The Effect of Sublethal Doses of the Molluscicide (N-tritylmorpholine) on the Development of Schistosoma mansoni in Biomphalaria glabrata (Say)

1. The effects of a sublethal concentration (0·0165 p.p.m.) of N-tritylmorpholine on the development of S. mansoni in B. glabrata are described. 2. A total of 160 snails were infected with S. mansoni and then divided into 4 groups. Each group was treated separately with N-tritylmorpholine for a period of 24 hours. 3. The first group was treated 10 days after infection (early prepatent stage); the second group 20 days after infection (late prepatent stage); the third group 42 days after infection (patent stage); and the fourth group was left untreated and kept as an infected but untreated control group. 4. Three groups of uninfected snails were treated simultaneously with the infected groups, and a fourth uninfected group was left untreated and maintained as an uninfected and untreated control group. 5. In the early and late prepatent groups treated with N-tritylmorpholine a relatively short incubation period was observed compared with those in the patent and untreated infected groups. 6. No significant difference was observed between the cercarial infection rates of the 4 infected groups of snails (x2 = 0·744; p > 0·5). 7. In all infected groups peak cercarial production was observed about 15–20 days after the emergence of cercariae was first noted, after which numbers declined. No significant difference was observed between the total cercarial production of the early prepatent, late prepatent or patent groups and that of the untreated infected control group (p > 0·4). 8. The mortality rate of snails in the patent group was significantly higher than in the corresponding uninfected control group (x2 = 6·04; p <0·02). 9. Treated infected snails in all three groups ultimately had a lower survival rate than did treated uninfected snails. 10. The survival rate of untreated infected snails while initially as good as that of the untreated and uninfected group, was ultimately much poorer.