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For Less Bee Bycatch, Leave Geraniol Out of Japanese Beetle Traps

Japanese beetle traps

Traps for monitoring for presence Japanese beetle (Popillia japonica) can also attract nontarget insects such as native bees. A new study shows traps with eugenol and phenethyl propionate—and leaving out geraniol—remain effective in catching Japanese beetles but significantly reduce bee bycatch. Plus, entirely green, brown, black, or red traps are least attractive to native bees. (Image originally published in Sipolski et al 2019, Environmental Entomology)

By Andrew Porterfield

The Japanese beetle (Popillia japonica) quickly became a major agricultural and home garden pest after it arrived in the United States from its native Japan in 1916. Since then, the beetle, which feeds on some 300 species of plants, has spread to every U.S. state east of the Mississippi River except Florida, and some infestations have been reported in midwestern states and eastern Canada.

Andrew Porterfield

Andrew Porterfield

In response, the U.S. government has ordered beetle quarantines in western states, which only addresses transport in aircraft. Beetles could still be inadvertently transported in plants, pots, or potting media. So, the U.S. Domestic Japanese Harmonization Plan was enacted in so-far uninfested states (Arizona, California, Colorado, Idaho, Montana, Nevada, Oregon, Utah, and Washington) to use beetle traps to evaluate infestations in each of these states.

These traps have been used extensively for several years, including 12,000 traps a year in California and 3,250 traps in Utah in 2007 and 2008, while California, Colorado, Oregon, and Utah have been able to eradicate beetle populations over the past 58 years.

Commercial traps and lures can monitor and control Japanese beetle populations, but they also attract and kill beneficial, nontargeted insects, including bees. Bumble bees (Bombus species), in particular, have been captured in traps in previous studies.

To determine ways to design traps that do not attract and kill bees, a research team from the University of Rhode Island, the USDA-Agricultural Research Service (ARS), and Tennessee State University evaluated several combinations of chemical lures and traps colors in search of a method that remained effective in capturing Japanese beetles but reduced the bycatch of bees. The results of this research were published in late August in Environmental Entomology.

The researchers, led by University of Rhode Island entomologist Steven Alm, Ph.D., set traps in mowed and unmowed horticultural research farms, a deciduous and brush area bordering an athletic field, and a forested edge of a nursery. The traps were set in Rhode Island, Ohio, and Tennessee. The field experiments were conducted between 2016 and 2018.

In the series of experiments, Alm’s team evaluated the three components of floral lures (geraniol, eugenol, and phenethyl propionate), as well as the colors, funnels, and floors of the trap cages (green, yellow, brown, black, red, or clear).

In 2016, the researchers captured 253 common eastern bumble bees (Bombus impatiens) and carpenter bees (Xylocopa virginica) at the mowed site and 603 B. impatiens and 79 X. virginica at the unmowed site. In 2017, 3,325 bees were captured in traps in five Rhode Island experiments, and 90 bees were captured in Ohio. In 2018, 647 bees were captured were captured in two Rhode Island experiments, 401 bees were captured in Tennessee, and 34 captured in Ohio.

The results indicated that pollinating bee capture can be reduced by using a floral lure combination that does not contain geraniol, which is found in fruits and spices and makes up part of a pheromone used by honey bees to find nest entrances. The researchers instead recommend a lure mixture containing a 7:3 ratio of eugenol and phenethyl propionate, in all-green Japanese beetle traps. Including geraniol significantly increased capture of bees, and both B. impatiens and X. virginica were primarily attracted to geraniol. Conversely, Japanese beetle captures in eugenol and phenethyl propionate combinations were not significantly different from traps containing the three-chemical combination, indicating that geraniol was not necessary for beetle trapping. The trap colors that caught fewer bees were green, brown, black, or red.

“Japanese beetle trap and lure manufacturers may want to offer a bee-friendly lure and trap color combination to reduce bee captures if future testing confirms that it would not significantly reduce Japanese beetle captures,” Alm and colleagues write.

Andrew Porterfield is a writer, editor, and communications consultant for academic institutions, companies, and nonprofits in the life sciences. He writes frequently about agriculture issues for the Genetic Literacy Project. He is based in Camarillo, California. Follow him on Twitter at @AMPorterfield or visit his Facebook page.

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