A simple way to deal with mosquitoes in the water tray is to use a can of non-stick spray for pots and pans. Simply spray a coat of PAM on the water surface. This creates a film of oil on the water surface. A mosquito, trying to breathe, cannot penetrate the oily layer and take in oxygen. Can't breathe, can't live. The spray is harmless to plants in their pots. Mosquitoes will no longer be a problem in your water trays. Quick, fun, and easy!!!