Multicolored Asian Lady Beetle

Summary

Multicolored Asian lady beetles are a non-native species that first became established in North America in 1988. They have since spread across the country. Larvae and adults are voracious predators of aphids, insect eggs, and other soft-bodied arthropods, so can be beneficial predators in home gardens and agricultural crops. However, they are out competing and displacing native lady beetles, can contaminate grapes and other fruit, and are fall invading pests in homes and other buildings.

Lady beetle vs ladybug

Some memes on social media purport to illustrate the differences between lady beetles and ladybugs. However, both "lady beetle", "ladybug", and "ladybird beetle" (a name used in Canada and the UK) are common names applied to all species of Coccinellidae. So Asian lady beetles could also be called Asian ladybugs. While common name use tends to vary by geographic locality, it is best practice to use "lady beetle" to avoid confusion with true bugs in the order Hemiptera.

Classification

Family: Coccinellidae (lady beetles)

Genus: Harmonia (no common name)

Scientific name: Harmonia axyridis (Fabricius, 1793)

Common name: Multicolored Asian lady beetle (MALB), harlequin lady beetle 

Description

Like other lady beetle species, multicolored Asian lady beetles are oval and convex in shape. They are larger than most native lady beetle species at 9/32 inch (7 mm) long and 7/32 inch (5.5 mm) wide.

Multicolored Asian lady beetles are so called because the adults have extremely diverse color patterns (Figure 1). Most individuals have red elytra (the hardened forewings that protect the body) with up to 18 black spots, which may converge and appear to form black bands in dark individuals. However, the black spots may be small, reduced to four spots, or even entirely absent. Other color forms have black elytra with two, four, or twelve orange to red spots.

A character that distinguishes multicolored Asian lady beetles from many other lady beetle species is the white pronotum (the section immediately behind the head) that has a black "W", although this "W" may be completely filled in so that it is just a black patch in dark individuals.

The eggs are yellow, oblong, and laid in clusters (Figure 2).

The larvae have been described as "alligator-like" and are dark grey with rows of orange markings and double-branched spines (Figure 3).

The pupae are orange with black spots. They can often be found attached to plants, walls, and other structures (Figure 4).

Distribution and Introduction to North America

Multicolored Asian lady beetles are native to East Asia from China, Japan, Korea and Siberia west to Kazakhstan and Uzbekistan. However, they have been introduced around the world, including across Europe, South Africa, New Zealand and Australia, South America, and North America.

Multicolored Asian lady beetles were intentionally released in North America for decades, with the first in California in 1916 and more frequent releases starting in the 1970s and 1980s. However, none of these populations appear to have successfully established.

The first established populations were found in Louisiana in 1988. There was no history of purposeful releases in this area, so it appears that these beetles, and their descendants that spread across the country, were accidentally introduced into North America, likely via shipping cargo.

Regardless of how the beetles came to North America, they were first observed in Pennsylvania during the fall of 1993, after which they quickly spread across the state.

Life Cycle

The eggs are laid on the undersides of leaves of low-growing plants, including ornamentals, forest trees, and agricultural crops like wheat, tobacco, and soybeans. The eggs take three to five days to hatch into larvae. The larvae develop through four instars, which takes twelve to fourteen days, before they molt into pupae. The pupae attach themselves to plants, walls, and other structures, and can sometimes be extremely conspicuous, especially when local populations are high. The pupal stage lasts four to five days, after which the adults emerge. The entire life cycle from egg to adult takes three to six weeks, depending on temperature and food abundance. There are usually four to six generations per year. Adults typically live for 30–90 days but can live for up to three years.

In warm areas that don't experience freezing temperatures, including the southern United States, adults are active year-round. In colder areas, including Pennsylvania, the adults overwinter together in protected areas, such as under the bark of dead trees, in leaf litter, and in buildings and behind siding.

Overwintering behavior beings around the beginning of October. During a sunny, warm afternoon following a cold night, multicolored Asian lady beetles congregate outside houses, sheds, and other buildings in search of overwintering sites. The beetles are apparently attracted to the sunlight reflecting off the south or southwest-facing sides of the building. A similar behavior is seen in Japan, where the beetles fly to south-facing rock cliffs and outcroppings.

Pest Status in Homes

It is not uncommon for tens of thousands of beetles to congregate in attics, ceilings, and wall voids. While the beetles stay put throughout the winter when found in more natural areas, they will move around inside these voids and exit into the living areas of a building due to the warmth that penetrates in the walls during the winter (Figure 5).

