Oviposition responses of Queensland fruit fly (Bactrocera tryoni) to mineral oil deposits on tomato fruit

Behavioural responses of wild and laboratory-culture females of Queensland fruit fly, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae), to mineral oil deposits on tomato fruit dipped in aqueous oil emulsions were assessed in a no-choice test and three choice tests. The oils were two commercial products used to manage plant pests and diseases, Ampol D-C-Tron NR and SK EnSpray 99, one distillation fraction of the base oil of the former, and four distillation fractions of the base oil of the latter. The initial and final boiling points of the fractions were equivalent to those of n-alkanes with chain lengths of C20-22 (Ampol), and C21-C23, C22-23.5, C22-24, and C22-24.5 (SK). For both fly types in the no-choice test, numbers of punctures and eggs per fruit declined strongly as concentrations of the nC20-22 Ampol fraction in emulsions rose from 0.25 to 2% (vol/vol). Fly type affected the extent of responses but there was no significant interaction for fly type*oil concentration. Responses of laboratory-culture females in the choice tests also declined as concentrations of SK and the four fractions of its base oil in emulsions rose from 0 to 0.25%. The SK nC22-24 and nC22-24.5 fractions had least impact. Responses of laboratory-culture flies to 0.5% emulsions of the nC20-22 Ampol fraction and the nC21-23 SK fraction in choice tests were not significantly different. Likewise, responses of laboratory-culture flies to 0.5% emulsions of the two commercial products were not significantly different. Emulsifier type did not affect numbers of punctures or eggs per fruit in choice responses of laboratory-culture flies to 0.5% emulsions of the Ampol nC20-22 fraction or 0.5% emulsions of the SK nC21-23 fraction. If the equivalence of no-choice and choice responses in the laboratory were to hold in the field, then unsprayed sacrificial' plants would not be necessary and oil emulsions could be used as cover sprays.