The susceptibility of Biomphalaria glabrata throughout its life-history to N-tritylmorpholine.

This study was undertaken as part of a detailed investigation of the molluscicidal properties of N-tritylmorpholine (Frescon, WL 8008). It is shown that the stage of development of Biomphalaria glabrata has a pronounced influence on its susceptibility to N-tritylmorpholine. As the snails grow from hatching to a diameter of 3 mm, the LC(50) falls from 0.04 ppm to 0.02 ppm, but further growth results in a progressive increase in LC(50) until, at a shell diameter of 20 mm, it is 0.17 ppm. N-Tritylmorpholine is much less toxic to snail eggs when used in short exposures. However, young embryos in capsules treated with 5 ppm for 24 hours developed abnormally and died without hatching. Older embryos developed normally but died after hatching. This delayed effect is attributed to contact, during hatching, with N-tritylmorpholine which is associated with the jelly. The difference in susceptibility between snails and eggs is attributed to a slow rate of penetration of the egg membrane.