SUMMARY
Warble fly larvae (Oedemagena tarandi) occurred in 97-100% of barren-ground caribou (R.t. groen-landicus) sampled in March from the Beverly herd. In December, they occurred in 98% of males and 75% of females. Larvae numbers increased up to several-fold from December to March. Within age classes, males generally were more heavily infected than females. Annual differences were small. Larvae occurred in 14 and 26% of two populations of Peary caribou (Rangifer tarandus pearyi) on the Canadian Arctic Islands. In them, incidences of larvae were unrelated to sex or age. Greater than average numbers of larvae in barren-ground caribou sometimes were associated with females in relatively poor condition and therefore less fecund. These results are discussed in relation to current hypotheses of the factors that affect warble infections.