what kind of damage do white flys do to plants

checked my girls this morn- as I bent a cola over to examine I noticed some white flys hovering around it- plants are 7 weeks into flower and after doing research in archive I have read post from Stinky Attic to use a pest strip to remedy problem- I am wanting to know what kind of damage will these pest cause and should I be alarmed- I have had many pest problems this year - I feel due to extreme drought and heat in my area- almost all my plants have been attacked by borers earlier this season and killed 7 plants already- I would hate to see more loss because of bugs