Effects of methoprene, a juvenile hormone (JH) analogue and JH-III, either injected or topically applied, were examined as they affected development of corpora allata and hypopharyngeal gland. Also studied was the α-glucosidase activity along with the behavior of worker honeybees, Apis mellifera L., primarily using the same sample bees. The development of corpora allata, which occurs during the first two weeks in intact bees, was inhibited in negative-feedback fashion by methoprene injection (0.1, 0.5, 1, 5 and 10 μg) in oil (0.5 μl) in each bee. The lowest dosage (0.1 μg) seemed to stimulate the development of the hypopharyngeal gland (the major source of bee milk), while higher dosages inhibited its normal development. Peak activity of α-glucosidase in the gland, which is normally observed in old foragers, was induced within one or two weeks by injection of 0.1 to 10 μg of methoprene. When methoprene-treated day-0 workers were introduced into a normal colony, guard bees and pollen-foragers appeared 7 and 5 days earlier than the case of untreated control, respectively. Therefore, JH is implicated in the physiological regulation responsible for the agelinked division of labor or polyethism.