Garden Word of the Day
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Asian Lady Beetles
Commonly referred to as ladybugs in the U.S. and ladybirds in Britain, a more correct name is lady beetle, even though some of them are male. In most cases, lady beetles are beneficial insects, eating a surprising number of soft-bodied, sap-sucking insect pests. The Asian lady beetle is something of an exception.
First introduced to the United States from Japan in 1916 to control aphids, Asian lady beetles (Harmonia axyridis) did not start to thrive in North America until 1988. First seen succeeding in the wild in Louisiana, Asian lady beetles were well established in the Northwest by 1991, the Northeast by 1994, and in the Midwest by 2000. Asian lady beetles are now found throughout the U.S. and Canada, and in parts of Europe and Africa. And for some, that’s a problem. We will get to that in a moment.
Asian lady beetle description
Slightly larger than other lady beetle species, Asian lady beetles have the same half-dome shape of other ladybugs. Legs tend to be brown while the antennae, head, and mouthparts are pale yellow, though they can be tinged with black.
This species appears in a very wide variety of colorations. They can range in color from red to yellow, or even black. The black variations may have 2 or 4 red spots, though not always. The red to yellow varieties may have up to 22 spots or no spots at all. The thorax, or middle part, (where the legs and wings attach) tends to be white, cream, or pale yellow, with variable black markings that can range from a few dark spots in an “M” or “W” formation to almost completely black. The pattern may also be in the shape of a trapezoid. Many other coloration patterns have also been recorded.
If you turn an Asian lady beetle upside-down, you would see that it is dark, with a reddish brown border. This, and the fact of its larger size, are the two most reliable methods of identification. Because of the variety of colorations, Asian lady beetles also have a variety of names, including harlequin lady beetle, Japanese lady beetle, multicolored Asian lady beetle, multivariate lady beetle, pumpkin lady beetle, and southern ladybird.
Asian lady beetle larvae, like other lady beetle species, look like miniature alligators, with spines and tubercles. These black to blue-gray larvae go through 4 developmental stages, or instars. The final stage can be quite colorful with bright orangish-yellow patches on the sides of the abdomen.
Asian lady beetle lifecycle
Also known as Halloween lady beetles, these insects often invade homes during October in search of a place to overwinter. Using visual cues and pheromones to signal each other, they will often congregate in huge numbers. As temperatures drop below 50°F, they slow and then stop moving. Before that time, unmated females will seek out dry, dark crevices, such as inside walls and furniture. They also gather in the upper corners of windows, where they collect the sun’s heat. They seem to prefer light-colored buildings and dark screening material. Subsequent generations will follow chemical trails to favored overwintering sites.
In spring and summer, mating occurs and bright yellow eggs are laid in clusters on the underside of leaves. Within 3 to 5 days, these eggs hatch, releasing the classic alligator-shaped ladybug larvae. The larval stage lasts 12 to 14 days, followed by a 5 to 6 day pupal stage. Adults can live 2 to 3 years and there can be multiple generations in a single year. A single female may lay 1,600 to 3,800 eggs in her lifetime. And Asian lady beetles are also known to swarm in summer, creating a nuisance for picnic-goers.
Asian lady beetles have good eyesight. When threatened, Asian lady beetles release a foul odor, staining bodily fluids (“reflexive bleeding” from their knees), and they bite. Yes. That’s right. Asian lady beetles will bite you. And some people are allergic.
Asian lady beetle diet and host plants
Asian lady beetles are commonly found on apple trees, alfalfa, Christmas trees, grains, maple trees, pecan trees, rose bushes, walnut trees, and wheat. A single adult Asian lady beetle can eat 90 to 270 aphids each day, and one larva can devour 600 to 1,200 aphids as it develops. Adelgids, asparagus beetle larvae, mealybugs, moth larvae, psyllids, scale insects, spider mites, thrips, and whiteflies are also popular food stuffs. So are other lady beetle species - and other Asian lady beetles. These predators are voracious!
The problem with Asian lady beetles
Being slightly larger than other lady beetle species. Asian lady beetles have been devastating to native populations. Suddenly, beneficial ladybugs went from predator to prey. In addition to eating indigenous ladybugs, Asian lady beetles outcompete our more gentle ladybugs, leaving them without adequate food supplies. Also, Asian lady beetles are highly resistant to common lady beetle diseases. If that weren’t bad enough, Asian species carry a parasite to which they are immune, but other lady bugs are not. This parasite infects and then kills local lady beetles.
As Asian lady beetles devour, outcompete, and infect local ladybug populations, biodiversity is reduced and a domino effect occurs in ways which we have only partially identified. Asian lady beetles are now considered one of the world’s most invasive species. Asian lady beetles are causing problems for grape farmers, too. As grapes are harvested, Asian lady beetles are often caught up in the harvest, ultimately altering the taste of the wine produced by those grapes.
Experts predict that things will settle down, once Asian lady beetle predators appear on the scene, but that can cause yet another set of domino-effects to become active. The delicate balances that evolve slowly over time have a difficult time dealing with the sudden changes we humans tend to create.
Asian lady beetle management
It is probably too late to do anything about this invasive insect. You are urged to not use pesticides. If Asian lady beetles appear in your home, you can gently sweep them up and toss them outside. Some people vacuum them up only to discover that alarming these insects results the stink and stain mentioned earlier. After kicking out the interlopers, inspect your home for points of entry around doors, windows, and pipes, and fill those spaces with expandable insulation or caulk.
Love ‘em or hate ‘em, Asian lady beetles are here to stay.
6/22/2021 03:55:20 am
Just found a load of these on my apple tree and have never seen them before (I'm based in the UK) and had no idea what they were. Thanks for the information!
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