Asian lady beetle (Harmonia axyridis) is an exotic beetle in the family Coccinellidae. The insect is native to Asia, where it is widespread. In the 1960s, the United States Department of Agriculture introduced Asian lady beetle to North America in an effort to control several agricultural pests, including aphids, mealybugs, and scale insects. It was first released in Connecticut, Maryland, Pennsylvania, South Carolina, Louisiana, Mississippi, Georgia, Washington, and South Carolina. This practice continued until the 1990s. By this point, the insect had proliferated, becoming established across most of the United States. Asian lady beetle is typically considered a beneficial insect, as it consumes many destructive pests. However, as temperatures drop in fall, the insect can invade households, and other buildings.
Distribution & Habitat
Asian lady beetle is common throughout Asia. It is especially prevalent in China, Russia, Korea, and Japan. Since the 1990s, Asian lady beetle has been reported across most of the United States, as well as sections of Canada.
In Asia, Asian lady beetle typically dwells in forests, fields, and orchards. In the United States and Canada, the insect’s hosts primarily consist of ornamental plants and agricultural crops. Some of the most frequently infested hosts include alfalfa, corn, soybeans, tobacco, and roses.
The eggs produced by Asian lady beetle are yellow, and oval shaped. The eggs are deposited on the underside of leaves and twigs. Immature larvae are often described as resembling small alligators. As the larvae grow, they turn orange and black. Once mature, the larvae pupate on plant material, and the exterior of buildings. They attach themselves to these surfaces with the skin they have molted from previous instars, or developmental stages.
The adults are oval and convex. They can measure up to ¼ inch long. The coloration exhibited by the adults ranges from various shades of orange to tan or red. The insect’s wing covers may develop several black spots. This occurs with regularity on the females. The males can also form spots on their wing covers, but they tend to be paler in color. On some males, the wing covers may be devoid of spots. Most adults have a characteristic white patch located behind the head, with a small, dark marking shaped like an “M” or “W”. The adults have piercing mouthparts, which they utilize to consume prey.
Asian lady beetle passes through four stages during its life cycle: an egg stage, a larval stage, a pupal stage, and an adult stage. The insect’s journey from egg to adult may be completed within a month. Several generations may be produced each year, depending on the geographic location. In spring, the overwintering adults resume activity, and proceed to feed on aphids, scale insects, mealybugs, and other agricultural pests. During this period, the females lay eggs in clusters on the underside of leaves and twigs. The females will generally select plants that have been infested with their prey. A single female can lay up to 1,000 eggs.
The eggs hatch within a week, revealing masses of larvae. The larvae seek out nearby prey, and readily devour them. As they feed, the larvae progress through four instars, molting and increasing in size as they mature. The larvae reach maturity within 1 to 2 weeks. Once mature, the larvae settle on host plants and buildings to pupate. Within 3 to 12 days, the larvae transform into adults.
The new generation of adults continue to feed on their prey, remaining active until temperatures cool in fall. As fall approaches, and temperatures begin to drop, the adults vacate their hosts to seek shelter from the cold. Many adults will attempt to penetrate into buildings situated closely to host plants. The adults will congregate on the southern and western exposures of buildings, where there is abundant sunlight. The adults are attracted to bright surfaces. As such, they tend to gravitate towards buildings painted with bright colors. Dilapitated structures are most prone to infestation. Swarms of the adults can often be observed on warm days following bouts of cold weather. Once the beetles have discovered a suitable location, they settle down to overwinter. The following spring, the beetles reappear, beginning the cycle anew. Asian lady beetles can survive for up to three years.
Symptoms of Infestation
In spring, the adults can be observed wandering on baseboards, windows, walls, attics, light fixtures, ceilings, and other surfaces, as well as on host plants. Asian lady beetle is a relatively benign pest: it will not damage wood, food, or clothing. However, when alarmed, the beetles emit a pungent yellow fluid from their leg joints, which can stain curtains, sheets, and other materials. If the insect makes contact with a human, it may use its mouthparts to bite or pinch bare patches of skin. This can cause minor irritation on the affected area. Interacting with Asian lady beetle may prompt other types of allergic reactions as well, most notably eye irritation. Asian lady beetle is considered a nuisance in the wine industry. If inadvertantly processed, the insect can have a deleterious effect on the flavor of the wine.
- Asian lady beetle has a few natural predators that help to limit its populations. The larvae and adults are parasitized by a bevy of tiny wasps and flies.
- Larvae that have not matured by the end of fall will often succumb to sub-freezing temperatures in winter.
- Asian lady beetles can be removed from the interior of buildings with a broom. Gently sweep the beetles into a dustpan or trash container, and place them outdoors. Avoid making fast sweeping motions. If struck violently, the beetles may be prompted to secrete the defensive fluid stored in their leg joints.
- When present, Asian lady beetles can be captured and disposed of using a vacuum cleaner. After vacuuming up the insects, empty vacuum bags and similar attachments outdoors.
- Seal cracks and wall openings to prevent the adults from entering buildings.
- Repair damaged window screens, and ensure that screening is installed behind attic vents.
- Insecticides are not recommended for indoor use, as they tend to be ineffective and costly.
- Residual insecticides can be sprayed on the exterior of buildings to deter the adults. Insecticides should be applied in fall, when the insects are still feeding.
Photo courtesy of Jacopo Werther CC-by-2.0