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Watch out for swarms of Asian lady beetles seeking shelterWatch out for swarms of Asian lady beetles seeking shelter

Invasive lady beetles resemble natives in appearance but will swam as weather cools, trying to seek shelter.

Walt Davis 1

November 8, 2016

4 Min Read

Blame it on the sugarcane aphid.

The abundance of the aphids is a primary reason that the summer of 2016 was an especially bug-filled one as predators that might have fed on species such as armyworms, corn earworms, greenbugs and chinch bugs were full to the brim with tasty aphids.

One particularly abundant insect was the Asian lady beetle, a lover of aphids and a species that researchers tried unsuccessfully to introduce in the 1980s as a biological control for scale insects that attack trees and shrubs.

In the 1990s, the beetles showed up in large numbers along the Gulf Coast, far from any of the release sites.


The beetles are believed to have hitched a ride to the Gulf Coast on container ships from Asia.

Kansas State University entomologist J.P. Michaud says the scientific name for the beetles is Harmonia axyridis, and they are very different biologically than the familiar, native red-spotted lady beetles that are valuable as a natural control for harmful aphids. They come in a variety of colors from light orange to red-spotted.

Because of the large infestations of sugarcane aphids that occurred last summer, unusually large numbers of Harmonia beetles have been produced.

Michaud says many people likely didn't notice them in the summer since they are very similar in appearance to native lady beetles. It is in late fall and early winter that they become noticeable for a behavior that is very different from native species. They gather in large numbers on the sunny side of buildings or in doorways and around windows, seeking heat or trying to come in from the cold.

Michaud advises homeowners to make sure that their windows and doors fit tightly and that eaves and other potential entry points are caulked.

"In their native habitat, they overwinter in mountain caves," Michaud says. "Kansas doesn't have mountains, so most of the population that arrived here during the summer will not be able to find shelter and will die when it freezes."

Michaud says the beetles produce a chemical that protects them from birds and other predators because it smells and tastes bad.

"If you ever have an inexperienced bird that eats a lady beetle, he only does it once," he says.

The large numbers that aggregate in November and December can cause a foul odor in barns, sheds or homes, he says.

Asian lady beetles do survive the winter months in the Gulf Coast states.

They have specific plants that they like and don't like.

They prefer trees and are often thought of as an urban problem because of their tendency to aggregate into huge swarms on houses and garages as cold weather approaches.

Initially, they were valued for providing control of agricultural pests in citrus groves and many other crops. However, they soon displaced less competitive lady beetles from many habitats and became a problem in fruit crops, such as pears and peaches, because they like to nibble on ripe fruit.

If they become abundant in vineyards, they may be harvested with the grapes and create a serious flavor contaminant in wine production.

The beetles can also cause allergic reactions in some people, and they have been known to nip human skin with their mandibles.

Michaud says that seems to be a matter of "personal chemistry," with some people being bitten and others not.

If they find a sheltered spot to hunker down for winter, they do not hibernate, he says, and on warm, sunny days in the winter, they will become active and swarm outside, especially on the sunlit side of light-colored buildings. However, they do not reproduce until spring.

When food is scarce, larvae survive by eating less and maturing into smaller beetles.

"In many areas with a friendlier climate, the Asian lady beetles are taking over agricultural ecosystems," Michaud says. "In Kansas, our environment is too tough for them to thrive. We have cold winters and hot, dry summers, and both of those are not conducive to their survival."

The Asian lady beetles will not interbreed with native species, he says, even though their pheromones do attract male beetles.

"The males will try to breed with females of other species, but specific crosses are sterile," he says.

Michaud says that, given time and sustainable agricultural practices, nature will control the infestations of sugarcane aphids, and Asian lady beetles will recede in numbers.

"Nature abhors a vacuum, and nature loves biodiversity," he says. "When you have a newly invasive pest, it may dominate for a time, but the ecosystem responds, and the domination doesn't last."

Part of the problem with sugarcane aphids, he says, is their prolific reproduction. Each aphid can produce eight or nine nymphs per day, and all the nymphs are female.

Past farming practices have worsened the problem with the use of chemicals that kill all insects, both harmful and beneficial.

He said a better, more sustainable solution is the development of more selective chemicals and the use of cover crops to encourage the growth of a population of beneficial insects that feed on the harmful ones.

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