Birch sawfly (Arge pectoralis)
Dusky birch sawfly (Croesus latitarsus)
Pest description and damage Mature birch sawfly larvae are yellowish with rows of black spots along the abdomen and 0.75 inch long. The head is reddish yellow with black eyespots. Adults have 3-segmented antennae and lay eggs in rows in the edges of leaves. Larvae feed on birch, alder and willow. Damage is usually localized and rarely do they cause significant defoliation. Dusky birch sawfly is a darker yellowish-green with 3 dark spots on each segment. They also feed on birch but usually cause only localized damage. Larvae feed gregariously along the leaf edge holding with their abdomen flipped upside down over their back. There are two generations of dusky birch sawfly; spring and fall. However, they overwinter in the soil as pupae with adults emerging in spring.
Watch for small larvae along the leaf edge in spring. Prune out leaf or area with larvae.
Stink bugs and other predator bugs have been known to prey upon the larvae.
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For more information
Furniss, R.L. and V.M. Carolyn. 1980. Western Forest Insects. USDA Forest Service, Misc. Pub 1339.