Larch Sawfly
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Hosts
Western larch.
Distribution
Wherever larch is found in Idaho and Montana.
Damage
Larvae eat chunks out of needles (fig. 119) on older twigs. Heavy populations can completely strip trees. Epidemics seldom last more than 2 years and permanent damage to trees is uncommon.
Identification
Colonies of larvae may be seen on needles from late June through August. Small larvae are cream colored with brown heads. Mature larvae are gray-green along the back and white beneath with shiny, jet black heads (fig. 121). They are wasps about three-fourths inch long. During the winter tough, papery, brown cocoons may be found in the duff. Adult sawflies appear in early spring. They are about three-eighths inch long with a characteristic orange band around the abdomen. Eggs are laid in new shoots causing them to curl.
Similar damages
Defoliation is similar to that caused by the larch looper. Light damage may be confused with larch needle cast, larch casebearer, larch budmoth, or larch needle blight damages. Close examination will reveal distinct differences.
References
Anonymous. 1982. For. Insect & disease identification and management. USDA For. Serv.,Northern Region; Idaho Dept. of Lands, Insect and Disease Control; Montana Dept. of State Lands, Division of Forestry. 192 p.
Drooz, A. T. 1956. The larch sawfly. USDA For. Serv., For. Pest Leaflet 8, 4 p., illus.
Furniss, R. L., and V. M. Carolin. 1977. Western For. Insects. USDA Forest Serv., Misc. pub. 1339, 654 p., illus.
Field Guide to Diseases and Insect Pests of Idaho and Montana Forests, USDA Forest Service Northern Region, Publication Number R1-89-54
