SummaryInfestation of honeybee (Apis mellifera) brood and of adult workers by Tropilaelaps clareae and Varroa jacobsoni was investigated in colonies in north Vietnam. All brood combs were removed from six infested colonies, and worker bees and mites from these combs brushed on to one uninfected brood comb which was then placed in each colony. Ten and eleven days later, the age of brood infested by mites was determined; thus the length of the mites' stay outside the sealed brood cells could be directly established. The ratio of number of workers to number of brood infested by T. clareae was one-tenth of that for V. jacobsoni indicating that T. clareae mites remained outside sealed brood cells for only about one-tenth as long as V. jacobsoni or around 1–3 days compared with 13 days.Eighty % of cells infested by T. clareae were sealed within two to three days after the new comb was introduced, whereas 80% of cells infested by V. jacobsoni were sealed within eight days, supporting the conclusion that T. clare...