Population dynamics of intermediate snail hosts of Fasciola hepatica and some environmental factors in San Juan y Martinez municipality, Cuba

The variation of abundances of intermediate snail hosts of Fasciola hepatica in Cuba (Fossaria cubensis and Pseudosuccinea columella) was studied during one year under natural conditions at five sampling sites in San Juan y Martinez municipality, Pinar del Rio province, Cuba. The effect of some environmental variables on the lymnaeid abundances was also studied. A canonical correspondence analysis showed that both species do not generally occur together in the same habitat and that most factors affect them in an opposite fashion, although both of them correlate positively through time to the diversity of the habitats. F. cubensis prefers the sites that are in or closer to the city whereas P. columella is more abundant in rural sites. Lymnaeid abundances are mainly affected by nitrite and nitrate concentrations as well as by the abundance of the thiarid Tarebia granifera. F. cubensis is more abundant in polluted habitats with low densities (or absence) of T. granifera whereas P. columella prefers cleaner habitats and can coexist with the thiarid, even at its higher densities. The implications of divergent preferences of the two lymnaeids for the control of fasciolosis are discussed.

The effect of isolation on reproduction and growth of Pseudosuccinea columella (Pulmonata: Lymnaeidae): a snail-conditioned water experiment

A snail-conditioned water experiment was conducted in Pseudosuccinea columella to test the possible role of a chemical interaction between snails on the diminished growth and fecundity rates found for snails raised in pairs compared to those raised in complete isolation. The results permit to discard the hypothesis of an inhibition of growth and reproduction between snails due to factors released into the water

The effect of isolation on the life-history traits of Pseudosuccinea columella (Pulmonata: Lymnaeidae)

A population of Pseudosuccinea columella was raised under laboratory conditions and its life tables were determined in isolated and paired snails. Isolated snails were significantly larger in shell size than paired snails from five weeks of age onward. Also, statistically significant differences were found for the number of eggs per mass per individual from week 5 to 9, isolated snails exhibiting the highest values. The intrinsic and finite rates of increase were greater in isolated than in paired snails. Either an inhibition of the reproductive output between individuals or the advantage of selfing may be the cause of the differences in this species, acting as a possible mechanism that increase the fitness of isolated snails

Life-history traits of Fossaria cubensis (Gastropoda: Lymnaeidae) under experimental exposure to Fasciola hepatica (Trematoda: Digenea)

The effect of exposing the lymnaeid snail Fossaria cubensis to the trematode Fasciola hepatica on the snail population's life-history traits was studied under laboratory conditions. Exposed individuals showed a lower survival rate than control snails, although from week 7 onward a slower decrease of this parameter in relation to the control group was observed. There were higher values of fecundity rate for the controls compared to the exposed group except during weeks 9, 10, 11 and 12, which was the time that followed the period when almost all of the infected snails died. Both the intrinsic and finite rates of natural increase were significantly higher for the control group, but exposed snails still attained a lower mean generation time. Age-specific trade-offs were found, mainly for the weekly increase in size versus the number of eggs per mass, the weekly increase in size versus the number of viable eggs per mass, the number of masses versus the hatching probability and the number of eggs versus the hatching probability. All these negative associations were significant for juveniles of both control and exposed snails and not for adults; however, exposed young individuals exhibited much higher values of the correlation coefficient than control animals.

Evaluación de la acción molusquicida de agave legrelliana sobre fossaria cubensis (mollusca: lymnaeidae), principal vector de fascioliasis en Cuba / Evaluation of the molluscicidal action of agave legrelliana on fossaria cubensis (mollusca: lymnaeidae) main vector of fascioliasis in Cuba

Se determinaron las dosis letales LD 50 y LD 90 del jugo extraído de las hojas de Agae legrelliana (Agavacea) sobre Fossaria cubensis, en condiciones de laboratorio, alcanzando los valores de 0,105 y 7.178 ml/l respectivamente. Aplicando estos valores se comprobó que éstas provocan una disminución notable en la frecuencia cardíaca de los moluscos

Comparación del crecimiento de Helisoma duryi (Wetherby, 1879); Helisoma scalare (Jay, 1839), (Mollusca: Planorbidae) / Comparison betew the growth of Helisoma duryi (Wetherby, 1879); Helisoma scalare (Jay, 1893), Mollusca: Planorbidae)

Se hace una comparación del crecimiento de Helisoma duryi (Wetherby, 1879) y Helisoma scalare (Jay, 1839) en condiciones naturales. Se informa que ambas especies se mantuvieron en cajas de cría en la Ciénaga de Zapata y se les calculó la curva de crecimiento mediante la ecuación de von Bertalanffy. Se indica que el crecimiento de estas especies en cuanto al diámetro máximo alcanzable es similar, pero los valores de las constantes de crecimiento señalan que H. duryi crece más rápidamente que H. scalare. Se plantea que este hecho puede contribuir a una ubicación sistemática definitiva de estas especies

Estudio de los moluscos fluviátiles de una localidad afectada por un brote de fascioliasis / Fluvial mollusks from a locality affected by a fascioliasis outbreak

Se informa que se ralizó un estudio de las diferentes especies de moluscos dulceacuícolas en la localidad de Fomento, afectada por un brote de fascioliasis. Se plantea que en el área del municipio se colectaron diferentes especies de moluscos, encontrándose entre éstos Lymnaea cubensis (Pfeiffer, 1839) y Lymnaea columella (Say, 1871): hospederos intermediarios de Fasciola hepatica (Linne, 1758). Se expone que los análisis de laboratorio corroboaron que L. cubensis es el principal vector en esta epidemia. Se indica la necesidad de realizar los estudios pertinentes sobre la posibilidad de aplicar el método de control biológico a los vectores de esta enfermedad