The molluscicidal activity of Commiphora molmol (myrrh) water suspension showed that Bulinus truncatus snails were found to be about 3 times more susceptible than Biomphalaria alexandrina snails. The 24-hour LC50 values recorded were 46.4 and 145.8 ppm, respectively. There was a significant negative correlation between LC values and exposure periods. The present study is yet the first attempt to investigate the toxicity of C. molmol aquous suspension (in vitro) against non-target aquatic organisms coexisting with vector snails in their habitat. The obtained results revealed that the plant water suspension was more toxic at the molluscicidal levels to the crustaceans Daphnia sp, Cypris sp, Cyclops sp. , Cardina nilotica and the fish Gambuzia affinis at a concentration of 50 ppm (in average) after 48 hr of exposure. Culex larvae were more tolerant to the plant suspension than other organisms. Chronic effects of sublethal concentrations of C. molmol water suspension on some biological parameters of B. truncatus snails showed a significant decrease in food consumption and egg production of snails. At the sublethal concentration of LC50, no hatching was observed after 17 days of exposure. After 24 hour of exposure to C. molmol water suspension 70% mortality of newly hatched snails (3-days old) was observed at 50 ppm. In addition, biochemical investigation showed significant differences as compared to the control regarding the total protein content, and the activity of transaminases (AST, ALT) and Lactate dehydrogenase (LD) except a mild decrease in glycogen concentration and alkaline phosphatase activity in digestive gland tissue of snails. Ultrastuctural investigation of exposed snails to C. molmol water suspension showed some alterations in the digestive gland of snails (i.e. marked vaculation, increased lysosomal activity, swollen mitochondria and consumption of stored lipid and glycogen). Based on the toxicity of C. molmol to the aquatic ecosystem at the examined sublethal levels, it is not recommended as a herbal molluscicide.
Key words: Commiphora molmol (myrrh), water suspen-sion, vector snails, molluscicidal activity, Toxicity, non-target aquatic organisms