Witcosky, J. J.; Schowalter, T. D.; Hansen, E. M. 1986. The influence of time of precommercial thinning on the colonization of Douglas-fir by three species of root-colonizing insects. Canadian Journal of Forest Research. 16(4): 745-749.
In plantations of Douglas-fir (Pseudorsuga menziesii (Mirb.) Franco) in western Oregon, precommercial thinning resulted insignificantly increased abundances of insect vectors of black-stain root disease. Hylastes nigrinus (Mann.), Pissodes fasciatusLeC., and Steremnius carinatus (Boh.) were monitored for 2 years (1983 and 1984) in unthinned plots and in plots thinned inSeptember 1982, January 1983, or May 1983. Abundances of these beetle species were significantly higher in thinned plots,relative to unthinned plots. However, the numbers of H. nigrinus and P. fasciatus caught by unbaited traps in plots thinned inMay was reduced relative to plots thinned in September or January. These results suggest that time of thinning can be manipulatedto reduce the activity of these vectors in plantations that are mechanically thinned.