Pest description and crop damage Adult insect is a small (0.125 to 0.375 inch) black sawfly. Mature larvae are flattened and may be up to 0.5 inch long. The larvae emerge and feed in leaf tissues, leaving blotch-shaped or winding brown mines. Repeated severe infestations may result in decline of trees. Vigorous gray, white, and paper birches are attacked most commonly.
Biology and life history The adult sawfly lays eggs in new leaves. Larvae drop to the ground and pupate in the soil for 2 to 3 weeks before emerging as adults. There may be up to four generations per year, depending on length of growing season.
Pinch leaves to kill larvae in minor infestations in small trees. Plant resistant species and cultivars, which include Betula costata, B. davurica, B. maximowicziana, B. utilis var jacquemontii, B. nigra, B. schmidtii, and the varieties 'Crimson Frost' and 'Purple Rain'.
Spray when first leaves are fully formed, usually about the first of May. Spray again from mid-June to mid-July.
For more information
Johnson, W.T. and H.H. Lyon (1991), Insects That Feed on Trees and Shrubs, 2nd ed., Cornell University Press (p. 128).