Scolytid Vectors of the Dutch Elm Disease in Ontario

Extract

Although many possible vectors of the Dutch elm disease, Ceratocystis ulmi (Buism.) C. Moreau, have been listed by Collins et al. (1936) and others, only two, Scolytus multistriatus (Marsh.), the European elm bark beetle, and Hylurgopinus rufipes (Eichh.), the native elm bark beetle, are known to transmit the disease with any regularity. In this capacity alone thcse two species of beetles are important pests of elm. The persistent spread of the Dutch elm disease in southern Ontario (Hord and Quirke, 1955) made it imperative that adequate surveys be maintained to indicate yearly changes in the occurrence of the introduced vector, and to ascertain more precisely the distribution of the native vector relative to the distribution of elm in Ontario. Consequently the Forest Insect Survey of the Forest Insect Laboratory, Sault Ste. Marie, intensified its elm bark beetle program in 1956, and from then to 1959, 138 positive samples of these two scolytid beetles have been received. An analvsis of these records and their relationihip to the current incidence of the Dutch elm disease in Ontario are presented in this paper.