Riassunto analitico
The freshwater snail Pomacea canaliculata is a highly invasive species with a robust innate immune system based on cellular and humoral components and only a few predators in nature. To date, no specific and lethal pathogens have been reported for the commonly known golden apple snails, although this information could be crucial for developing sustainable and eco-friendly approaches for controlling P. canaliculata diffusion.
In this context, we tested the effects on adult P. canaliculata of a commercial molluscicide developed against terrestrial slugs and constituted by the living nematode, Phasmarhabditis hermaphrodita. At the standard temperature of animal maintenance, i.e., 25 °C, the molluscicide proved to be effective against adult specimens of P. canaliculata in a dose-dependent fashion. During one-week experiments, lethal effects have been observed at the highest concentration tested (17 g/L). After incubation at a sub-lethal concentration (1.7 g/L) the snails reduced the mobility and stopped eating while no evident effects were observed for the lowest concentration tested, 0.17 g/L. The molluscicide efficacy is also temperature-dependent since, especially for the 17 g/L concentration, significantly stronger effects have been observed at 18 °C, whereas no effects on survival or feeding rate have been recorded after incubations at 30 °C.
Real time PCR experiments performed on animals exposed for 24 h at the concentration of 1.7 g/L revealed organ- and temperature-specific changes in the mRNA expression of the antimicrobial peptide Bactericidal/Permeability-Increasing protein (BPI). More in details, bpi expression significantly dropped in the anterior kidney at 18 °C and in the gills at 25 °C (p=0.030 and p=0.0111, respectively) compared to control snails. bpi did not change its expression in any tested organ after incubation at 30 °C.
Fluorescent in situ hybridization of BPI in tissues obtained from control animals did not show any positivity of the cell constituting the analyzed tissues, but hemocytes collected from control animals express bpi.
On the whole, we have observed that at sub-lethal concentration the molluscicide induced a reduction of feeding rate and negatively influenced the immune defense in key sentinel organs, namely anterior kidney and gills. Our results indicate that nematode-based molluscicides may represent an efficient solution for a sustainable control of P. canaliculata spread, and could be used as a tool to induce a more natural and physiological immune response in P. canaliculata.
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