Research "apple snail sexing".
The differences between the sexes are not visible at the shell color or patterns, but in several species, a difference in shell shape has been described. For example in Pomacea canaliculata, the aperture (opening) in the male has a rounder opening than in the female because of the large penial complex. This sex-difference is not very well visible and it's not a very reliable to discriminate on individual base, but clear when measuring large amount of snails (in other words, it's possible to show the difference based on statistics). Despite the shape difference, it often easier to determine the sex by looking inside the mantle cavity to spot the penial complex or the absence thereof in case of a female snail. To do this one should take the snail out of the water and keep it upside down for a minute or 10 and blow some fresh air over the snails body. The animal will (hopefully) stretch its foot out to turn the shell upright. When this happens it's possible to look inside the right mantle cavity, where one should look for the relatively large penis sheath in front of the gills. The female snail lack such structure (obvious). The picture below should help to see the difference between the sexes.
Last, but not least: in very thin shelled apple snails and in specimen with translucent shell (albino Pomacea bridgesii), one can also observe a colour difference in the upper whorl (spine) of the shell in periods that the snails are in a reproduction stage. The female ovaria can then show up as a dark organ at that place (see picture below). Note however, that this method is not reliable at all times and can only be used when the snail are sexual active. In the latter case the snails mate anyway, so that one can see the male snail mounting the female repeatedly.
A sex change from male to female (proandry) has been described for some Pila and Pomacea apple snails. In case of Pila snails, the male needs a preparatory aestivation period to become a female, while the Pomacea snails can change sex at all times (at least in certain species). During this sex change, the testis change in color and decrease in size. The frequency at which this sex change occurs is not certain and not much literature is available about this subject. There is some very interesting research about the effects of certain chemical substances that are known of suspected to have influence on the development of the reproductive organs. Many of these substances are of great concern as they can be found in habitats due to pollution.
Or so says Aquariacentral
, apple snails are more active at higher temperatures. At higher temperatures, they eat faster, creep faster and they grow faster. Also higher temperatures mainly induce the reproduction of the apple snail. At lower temperatures (18°C/65°F) the apple snail enters a dormancy state in which they creep away in the mud and become very inactive. Temperatures below 18°C/65°F should be avoided as the mortality rate quickly increases.
I have seen the water in my tanks drop into the 60's without a heater