Multicolored Asian lady beetles: When good bugs go bad!

Multicolored Asian lady beetles attempting to enter a house. (Marlin E. Rice)Multicolored Asian lady beetles attempting to enter a house. (Marlin E. Rice)

A participant in the recent soybean aphid short course asked whether Iowa State University was responsible for releasing the multi-colored Asian lady beetle in Iowa. The answer is no! I'm not sure whether the inquisitive individual wanted to thank us for bringing the lady beetles into Iowa to help control soybean aphids, or he wanted to blame us for the lady beetles invading our homes and being a general nuisance. Either way, the entomologists at Iowa State can't take blame or credit.

But the question still remains, where did the multi-colored Asian lady beetles, Harmonia axyridis, come from? Their original distribution is China, Japan, and Siberia. They are not native to North America, but they have been intentionally released in the United States by entomologists. This lady beetle was extensively released for biological control of other insects beginning in 1916 in California. During 1978-1981, the beetle was additionally released by state and federal (USDA) agencies in several states along the Atlantic Coast and Gulf of Mexico, but the personnel responsible for these releases claim that the beetles never became established and eventually died out. Accidental entries have arrived on nursery stock at ports in Delaware and South Carolina. The first extensive populations were found in the United States in 1988 near the port of New Orleans, Louisiana, and it is assumed that these beetles arrived on a container ship from eastern Asia. Therefore, it is not known for certain whether the lady beetles' establishment in the United States was the result of accidental entries, planned releases, or both.

The multicolored Asian lady beetles we have in Iowa are most likely the result of the beetles probably flying here from Louisiana, or hitchhiking in a vehicle, although we will never know for sure how they arrived. They were first reported in Iowa in 1994. Since then, it has become a serious pest in Iowa vineyards--the alkaloids from a single beetle crushed in a cluster of grapes can ruin large quantities of juice, resulting in off-flavor wine. The beetles also are known to painfully bite humans (speaking from personal experience) and pets (from my black lab's experience). And if you live in a house in Iowa, you probably appreciate the nuisance factor of these little beetles during October when they defy all our efforts to keep them outside and off our walls, curtains, and light fixtures.

Fortunately, there also is a good side to this lady beetle. It is a known predator of the soybean aphid, and in that sense, it is a beneficial insect. Robert Koch, an entomologist at the University of Minnesota, reported that the total number of aphids consumed through the larval stages varied from 90 to 370 aphids, depending on the species, and across all larval stages averaged 23.3 aphids consumed per day. Adult consumption typically ranges from 15 to 65 aphids per day, again depending on aphid species. Adults typically live 30 to 90 days, but they are recorded as living up to three years.

Regardless of what your perceptions are about the multicolored Asian lady beetle, it is now a permanent, although sometimes unwanted, resident of our state. And it's not our fault.

Marlin E. Rice is a professor of entomology with extension and research responsibilities in field and forage crops.

This article originally appeared on page 75 of the IC-498 (3) -- March 26, 2007 issue.

Updated 03/26/2007 - 4:15pm