The flight capacity (duration and velocity) is an important phase of the flight behaviour of economically significant insects such as the Douglas-fir beetle, because it influences the feasibility of control or preventive measures which might be considered. An understanding of the flight capacity and how it varies in relation to environmental factors is necessary to evaluate the beetles' power of dispersal under different seasonal conditions. This would help to detect new areas of infestation by directing or narrowing the search. It also would help evaluation of the hazard at hand in timber surrounding the infestation and be a further aid in determining the size of areas of sanitation required around the comparatively beetle-free areas needed for special purposes, such as parks.