Collateral damage: Japanese beetle traps snare nature’s helpers

A Japanese beetle on a marigold
Photo Credit: Joseph Moisan-De Serres

Scientific Frontline: Extended "At a Glance" Summary: The Ecological Cost of Japanese Beetle Traps

The Core Concept: A recent study reveals that traps specifically designed to combat the invasive Japanese beetle (Popillia japonica) unintentionally capture and kill critical beneficial insects, including pollinators and carrion beetles.

Key Distinction/Mechanism: While these simple, pesticide-free devices are marketed as green solutions by utilizing sex pheromones and floral compounds to lure pests, their mechanism inadvertently creates an ecological trap. The floral scents (such as geraniol) actively attract pollinators early in the summer, while the subsequent smell of decomposing beetles in full traps attracts carrion beetles later in the season.

Origin/History: The Japanese beetle was introduced to the United States in the early 20th century and has since become a major agricultural threat. The ecological impact of the traps used to combat them was detailed in a study published in the March 2026 issue of Biological Conservation, led by Université de Montréal researcher Simone Aubé.

Major Frameworks/Components: 

• Bycatch Analysis: The quantification of non-target species captured accidentally alongside target pests across various agricultural landscapes.
• Seasonal and Meteorological Variables: The observation that pollinator bycatch spikes early in the season during hot, low-humidity days, whereas carrion beetles are predominantly caught in late August during cooler, rainier conditions.
• Mitigation Protocol: Strategic recommendations to limit ecological damage, such as avoiding early-summer trap placement, eliminating the use of yellow or white traps, and removing the floral compound geraniol from the lures.

Branch of Science: Ecology, Entomology, and Conservation Biology.

Future Application: These findings will drive the development of more species-selective pest control lures and inform better agricultural protocols, such as restricting trap usage to high-density placements at agricultural field edges rather than in private gardens.

Why It Matters: This research underscores a fundamental law of ecology: intervening in complex biological systems, even with seemingly benign and pesticide-free methods, often yields unintended consequences that can harm vital ecosystem components like pollinators and organic-matter recyclers.

Simone Aubé and Jacques Brodeur
Photo Credit: Jacques Brodeur

The Japanese beetle (Popillia japonica) is one of most dreaded insects to have invaded North America and parts of Europe. Accidentally introduced to the United States in the early twentieth century, it can now be found from Vancouver to the Alps and beyond. 

Japanese beetles aren’t picky eaters; they will happily consume more than 300 species of plants and trees, devastating crops and gardens.  

Farmers and homeowners are fighting back with an array of control strategies, including traps that use a combination of sex pheromones and floral compounds to lure the beetles. At first glance, these simple, inexpensive, pesticide-free devices seem like an ideal green solution. 

However, a new study led by Simone Aubé, a former Université de Montréal student supervised by ecologist and UdeM biology professor Jacques Brodeur, suggests a closer look is needed to see what these traps catch and their impact on biodiversity. 

Abundance and diversity 

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, holder 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.” 

A pheromone trap
Photo Credit: Jacques Brodeur

Rethinking the fight 

The research team doesn’t advocate abandoning pheromone traps, but considering 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 honors 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.” 

Reference material: What Is: Invasive Species

Published in journal: Biological Conservation

Title: Victims of the cure: Determining the pollinator and necrophage biodiversity costs of Japanese beetle [Popillia japonica] traps

Authors: Simone Aubé, Simon Legault, Josée Doyon, and Jacques Brodeur

Source/Credit: Université de Montréal | Béatrice St-Cyr-Leroux

Reference Number: eco022526_01

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