Abstract

Tomato is an economically important crop that is attacked by several pests, including the cotton whitefly, Bemisia tabaci (Genn.). B. tabaci causes direct and indirect damage to crops by piercing and sucking the plant foliage and transmitting viruses. In this study, we investigated the efficacy of individual and sequential treatments with a commercial formulation of the Beauveria bassiana, azadirachtin and imidacloprid against both eggs and nymphs of B. tabaci on tomato plants under laboratory and greenhouse conditions. Results of the leaf-dip bioassay, comparing the individual treatments, revealed that imidacloprid exhibited the highest toxicity (LC50= 151 and 153 mg/L) against the eggs and the 2nd nymphal instar, respectively, followed by azadirachtin and B. bassiana. The leaf spray bioassay results indicated that, B. bassiana alone caused 66.5% and 70 % mortality of eggs and the 2nd nymphal instar, respectively, while its toxicity was elevated in either sequential treatments [B. bassiana/imidacloprid] to 85.7% and 88.2%, or [imidacloprid/B. bassiana] to 90% and 80%, respectively. Concerning the greenhouse experiment, all treatments resulted in a significant reduction in the nymph and egg populations of B. tabaci at all period intervals after treatment. With the prolongation time, the residual effect of B. bassiana on eggs and nymph populations in the individual treatment decreased gradually to reach 8.5 and 2.52% mortality, respectively, day 15 after treatment, while it significantly increased when it was applied in sequences with both imidacloprid and azadirachtin treatments. These results emphasize the importance of integration between chemical and biological agents to improve control efficacy and achieve environmentally friendly requirements.