Leaf-mining sawfly
July 30, 2015
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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.
Blotches on alder leaf -- caused by alder leafminer.
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.
Top: Adult leafmining sawfly. Bottom: Egg laying sites on alder leaf.
Management
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.
Top: Sawfly larva from hawthorn. Bottom: Elm leafminer injury.
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