Efficiency and Midgut Histopathological Effect of the Newly Isolated Bacillus thuringiensis KS δ-Endotoxins on the Emergent Pest Tuta absoluta

Tuta absoluta (Povolny, 1994) is a devastating moth to the Solanaceae plants. It is a challenging pest to control, especially on tomatoes. In this work, we studied the entomopathogenic activity of the Cry-forming delta-endotoxins produced by Bacillus thuringiensis strain KS and B. thuringiensis kurstaki reference strain HD1 against T. absoluta. These strains carried the cry2, cry1Ab, cry1Aa / cry1Ac, and cry1I genes, and KS also carried a cry1C gene. The delta-endotoxins of KS were approximately twofold more toxic against the third instar larvae than those of HD1, as they showed lower 50% and 90% lethal concentrations (0.80 and 2.70 mu g/cm(2) (delta-endotoxins/tomato leaf)) compared with those of HD1 (1.70 and 4.50 mu g/cm(2)) (p < 0.05). Additionally, the larvae protease extract showed at least six caseinolytic activities, which activated the KS and HD1 delta-endotoxins, yielding the active toxins of about 65 kDa and the protease-resistant core of about 58 kDa. Moreover, the histopathological effects of KS and HD1 delta-endotoxins on the larvae midgut consisted of an apical columnar cell vacuolization, microvillus damage, and epithelial cell disruption. These results showed that the KS strain could be a candidate for T. absoluta control.