The phenology of flight and walking movements ofLeptinotarsa decemlineata(Say) adults was studied in a potato field in western Massachusetts using windowpane and pitfall traps. There were two periods of flight activity concurrent with postdiapause and appearance of first-generation adults in the field, and three periods of walking activity concurrent with postdiapause and appearance of first- and second-generation adults. Second-generation adults did not fly. We observed three distinct flight behaviors: local flight in and around the study field, long-distance flight that removed the beetle from the habitat, and diapause flight to nearby woods. Use of rubidium chloride as a marking agent allowed us to determine the origin of adults collected in the windowpane traps. The traps detected mostly local flight activity and were inefficient at monitoring migratory flights. A study in which first-generation adults were netted while they initiated long-distance flight on 24 July and 11 August 1987 revealed two distinct flight behaviors: the first group fed and oviposited after being captured and the second group did not feed or oviposit but entered diapause. We suggest that adults that emerge in July engage in aseasonal migration, which is a regular part of their life cycle, whereas adults that emerge later exhibit diapause-mediated seasonal migration, which is in response to diapause-inducing conditions.