In most cases, multicolored Asian lady beetles are pests because of their presence when found in homes and other buildings. However, they occasionally bite people, which can vary from slightly annoying to painful. Blood-fed lady beetles die at higher rates than those not fed on blood, and biting is not correlated to feeding rates, so it is unknown why lady beetles bite people.

Allergies to other insects, including cockroaches, can be common when people are continuously exposed to them through living or work situations. Rhinoconjunctivitis, asthma, and even angioedema of the face have been linked to lady beetle infestations in homes. Some people cross-react to lady beetles and cockroaches, so may become sensitizes to lady beetles before encountering them.

When disturbed, multicolored Asian lady beetles exude a stinky, yellow defensive chemical from their leg joints, which can cause spotting on walls and other surfaces. Most people are only annoyed by the odor of these chemicals. However, some individuals experience a dermal reaction to these defensive excretions, which often appears as a small, localized welt. Additionally, pets that consume multicolored Asian lady beetles may receive chemical burns inside the mouth.

Impact on Home Gardens

Multicolored Asian lady beetles are available for purchase to release as biocontrol agents in home garden settings. However, the beetles are almost always already present in the surrounding environment, so if aphid populations were high enough they will attract the already-present beetles. Additionally, adult beetles can fly so releasing beetles when aphid populations are low means most, if not all, of the individuals will disperse away from the garden in search of food. In short, it is generally not effective to purchase and release multicolored Asian lady beetles for the control of aphids and other pests in most home garden settings. 

Impact on Agriculture

Larval and adult multicolored Asian lady beetles are voracious predators of soft-bodied insects, particularly aphids, and are often one of, if not the most, dominate lady beetle species in certain commercial agricultural settings, especially orchards. In such circumstances, lady beetles can act as efficient biocontrol agents to keep aphid populations suppressed below damaging levels. Additionally, lady beetles can be released in greenhouses and other protected culture operations to control aphids, thrips, scales, and other soft-bodied arthropods. In these circumstances, it is best to release eggs as the larvae are wingless and so will not disperse out of the area like adults may (e.g., out of high tunnels with open sides). 

Multicolored Asian lady beetles sometimes infest fruit including grapes, apples, peaches, plums, pears, pumpkins, and raspberries. The beetles show a strong preference for damaged over undamaged fruit and, in most cases, they feed on fruit that has been injured through other means rather than being the primary cause of the damage (Figure 6). 

While the adult beetles are minor pests in most fruit, they tend to infest grape clusters a week or two before they are fully ripe. When the grapes are harvested and juiced, the adult beetles are crushed and release their foul-smelling defensive compound. This results in "lady beetle taint", which renders the resulting juice or wine unmarketable. 

Impact on Native Species

The spread of multicolored Asian lady beetles has been implicated in the decline of multiple species of native lady beetles, including two-spotted lady beetle (Adalia bipunctata) and pink spotted lady beetle (Coleomegilla maculata). Both species have similar prey requirements to multicolored Asian lady beetles, so direct competition for food resources is the likely driver for their decline. 

Management and Control

Mechanical exclusion is the best method of control to keep multicolored Asian lady beetles from entering homes and buildings. Cracks around windows, doors, siding, utility pipes, behind chimneys, and underneath the wood fascia and other openings should be sealed with good quality silicone or silicone-latex caulk. Damaged screens on doors and windows should be repaired or replaced. Attics, fireplace chimneys, and exhaust vents should be covered with number 20 (or smaller) screen mesh.

Exterior applications of insecticides may offer some relief from infestations where the task of completely sealing the exterior is difficult or impossible. Applications should be applied by a licensed pest control operator in late September or early October just prior to beetle congregation. Unfortunately, because insecticides are broken down by sunlight, the residual effect of the material will be greatly decreased and may not be effective much beyond several days to a week or two.

If numerous lady beetles are entering the living areas of the home, it is advisable to locate the places where the beetles gain access. Typically, beetles will emerge from cracks under or behind baseboards, around window and door trim, and around exhaust fans or lights in ceilings. Seal these openings with caulk or other suitable materials to prevent the beetles from crawling out. A temporary solution is to use tape to stop the beetles. A helpful hint to remember: the beetles are attracted to light and can see light entering through cracks in the walls or ceilings. Initially, concentrate on sealing cracks in the rooms where beetles are most prevalent.

After the beetles have gained access to the wall voids or attic areas, it is not advisable to use an insecticide to control them. Insecticidal treatment of the voids may kill thousands of beetles, but there is the likelihood that carpet beetles will feed on the dead lady beetles and might subsequently attack woolens, stored dry goods or other animal products in the home.

