Photos from the WFIWC Archives:
Insects and Damage

Robert Oakes releasing larch casebearer parasites,
Latah County, Idaho. M. Furniss photo #1327.
 

Tips of western larch needles mined by over-wintered larvae
of the introduced larch casebearer prior to collapse
of the population in 1967; Idaho. M. Furniss photo

The larch casebearer (Coleophora laricella), a native of Eurasia, was accidentally-introduced into Massachusetts by 1886. It was discovered in the western U.S. in May 1957 by David Fellin and Richard Schmitz near St. Maries, ID. They were students at Oregon State University en-route to Missoula, MT, for summer employment with the Forest Insect Laboratory. On a downgrade south of town, they observed discoloration of western larch foliage and collected some case-bearing caterpillars feeding on the needles. Subsequently, numerous native parasites adapted to the casebearer and several European hymenopterous species were released in an effort to control it (photo). However, for the next ten years, the casebearer continued to spread over the range of western larch and every spring the larch forest looked as though it was dying. The phone in my office would ring repeatedly as the public wanted to know what was wrong. At one point, the Forest Service regional office decreed that larch should be discriminated against in favor of propagating other tree species, although no convincing evidence existed that needle mining was having any impact due apparently to inherent characteristics of this deciduous conifer and the nature of the mining itself.

However, in summer of 1967, a nearly total collapse of the casebearer occurred due to extreme hot, dry, weather which desiccated needles containing the fragile young larvae. Aided by this decimation of the population, the various introduced and native parasites gained control of the casebearer to where it can be noted only by careful scrutiny of many needles. I recall Donald Parker, who had experience with the casebearer in the eastern U.S., saying at the start that: "Give it 20 years and it will become "naturalized" (under natural control)". He missed it by only 10 years too long. Although future forest insect immigrants may settle down at different rates and under different influences, perhaps we can take solace in the resilience of the forests as they have adapted in the ever going evolutionary process. That has proven to be difficult for Man and his short life span and inherent need to intervene in nature's processes. -- Malcolm Furniss

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