Asian Ladybugs (Lady Beetles)
About 450
species of ladybugs (or lady beetles) exist in the United States and
Canada. As a general rule,
most ladybug species are extremely beneficial insects.
Ladybugs feed on other insect pests, such as aphids, mealybugs,
scale insects, mites, and other outdoor plant pests.
However, certain
species of ladybugs not native to North America have been introduced as
biological controls to serve agricultural interests.
One of these species, the Asian ladybug (Harmonia axyridis), was
introduced
back in 1980 by the U.S. Department of Agriculture in the Yakima Valley
of Washington state as a biological control for aphids.
Eventually other introductions of these Asian ladybugs, coupled
with ideal environmental conditions, mushroomed their numbers to the
extent that these Asian ladybugs not only overwhelmed local native
species such as convergent and transverse ladybugs but they began to
overwhelm many local homes as well during the fall and early winter
months in various areas of the Northwest.
Asian ladybugs can be identified from other ladybugs by what appears to
be a dark “W” on their mostly white colored pronotum behind the head.
Other ladybugs have different marking characteristics.
During the fall months, Asian ladybugs seek out shelter to hibernate.
These areas typically include under rocks, landscape timbers, and
under leaves. However,
these bugs have increasing been attracted to the sunny exterior sides of
buildings in a fashion similar to box elder bugs.
In sufficient numbers, Asian ladybugs find themselves inside a
dwelling, where they can leave a yellow, odorous stain on walls and
furnishings that is extremely tough to remove.
The stain is actually a chemical called pyrazine that serves as a
natural defense against would-be predators. When frightened or molested,
the ladybugs will secrete this staining chemical for protection.
Corrective
measures:
Inspect the home to ensure that all roof and weep hole vents outside the
home are well screened with 16-mesh screening.
Caulking cracks around windows, doors, overhangs, fascia boards,
etc. is also advisable.
Inside, seal around windows, behind electrical cover plates with
insulation foam and ceiling light fixtures around the base plates with
appropriate sealant can also help.
If Asian ladybugs get inside, one of the best ways of removing them
without spraying is with a vacuum cleaner.
Dispose of the vacuum bag or empty the vacuum cleaner’s contents
outside immediately after vacuuming the bugs to prevent inadvertent
reintroduction of the pests.
It is not advisable to randomly treat these bugs with
insecticides inside the house as the dead bugs can attract carpet
beetles inside to eat the carcasses, thus one indoor pest problem may be
simply traded for another.