January 2006 Forest Health Protection and State Forestry Organizations

6.13 Management Guide for WEB Feb 2010 Larch Sawfly By Lee Pederson US Forest Service Pristiphora erichsonii (Hartig) (Hymenoptera: Tenthredinidae)

Outbreaks can occur at Host: irregular intervals in any  Western western larch stands larch throughout the host range.

Topics Damage Damage 1 Larvae feed on needles of older Defoliation is similar to that caused Life History 1 twigs, resulting in needles with a by the larch looper. Light damage “notched” appearance. Heavy may be confused with larch needle Identification 1 populations can completely strip cast, larch casebearer, larch Management 2 trees. Epidemics seldom last more budmoth, or larch needle blight Other Reading 2 than 2 years, and permanent damages. Close examination will damage to trees is uncommon. reveal distinct differences. Field Guide

Management Guide Index Life History Pre-pupal larvae overwinter in about 10 days and feed cocoons in duff. Pupation occurs gregariously until late August. in the spring, and adults emerge Mature larvae drop to the forest Key Points from June into July. The female floor, crawl into the duff and spin “saws” slits into the underside of tough, papery, brown cocoons for  Larvae feed on current shoots and deposits a single overwintering. needles of older egg in each slit. Larvae emerge in twigs, resulting in needles with a “notched” Identification appearance. Adult larch sawflies are  Heavy actually non-stinging wasps that populations can appear early to mid-summer. They completely strip are about three-eighths inch long, trees. black in color, with a characteristic  Adult larch orange band around the abdomen. sawflies are Look for colonies of larvae actually non- typically feeding on needles from stinging wasps late June through August. New that appear larvae are cream-colored with Photo above shows mature larch brown heads. Mature larvae are sawfly larva feeding on larch early to mid- needles. Photo by James Hanson. summer. gray-green along the back and whitish beneath with shiny, jet- black heads. Page 2 Back to menu Larch Sawfly 6.13

Identification They are about three-fourths inch larvae can be found overwintering long. Papery, capsule-shaped brown in duff. cocoons containing pre-pupal One of the largest occurred in western Management Montana and There are no insecticides registered or silvicultural methods northern Idaho developed for control of this insect on a forest landscape or in the mid- stand setting in our Regions. The reduction of larch basal area 1960’s, and ended by 1967. in stands may make them less susceptible to outbreaks. Another outbreak caused Natural control. –Factors contributing to larch sawfly considerable mortality include parasites, predators, disease organisms, damage in weather, flooding, and competition. Two introduced northwestern ichneuman wasps Olesicampe benefactor Hinz and the Montana in Bavarian strain of Mesoleius tenthredinis Morley have proven 1977. to be very effective in suppressing outbreak populations.

Other Reading Coulson, R.N., and J.A. Witter. 1984. Forest entomology. John Wiley and Sons, Inc. New York. 374-377p. Forest Health Protection and State Forestry Organizations Drooz, A.T. 1956. The larch sawfly. USDA Forest Service, Forest Pest Leaflet 8. 4pp. Assistance on State Assistance on And Private Lands Federal Lands Furniss, R.L., and V. M. Carolin. 1977. Western forest Montana: (406) 542-4300 US Forest Service insects. USDA Forest Service Miscellaneous Region One Publication no. 1339. Washington, DC: U.S. Idaho: (208) 769-1525 Missoula: (406) 329-3605 Coeur d’Alene: (208) 765- Department of Agriculture, Forest Service. 450- Utah: (801) 538-5211 7342 452p.

Nevada: (775) 684-2513 US Forest Service Hagle, S., K. Gibson, and S. Tunnock.- 2004. Field guide Wyoming: (307) 777-5659 Region Four to diseases and insect pests of northern and central Ogden: (801) 476-9720 rocky mountain conifers. Forest Health Protection Boise: (208) 373-4227 Rpt. No. R1-03-08. Missoula, MT: U S Department of Agriculture, Forest Service. 125p. http://www.fs.fed.us/r1-r4/spf

Ives, W.G. 1976. The dynamics of larch sawfly (Hymenoptera: Tenthredinidae) populations in southeastern Manitoba. Can. Ent. 108: 701-730.

Johnson, W.T., and H.H. Lyon. 1991. Insects that feed on trees and shrubs. Cornell University Press. Ithica, NY. 16p.

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