Entomopathogenic bacteria Photorhabdus luminescens as natural enemy against the African migratory locust, Locusta migratoria migratorioides (Reiche & Fairmaire, 1849) (Orthoptera: Acrididae)

Abstract

Background: The African Migratory Locust, Locusta migratoria migratorioides (Reiche & Fairmaire, 1849) (Orthoptera: Acrididae), is a major threat to agricultural crops and food security on a worldwide scale; hence, maintaining control over it is crucial. Photorhabdus luminescens bacteria can accomplish the efficient biocontrol agent criteria. As a result, the aim of this study was to assess the efficacy of the P. luminescens (EGAP3) strain and its cell-free filtrate against L. migratoria migratorioides, as well as to investigate changes in the activity of carbohydrates hydrolyzing enzymes, amylase, invertase, and trehalase in whole-body homogenates of the 5th nymphal instar under laboratory conditions and to investigate the histopathological changes in the midgut of the locust. Results: The virulence of entomopathogenic bacteria was determined at different densities of 4 × 107, 4 × 106, 4 × 105, and 4 × 104 colony-forming units (CFU)/ml at different exposure times as well as different concentrations of its cell-free filtrate, undiluted cell-free filtrate (100, 50, 25, and 12.5%). The results indicated that higher-density cell suspension up to 4 × 107 cells.ml−1 and undiluted cell-free filtrate (100%) were the most effective insecticidal fluids, reaching up to 76.7 and 80%, respectively, after 7 days. The estimated LC50 value was 2.7 × 106 cells.ml−1 for bacteria, and the estimated LC50 value for cell-free filtrate was the 2nd dilution (50%). Conclusions: The data clarified the toxicological and histopathological effects and carbohydrate hydrolyzing enzyme activities of the host insect L. migratoria migratorioides, following bacteria and cell-free filtrate infection; that provides an overview of the efficiency of bacteria and their cell-free filtrate on the host. In conclusion, P. luminescens (EGAP3) and its toxins can be an optimal option for bio-controlling of L. migratoria migratorioides.