Lady beetle (convergent lady beetle, Mexican bean beetle, Asian lady beetle)
Canada, United States
Damage, symptoms and biology
Lady beetles belong to the beetle family Coccinellidae, which means “little sphere”. There are approximately 4,000 species found worldwide and over 350 kinds are found in North America.
Most species of lady beetles, also known as lady bird beetles or lady bugs, are considered to be beneficial because they consume huge numbers of plant-feeding insects, mostly aphids. Most people have a good opinion of them because of their eating habits and their attractive appearance. The French call them '' les bêtes du bon Dieu '' or '' creatures of the good Lord '' and '' les vaches de la Vierge '' or '' cows of the Virgin ''. The Germans call them '' Marienkafer '' or '' Mary’s beetles ''.
Like all beetles, the lady beetles go through what is known as a complete metamorphosis with distinct egg, larva, pupa, and adult stages. In North America, most lady beetles appear to go through one generation each year.
Adults of a common species known as the convergent lady beetle, Hippodamia convergens , spend the winter in protected hiding places such as log piles, buildings, leaf piles, ground covering vegetation and similar niches where many hundreds of these beetles cluster together. When spring arrives, the adults leave their winter homes and fly to fields and yards where mating takes place. Female beetles deposit their eggs in clusters of up to a dozen per mass. The larvae hatch in about a week and start to eat aphids or other appropriate food. The larva is a rather fearsome looking beast. It is alligator-shaped and covered with bumps and spines. In most species it is a fierce predator. Just looking at its sickle-shaped jaws will tell you so. Despite its small size it can deliver a distinct bite. In about a month the larvae will pupate; this stage lasts about a week. When the adults emerge they too feed on aphids, but as fall approaches they may eat some pollen, which supplies fat for winter hibernation.
A lady beetle’s appetite is remarkable. For example, an adult female convergent lady beetle can consume up to 75 aphids a day while the smaller male may consume up to 40! One larva may eat up to 350 aphids during its life.
Most lady beetles are predators that feed on other insects that eat and damage plants, mostly aphids and scale insects but also psyllids and adelgids. There are a few species of lady beetles that eat plants. One of these lady beetles is the Mexican bean beetle, Epilachna varivestis , which is a serious pest of bean crops. Upon inspection of these beetles you will notice that they are less convex in shape than most of the members of this family and they tend to be dirty yellow in colour rather than bright black and red. Both adults and larvae of the Mexican bean beetle eat the lower surface of bean leaves leaving them with a lacy appearance.
If a lady beetle is poked with a pin or a small twig, the beetle will respond by releasing toxic, sticky blood from its leg joints, a phenomenon known as reflex bleeding. This toxic blood is a defensive weapon against predators because it smells and tastes bad. The lady beetle’s bright colours are probably advertising that they taste bad. Another defensive habit that lady beetles exhibit is to play dead when they feel that they are in danger. This also keeps predators away because many of them will not eat an insect that does not move.
The multicoloured Asian lady beetle, Harmonia axyridis, was introduced as a biological control agent in the United States in 1979 and it quickly spread throughout North America. Despite the fact that it is an effective biological control agent it has become a major nuisance to homeowners because of its habit of invading houses and buildings in large numbers. They begin seeking shelter, to overwinter, from about mid-October to early November and appear in peoples’ homes on warm sunny days as early as February and March. In addition these beetles may get in picnic food and drinks, “swarm” like bees and land on people.
In the spring, the majority of the adults leave their overwintering sites and mate later in the spring. Eggs hatch in about 3 to 5 days with the larval stage lasting 12 to 14 days and the pupal stage lasting 5 to 6 days. Development from egg to adult depends on the weather and when the spring is cool, development can last 36 days or longer. Adults can live as long as 2 to 3 years under optimal conditions.
Many people ask how to control lady beetles in the home.They should understand how beneficial they are and how they fit into the natural scheme of nature. It is considered in many cultures good luck to find a lady beetle in your home or yard but when they become too numerous people just do not want to deal with them. Try to find out how they got into the home in the first place. Make sure your home is insectproof by keeping windows and doors fitting tightly, caulking cracks and crevices leading from the outside to the inside and screening all vents especially in the attic. If you find them in your home in great numbers vacuum them up and then put the vacuum cleaner bag in a sheltered spot, perhaps your shed, garage, or woodpile. When the warmer weather comes along they can conveniently crawl away. Some people are so reluctant to kill them or to toss them out into the cold in mid February that they gather them up in jars and put them in their refrigerator. They then put them out in the spring when the weather is more favourable. There really is no justification for spraying a chemical insecticide to control these beneficial insects.
The multicoloured Asian lady beetle is a promising biological control agent of several insect pests on a wide variety of ornamental and agricultural crops. Its large and even explosive populations are probably caused by the massive abundance of prey, mostly aphids and scale insects, the apparent lack of competition from native lady beetles and the apparent lack of native natural enemies. The multicoloured Asian lady beetle populations will become more balanced when its prey numbers decrease and it falls prey to native natural enemies.
Canadian Forest Service Publications
Diet and feeding behaviour
- Predator : Hunts, captures and kills several types of prey (insects and acarids) over the course of its development.
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