Eggs of Oncomelania formosana were isolated from petri dishes used as laying chambers by daily inspection and were placed in various dilutions of experimental molluscicide solutions (EMS) or controls of spring water. The sulfonated hydrocarbon Tide in 1:1,000 dilution continuously applied, destroyed all eggs while 1:10,000 caused 90% mortality. Copper sulfate 1:100,000 prevented most eggs from hatching while sodium pentachlorophenate 1:2,000,000 continously applied prevented 90% hatching.
All molluscicides were more effective when applied for seven days or continuously than when applied for a day only.
Eggs left undisturbed and exposed to the molluscicides were found much more resistant to sulfonated hydrocarbon and sodium pentachlorophenate but not to copper sulfate. Increased concentration of the molluscicides erased this differential thought to be caused by the relative sizes of the molecules.