ABSTRACT
Effect of the dry leaves powder water suspension of the plant Furcraea selloa marginata, belonging to family Agavaceae and Bacillus thuringiensis kurstaki (Dipel-2x) was evaluated against non-infected and Schistosoma mansoni-infected Biomphalaria alexandrina snails as well as their efficacy against the free larval stages of S. mansoni. The obtained results indicated that the LC50 and LC90 values after 24 hrs exposure were 53.66 & 84.35 ppm for F. selloa marginata and 392.3 & 483.64 ppm for B. thuringiensis kurstaki against adult B. alexandrina snails, respectively. The plant F. selloa marginata and B. thuringiensis kurstaki have a larvicidal activity against S. mansoni larvae (miracidia and cercariae), the plant F. selloa marginata was more toxic against larvae than B. thuringiensis kurstaki, the miracidia were more sensitive towards the toxic action of the tested agents than cercariae and the mortality percent of miracidia and cercariae is directly proportional to the time and the tested concentrations. The results revealed that the tested sub-lethal concentrations (LCo, LC10 and LC25) reduced the survival, growth rates and egg laying capacity of both non-infected and S. mansoni-infected snails during 12 weeks of exposure in comparison with their control group. The hatchability percent of B. alexandrina eggs of one, three and six days old exposed to LCo, LC10, LC25, LC50 & LC90 concentrations of F. selloa marginata and B. thuringinesis kurstaki, significantly decreased by increasing their age and the tested concentrations. Exposing B. alexandrina snails to sub-lethal concentrations of the tested agents for 24 hours either pre-, during or post exposure of snails to S. mansoni miracidia caused a marked reduction in the infection rate and decreased the mean total number of shedding cercariae/snail. Also, elongated their prepatent period (cercarial incubation period) and shortened the duration of cercarial shedding in comparison with their control group. Under semi-field conditions the more time of exposure to the concentration (LC90= 84.35 ppm) of the plant F. selloa marginata the more mortality among snails. The mortality rates of the snails were 0%, 2%, 18% and 30% at 3, 6, 12 and 24 hrs post exposure, respectively.