Effects of fruit abundance within a tree canopy on the behaviour of wild and cultured Queensland fruit flies, Bactrocera tryoni (Froggatt) (Diptera :Tephritidae)

Individual flies of Bactrocera tryoni (Froggatt) were observed on potted or ange trees bearing zero, one or six fruit. Results showed that behaviour de pended not only on fruit abundance, but also on the sex of the fly and whet her the fly was cultured or wild. Female wild flies responded to higher fru it abundance by visiting more leaves and hence tended to scan trees more th oroughly. In addition, spending more time pet leaf resulted in a significan t trend to spend more time per tree with increasing abundance of fruit. Tak en together, these responses would be expected to lead, in natural circumst ances, to an increased probability of finding fruit and a tendency to accum ulate 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 spend ing more time pel leaf rather than visiting more leaves. This response in t he natural environment would be expected to lead to the accumulation of mal es in the same kind of places that accumulated females. Neither sex of cult ured flies responded differentially to trees with differing amounts of frui t. They visited leaves at a rate similar to that of wild flies of either se x that were in tries with no fruit. However, they tended to spend much long er pet leaf, thus spending more time per tree than wild flies in any of the treatments. If released sterile flies (used in sterile insect technique) b ehaved in a similar manner, then they would not tend to accumulate preferen tially in fruiting trees as wild flies are expected to do. The pertinence o f these findings to fruit stripping and spot spraying is also discussed.