The sweet potato whitefly Bemisia tabaci is an invasive species thought to have originated in India, but in the last 15 years has spread, most likely on ornamental plants, to become a pest of enormous and escalating economic impact around the world. Although its native climate is tropical and subtropical, it is now found through out temperate areas as well, although it is susceptible to cold temperatures. Bemisia tabaci ranks in the top 100 Worst Invasive Species in the Global Invasive Species Database maintained by the International Union for Conservation of Nature (IUCN). The sweet potato whitefly is considered a species complex of about 19 molecularly-identified “biotypes”, which show different behavior, host range and pesticide resistance. Two of these may be two distinct cryptic species, Bemisia tabaci and B. argentifolii (also known as the silverleaf whitefly or Sweet potato whitefly B biotype), although this interpretation is not universally accepted.

The sweet potato whitefly is not actually a fly, rather, it is a hemipteran which congregates on the undersides of leaves to mate, lay eggs and feed, using piercing and sucking mouthparts to extract juices from its host plant. More than 500 species in 74 families are described as plant hosts for the polyphagous Bemisia tabaci. The small size of the sweet potato whitefly, its ability to fly and disperse long distances and its rapid reproduction predispose this species to explosive population growth. Bemisia tabaci is destructive in multiple ways. Areas of plants fed on by whiteflies whither and lose leaves. In addition to directly damaging plants by eating them, the whitefly larvae produce a sugary honeydew, which builds up on leaf surfaces and supports growth of sooty black and other molds. This mold residue reduces the plants’ ability to photosynthesize and thus also reduces the health of the plant, and on crop plants requires expensive washing to remove mold before they can be marketed. The sweet potato whitefly is also devastating in being a vector for over 100 plant viruses, especially Begomoviruses, which are responsible for a significant amount of crop damage and loss world-wide.

Bemisia is difficult to control with insecticides because it is difficult to reach the underside of leaves where the pests infect the plants, and also because it rapidly develops resistance to every group of insecticide developed for its control. There is hope in managing Bemisia populations through host plant resistance to viruses as well as developing plant strains that discourage these pests, e.g. with smooth, rather than hairy leaves and less waxy leaf coats, which are less attractive for whitefly oviposition. Biocontrol methods taking advantage of natural predators, parasitoids and pathogens of Bemisia are the leading long term solutions. Insect growth regulators specific to whitefly larvae can also be used help control the pest without indiscriminately killing beneficial species.

(McAuslane, 2009; Wikipedia 2011; CABI 2001; Fasulo et al. 1995)