Biocontrol potential of some bacterial and fungal isolates against the terrestrial snail, Monacha obstructa, evaluating their laboratory and field efficiency

Abstract

Abstract Background The land snail Monacha obstructa, commonly known as the glassy clover snail, poses a significant threat to crops, causing substantial damage in agriculture and horticulture. It particularly thrives in regions of Egypt, where it can reproduce rapidly, leading to substantial population increases and consequent damage. This study aimed to perform laboratory experiments and field trials to assess the effectiveness of bacterial (Bacillus thuringiensis) and fungal (Metarhizium anisopliae and Trichoderma harzianum) isolates, as well as methomyl, a carbamate compound approved by the Ministry of Agriculture in Egypt against the terrestrial snails. Various methods including contact and leaf dipping as well as baiting techniques were applied under both laboratory and field conditions, using spray and baiting techniques. Results Bacillus thuringiensis (Bt) and M. anisopliae isolates showed the most effective results outcomes in comparison with methomyl against M. obstructa. Out of all the application approaches tested, the residual film (contact) technique of these microorganisms proved to be the most potent, with LC50 values of 6.49 × 106 cells/ml Bt (after 14 days), 1.24 × 108 and 1.49 × 108 spores/ml (M. anisopliae, T. harzianum, respectively), after 21 days and 620 ppm, for methomyl after 7 days of treatments. Besides, the findings demonstrated that Bt exhibited the highest success rate in decreasing the number of snails in the field. It was also observed that pathological symptoms increased as the duration of exposure increased, and the snails ceased to feed and showed a noticeable decline in their activity. A slimy, almost tan-like substance coated the exterior of their shells for Bt, and part of the soft body came out of the shell for M. anisopliae. In the case of T. harzianum, fungus hypha growth took on a white color formed inside the shell, and in addition, a black substance formed on the mouth of the shell. Conclusions The gathered data revealed that Bt and M. anisopliae effectively combatted the terrestrial snail, making them viable options in integrated pest control as substitutes for pesticides.