Lady beetles or bean leaf beetles

Misidentification of insects is not uncommon. The colors, shapes, and sizes of the legions of insects that inhabit Iowa often exceed our own imaginations. However, for those of us involved in agriculture, there are several dozen insects that we should recognize. Two are the twelvespotted lady beetle (also called the spotted lady beetle) and the bean leaf beetle. The former is a beneficial, and the latter a serious pest. I would not have given the confusion over the identification of these two insects serious thought if not for a surprise encounter this week. A clear plastic bag, containing dozens of twelvespotted lady beetles was delivered to campus along with the comment, "This sure looks like a bad year for bean leaf beetles."

Coleomegilla maculata, the twelvespotted lady beetle, is a common beneficial insect in Iowa.

Bean leaf beetles are recognized by the four large rectangular (or trapezoidal) spots on the wing covers and the black triangle behind the "neck." The twelvespotted lady beetle has 10 oval spots on the wing covers. The colors of these beetles also vary. The lady beetle is pink with black spots, whereas the bean leaf beetles are tan, dull yellow, or brick red with black spots. Both species are very common in alfalfa during May, but only the bean leaf beetle is commonly found in soybean in May.

Bean leaf beetle (red phase).

This article originally appeared on pages 76-77 of the IC-488 (9) -- May 20, 2002 issue.

Updated 05/19/2002 - 1:00pm