This paper describes a successful attempt to tag adult females of the European pine shoot, Rhyacionia buoliuna (Schiff.) with Co60, chosen as a tagging agent because it is a gamma emitter with a sufficiently long half-life (5.3 years). Emphasis is placed on the preparation and application of the tracer material, the absence of immediately harmful effects of radiation on the insects, and the ability of the insects to behave normally with the tags in place. This work was undertaken in order so develop techniques for following the movements of large numbers of these insects.