A Comparative Study on the Food-Locating Ability of Helisoma duryi, Biomphalaria camerunensis and Bulinus truncatus (Pulmonata: Planorbidae)

Abstract

1. Helisoma duryi, a planorbid snail has been suggested as a biological control agent against the snail intermediate hosts of schistosomes, Biomphalaria and Bulinus species. It has been demonstrated that competition for food resources is involved. The aim of this paper is to compare the ability of these species to locate food sources. 2. The paper compares the accumulation of groups of Helisoma duryi, Biomphalaria camerunensis and Bulinus truncatus on varying amounts of two different artificial food preparations and the movement of individual snails of these three species when approaching a food source by analysing their tracks. 3. There were slight differences in the ability of H. duryi and B. camerunensis to locate food preparations, but both were superior to B. truncatus. The two types of food preparations differed markedly in their attraction of B. truncatus. H. duryi was less attracted to the food preparations with the two lowest amounts of food of both types than to preparations with larger amounts of food, while this was not observed for B. camerunensis and B. truncatus. Medium-sized H. duryi were superior to small and large snails in their ability to locate food, while no significant differences were found among three size groups of B. truncatus. 4. Analysis of snail tracks did not reveal an increased frequency of turning in any of the three species as the food source was approached. The reason for the higher accumulation of H. duryi and B. camerunensis on the food could in part be explained by their higher activity level. Other explanations are also discussed.