Hylastes nigrinus (Coleoptera: Scolytidae) Pissodes fasciatus, and Steremnius carinatus (Coleoptera: Curculionidae) as vectors of black-stain root disease of Douglas-fir

This study demonstrates that Hylastes nigrinus annerheim) Pissodes fas-ciatus LeConte and Steremnius carinatus (Boheman) are vectors of Vertinciadiefla wage-nert Kendrick. the causal agent of black-stain root disease of Douglas-as, Pseudotsuga men-=tent (Mirbel) Franco. These insects, known associates of diseased hosts, wound and createsuitable infection courts in susceptible hosts, carry inoculum in the field, and transmit thepathogen to hosts under laboratory conditions. Root systems of 12-year-old Douglas-fir, cutduring precommercial thinning, were infested by these insects and were susceptible to V.wagerieri infection for at least 7 months, confirming that V. wagenert may be introducedto thinned stands via these hosts. Male and female H. nigrinus created wounds suitable asinfection courts on roots and root collars of crop trees for 1-2 years after precommercialthinning and may, therefore, introduce V. wagenert to thinned stands via these hosts. Insect-mediated transmission of V. wageneri to Douglas-fir by H. nigrinus in the field is docu-mented.
KEY WORDS Ceratocystis, disturbance, forests, conifer, epidemiology