An exotic invasive shrub, introduced in the 1800s as a garden plant, is being studied to demonstrate how its presence has a cascading damaging effect on natural flora and fauna, agriculture and public health.

Ohio State University entomologists are collaborating with Michigan State University and Iowa State University in a 3-year research project to determine the distribution of buckthorn throughout Michigan, Ohio, Minnesota and Iowa. The study, “Common Buckthorn as a Keystone Invader in Agricultural Landscapes,” is supported by a $494,000 Agricultural and Food Research Initiative grant funded by the U.S. Department of Agriculture.

Buckthorn is the link in a chain of invaders that has a negative impact on the ecosystem. Not only does the shrub choke out native plants, but it's also the overwintering host for the soybean aphid, an invasive sapsucker that damages soybeans and spreads viruses to vegetable crops.

In turn, the soybean aphid is food for the multi-colored Asian ladybeetle, an invasive insect that damages grapes, outcompetes native ladybeetles for food and habitat, and finds its way into the homes of many Midwesterners.

“Without the invasion of buckthorn, it’s probably unlikely that the soybean aphid would have established itself, and as a result, we’d have less impacts on crops and fewer issues with the multicolored Asian ladybeetle,” says Andy Michel, an Ohio State University entomologist.

By determining how much buckthorn is spread across the four states, researchers hope to learn more about how buckthorn influences aphid dispersal and populations of the multicolored Asian ladybeetle. The goal, ultimately, is to identify best management practices for buckthorn to best control both insects.

One aspect of the study is to determine if soybean aphids found in Ohio are originating from buckthorn established in Ohio, or are migrating from more northern latitudes like Michigan.

“We are collecting aphids from Ohio and Michigan and using genetic markers to determine if aphids plucked from Ohio soybean fields are genetically similar to aphids being found on buckthorn in Ohio, or if perhaps they are originating from other locations, like Michigan,” Michel says.

The outcome of that work, says OARDC entomologist Mary Gardiner, is managing the soybean aphid by going back to the overwintering source.

“If we determine that aphid colonization in Ohio is localized, that is, if aphids in soybean fields are originating from local buckthorn establishments, then we can manage the aphid by eradicating the buckthorn within the local area,” Gardiner says. “If we determine that aphids are migrating from more northern locations, then we can conclude that intensive buckthorn management in Ohio may not be as effective for soybean aphid control, and that aphids can migrate long distances and their management may be more difficult.”

Other objectives of the research include:

• Determining if the density of buckthorn within the landscape surrounding soybean fields influences the likelihood and timing of aphid infestation.

• Examining whether aphid populations in areas with high density of buckthorn serve as a source of aphids in areas lacking significant buckthorn establishment.

• Determining if soybean fields in buckthorn-infested landscapes colonized early in the season with soybean aphid are more likely to attract the multicolored Asian ladybeetle.

• Studying whether buckthorn surrounding vegetable cropping systems increases the likelihood of virus transmissions from the soybean aphid to the crops.