A commercial sawmill in British Columbia, Canada, was surveyed in 1979 for the presence of the ambrosia beetles Trypodendron lineatum (Olivier) and Gnathotrichus retusus (LeConte) using pheromone-baited traps. The temporal and spatial distribution and relative abundance of these species were determined. This information was used during 1980 and 1981 to develop a mass-trapping program for these species while maintaining the integrity of an existing trapping program for a third ambrosia beetle species, G. sulcatus (LeConte). A fourth ambrosia beetle species, Platypus wilsoni (Swaine) responded in significantly larger numbers to traps baited with the pheromone sulcatol plus ethanol and α-pinene than to those baited with the pheromone lineatin or unbaited. Several experiments were conducted in order to improve or assess the trapping system. It was found that both G. retusus and T. lineatum response to their respective pheromones was increased by the inclusion of ethanol and α-pinene on the traps. T. lineatum response to lineatin was significantly reduced when sulcatol was included in the bait. An experiment conducted to determine optimum trap height showed that largest numbers of T. lineatum were caught on the lowest traps that cleared surrounding understory vegetation. A mark-recapture technique was tested as a potential means of assessing trapping efficiency. Recommendations were made that could result in this technique becoming a useful means of optimizing and evaluating ambrosia beetle mass-trapping programs. This concurrent mass-trapping program for three species of ambrosia beetles demonstrated that large numbers of beetles can be captured using pheromone-baited traps. The relatively low cost of this pest management tactic compared with the high values at risk has already resulted in much of the technology developed in this thesis being incorporated in ambrosia beetle management programs by forest industries in British Columbia. / Forestry, Faculty of / Graduate