While it’s white, it’s not a fly.

Whiteflies are not flies. They are only remotely related to flies, as they are both insects. Flies belong the order Diptera, meaning di-two and ptera-wing.  Whiteflies belong to the Homoptera or Homo-same and ptera-wing.  Whiteflies are relatives of aphids, scale insects, leafhoppers, and mealybugs.  All are horrible garden pests.

Whiteflies, while they are incapable of sucking, they are commonly called sucking insects. They lack a diaphragm which would allow them to suck plant juices. Instead, they stick their stylus or mouth into the plant and the plant’s turgor pressure force feeds them.  Like most of the other Homoptera, they have a bypass tube and valve that allows excess plant sap to bypass their stomach and be excreted unadulterated out the opposite end as honeydew. If they did not have this bypass system, their stomach would continue to fill and burst like a balloon. This honeydew is the shiny sticky sap dots that you find on your car, garden structures and other plants below their feeding activities. Often, this rich sugary honeydew is a primary food source for sooty molds, often resulting in a black coating developing on the dewed surfaces.  On pavers, steppers and other hard surfaces, a paver cleaner, cryptocidal soap or mild bleach (careful with bleach as it will also kill other plants) solution will kill the sooty mold and clean the surfaces. 

Whiteflies, like many other Homoptera, are hosts to a number of plant viruses, including some viruses that are causing devastating diseases on food, fiber and ornamental crops, according to The American Phytopathological Society.  Bemisia tabaci Whitefly infects hundreds of garden and agricultural plants species. Treating your whitefly infestations helps prevent the spread of viruses and others plant afflictions. A number of pesticides are registered for white fly control. Yellow tents with tangle foot do a nice job of keeping them under control.

For further information, see http://www.apsnet.org , and type whitefly in the search box. Or http://wihort.uwex.edu/gardenfacts/X1127.pdf