Molluscicidal activity, effects on mucus secretion, and joint actions of Brassica rapa and Salvia officinalis extracts with metaldehyde against Monacha obstructa

Abstract Turnip seed ( Brassica rapa ) and sage leaf ( Salvia officinalis ) extracts were prepared by macerating plant materials in 80% methanol at a ratio of 1:10 (w/v) for five days. The molluscicidal activity of the tested plant extracts and metaldehyde was evaluated against Monacha obstructa (Pfeiffer) using the contact method over 72 h under laboratory conditions. Five concentrations of each tested compound were prepared and screened against the target snails. The effects of the tested plant extracts and metaldehyde on mucus secretion were determined. The joint action of LC 25 concentrations of both tested plant extracts, individually and in combination with metaldehyde, was investigated under laboratory conditions. This approach aimed to evaluate the interaction between combined treatments and determine their effects on mortality responses under laboratory conditions. The results revealed that S. officinalis leaf extract exhibited a higher molluscicidal activity against M. obstructa compared to B. rapa seed extract, whereas metaldehyde displayed the strongest toxicological effect among treatments. The LC 50 values of B. rapa , S. officinalis extracts and metaldehyde were 183.43, 41.50, and 18.66 ppm, respectively. Moreover, exposure of M. obstructa to both tested plant extracts and metaldehyde significantly increased mucus secretion compared with the untreated control, suggesting a physiological stress response associated with chemical exposure. The data of joint action trials emphasized that mixing treatments at LC 25 concentrations did not increase molluscicidal activity and exhibited antagonistic interactions according to the Co-toxicity Factor (CTF) classification. The results established a significant toxicity of all tested treatments. Metaldehyde exhibited the highest toxicity, followed by S. officinalis and B. rapa . The tested extracts affected mucus secretion in treated snails, indicating additional physiological responses associated with their molluscicidal activity. Combined treatments did not improve molluscicidal efficacy and caused antagonistic interactions according to the CTF classification. The present study indicates that the investigated plant extracts, especially S. officinalis , show promising molluscicidal potential under laboratory conditions and warrant further evaluation under field conditions and environmental safety assessments.