R.L. Koch and W. D. Hutchison
Department of Entomology, University of Minnesota
The multicolored Asian lady beetle (MALB), Harmonia axyridis (Pallas), is a predatory lady beetle native to eastern Asia. In 1988, MALB was first detected in the United States in Louisiana. It has been debated whether MALB arrived in the United States through intentional releases for biological control or through accidental seaport introductions. Since its initial detection, MALB has rapidly spread to cover much of the continental United States and parts of Canada. MALB was first detected in Minnesota in 1994.
In its native range, MALB is a known predator of aphids and other soft bodied insects. The potential of MALB as a biological control agent in the United States is becoming apparent. Unfortunately, MALB, like many other exotic insects, may also have adverse impacts on humans and the environment.
MALB adults are 4.9-8.2 mm long by 4.0-6.6 mm wide. The general body shape is a convex, shortened oval. The coloration of MALB adults ranges from orange to red with zero to 19 black spots to black with red spots. The most distinguishing feature of the MALB adults are the light colored oval shaped markings on both sides of a black marking in the center of the pronotum (shield-shaped area behind the head). The black central marking on the pronotum is often 'M'-shaped, but it could also be four black spots, two black curved lines, or a solid black trapezoid. Eggs of MALB are yellow, oval-shaped, and laid on end. The 'alligator'-shaped larvae are black with orange markings and are spiny in appearance (see photo, left). Larvae develop through four instars (stages). The final larval instar will molt into a sessile, orange pupa with black markings (see photo, right). Then, the pupa will molt into an adult.
Biology and Life cycle
MALB adults typically live for one to three months, but may live up to three years. In autumn, MALB adults migrate from fields and forests to buildings and other prominent objects on the horizon. In Ohio, researchers have shown that migratory flights generally begin on the first day with temperatures exceeding 18ºC after the first cold spell with temperatures dropping to near freezing. Upon arriving at a building or other structure, MALB seek out cracks or holes, in which they will spend the winter in clusters of few to many individuals. The arrival of warm temperatures in spring stimulates dispersal from overwintering sites and mating of MALB. Adults then seek out colonies of aphids. The eggs of MALB are generally laid in clusters of 20-30 on the underside of leaves near aphid colonies. An individual female may lay up to 1,600 to 3,800 eggs. At temperatures near 26ºC, development from egg to adult requires about 18 days. The developmental rate will increase with increasing temperature. In the United States, two generations of MALB are generally observed per year.
Uses in Biological Control
MALB is a voracious predator of numerous aphid species, but will also feed on other pests, such as mites, psyllids, scales, and beetle, moth and butterfly larvae. When other prey are scarce, MALB may feed on pollen and nectar. Through its larval stages, MALB may consume up to 370 aphids. MALB adults will also consume up to 65 aphids per day.
MALB has proven to be an effective biological control agent. Established populations of MALB may be contributing to biological control of aphids and other soft bodied pests in numerous systems, such as pecans, red pines, apples, citrus, soybeans, corn, alfalfa, cotton, tobacco, and small grains. Augmentative releases of MALB have also been effective in systems, such as strawberries, roses, pecans, pine forests, and hops. MALB is commercially available in North America. Unfortunately, the mobility of adult MALB may lessen the effectiveness of MALB in augmentative biological control programs. However, researchers in France have developed a flightless strain of MALB to overcome this problem. Conservation biological control utilizing MALB has centered on the use of selective insecticides. Newer pesticide formulations, such as spinosad, indoxocarb, and pyriproxyfen, appear to have low toxicity to MALB. MALB also appears to be compatible with transgenic crops, such as Bt corn, resistant to the European corn borer.
MALB may be most well known through its tendency to aggregate on homes and other structures in autumn. Oftentimes MALB will find their way inside of homes where they will overwinter (see photo, left). Homeowners become annoyed with MALB flying and crawling around inside the building. In addition, a MALB, when disturbed or crushed, will emit an orange liquid that can stain carpet, furniture, or drapes. During winter and spring, activity MALB inside buildings tends to increase on warm days. Not only is the presence of MALB annoying, but some people develop an allergic rhinoconjunctivitis to MALB. Many people are caught off guard by the fact that MALB will bite humans, especially in the autumn.
MALB problems in households may be managed in several ways. First, it is recommended that homeowners seal up any cracks or holes through which MALB might enter the house. Second, various black light traps are available for trapping beetles after they enter a home (e.g., Ohio State University, MALB site). Third, synthetic pyrethroid insecticides are being used on the exteriors of homes to prevent MALB from entering the home. Due to concerns about human exposure to pesticides, we recommend that pesticides be used only if other management tactics are unable to suppress MALB to tolerable levels. Insecticides approved for homeowner use are summarized at http://www.extension.umn.edu/garden/insects/find/multicolored-asian-lady-beetles/.
Pest of fruit production
In autumn, MALB has shown a tendency to aggregate on late season fruits, such as grapes (see photo, below left), apples (below right), and raspberries (below middle). In some cases, MALB has been reported feeding on fruits that have been damaged by birds or other insects (see image, left). The extent of feeding damage caused directly by MALB remains uncertain. Perhaps a greater concern is that MALB may be a contaminant in vineyards growing grapes for wine production. MALB is difficult to remove from clusters of grapes during harvest. Subsequently, some of the MALB may be crushed with the grapes during processing. The flavor of the resulting wine can be tainted by the alkaloids contained in MALB.
Impacts on non-pest insects
Exotic organisms often have adverse impacts on native species. There is much concern that MALB may be adversely impacting populations of native lady beetles and other predatory insects. Laboratory studies have shown that MALB will feed on some native predators, including the 12-spotted lady beetle, Coleomegilla maculata. Field observations have shown concurrent decreases in the abundance of some native lady beetle species with the increase in the abundance of MALB. MALB may also be impacting other non-pest insects. For example, MALB has recently been identified as a potential hazard to monarch butterflies developing in agricultural systems.
- Ellis T., R. Isaacs, D. Landis, J. Landis. 2003. The multicolored Asian lady beetle: a good bug with some bad habits. Michigan State University.
- Koch, R.L. 2003. The multicolored Asian lady beetle, Harmonia axyridis: A review of its biology, uses in biological control, and non-target impacts. Journal of Insect Science. 3:32. 1-16. https://academic.oup.com/insect-science/
- Koch R.L, W.D Hutchison, R.C. Venette, G.E. Heimpel. 2003. Susceptibility of immature monarch butterfly, Danaus plexippus (Lepidoptera: Nymphalidae: Danainae), to predation by Harmonia axyridis (Coleoptera: Coccinellidae). Biological Control 28: 265-270.
- Magnan E.M, Sanchez H., Luskin A.T., Bush R.K. 2002. Multicolored Asian lady beetle (Harmonia axyridis) sensitivity. Journal of Allergy and Clinical Immunology 109: 205.
- Multicolored Asian lady beetle. Ohio IPM Program. Ohio State University Extension. https://ohioline.osu.edu/factsheet/ENT-44
- Numerous links to other MALB fact sheets view: http://www.ipmcenters.org/