We observed behaviors and compiled activity budgets of adult Anoplophora glabripennis (Coleoptera: Cerambycidae) given a choice of different species of living trees as hosts in a greenhouse. Frequency of observation of beetles on different tree species provided a good overall indicator of host preference. Beetles were most often observed resting; they were least active early in the day and most active late in the day, but mating was observed with equal frequency during all 4-h time intervals between 0800 and 2400 h. Adults of both sexes were promiscuous, mating repeatedly and with different partners. Males engaged in mate guarding for periods of several hours or more to ensure paternity of the guarded female's progeny.