They’re back: Multicolored Asian ladybeetles out and about
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Not since the fall of 2003 have I fielded so many calls about multicolored Asian ladybeetles. Apparently the summer of 2009 was a very good year for these little house guests. They invaded our homes last fall and spent the winter hiding under siding, in attics and wall voids. As temperatures warmed in the spring, the beetles became more active. Many people called recently to complain that this increase in activity levels resulted in the beetles finding their way into their interior living space, which they found totally unacceptable. They were not happy to hear that there is not much that can be done at this point and worse yet, that it’s likely that they will continue to see the beetles inside their home until all the beetles have found their way outside or have died trying.
The multicolored Asian lady beetle, Harmonia axyridis, can be easily distinguished from other species of lady beetles by the presence of a black M-shaped pattern directly behind the head. Adults are large for ladybeetles and are about ¼-inch long and 3/16-inch wide. Coloration varies from bright orange with up to 19 black spots in some individuals to dull yellow with pale or no visible spots on others (hence their common name).
Female beetles lay yellow, oval-shaped eggs in clusters on the underside of leaves where aphids are present. The eggs hatch into soft-bodied larvae with long legs and are black in color with red-orange markings. The larvae are voracious and consume many aphids and scale crawlers during this stage of development. They eventually form pupae that are attached to plant leaves. Adults emerge from the pupae and begin feeding, mating and laying eggs. Several generations are produced each summer. These adults can be found on a wide variety of trees including apple, maple, oak, pine, and poplar. Adults can live up to three years. They also like to eat soybean aphids. Many people noted last summer that aphid numbers seemed way up compared to other years. With so many aphids to eat, it is not surprising that we saw a big bump in numbers of Asian lady beetles overwintering in homes last winter.
As you might have guessed, the multicolored Asian lady beetle is a native of Asia. There were several attempts to introduce the beetle into the southeastern and southwestern portions of the United States to help control aphids on pecan trees back in the late 70’s. Some say that none of these deliberate attempts succeeded and the beetle became established in the United States after “jumping ship” somewhere along the Gulf coast. Since then it has spread rapidly throughout the United States and southern Canada. It was first found in Ontario in 1992. Despite popular rumors, the beetle was not released by the DNR, MSU, or chemical companies.
The ladybeetle is known primarily as a tree-dwelling species, but it can be found on almost any plant where aphids occur. The beetle has also been reported to eat shallow holes in ripening peaches, apples and other fruit. During the fall, many people complain that the beetles bite, which in fact they do. These “bites” are very different from the bite of a mosquito and other blood sucking parasites. The bite of the multicolored Asian ladybeetle is more like a pinch and no blood meal is taken. The bite can be painful and very annoying if many of the beetles are present.
The multicolored Asian ladybeetle is a nuisance pest because the adults tend to congregate and overwinter inside buildings in large numbers. Some bug people say the beetle does this because in their homeland of China they inhabit tall cliffs to overwinter and that buildings are the closest thing we have to tall cliffs in Michigan. To make matters worse, they supposedly release a pheromone that attracts more beetles to the same area. Although these ladybeetles may bite, this bite does not seriously injure humans or spread diseases. If crushed, the beetles will emit a foul odor and leave a stain. The dust produced from an accumulation of dead multicolored Asian ladybeetles behind wall voids may trigger allergies or asthma in people.
The beetles do not breed or reproduce indoors. They are attracted to lights and light-colored buildings, especially the south side where it is warm. The beetles then work their way into buildings through soffit vents, openings around windows, and other cracks and crevices in the building’s exterior finish. Once inside the walls and ceilings, the beetles find their way into the living space through openings in the building’s interior walls such as outlets, switches, heating/cooling vents, and ceiling fixtures. Dark-colored buildings are reported to generally have fewer problems with the beetles.
Beetles might be prevented from entering older homes with wooden clapboard siding by caulking or sealing cracks and crevices. No amount of caulk will keep the beetles out of homes with vinyl siding because vinyl siding and soffits are “hung” or loosely nailed to permit the vinyl panels to expand and contract with changing temperatures. Even with wood siding, complete sealing with caulk can be difficult, if not impossible, to accomplish in some homes. If sealing the exterior walls does not help, then caulking around outlet and switch boxes, ceiling fixtures, heat ducts and other openings in interior walls may at least keep the beetles in the walls and out of the living space. Sweeping or vacuuming can remove beetles already in homes. You want to use an old “junker” vacuum for this purpose because many who called have complained that their vacuum cleaner stunk to “high heaven” after using it on the lady beetles. Commercially available indoor insect light traps are available on the internet, but I have my doubts about the effectiveness of these expensive traps.
In kinder and gentler times when ladybeetles were not overwhelming, we would not recommend killing the beetles because they are beneficial insects, but desperate times often require desperate measures. The multicolored Asian ladybeetle is NOT a protected species (another popular rumor). Spraying the exterior surfaces where the beetles are seen congregating in the fall with a persistent insecticide that is registered for this use, can help reduce the numbers of these insects that find their way inside. This may not be a politically or socially correct action, but treating one’s home in the fall of the year is an option. It is difficult to imagine that the overall population of multicolored ladybeetles will be much reduced by folks spraying their homes. Those who fancy the cute little beetles can sweep them up and then release them some distance away from their house.
Homeowners who choose to spray their homes to reduce their numbers can hire a professional pest control company to treat the building exterior. The treatments need to be made in late September or early October when the first beetles appear on the building. They normally begin migrating to homes during the first few warm days that follow the first cold snap in the fall. Do-it-yourselfers can use permethrin (sold under a variety of brand names) or cyfluthrin (sold as Bayer Advanced Home Insect Control) or bifenthrin (sold as Ortho Max Home Defense). Before treating the whole house, spray a small test area to make sure the insecticide does not stain the siding or paint. Be sure to read and follow all directions on the pesticide label. Spraying the outsides of homes will, no doubt, involve spraying above one’s head. Be sure to wear protective clothing such as a wide-brimmed hat and raincoat. Eye goggles are a must