By Virginia Barlow
posted
Jan 10, 2013
In the old days, ladybeetles (or ladybugs) used to "flyaway
home" to their children, as per the old nursery rhyme. Now one
species, the Halloween ladybeetle, is instead flying into our homes
in droves, where its bad odor and habit of falling into cups of
coffee have contributed to its dramatic fall from grace.
The ladybeetle family includes many cute and shiny beetles-
they're usually bright orange or red, with some black and white
thrown in for contrast. As a group, they specialize in consuming
agricultural pests, especially aphids, and they don't sting or
bite. These attributes and the fact that there are so many of them
- about 5,000 species worldwide and around 475 in the U.S. - have
contributed to making ladybeetles among the most beloved of all the
insects.
Properly called the multicolored Asian ladybeetle, this little
insect has so many other names that in the U.K. it's sometimes
known as "the many-named ladybird." What we know as "ladybugs" are
called "ladybirds" in other English speaking countries.
Properly, they are not bugs or birds; they are beetles. This
species is unusually varied in appearance, ranging from pale orange
to deep red, occasionally with no spots and sometimes with as many
as 16 spots, but they do have a distinctive feature: between the
wings and the head, on the prothorax, are markings in black and
white that can be read as a "W" or an "M."
In 1888, an Australian species of ladybeetle was brought to
America to control a scale insect that threatened the California
citrus crop; this was the very first recorded case of a predatory
insect being deliberately imported to the U.S. The release was
enormously successful, so much so that it spurred the widespread
and haphazard release of various ladybeetle species all around the
world.
The Halloween ladybeetle, native to eastern and central Asia,
soon became a favorite for biological control projects because it
eats a wide variety of insects in the egg and larval form. Since
its introduction the species has devoured aphid species that feed
on soybeans, roses, strawberries, red pines, balsam firs, and
pecans; it has also been found to feed on red pine scale and pine
bark adelgid. The beetle is a voracious predator and a friendly
alternative to toxic pesticides; unfortunately, its
indiscriminating palette has gotten it into deep trouble. The very
trait that enabled it to colonize most of the world has also
inspired a backlash.
After it has done in the aphids, both adult and larval Halloween
ladybeetles move on to feed upon the larvae of other ladybeetle
species and the eggs and larvae of many other kinds of insects. In
some studies, it has been shown to have an adverse effect on
monarch butterfly populations, and in several states the decline of
native ladybeetles has been documented not long after the
Halloweens arrived. Winemakers really hate Halloween ladybeetles
because not only do they eat the grapes, but those that get
harvested with the grapes produce a most unpleasant flavor in the
wine. This ladybeetle has recently made its way to the U.K., and
some scientists believe that 1,000 native species there could
disappear if the new beetle flourishes.
Halloween ladybeetles are a bit larger than most of our native
species, which may help explain their success. Depending on the
size of the aphid, a ladybeetle will eat from 90 to 370 aphids
during its larval stage. The beetles usually produce two broods
each year, and in the laboratory, where it's possible to count,
females each laid an average of 1,600 eggs. All ladybeetles use
defensive chemicals in their hemolymph (circulatory fluid) to
discourage would-be predators, but the Halloween has these
foul-tasting and-smelling compounds in higher concentrations than
its relatives. Nobody eats them or their egg or their larvae. In
winter, they maximize the effectiveness of these deterrents by
glomming together in groups. They vary in behavior and morphology
as well as in appearance, which allows them to adapt to changing
environmental conditions.
Many introductions of the beetle have been made since 1916, but
the beetle population showed no sign of taking off until1988. No
one knows what might have triggered the population explosion.
Once a beetle population becomes established, the rapidity with
which it colonizes new territory is astounding. In 2004, only one
of these beetles was found in Switzerland, and none were found in
2005. Yet, by 2006, it was established in 10 cantons; in 2007, in
some areas, it was the most abundant ladybeetle on deciduous trees;
and in 2008, it was more abundant than all the native ladybeetles
added together.
Now the Halloween ladybeetle is finding food in 24 countries in
Europe and has been seen checking the menu in South America, South
Africa, and Egypt. Though it has been in the U.S. for almost 100
years, it was just over 20 years ago that the population explosion
came to people's attention here.
Virginia Barlow is a founding editor of Northern Woodlands. The
illustration for this column was drawn by Adelaide Tyrol. The
Outside Story is assigned and edited by Northern Woodlands magazine
and sponsored by the Wellborn Ecology Fund of New Hampshire
Charitable Foundation:wellborn@nhcf.org.
Tagged:
The Outside Story, Halloween Ladybeetle
