ANNAPOLIS, MD (Oct. 6, 2003) – In recent years, the multicolored Asian lady beetle (Harmonia axyridis) has become a common visitor in and around homes and gardens in Maryland. A native of Asia, this lady beetle was initially released in California in the early 1900's, but was also released many times from 1978 to 1985. From these later releases it became permanently established in the United States. Its presence has both positive and negative effects.
This beetle is primarily a tree inhabitant, but is also found in other habitats such as orchards, field crops, and gardens. It is considered a beneficial insect and can consume large numbers of aphids during its lifetime. Adult beetles can also be a pest on ripening fruit such as apples, peaches, grapes (especially wine grapes), etc. No insecticides are currently listed for control of beetles on fruit.
Its habit of congregating and seeking sheltered overwintering sites in the fall has made it a nuisance in and around homes and buildings. Adults reportedly emit a pheromone that results in large numbers of beetles gathering at favorable sites, including attics, basements and living areas of homes. On warm sunny days during the winter, adults may fly towards the windows and are often seen walking on walls and ceilings.
Prevention is the best way to manage the problem of beetles entering the home. In late summer and early fall, caulk cracks and seal any entry points around windows and install screening over vents. If the beetles do enter the home, vacuum them up and dispose of the bag outdoors. Do not swat or crush the lady beetles because they release a yellow-orange liquid that can stain fabrics and walls. The multicolored Asian Lady Beetle is considered a beneficial predator and the use of insecticides to control them should be discouraged. It is expected that populations will eventually decline due to natural control factors.
The multicolored Asian lady beetle resembles native lady beetles. The adults are approximately ¼ inch long and vary in color from pale yellowish brown to bright orange red. The pattern and number of spots on the "hardshell" that covers the wings vary. Most adults have 19 spots, though some beetles may have faint spots or none at all. The multicolored Asian lady beetle can be distinguished from other species by a pair of white markings behind the head that forms the shape of an "M".
The larvae are "alligator-shaped" like most lady beetle larvae. They are black with two lateral orange stripes, and covered with small flexible spines. Both larvae and adults feed on aphids and scales. The life cycle from egg to adult takes about a month in warm weather. Eggs hatch in three to five days and larvae feed for 12-14 days. Larvae then pupate, which lasts another five to six days. Adults can live two to three years. Adults overwinter in sheltered sites and mate in the spring.
Prepared by Mary Kay Malinoski, University of Maryland, Home and Garden Information Center.
Adapted in part from: "Multicolored Asian Lady Beetle", Memorandum by John A. Davidson, 1994. Cooperative Extension Service, Department of Entomology, University of Maryland.