Observations on the predation of the snail Huttonella bicolor on the snail Allopeas gracile

Abstract

The predatory snail Huttonella bicolor (Hutton 1834) (Gastropda: Streptaxidae) was encountered along with Allopeas gracile (Hutton 1834) (Gastropoda: Subulinidae) during a survey of small land snail species from several terrestrial habitats in Kolkata, India. An evaluation of the predation of H. bicolor as a function of prey size and predator density was carried out using A. gracile as a model prey snail. The predatory interactions were noted with an increasing ratio of 1, 2 and 4 H. bicolor against 10 A. gracile of varied size classes in a defined terrarium. At the end of a 48 h period of exposure, H. bicolor was observed to consume on an average 5.32 ± 0.50 snails depending on the size class and the predator density. The predation pattern varied significantly with the prey size class, as revealed through the logistic equation, y (prey-consumed) = 1 / (1 + exp (-(0.97–0.71*size class-prey))). In a separate experiment, it was observed that the presence of H. bicolor induced a reduction in the fecundity in A. gracile, as revealed through the logistic regression, y (egg laid) = 1 / (1 + exp(-(3.45–0.67*predator-density))). The direct effect of predation and indirect effect of oviposition reduction reflect the efficacy of H. bicolor on population regulation of A. gracile. In view of conservation biological control, the use of the snail H. bicolor as a biocontrol agent may prove beneficial in situations where A. gracile is a pest.