In studies of the behaviour of adults of the white pine weevil, it has been reported by Sullivan (1953) that the movenients of the beetles can be traced over long periods of time by means of Co60 tags attached to the elytra. Observations of the labelled insects over several months were feasible because of the long half-life and high specific activity of this isotope. Tags containing approximately 200 to 500 μc of radioactive cobalt did not have any appreciable effect on the survival of the insects over periods of one to two months, but records of the longevity of labelled insects revealed excessive mortality after several months. As field trials had indicated that the amount of isotope in the tags was in excess of that required for accurate detection of the insects, the work was continued in an effort to determine the effects of different quantities of the isotope on short-, and long-term survival.