Life-history parameters and the fitness of tephritid flies are closely linked to diet. Studies of locomotor behaviour can provide insights to these links, although little is known about how locomotor behaviour is influenced by diet. In the present study, video recordings of Queensland fruit flies Bactrocera tryoni Froggatt (Diptera: Tephritidae) ('Q-flies') that are maintained individually in cages are used to determine how diet affects the activity patterns (flight, walking, grooming, inactivity) of males and females at ages ranging from 4 to 30days. The frequency and total duration of activities over 10-min trials are affected by diet, age and sex. Supplementation of diet with hydrolysed yeast results in a higher frequency and duration of flight in flies of all ages and both sexes. The effect of diet on other activities varies with age. Q-flies fed sugar only increase walking frequency steadily from 4 to 30days post-eclosion, whereas flies fed sugar+yeast have higher walking frequencies at 4 and 10days than flies fed sugar only, although they then exhibit a sharp decline at 30days post-eclosion. The frequency and duration of inactivity remain consistent in flies fed sugar+yeast, whereas flies fed sugar only exhibit a marked increase in inactivity from 4 to 30days post-eclosion. Compared with older flies, 4day-old Q-flies fed sugar only spend considerably more time grooming. The potential of activity monitoring as a quality control test for flies that are mass-reared for use in sterile insect technique programmes is discussed.