Cercaricidal activity of phenylheptatriyne and α-terthienyl, naturally occurring compounds in species of Asteraceae (Compositae)

Abstract

The susceptibility of some digenetic trematode cercariae to the polyacetylene phenylheptatriyne (PHT), from leaves of Bidens pilosa L. (Compositae), and the thiophene α-terthienyl (α-t), from roots of Tagetes patula L. (Compositae), with and without ultraviolet (UV) activation, was examined. In darkness the lethal concentration for 100% (LC100) for both substances was 0.3 ppm. Under UV irradiation of 300–400 nm and incident intensity of 6 W/m2, the LC100 for PHT was not markedly lowered, but for α -t it was reduced by a factor of 30 (to 0.01 ppm). A cercaricidally effective aqueous infusion (1:1000) of Tagetes roots protected the snail hosts Physa occidentalis Tyron (Physidae) from bacterially complicated death but did not reduce cercarial production or predispose the emerging cercariae to subsequent UV injury.