Seasonal variation in molluscicidal activity of Solanum nigrum L.

Solanum nigrum L. leaves and fruits were shown to have molluscicidal activities against snails transmitting schistosomiasis and fascioliasis. In the present study, their molluscicidal activity against adult Biomphalaria alexandrina snails was assessed to determine whether plants collected at various seasons would have different degrees of toxicity. Leaves and fruits of three S. nigrum varieties were collected from Faiyoum and/or Giza during the four seasons. Leaves collected in autumn had the highest effect (LC50-35.4) followed by spring (LC50 = 44.36), summer (LC50 = 46.7) and winter (LC50 = 100.4). Toxicity of plant extracts was also affected by other seasonal dependent factors. These are the duration of plant exposure to direct sunlight and the size of the fruits. S. nigrum (black fruits) was more toxic (LC50 = 18.1) than the other two types, S. nigrum v. vellosum (yellow fruits) (LC50 = 38.9) and S. nigrum v. juidaicum (red fruits) (LC50 = 34.7).