Gardenias and privets are the most heavily affected by whiteflies in the Southeast. Whiteflies, like aphids and spider mites, are also sucking insects. They excrete a sticky, shiny substance called "honeydew" all over the plants they feed upon. Later in the Summer, this honeydew is colonized by sooty mold fungi. The fungi feed on the honeydew and not the plant, so very little damage is actually done to the plant. The sooty mold turns much of the plant soot black. 

Whiteflies often occur in tremendous numbers. When a heavily infested plant is disturbed, the air is filled instantly with a white cloud of these insects.