Photos from the WFIWC Archives:
Control Methods
Control of western hemlock looper outbreak, Pacific County, Washington, 1931. Plume of dust applied 40 feet above the forest. (Photo 8776 by F.P. Keen).
Western Hemlock Looper. (Prepared by M. Furniss from the appended references). The first known record of extensive tree-killing by a forest insect in the western United States involved the western hemlock looper, Lambdina fiscellaria lugubrosa (Hulst). It killed a vast amount of western hemlock, Tsuga heterophylla, in Tillamook and Clatsop Counties, Oregon, about 1889-1891 (Keen 1938). A subsequent outbreak killed 200 million board feet (bd ft) of hemlock in Pacific and Grays Counties, Washington from 1929-1932. Losses in Pacific County were reduced in 1931 through the first airplane dusting experiment attempted against a forest defoliator in the western United States (Keen 1932). Keen was involved with the operation and voiced his concern in a letter to Craighead (13 July 1931) regarding toxicity of the calcium arsenate contained in the dust:
Ryan monoplane beneath a hopper and platform used for loading calcium arsenate dust to control a western hemlock looper outbreak in Pacific County, Washington, 1931. This was the first airplane dusting experiment attempted against a forest insect in western United States. (Photo 8768 by F.P. Keen)
In connection with the airplane dusting project, we are naturally experiencing some criticism from people who object to having poison scattered around in wholesale lots for fear of killing off the wildlife and even domestic animals. I have tried to get some information from the local Boards of Health as to what constitutes lethal doses of calcium arsenate for birds, mammals and humans but with very little success...
Results of the project were reported periodically by Keen and seemed to vary with time. Craighead wrote, 2 September 1931:
I was much interested in your report... covering ... the dusting results on the hemlock looper. I am not surprised that the effects of the dust at this time did not look so encouraging as they did a couple of months ago... Obviously what is needed is a dust that has good adherence.
And later (21 December 1931):
As I interpret your presentation the dusting project has turned out like most all experiments over forested areas. The results are inconclusive and therefore more negative than encouraging... I am convinced that we do not yet have satisfactory flying equipment for applying the dust.
Nonetheless, the Chief noted:
"... it is evident that you made marked progress in your knowledge of this species (hemlock looper) and I agree with your suggestion that you prepare your observations for publication." [see Keen (1932) that, however, dealt with project details, not biology].
In 1945, the hemlock looper again became destructive, this time in Clatsop County, Oregon. Part of this infestation was dusted with DDT by airplane, marking the first such use of this insecticide in a west-coast forest. Stewart Holbrook, a well known Portland author, described the result (Portland Oregonian, 26 August 1945) under the heading: "DDT: Atomic bomb for parasites of the forest. Miracle chemical spells sudden death for insects, knocks the hemlock looper for a loop in dusting of Oregon's woods".
He noted that the extent of the infestation had been surveyed by Robert L. Furniss: In this tall forest, its ground a jungle, a hundred men on foot could not learn the damaged area in a year's time ... So Furniss got into a plane and for the next few weeks ... (looked) for the brown (infested) areas, and mapped the infestation.
Holbrook recounted further:
... I saw the incredible thing with my own eyes ... We got a brief sight of the plane and its tail-spray going over an opening in the tree tops ... Twenty minutes passed while all of us kept our eyes on the muslin; and then they began to fall, looper after looper ... and lay very still ... On this single 2 x 3 - foot (muslin) screen we counted 360 loopers ... The ... dead ... calculated from counts of 60 screens ... ran to 4,300,000 loopers to the acre.
References
Keen, F.P. 1932. Control of the hemlock looper by airplane dusting. J. For. 30: 506-507.
Keen, F.P. 1938. Insect enemies of western forests. USDA Misc. Publ. 273 (Rev. 1952).
Wickman, B.E., Torgersen, T.R., and M.M. Furniss. 2002 Photographic images and history of forest investigations on the Pacific slope, ca. 1910-1953. Part 2. Oregon and Washington. Amer. Entomol. 48: 178-185.
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