Screening and identification of Bacillus thuringiensis strains in Tunisia with high larvicidal toxicity against Ceratitis capitata Wiedemann (Diptera : tephritedae)

Bacillus thuringiensis is a unique bacterium in that it shares a common place with a number of chemical compounds which are used commercially to control insects important to agriculture and public health. This bacterium was recognized for its entomopathogenic activities related to Cry and Cyt proteins forming the δ-endotoxins and some extracellular activities like the vegetative insecticidal proteins (VIP) and Cry1I. These activities may act specifically against diverse organisms and some of them typically characterize each strain. The objective of the present work is to study the effect of toxins (delta-endotoxins), extracted from different strains of Bacillus thuringiensis on Ceratitis capitata, a devastating of citrus and fruit trees. Strains of B. thuringiensis were isolated from the mud of Sebket Sejoumi in Tunisia. The isolated strains were characterized by morphological (macroscopic and microscopy) and biochemical (SDS-PAGE 10%). From soil samples collected in the mud of Sebket Sejoumi in Tunisia, 284 bacterial colonies were obtained, 70 (24.64%) of which were identified as B. thuringiensis . Among 70 selected strains, 15 showed a significant insecticidal activity in which 5 isolates led to mortality rates ≥ 90%. These mortality rates are caused by endotoxins of B. thuringiensis . The isolates of B. thuringiensis from soil constitute potential new means of biological control for C. capitata , because of their larvicidal activity and the possibility that they may also contain new combinations of toxins. The preliminary results of this study encourage us towards the characterization of the insecticidal activity produced by B. thuringiensis strains for large scale application.