Pesticide may harm butterflies, ladybugs

Neonicotinoids from other plants might be affecting butterfly food.

Ethan Nelson

Bachman’s floral company’s customers want pollinator-friendly plants, staff say, so the company doesn’t use a common type of insecticide that is harmful to bees.

 And a University of Minnesota study that’s set to be released this month suggests that the type of pesticide may be unintentionally harming other insects, too, like monarch butterfly larvae and ladybugs.

Large amounts of the pesticide, which has previously been touted as being minimally harmful to mammals, might be on milkweed plants after rubbing off of neighboring plants, said University entomology professor Vera Krischik.

The pesticide, called neonicotinoid, is problematic because monarch butterfly larvae eat milkweed plants, she said.

For the study, Krischik and horticulture professor Mary Rogers fed four species of ladybugs, painted lady butterflies and monarch butterflies milkweed that had been treated with the pesticide for a week. Adult butterflies weren’t affected, Rogers said, but the larvae and three ladybug species died.

The research also found it took fewer neonicotinoids than those used in the study to kill bees, but the amount used by farmers on crops could potentially kill butterfly larvae, Krischik said. Farmers, on average, use 75 times less than what’s used on garden plants, she said.

Neonicotinoids are the most commonly used insecticide in the world, she said. They’re often applied to seeds, so then they last in plants for up to a year. Sprayed pesticides, on the other hand, only last a few weeks.

Neonicotinoids in particular tend to continually appear in the plant’s pollen and nectar, Krischik said.

Krischik said her research shows that this type of pesticide could pose a risk to butterflies and beetles when it’s used on backyard plants.

Previous research has centered on insects that eat the leaves, rather than those that pollinate plants, said Karen Oberhauser, an entomology professor who specializes in monarch butterflies.

“Most of the research has focused on herbivores and not insects that are consuming the pollen,” she said.

In 2014, the state Legislature made it illegal to label plants as beneficial to pollinators if they had been treated with pesticides like neonicotinoids. A license is also required to use some insecticides, Rogers said.

“In small doses they’re harmful,” said Marla Spivak, an entomology professor. “But they’re not the only thing that’s harmful.”

She said other pesticides can be equally or more harmful to pollinators than neonicotinoids.

Bachman’s floral company consulted with University experts before the company reduced its use of the pesticide, company spokeswoman Karen Bachman-Thull said.

“There’s an eagerness for knowledge about this,” she said. “It seems as though there’s a lot of support for it.”

Krischik said her research doesn’t reach far enough to definitively say whether neonicotinoids contaminate other plants extensively, killing butterfly larvae and ladybugs.

“If you buy a greenhouse plant and then install it next to a rose where you apply a neonicotinoid insecticide,” Krischik said, “you have a chance of having high enough levels to kill caterpillars.”