Striped Alder sawfly, Hemichroa crocea
 

Fig. 336  Striped alder sawfly larvae, feeding on leaf.

Distribution:  Throughout B.C. but most common on the coast. 

TREE SPECIES ATTACKED: Red alder and occasionally paper birch are attacked. The striped alder sawfly is also found on willow. 

WHAT TO LOOK FOR: Skeletonized leaves and yellowish sawfly larvae with black heads and dark brown subdorsal stripe and blotches.

INSECT DESCRIPTION & DAMAGE SYMPTOMS: Larvae are about 2.0 cm long when fully grown. They have a shiny black head and a yellowish body marked by a dark brown subdorsal stripe, and two lateral rows of blotches. Adults are medium-sized nondescript sawflies. Eggs are laid in a row of slits cut on either side of the midrib on the underside of the leaves. Larvae feed gregariously, initially eating holes through the leaf from the underside, giving it a characteristic riddled appearance. Eventually, the entire leaf is consumed except the larger veins. Striped alder sawflies overwinter as prepupae in cocoons in the soil. There are two generations each year.

DAMAGE: This sawfly periodically causes heavy defoliation on the coast, virtually stripping the foliage from extensive stands. This can potentially result in reduced growth of attacked trees, but damage is seldom any worse than this.

SIMILAR DAMAGE: Damage may be similar to that caused by the woolly alder sawfly. The larvae will help in determining which species is responsible for the damage. Leaves skeletonized by leaf beetles, however, will still have all the veins, even the smallest ones.

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Contact Tim Ebata if you have comments on the presentation of this information.

BC Ministry of Forests
Forest Practices Branch
P.O. Box 9513 Stn. Prov. Gov.
Victoria, BC
V8W 9C2

Section phone: (250) 387-8739
Section fax: (250) 387-2136

Last updated March 04, 2002