Biochemical and Molecular Identification of a Native Bacillus thuringiensis gv. cytolyticus Isolate with Insecticidal Effect Against the Pod Borer Larvae (Helicoverpa armigera)

Abstract

The aim of this study is to isolate and identify autochthonous bacterial strains with insecticidal effect against the larvae of the tomato  moth Helicoverpa armigera. Dead and diseased larvae were collected from chili plots in the region of Gotraniya from the governorate of  Kairouan, Tunisia. These larvae were used to isolate eight bacterial strains named Hr1 to Hr8. The bacterial isolates were characterized by macroscopic and microscopic observations and 16S rRNA sequencing. Hr1, Hr2, Hr4, Hr5, Hr6, and Hr8 were identified as Bacillus spp.,  Hr3 as Staphylococcussp., and Hr7 as Enterobacter sp. Their insecticidal activity was evaluated against third-instar larvae of H. armigera. A  Hr1 bacterial isolate showed an insecticidal effect against H. armigera larvae, causing 60% larval mortality four days post-treatment at  a dose of 1.8 × 10⁹ CFU/ml. Based on further characterization studies, Hr1 was identified as Bacillus thuringiensis gv. cytolyticus following  Biolog biochemical tests and multi-locus sequence analyses studies based on sequencing of seven housekeeping genes.