The "multicolored Asian lady beetle" (Harmonia axyridis), has been a common nuisance in many areas of the eastern U.S. for several years. This lady beetle, like the others, is beneficial as a natural enemy of aphids and other small insects. Unfortunately, this species has the undesirable habit of congregating on the south sides of houses and other buildings and wandering indoors by accident in the fall of the year.
The first specimens of this introduced insect were found in Iowa in 1994. Until this summer, the beetles were known from only a limited number of sites. That changed in the past two weeks, however, as masses of lady beetles were reported for the first time from most of eastern Iowa. See the distribution map below.
Description. The Asian lady beetle is approximately 1/3 inch in length and semispherical or dome-shaped. They vary from yellowish to orange to reddish; though deep orange is the most common color. There are 19 black spots on the back that vary in darkness among individuals. The spots may be faint or missing on some beetles. There is a black marking (on a white background) in the shape of the letter "W" on the thorax.
The Asian lady beetle, like boxelder bugs, pine seed bugs and elm leaf beetles, is an "outdoor" insect that becomes a nuisance pest as an accidental invader. As with other accidental invaders, the Asian lady beetles are harmless. They cannot bite or sting, they do not carry diseases, and they do not feed or reproduce indoors. They may leave a slimy smear and they have a distinct odor when squashed.
Accidental Invader Management. The most effective management option is to prevent invasion by sealing cracks, gaps and openings on the outside before beetles (boxelder bugs, pine seed bugs, wolf spiders, etc.) wander in during late summer. Exterior insecticides are of limited usefulness, as large areas must be heavily sprayed on a repeated basis for significant control. Treatment must be applied before the invaders begin to enter buildings. Synthetic pyrethroid insecticides applied by professional pest control firms are more effective than insecticides available to homeowners. Indoor sprays are of very limited benefit. The practical solution is to vacuum and discard invader lady beetles as they appear.
New County Records are still being accepted. If you have observed Asian lady beetles from a county not shaded on the accompanying map, please report your observations to: Extension Entomology, Iowa State University, Ames IA 50011. Phone 515-294-1101. Email firstname.lastname@example.org .
Iowa Reported Distribution of Asian Lady Beetle
This article originally appeared in the November 6, 1998 issue, p. 125.