Purdue News
Purdue News
October 25, 1996
While ladybugs are beneficial insects, and some of the more than 4,000 species often are released to enhance biological control of harmful insects, the overwintering behavior of one species has become a nuisance throughout the eastern and Midwestern United States. Asian lady beetles, Harmonia axyridis , congregate in groups during late fall rather than overwintering individually under bark or in leaf litter as most lady beetles do.
Purdue University Extension entomologist Tim Gibb said the Asian lady beetle is attracted to light-colored buildings, especially those illuminated and warmed by sunlight, which makes southwest-facing walls a popular resting spot. The beetles spend most of their time feeding in treetops until they're ready to migrate, so they may be quite common on buildings close to wooded areas, as well.
"Asian lady beetles prefer to cluster on the sides of homes and other buildings," Gibb said. "They eventually work their way into the home through small cracks or crevices. Once inside the home, they essentially laze about in a hibernation-like mode, neither eating nor moving much until the first warm days of late winter or early spring. At that time, the beetles seem to come to life again and begin crawling about.
"After spending the winter months tucked away in a wall void or other secluded place, they have simply forgotten how they got in," Gibb said. "They're merely looking for a way to escape to the out-of-doors. The best suggestion is to help them in their quest by sweeping them up and depositing them outside if possible."
He also said vacuuming will work, but the vacuum bag should be emptied each time because live beetles can easily find their way out into your closet. Chemical control could be used, according to Gibb, but dead beetles have to be removed the same as live ones. In addition, chemical control isn't effective at penetrating wall voids, false ceilings and other beetle hiding places.
The good news, according to the entomologist, is that the beetles don't feed on or damage anything in the home. They don't bite humans or pets. They don't infest stored foods. And they don't destroy household furnishings. They're just annoying, especially when they reawaken after the winter.
The bad news, he said, is that the beetles seldom all become active at the same time. Depending on temperatures and the size of the population, it could take weeks.
"It may seem like there's an endless population, or that they're somehow breeding in the home," Gibb said. "Rest assured that they are not and cannot breed inside the home. The Asian lady beetles must feed on leaf-dwelling insects prior to mating in the spring. Eggs are deposited on leaves. The beetles enter homes during the fall to pass the winter only."
Preventing the lady beetles from entering in the first place is another simple control method. Gibb suggested caulking cracks, crevices and utility service openings, and fixing broken window screens and doorjambs.
Gibb expects the Asian lady beetle population to continue to increase in the Midwest for a while -- how long is hard to say. No-one knows for sure when the species was first introduced into the United States, but first reports of home invasions began in 1993. Since then, Gibb said, their spread has been remarkable.
"It's quite weather hardy and is highly reproductive," he said. "These qualities are what attracted scientists to collect it and introduce it to the United States for the control of orchard and field crop pests here."
Gibb said the beetles out now are the progeny of the ones first released, which originated in Asia. They're a different species than the ones homeowners can buy through mail-order catalogs. Because they're from a foreign country, there are no naturally occurring diseases, parasites and predators in the United States to keep them in check. The entomologist said natural controls for the Asian lady beetle eventually will build up, but there may be a lag time of several years. Once it develops natural enemies, here, though, its populations will begin to decline.
ACS code/961025 Ag Gibb/9610f48
Source: Tim Gibb, (317) 494-4570; e-mail, Tim_Gibb@entm.purdue.edu
Writer: Andrea McCann, (317) 494-8406; e-mail, mccann@aes.purdue.edu
