators love.

“These traps work very well in agricultural settings when arranged in high density at the edges of fields, against prevailing winds,” said Brodeur. “They are not recommended for use in private gardens.”

More broadly, the study illustrates a fundamental lesson in ecology: intervening in a complex system almost always comes with unexpected consequences.

A side note on the study itself: while it was being conducted, Aubé was still quite new to academia, working on her honours bachelor’s degree in biological sciences.

“In six months, while still an undergraduate, Simone managed to complete the study and publish it in a major journal,” said Brodeur. “This achievement earned her an invitation to pursue a PhD at the University of Oxford. It’s an outstanding accomplishment.”