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Abstract Individual flies of Bactrocera tryoni (Froggatt) were observed on potted orange trees bearing zero, one or six fruit. Results showed that behaviour depended not only on fruit abundance, but also on the sex of the fly and whether the fly was cultured or wild. Female wild flies responded to higher fruit abundance by visiting more leaves and hence tended to scan trees more thoroughly. In addition, spending more time per leaf resulted in a significant trend to spend more time per tree with increasing abundance of fruit. Taken together, these responses would be expected to lead, in natural circumstances, to an increased probability of finding fruit and a tendency to accumulate in fruiting rather than non-fruiting trees. Male wild flies tended to spend longer in trees with fruit, but this was primarily due to them spending more time per leaf rather than visiting more leaves. This response in the natural environment would be expected to lead to the accumulation of males in the same kind of places that accumulated females. Neither sex of cultured flies responded differentially to trees with differing amounts of fruit. They visited leaves at a rate similar to that of wild flies of either sex that were in trees with no fruit. However, they tended to spend much longer per leaf, thus spending more time per tree than wild flies in any of the treatments. If released sterile flies (used in sterile insect technique) behaved in a similar manner, then they would not tend to accumulate preferentially in fruiting trees as wild flies are expected to do. The pertinence of these findings to fruit stripping and spot spraying is also discussed.