Mosquito larvaes can be rid by cleaning the tray. Although it is a slow and tedious method. I realise that blue trays are the one that are usually infested with mosquito larvae the fastest. This is because, most mosquitoes are attracted to blue colour.
PY, the most important thing is that never let the media dry out completely. Always keep it wet. The water tray method is to keep the media wet while saving you time from constantly watering the plant. But don't overwater the plant! You will kill it by root rot, thats what I did to my first VFT.
Cheers