Monarch butterfly populations dropped significantly over the past two decades — partly because they’re losing their main food source, milkweed. To help them survive, some people plant milkweed in their yards. But a new study suggests planting it close to farm fields may not be the best idea.
Researchers with Purdue University’s Department of Entomology analyzed more than 1,500 milkweed plants in northwest Indiana. They found a mixture of 14 pesticides — including some thought to harm pollinating insects.
“There’s really very little known about pesticides that you’d find in a common Midwestern landscape and how it affects monarchs," says Purdue Entomology professor Ian Kaplan.
Kaplan says his team is working on another study that will look into how this mix of pesticides affects the butterfly’s health.
This current study suggests that how far a milkweed plant is from agriculture affects the concentration of pesticides.
Some organizations say people should plant milkweed at least 125 feet away from agricultural land. But Kaplan says because all 14 pesticides react differently, there's no one "magical number" of feet that will ensure a milkweed plant is safe from all of these exposures.
In fact, Phd student Paola Olaya-Arenas found certain pesticides more than a mile away from some farm fields.
She says there are ways that farmers can help monarchs.
“Reduce application at the edges of the crop,” she suggests.
Olaya-Arenas says this can help keep plants that aren’t the intended target of the pesticide from being affected.
READ MORE: Monarch Butterfly Numbers Are Up
Indiana Environmental reporting is supported by the Environmental Resilience Institute, an Indiana University Grand Challenge project developing Indiana-specific projections and informed responses to problems of environmental change.