Ladybird, ladybird, fly away home
Nature's Notebook - Tim Abbott
October, 29, 2009
If Alfred Hitchcock were alive today, he might well have substituted the ladybird for the feathered sort in his classic horror film, “The Birds.” Just in time for Halloween, these insects are swarming beyond my window, crawling up the clapboards all over the old building where I work and squeezing through the cracks to invade my space.
These are not the sweet, friendly red-and-black ladybugs of childhood memory, the benign foe of aphids, the farmer’s friend. They are an alien species with rusty orange shells, once intentionally released as a biological control for crop and landscape pests and now here to stay.
And they want to come into your home.
Multicolored Asian ladybird beetles (Harmonia axyridis), also known as the harlequin ladybug, are very effective predators indeed, but they also display the disconcerting ability to rapidly expand and naturalize in varied environments — an attribute that they share with other invasive species.
Beginning in 1979, the U.S. Department of Agriculture made multiple introductions of this species in the southeast United States, and the lady beetle became well established there within 15 years.
They are now widespread across the country, and are most often encountered when invading human habitats as they congregate to overwinter in our houses.
The Asian ladybird beetle emits a pheromone that alerts other beetles to swarm at favorable overwintering sites, such as attics, windowsills and other areas. Older homes are particularly susceptible to ladybird beetles seeking shelter from the storm, clustering around window panes like flies on a sunny day. A sure sign of spring in these parts is the layer of ladybug shells one inevitably encounters the first time it gets warm enough to open a window. Swatting them produces a foul, yellow liquid that stains, and there is no insecticide currently listed to control them on fruit. They are partial to ripening fruit, especially wine grapes. You can destroy your vacuum cleaner by trying to get rid of them this way, as they can easily clog the machinery.
Boon or bane?
So are they truly invasive, or just an introduced species with certain admirable qualities but annoying habits?
A quick search of the Web shows a number of sites expressing concern about this species as a nuisance for humans. It clearly has the ability to naturalize in native (and built) habitats, including agricultural areas, disturbed areas, natural forests, planted forests, riparian zones, scrub/shrublands, urban areas and wetlands.
It is not a restrictive predator, but rather enjoys a wide variety of food sources, from garden pests to peaches. Asian ladybird beetles have been observed swarming spills at picnics.
But to be defined as invasive, they should also displace native species.
The Wisconsin Council on Invasive Species is unequivocal on this question, declaring; that “Multicolored Asian ladybird beetles have negative impacts on human health and aesthetics, on the fruit industry, and on native lady beetle populations.”
Those are fighting words. The impact on human health was a surprise discovery for me, but apparently there is growing concern that all those dead lady beetle shells in our homes constitute a significant allergen, comparable to cockroaches and cat hair for people with allergic sensitivities.
Not surprisingly, people with Asian lady beetle allergies more frequently live in rural areas. Symptoms of Asian ladybird beetle sensitivity include cough, rhinitis, conjunctivitis and acute asthma.
As for displacing native species, they have become a top predator of native ladybird beetles and other species that eat aphids. When there aren’t enough aphids to go around, the Asian ladybird beetle goes after the competition. It also preys on eggs of Coleoptera and Lepidoptera species, including monarch butterflies.
What preys on Asian ladybird beetles, and are there sufficient natural checks on its populations in North America? Thus far, the species is rapidly expanding and now the most widespread ladybird population is in North America — suggesting that in the absence of natural predation, they will continue to expand and multiply here.
The answer to whether they will become as ubiquitous as dandelions (but also just as ecologically benign), or turn out to be a major stressor on native diversity as well as a nuisance, will likely unfold in the next decade or so.
We can always look to Europe for its experience with Asian ladybird beetles. It is now widespread across much of the continent and recently invaded the British Isles.
Tim Abbott is program director of Housatonic Valley Association’s Litchfield Hills Greenprint. His blog is at greensleeves.typepad.com.
© Copyright 2009 by TCExtra.com
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