Elm Bark Beetles in Southwestern Ontario

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Abstract
The Dutch elm disease is caused by the fungus Ceratostomella ulmi (Schwartz) Buis. It was first reported in the United States at Cleveland, Ohio, in 1930 (ll), and has since spread westward to Colorado and northeastward into Vermont (22). It is believed that the disease was accidentally introduced into the United States from Europe, where it has caused heavy mortality of elms since its discovery in 1919 (7, 19, 20). In Canada the disease was first recorded by Pomerleau (14) at St. Ours, Que. This infection proved to be centred around Sorel, Que., and since it was isolated from the nearest known infection in the United States by approximately 200 miles, is regarded as a separate introduction from Europe. The Sorel infection spread very rapidly, and by the end of 1950, the area between Montreal, Quebec City, and Sherbrooke was heavily infested by the fungus (17). I t has since spread westward as far as Ottawa and Kingston in 0ntario (16).