Last March and April may seem like a long time ago, but for those who were besieged with multicolored Asian lady beetles inside their homes, it is a recent memory. Whether they were a problem for you last spring or not, the big question is, “How are the lady beetles doing this year?” In the Sept. 1 issue of Yard and Garden Line News, Jeff Hahn, University of Minnesota assistant extension entomologist, reported that Asian lady beetle numbers are down. A large part of that seems to be the small number of soybean aphids, as they are an important food source for lady beetles. However, corn has been infested with a fair number of corn leaf aphids, which also provide food supply. Hahn further reports that, while there are fewer adults in some areas, there are a fair number of mature larvae and pupae. Their numbers could rebound somewhat by the end of the summer but, overall, their numbers are still likely to end up less than last year. These lower numbers are undoubtedly attributable to the cool spring and summer we have experienced. So, do fewer numbers of Asian lady beetles mean we won’t see them invading our homes this fall? Not quite. Asian lady beetles are still present, and we can expect them to invade our home to some degree. An interesting question is what signals the multicolored Asian lady beetles to begin their flights from trees and fields to homes and other structures. We have observed that temperature gives them a cue, but it is likely that a more complicated set of signals tells Asian lady beetles when to begin aggregation on buildings. Hahn states that in addition to dramatic changes in temperature, they also probably need to experience a combination of shorter day lengths and differences in food quality. Typically, Asian lady beetles do not begin to move until late September or early October. We can expect them to begin to congregate on the south and west sides of homes on the first sunny day following a hard frost. Regardless of the number we expect, if you want to protect your home from multicolored Asian lady beetles, now is the time to act. Preventing their entrance into our homes is the best control. Keep these lady beetles out by using a two-pronged approach. First, seal as many openings as possible that allow lady beetles in your home. Concentrate around doors, windows, along fascia boards, openings where utility lines enter the home, and similar places that may provide an opening large enough for them to enter. Seal any openings 1/8 inch or larger. This should be done by the end of September before the lady beetles start to enter homes. Physical exclusion should be supplemented with residual insecticide treatment. Make any applications of insecticides before insects begin to enter buildings, again by late September. Spray the insecticide around doors, windows and roof lines, paying particular attention to the south and west sides where the insects are most common. You can spray your home yourself or contact a licensed pest control service to do it for you. Effective insecticides available to the public include bifenthrin, cyfluthrin, cypermethrin, deltramethrin and permethrin. Whenever applying any of these insecticides, read the label carefully and follow all precautions and directions. These steps are not always going to prevent 100 percent of the lady beetles from entering your home, but they will reduce the number that get inside. Once lady beetles get into your home, you have few options to control them. They will remain in the home until they die or are removed. Some of the lady beetles will get into walls and attics and will periodically emerge during mild winter days, and again in the spring. The important thing to remember is that they do not reproduce indoors and, therefore, all of the lady beetles you find in your home entered from outside.
