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Western Hemlock Looper

H. P. Koot

 

Introduction

The western hemlock looper, Lambdina fiscellaria lugubrosa (Hulst) (Lepidoptera: Geometridae), is one of the most destructive defoliators of conifers in British Columbia. Populations can increase suddenly and outbreaks may persist for several years. Outbreaks of the western hem-lock looper can result in severe defoli-ation and extensive mortality.

The first recorded damage in the province occurred in Stanley Park, Vancouver, in 1911. In 1928-1930 severe defoliation occurred in the Indian River Valley. There were signifi-cant timber losses on Vancouver Island in the Klanawa, Sarita, Caycuse and Nitinat valleys between 1945 and 1947 and also in the Interior in the Big Bend, Lardeau, and Wells Gray Park areas. Severe defoliation occurred in the McBride area in 1955. The looper again reached epidemic levels in Stanley Park in 1959, and caused severe defoliation at Hidden Lake in the Interior. From 1969 to 1972 many hemlock, cedar and amabilis fir were killed at Coquitlam Lake and in 1972 and 1973 defoliation extended from Nakusp to Boat Encampment on the Columbia River. Loopers killed trees over 1200 ha in Wells Gray Park in 1976. Between 1982 and 1984 defolia-tion occurred in many mature hemlock-cedar stands from Upper Arrow Lake to Mica, Seymour River, near Shuswap Lake, Quesnel Lake and along Canoe Reach on McNaughton Lake. The most recent infestations originated in the Revelstoke area and along the Columbia River in 1990. From 1991 to 1993 defoliation contin-ued in this area and also extended along the North Thompson Valley, including Adams River and Wells Gray Park, along the Fraser River between Prince George and McBride, and along McNaughton, Horsefly and Quesnel lakes. Scattered tree mortality was common in most areas.

Although most outbreaks have occurred in mature and overmature hemlock and hemlock-cedar stands, some infestations were in vigorous 80- to 100-year-old stands. Tree mortality in mature and immature stands ranged from 20-100% when trees were 80% defoliated and subjected to subsequent secondary insect attack.

 

For more information, see the Western Hemlock Looper Forest Pest Leaflet in the Canadian Forest Service bookstore.