As we flip through garden catalogs and scroll horticulture supply websites, products new and old advertise the ways they can make our gardens plentiful, flowers bright, and lawns green. With the surge of Japanese beetles in Minnesota in recent years, any solution to this pest can look attractive. While the University of Minnesota is still performing research to understand this pest, one thing we do know is Japanese beetle traps do not reduce beetle feeding.
What do we mean by this? It isn’t hard to find pictures of the lure-baited funnels and bags overflowing with beetles. Beyond the emotional satisfaction of capturing hundreds of beetles in the bag, what’s actually going on? Does your yard or garden actually benefit?
Luring beetles to your yard
Japanese beetle traps are baited with lures. These lures may have the scent of flowers or the scent of beetle pheromones (sometimes both). These smells travel through the air and the beetles pick up on the scent using their antenna, inviting the beetle to come on over. Beetles end up both inside and outside the trap, and as large numbers of beetles congregate, they put off more pheromones that attract more beetles, whether they are in the trap or not!
Studies have shown that traps lead to more plant damage in the areas they are placed in. One study found that a trap placed alone led to nearby vegetation having more damage than in similar areas where no traps were placed.
Sometimes sellers highlight how placement can make traps more effective. One study investigated the impact of where traps were placed in terms of their number (one trap or multiple traps), location (near vulnerable plants or not), and wind direction (upwind or downwind from susceptible vegetation). Regardless of number or placement, the areas around the traps had more beetle feeding damage than if there had been no trap at all.
While the masses of gleaming beetles are unsightly and the holey leaves they leave behind annoying, Japanese beetles aren't going anywhere and Minnesotans will have to learn to live with them.
F. Carter Gordon, Daniel A. Potter, Efficiency of Japanese Beetle (Coleoptera: Scarabaeidae) Traps in Reducing Defoliation of Plants in the Urban Landscape and Effect on Larval Density in Turf, Journal of Economic Entomology, Volume 78, Issue 4, 1 August 1985, Pages 774–778, https://doi.org/10.1093/jee/78.4.774
Carter F. Gordon, Daniel A. Potter, Japanese Beetle (Coleoptera: Scarabaeidae) Traps: Evaluation of Single and Multiple Arrangements for Reducing Defoliation in Urban Landscape, Journal of Economic Entomology, Volume 79, Issue 5, 1 October 1986, Pages 1381–1384, https://doi.org/10.1093/jee/79.5.1381