Feeding damage by maple petiole borers may be the cause of fallen maple leaves beneath your trees.  Examination of the petiole on fallen leaves should reveal a hollow hole. The tiny larvae tunnel in the petioles, or leaf stems, causing them to break from the blade of the leaf. The adult is a small, four-winged wasp known as a sawfly. Maple petiole borer infestations are infrequent and unpredictable and do not appear to harm tree health so insecticidal control is not recommended.

Images courtesy of Mick and Connie Hardy, Summitville, IN

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