Birch leafminer (Fenusa pusilla), Elm leafminer (Fenusa ulmi), Alder leafminer (Fenusa dohrnii) and Hawthorn leafminer (Profenusa Canadensis). The larvae of all of these leaf-mining sawflies feed on leaf tissue between the upper and lower surfaces of the leaf, causing papery brown blotches to appear on the leaves.
The adult females lay eggs in leaf tissue with their ovipositors when leaves are about half grown. Adults are black, about 3 mm long, except for alder leafminer (6 mm) and resemble small flies. Larvae are translucent, yellowish-white with greatly reduced prolegs.
Target young larvae with systemic insecticides. Look for birch leaf miner larvae as Vanhoutte spirea or European cranberry-bush viburnum are blooming. Newly developing larvae of hawthorn, alder and elm leaf miners are present a little later as black cherry or black locust begin bloom. There may be several generations per year, depending on the weather.
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