Dusky Birch Sawfly
Description: Sawfly larvae are often mistaken for caterpillars. However, sawflies are different in their habits and how they must be controlled. Caterpillars grow up to be moths and butterflies, but sawflies grow into wasp-like insects. Caterpillars have one to four sets of abdominal prologs (false legs), whereas sawflies have six sets of prologs. Sawflies also tend to roll into an ‘S’ shape when they are disturbed. Larvae are yellow-green with black blotches on their sides and have a black head. They are about one inch long when full grown. The primitive, stingless winged sawfly adults are small and generally dark in color. They do not have the constricted waist of many stinging wasps. The females have saw-toothed ovipositor, which is used to ‘saw’ into plant material and deposit eggs.
Symptoms: Dusky birch sawfly have two generations per year and can start out very small, almost too small to see. The first generation larvae feed from May to early July. The second, overlapping generation feeds though September. They begin by gradually skeletonizing the leaves, as the early larvae will not eat the veins. As they mature, they start to eat the entire leaf, feeding in groups. Whole trees or shrubs can be defoliated.
Action: The dusky birch sawfly’s primary host is River birch, but sometimes grey, black, red paper and yellow birch are also attacked. Insecticides can control the pest or small populations can be removed by hand and destroyed.
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