Distribution and survival of overwintering adults of the Dutch elm disease vector, Hylurgopinus rufipes (Coleoptera: Scolytidae), in American elm trees in Manitoba

Abstract 1 The native elm bark beetle, Hylurgopinus rufipes, is the principal vector of Dutch elm disease in Manitoba, Saskatchewan and North Dakota, and disease management measures include applying residual insecticides to the lower part of elm tree trunks where the adult beetles overwinter. 2 In American elm trees in southern Manitoba, we counted entrance holes produced by beetles then felled and dissected trees to determine numbers of tunnels and numbers and survival of overwintering beetles. 3 Densities of entrance holes, tunnels and beetles followed a logistic relationship with tree trunk diameter; densities were near zero at diameters < 10 cm and reached a site‐specific asymptote at diameters > 20 cm. 4 Asymptotic densities of holes, tunnels and beetles in samples from 55 to 190 cm above the ground were, respectively, 22%, 22% and 0.7% of those within 25 cm of the ground. 5 Within the height range 0–190 cm, the proportion of living beetles declined steeply with increasing height. 6 Average density of holes at height 0–25 cm estimated from a sample of several trees of diameter ≥15 cm could be used to predict the asymptotic maximum density of overwintering beetles in the site; predictions of beetle densities for individual trees were not reliable.