Issue 9, June 21, 2013

Boxelder Bugs

Boxelder bugs have two generations per year, with the second generation becoming adult at this time. Boxelder bugs feed primarily as nymphs and adults on seeds of box elder, a native maple. They also feed on the seeds of silver maple and other maples, but apparently not very heavily.

Boxelder bug nymphs and adults

Boxelder bugs are common every year, but are very numerous this year. Their numbers are typically much larger in hot, dry years, and we had higher numbers last year. We are currently seeing large numbers of red nymphs in many areas of Illinois. Their high numbers this year may be related to their being numerous last year, but I don’t remember them previously being numerous in normal or wet year.

Boxelder bug adults are flat-topped, red and black bugs that are about 1/2 inch long. We have become used to them coming to the sunlit south and western walls of buildings in the fall. Their nymphs are similar in appearance but smaller. Their red abdomen and black wing buds make them different enough in appearance that many people don't recognize them.

Although boxelder bugs are primarily a household insect of little importance to landscape professionals, they are commonly found in masses on the trunks and at the bases of boxelder and other maples. They are effectively killed on contact with insecticidal soap spray both on tree trunks and outside building walls. Because insecticidal soap has little residual activity, spraying may be needed every other day or even every day. Boxelder bugs are not effectively controlled by insecticide residues.

Phil Nixon

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