Definition - What does Whitefly mean?
Whiteflies are small insects that feed on the undersides of plants. To most people, they would appear to be tiny moths. There are more than 1,500 known species around the world.
MaximumYield explains Whitefly
Whiteflies are sap-sucking insects that feed on the nutrients plants receive and can literally suck the life out of the plant, ultimately killing the leaves or the plant. As the insects feed, the leaf will yellow, wither, and die as the vital nutrients that should feed the plant are going to the insect.
Whitefly rarely arrive as just one insect and often swarm a greenhouse by the hundreds without any warning.
Whitefly can be a real problem in the greenhouse and are notoriously difficult to prevent. Most often a grower will cover the plants with fine netting in order to prevent the flies from even landing on the plants.
There are some commercial insecticides available to prevent and control whitefly, which are considered very effective.