Potential exploitation of Bacillus flexus biofilm against the cowpea weevil, Callosobruchus maculatus (F.) (Coleoptera: Bruchidae)

Abstract

The present study aimed to investigate new insecticidal compounds used as environmentally safe alternative to synthetic insecticides. A laboratory study was conducted to investigate the effects of Bacillus biofilms and their extracellular matrix (ECM) on the adult’s mortality and reproduction of the cowpea weevil, Callosobruchus maculatus (F.) (Coleoptera: Bruchidae). Among 30 bacterial isolates, only 4 exhibited high abilities to form biofilm and showed potentials against the pest at different concentrations 5, 10 and 20%. Results showed that the mortality percentage of C. maculatus adults ranged between 13.36 and 63.43% overall and it increased significantly with raising the concentration of ECMs. While the latent larval mortality did not exceed 31.42%, which was recorded with ECM of isolate no. 13 at the highest concentration (20%). Further, all tested concentrations reduced female fecundity and egg hatchability. The most potent biofilm-producing isolate having the highest adverse activity of ECM extract was identified as Bacillus flexus S13, using 16S rDNA gene sequence and submitted in GenBank under accession number MK292147. These results demonstrated that B. flexus S13 biofilm is a good strategy for the development of new biocontrol agents against C. maculatus.