There was an extensive article about outdoor whiteflies in issue no. 15, August 13, 2007. These insects have become more numerous in Illinois over the intervening weeks. Most appear to be silverleaf whitefly, Bemisia argentifolii, although identification of the adults is difficult. Adult whiteflies are very small, with six or more easily fitting on the head of a straight pin. They are covered with a white dust and fly readily when foliage is disturbed.
Silverleaf whitefly adults on hibiscus.
Although these adults are undoubtedly feeding by sucking the sap from leaves of various plants, no leaf distortion damage has been noticed. The silverleaf whitefly is a tropical to subtropical species. There does not appear to be any reproduction occurring. This is probably due to this species’ needing temperatures over 60°F to reproduce. The nymphs die at temperatures below 48°F. All stages die at temperatures below 23°F, explaining why this species does not overwinter in Illinois.
Treatment is not likely to be warranted. However, if you have clientele who are bringing houseplants indoors that have been sitting outside this summer, these plants should be sprayed with insecticidal soap if there are whiteflies on them.