Japanese beetles to blame for declining Kentucky monarch butterfly population

Published: Sep. 10, 2018 at 4:11 PM EDT
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There is only one type of monarch butterfly in Kentucky, and they love to eat milkweed plants, but Japanese beetle competition is leading to their declining population.

University of Kentucky researchers are now researching both insects, and they are noticing an extreme decline in the monarch butterfly population.

"Over the last 20 years, we've had about a 90% reduction in the monarch population," UK entomology Ph.D. student Adam Baker said.

The decline in population, in large part, is due to the loss of milkweed plants. Baker first found the Japanese beetles on milkweed plants while conducting routine surveys in 2017. but the beetle has been around this area for a while.

"They've been established in Kentucky for a long time. so we're seeing high numbers of them, but they're moving westward into the primary monarch breeding grounds," Baker said.

The westward movement is potentially troubling as these Japanese beetles limit milkweed reproduction.

"We're putting more and more mikweeds into the landscape which is our main conservation strategy," Baker explained, "We run a risk of having these beetles feed on the flowers and limit the reproduction of the mikweeds."

The common milkweed plant blooms from top to bottom, and it's the blooms the Japanese beetles are most interested in, not the plant itself.

"The Japanese beetle, when it comes in it'll feed exclusively on the flowers," Baker explained, "It'll aggregate on those flowers which is why it's going to suppress the seed production of milkweed. it's not interested in the leaves. It's interested in the sugars inside the plant."

The monarchs are an important species for our environment.

"We use the monarchs as an umbrella to help all other pollinators. Native bees and butterflies as well, because monarchs themselves are a very charismatic butterfly, and they're a beloved butterfly -- one of the most well-known insects in the world."