No Ann, hoverflies don't bite, they are sweet little winged creatures, as adults they are important for the pollination, they only live from pollen of flowers.
Whiteflies have many natural enemies like spiders, ladybeetles, lacewings etc.. using pesticides also kills the natural enemies. A garden maintained without these nasties soon reaches a natural balance and rarely has pest problems..I wouldn't know why you have these pests only since the last 6-8 years, maybe the spot you grow them attracts them, is the air not too dry maybe you grow your tomatoes in a greenhouse. I only (sometimes) have whitefly problem when I grow up seedlings inside the house, usually they disappear soon once I bring them outside where the air is more humid.They love dry and hot conditions..
Cubits has a very interesting cubit owned by JRsBugs who is very knowledgeble about insects and passionate to know all about the creatures in her garden..anyone is welcomed..
http://cubits.org/buglife/