Although aerosol-type foggers, commonly called bug bombs, will kill beetles that have amassed on ceilings and walls in living areas, they will not prevent more beetles from emerging shortly after the room is aerated. Therefore, such devices do not provide long-term management of the problem. Similarly, spray insecticides directed into the cracks and crevices where beetles emerge will not prevent them from emerging and are not a viable or recommended treatment.

In most situations, vacuuming up clusters of beetles is the most efficient method of removing beetles once they enter the indoor spaces of a building. For bagged models, it is advisable to remove the bag after each vacuuming and either tape and discard it or freeze it so that the beetles do not reemerge into the home. For bagless models, place a nylon stocking into the vacuum hose and secure it with a rubber band. The beetles will collect in the stocking, which can be tied up and discarded after vacuuming. Because the beetles can discharge their foul-smelling defensive compound, which is then circulated into the air by the vacuum exhaust, people who are allergic to multicolored lady beetles may not be able to vacuum them up.

Warning

Pesticides are poisonous. Read and follow directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams, or ponds.

References

Bahlai, C. A., M. Colunga-Garcia, S. H. Gage, D. A. Landis. 2014. The role of exotic ladybeetles in the decline of native ladybeetle populations: evidence from long-term monitoring. Biological Invasions 17: 1005–1024.

Brown, P. J., H. E. Roy. 2017. Native ladybird decline caused by the invasive harlequin ladybird Harmonia axyridis: evidence from a long-term field study. Insect Conservation and Diversity 11: 230–239.

Davis, R. S., M. L. Vandewalker, P. S. Hutchenson, R. G. Slavin. 2006. Facial angioedema in children due to ladybug (Harmonia axyridis) contact: 2 case reports. Annals of Allergy, Asthma & Immunology 97(4): 440–442. doi.org/10.1016/S1081-1206(10)60930-1

Goetz, D. W. 2008. Harmonia axyridis lady bug invasion and allergy. Allergy and Asthma Proceedings 29(2): 123–129.

Harmon, J. P., E. Stephens, J. Losey. 2006. The decline of native coccinellids (Coleoptera: Coccinellidae) in the United States and Canada. pp. 85–94. In T. R. New (ed.) Beetle Conservation.

Hutchison, W. D., T. L. Galvan, E. C. Burkness, R. L. Koch. 2010. Harmonia axyridis as an economic pest of wine grapes in the U.S.: Progress in developing an IPM program and potential impact in Europe. Benefits and Risks of Exotic Biological Control Agents, IOBC/wprs Bulletin Vol. 58: 47–52

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(1; 32): 1–16. doi.org/10.1093/jis/3.1.32

Koch, R. L., T. L. Galvan. 2008. Bad side of a good beetle: the North American experience with Harmonia axyridis. BioControl 53: 23–35.

Koch, R.L., R. C. Venette, W. D. Hutchinson. 2006. Invasions by Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) in the Western Hemisphere: Implications for South America. Neotropical Entomology 35(4): 421–434.

Nakazawa, T., S. M. Satinover, L. Naccara, L. Goddard, B. P. Dragulev, E. Peters, T. A. E. Platts-Mills. 2007. Asian ladybugs (Harmonia axyridis): A new seasonal indoor allergen. Journal of Allergy and Clinical Immunology 119(2): 421–427. doi.org/10.1016/j.jaci.2006.11.633

Pickering, G. J., A. Botezatu. 2021. A review of ladybug taint in wine: origins, prevention, and remediation. Molecules 26(4341): 1–16. doi.org/10.3390/molecules26144341

Ramsey S., J. E. Losey. 2012. Why is Harmonia axyridis the culprit in coccinellid biting incidents? an analysis of means, motive, and opportunity. American Entomologist 58(3): 166–170. doi.org/10.1093/ae/58.3.166

Riddick, E. W. 2016. Spotlight on the positive effects of the ladybird Harmonia axyridis on agriculture. BioControl 62: 319–330.

Roy, H. E., P. M J. Brown, T. Adriaens, N. Berkvens, U. Borges, S. Clusells-Trullas, et al. 2016. The harlequin ladybird, Harmonia axyridis: global perspectives on invasion history and ecology. Biological Invasions 18: 997–1044.

Stocks, I. C., D. E. Lindsey. 2008. Acute corrosion of the oral mucosa in a dog due to ingestion of Multicolored Asian Lady Beetles (Harmonia axyridis: Coccinellidae). Toxicon 52(2): 389–391. doi.org/10.1016/j.toxicon.2008.05.010