Behavioural responses of Biomphalaria glabrata(Say) to chemical factors from aquatic macrophytes including decaying Lemna paucicostata(Hegelm ex Engelm)

SUMMARY. 1. The behavioural responses of the freshwater pulmonate snail Biomphalaria glabrata to homogenates of various aquatic macrophytes were investigated with the aid of diffusion olfactometers.
2. Of the eleven species studied, three lacked any attractants or arrestants, two contained weak arrestants, and three induced strong repellent effects. Only two, Apium nodiflorum and Lemna paucicostata , induced significant attractant and arrestant effects comparable to those obtained with lettuce (Lactuca sativa) controls.
3. Decaying Lemna paucicostata homogenate proved to be a significantly stronger attractant and arrestant than fresh homogenate. Evidence is given that these effects are mainly due to low molecular weight compounds (<1000 mol. wt) of which the major end products of microbial decomposition, short chain carboxylic acids (C₂-C₅), are likely to be the most important. However, as carboxylic acids account for only a fraction of the total response, other low and high molecular weight compounds are also implicated.
4. The ecological relevance of these results is discussed with particular reference to the hypothesis that the relationship between the snails and macrophytes is essentially mutualistic.