The "Asian lady beetle" (Harmonia axyridis), an introduced species that has been common in many areas of the eastern U.S. for the past several years, is now found in a limited number of sites in Iowa. This new biological control natural enemy is not just a lovable and beneficial inhabitant of the garden. It is a serious household pest in those areas where it has become well established and abundant.
The Asian lady beetle is another "outdoor" insect that becomes a pest as an accidental invader. From late fall through winter, homeowners in many regions of the eastern half of the U.S. suffer the annoyance of having large, brightly-colored lady beetles saunter across the dining table or kitchen counter or fly against the bathroom mirror every morning. As with other accidental invaders, the Asian lady beetles are harmless -- they cannot bite or sting and they do not carry diseases (though they do sometimes leave a slimy smear and they also have a distinct stink when squashed).
Their beneficial role outdoors and harmlessness indoors do not make them any less annoying as homeowners face up to hundreds of these in their house every day. As a southeastern Missourian wrote on the "Internet" recently, "They come out in the hundreds, sometimes covering large sections of walls or ceilings. It is a trial getting dressed in the morning when ladybugs are inside your underpants or bathing when the little jewels are in your bath tub."
So far, the Asian lady beetle has only been reported in five Iowa counties: Story, Boone, Iowa, Johnson, and Cass. The first known areas of infestation were outdoors on the ISU campus and at Ledges State Park. Later infestations at Woodward, Belle Plaine, Iowa City and Massena were discovered as accidental invaders indoors. The widespread distribution of known infestations suggests this beetle is already well-established in Iowa and probably exists in many more areas than those so far known.
The Asian lady beetle (or ladybug, if you prefer) is a larger-than-average species at approximately 1/3 inch in length. Like other ladybugs, it is roundish, and dome-shaped. The color of the wing covers varies from yellowish to orange to reddish, though deep orange is the most common color. There are 19 black spots on the back but there is tremendous variation among individuals and on some beetles spots may be faint or missing. There is a white marking in the shape of the letter "W" on the thorax.
The lady beetles and larvae feed voraciously on aphids and scale insects. For this reason the beetles were introduced into the U.S. from eastern Asia. They have been rapidly spreading throughout the eastern part of the country, up the Atlantic coast and as far west as Missouri and Iowa.
Larvae are found only on plants in the summer. Reproduction inside, during the winter is not possible. The larvae resemble tiny black and orange alligators and grow to about 3/8-inch long.
As with other accidental invaders, the most effective management option will be to prevent invasion by sealing cracks, gaps and openings on the outside before the beetles wander in during late summer. The effectiveness of perimeter spray treatments has not been determined. Indoor sprays will be of very limited benefit. For now, the practical solution is for homeowners to vacuum and discard invader lady beetles as they appear.
We are anxious to document the distribution of this new species within the state. Please submit samples (several specimens, if possible) that you suspect of being Asian lady beetle to the Insect Diagnostic Clinic, Department of Entomology, ISU, Ames IA 50011.
This article originally appeared in the March 22, 1996 issue, pp. , 1996 issue, pp. 36-37.