The purpose of this work was to analyze the efÞcacy of Bacillus thuringiensis Berliner on the control of Phyllocnistis citrella Stainton (Lepidoptera: Phyllocnistidae) in laboratory and Þeld trials. In the laboratory, four B. thuringiensis were used: Dipel (commercial formulation) tested at the concentrations of 25 ϫ 10 6 and 25 ϫ 10 8 spores/ml and the isolates K, 6, and 15 (collections of the University of Azores) at the concentration of 25 ϫ 10 6 spores/ml. A surfactant solution of nonoxinol

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... also was tested with or without the different suspensions of B. thuringiensis. Leaves of Citrus sinensis (L.) Osbeck with second or third instars of leafminer larvae were used in all tests. Bacterial suspensions were applied topically on the surface of intact leaf mines or by injection inside the mine, near the head of the leafminer. When injecting both concentrations of Dipel into the mines, mortality of the leafminers increased compared with the topical application, although no signiÞcant differences were observed. The addition of the nonoxinol to the Dipel suspension, applied topically, increased the effect of B. thuringiensis, but differences were not signiÞcant. The mortality of the leafminers treated only with the nonoxinol solution increased signiÞcantly 48 h after treatment, compared with the control group, suggesting an insecticidal effect of this surfactant when used at a concentration of 0.01%. All the tested B. thuringiensis were equally active against the leafminer, either when applied topically or by mine injection. Field trials showed a signiÞcant difference between larval mortality of the control group and the results observed at the trees treated with B. thuringiensis 48 h after treatments.