Reno Reporter

Plant lovers should be wary of purchasing milkweed plants from nurseries because they could be tainted with pesticides that are dangerous to monarch caterpillars.

According to a news release shared by the University of Nevada, Reno, researchers discovered the information after studying 235 milkweed leaf samples from commercial nurseries across the United States.

Milkweed is the main source of food for Western monarch caterpillars. It can, however, be poisonous to other critters. 

"In a previous study in California that primarily looked at milkweed in agriculture and urban interfaces, we had looked at a small number of plants from retail nurseries, and found that they contained pesticides," said Matt Forister, a biology professor at the university who studies insect ecology, in the release.

The joint study was done with the Xerces Society for Invertebrate Conservation and the information was released in Biological Conservation, a peer-reviewed science journal. The research found 61 pesticides with an average of 12 per plant and some having as many as 28.

“That was the most shocking part,” said Christopher Halsch, the lead author of the study and a doctoral student at University of Nevada, Reno. “The fact that plants labeled as potentially beneficial, or at least friendly to wildlife, are not better and, in some cases, might be worse than other plants available for purchase. 

"This research sheds light on how pesticides may impact Western monarchs, but many other butterflies are facing even steeper population declines, and pesticides are likely one driver,” he added.

The impact for monarch caterpillars who eat toxic milkweed plants could be reduced wing size and other hazardous effects, the release stated.

"We were prepared for this much larger sample of nursery plants to again uncover contamination, but it was surprising to see the great diversity of pesticides found in these plants,” Forister said. “In many ways, they are as contaminated or even worse than plants growing on the edges of agricultural fields. That was a surprise, at least to me."