As you may have heard, people call ladybugs with several common names depending on what part of the world you are at. Ladybirds, ladybird beetles, lady beetles, and Halloween lady beetles are the most known ones. Ladybugs have a critical role as beneficial predators of soft-bodied arthropods, such as aphids and scales. They also have traditional values in some cultures. For example, the presence of lady beetles in a house is often considered a symbol of good luck. However, in this article, we will cover only the multicolored Asian lady beetles (MCALB), Harmonia axyridis (Pallas) as seasonal structural pests; while, other species of lady beetles are beyond the scope of our discussion.
In 1916, the MCALBs were first introduced to North America from Asia to manage aphids. Henceforth, various releases of this species were carried out in different parts of the US. Abnormally, in the fall of 1988, numerous adults of this species were found entering homes in Louisiana. Several years later, MCALBs were found well established throughout the country.
Before the abnormal outbreak of the MCALB population, we used to tell people, just pick up the little guy and let him go outside, or vacuum them up. Today, they’ve become a quite big fall invader problem. The MCALB has been described as the most invasive lady beetle on Earth. In North America alone, they have been found feeding on 36 different species of aphids and other pests, and have greatly reduced the number of native lady beetles in North America. In addition and contrary to popular belief, these beetles can and do bite humans, and are a source of allergic reactions that range from sneezing to asthma depending on the sensitive individuals. Moreover, dead insect bodies of seasonal invaders inside wall voids, cracks and crevices attract dermestid beetles, such as hide beetles, larder beetles, carpet beetles, etc. They also attract ants, especially carpenter ants. However, unlike mosquitoes, the bite of MCALB is similar to a pinch and no blood meal is taken from the person being bitten.
There are about 5,000 species of lady beetles worldwide and over 400 species in North America. MCALBs were first introduced to North America for biological control of aphids in California in 1916, and have since spread reaching Canada in 1994. In Asia, the adults of MCALBs habitually seek cracks and crevices in cliff faces to hibernate, while in the USA, cliff faces are not common, therefore they have elected to hibernate over-winter, in and around buildings instead. In nature, the population of MCALB consists of 50% males and 50% females. However, inside houses, it has been estimated that 66% of MCALB are females and 34% are males.
Adults are about 1/3-inch long. Unlike most lady beetles, MCALB adults have various color patterns, such as, orange with black spots, red with black spots or solid orange with no black spots. Adults have a pattern of W or M-shaped mark on the thorax
Both adults and larvae are predators. They feed on aphids and soft-bodied arthropods. Adult MCALBs consume about 90-270 aphids per day, while larvae consume 600-1200 aphids during their development. Females lay eggs in clusters of 20-30 eggs on the underside of leaves usually near aphid colonies. Eggs hatch in 3-5 days. Larvae develop through four instars before they pupate within 11 days. Pupae stage usually last 5 days. The life cycle from egg to adult requires about two to four weeks. Between late September and late October, adults fly to over wintering sites. Healthy MCALBs can live up to 3 years depending on the temperature and food availability. In the USA, there are two generations of multicolored Asian lady beetles per year.
As the cold weather approaches, food availability often become challenging for many insects. Additionally, environmental cues, such as temperature, daylight, and relative humidity, along with species-specific developmental factors promote specific insects, including MCALBs to invade homes.
There is some controversy about what is involved in the orientation of the beetle’s overwintering flight. Some researches have indicated that MCALBs orient themselves towards tall buildings or hills, but may encounter your building on the way. While other studies have mentioned that they are attracted to contrast, such as shadows or dark shutters, etc., which loosely resembles the white cliff faces of their native habitats in Asia. Other researches have suggested that they are attracted to light-colored houses. More controversially, scientists from the North Carolina State University have pointed out in their published article that MCALBs are not visually attracted to the white colored areas nor they are oriented by any pheromones during over-wintering flight.
At over wintering sites, they congregate on the sunlit south and west parts of the building before they finally conceal themselves in protected places. In cold unheated areas or outside, these insects will seek out sheltered areas to over winter, such as cracks or crevices along walls, under siding, roofs, overhangs, or the bark of trees etc. In the heated or warmer areas of a structure, MCALBs may hide in cracks, crevices or voids in attics, crawlspaces, empty roof spaces, vent openings and ceilings.
On warm sunny days during the winter, where pests have chosen to hibernate, it is possible to see live insect activity. Obviously any insects noted indoors during the winter are not coming in from the outside; they are coming from the structure. Temperature is an essential factor for regulating the MCALBs activity. They need 50°F to fly and 65°F to swarm.