For those that might be interested in the dietary preferences of P. insurlarum in one of it's introduced ranges, Patrick Baker and colleagues have just published the result of their feeding studies in the Journal of Molluscan Studies. Hopefully this will help put an end to the idea of using apple snails as biological controls of non-native plants.
The abstract can be found here http://mollus.oxfordjournals.org/cgi/content/abstract/eyp050