Ecologia e dinâmica populacional de Biomphalaria tenagophila (Orbigny, 1835) (Mollusca, Gastropoda) em cultura de agrião (Nasturtium officinale) no Alto da Boa Vista, Rio de Janeiro

Abstract

Irrigated cultures of sugar cane, rice and water cress play an important role in the transmission of schistosomiasis in south-east Brazil. However, little is known about the ecological interactions of the vector snails of schistosomiasis in these modified lotic environments, and especially about the biology of Biomphalaria tenagophila. This work was done in a water cress garden in Alto da Boa Vista, an isolated focus of schistosomiasis in the city of Rio de Janeiro. The investigation was carried out in three steps. The first step involved collecting B. tenagophila in the field and determining its relative populational density. The results show that this parameter may be plotted on a graph as a logistic growth curve with a sigmoid shape, with a decrease in the beginning of the rainy season. At the end of the same season the population is formed mainly by adults (92,8% in March, 1985 and 82,9% in April, 1986). ln the second step the key ecological factors determining the establishment of B. tenagophila in the study area were assessed through a comparative analysis of measurements done in colonized patches and in those patches where it does not occur. ln this analysis hydrological parameters, physico-chemistry of the water, type of sediment and biomass of aquatic plants were considered. The third step of the investigation involved an environmental manipulation aímíng to control the B. tenagophila population in the watercress garden. This manipulation was based on previous results dealing with the effects of environmental factors on the population dynamics of B. Tenagophila. It may be concluded that successful snail control in irrigated areas should involve a wider understanding of the utilization of multiple and combined manipulations in the habitat.