Molluscicidal potential of Bacillus thuringiensis and endogenous bacteria against Theba pisana

Abstract

In an agricultural context where the chemical control of pest gastropods is showing its limits, due to the environmental impact of molluscicides and the emergence of resistance, this study explored sustainable biological alternatives. The objective was to identify and characterize the molluscicidal potential of bacterial strains against two major pests in Morocco, Theba pisana and Helix aspersa. The methodology was based on the isolation of bacterial strains from snail cadavers, followed by laboratory bioassays to evaluate their efficacy in comparison with a commercial strain, Bacillus thuringiensis var. kurstaki (BT). Virulence was quantified by measuring mortality rates and calculating the median lethal dose (LD50). Potential mechanisms of action were investigated by analyzing the activity of key enzymes (proteases, chitinases, lipases). The results revealed a remarkable efficacy of the BT strain against Theba pisana, causing 100% mortality within 21 days, with a calculated LD50 of 1.5×10⁸ CFU/ml. The endogenous strains, identified as Pseudomonas iridis (B9) and Enterobacter aerogenes (B3), showed more moderate efficacy against the same snail. Regarding Helix aspersa, only the BT strain demonstrated lethal activity, although it was limited (34% mortality). The investigation of the mechanisms of action highlighted distinct enzymatic profiles: high protease activity for BT, a pronounced chitinase activity for E. aerogenes, and significant protease activity for P. iridis. Although promising, these laboratory results do not guarantee success in field conditions, where environmental factors such as temperature, humidity, and UV radiation can affect bacterial viability. It is therefore imperative to validate their efficacy in the field, develop protective formulations, and conduct safety studies before integrating these agents into sustainable control strategies.

Keywords: Biological control, Theba pisana, Helix aspersa, Bacillus thuringiensis, Pseudomonas iridis, Enterobacter aerogenes, Enzymatic activity