Influence of gibberellic acid (GA3) on susceptibility of citrus fruits to infestation by Bactrocera zonata was studied under field conditions. The susceptibility of navel orange and mandarin fruits to infestation by PFF was affected firstly by GA3 treatments in a dose-dependent manner and secondly by host type. GA3 treatment was more effective on mandarin than navel orange in terms of rate of false punctures and egg-laying density, whereas it showed more effect on the true puncture numbers of navel oranges than mandarins. The results also showed that fruit infestation parameters were inversely proportional to fruit peel hardness. Fruit peel hardness was GA3 dose-dependent, with significant differences between host types, as well as among GA3 concentrations, with higher values on navel orange than mandarin. Results also revealed that date (progress of fruit age) had a weak effect on both infestation parameters by PFF, and fruit peel hardness. The study provides clear evidence that exogenous application of GA3 could be incorporated in IPM programmes for citrus to decrease the infestation rates by PFF.
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Vol. 28 • No. 1