ORDER: Hemiptera, SUBORDER: Sternorrhyncha, SUPERFAMILY: Aleyrodoidea, FAMILY: Aleyrodidae

Two subfamilies: Aleurodicinae (found mainly in South America), Aleyrodinae (larger and more widespread); third tentative: Udamoselinae (insufficient data to determine status) (Mound and Halsey 1978).

"The species included in the hemipterous family Aleyrodidae were first catalogued by Kirkaldy in 1907 and a checklist of species was also provided by Quaintance in 1908. Kirkaldy refers to 150 species in two genera, whilst Quaintance refers to 156 species in three genera. The basis for the present generic classification was laid by Quaintance & Baker (1913-14) who divided the group into three subfamilies, including one, four and eighteen genera, respectively. Since then large numbers of species and genera have been described. . . . " (Mound & Halsey 1978).

Most species of whiteflies are monophagous (feed on only one host plant). However, a few species are oligophagous or polyphagous.

Some whitefly species can be agricultural pests and vectors of plant viruses.

Whiteflies cause damage to plants by feeding on phloem sap. They also excrete a sugar-rich substance called 'honeydew', which at times encourages the development of sooty mold fungi that reduce the plants' photosynthetic capability.

The emergence of new, aggressive biotypes or variants has presented new challenges to disease and pest control.

Currently, quarantine of infested plant materials is an important means of preventing the introduction and dispersal of new whitefly species.

Adult whiteflies measure from 1 - 3 mm in length, are four-winged and fully mobile with a feeding rostrum and seven-segmented antennae. "Forewing venation is reduced to a simple or once-branched major vein" (Martin and others 2000).

Reproduction can be sexual or parthenogenic. Unmated females (2N) produce male offspring (1N), and fertilized eggs yield female offspring (2N). Eggs are oviposited on the leaf or other plant surfaces.

"First instar larvae are minute but have relatively long legs and antennae. They can crawl actively although they probably do not leave the leaf on which they have hatched. The legs and antennae of the second, third and fourth instar are atrophied, and these instars are sessile. The adult develops within the fourth instar and this is then known as the pupal case. Many species produce large quantities of wax around the margins and on the dorsal surface of the larvae, and in a few species the cast skins of earlier instars may be found on the dorsal surface of a pupal case. In most species the adult emerges through a T-shaped split in the dorsal surface of the pupal case, but in a few species the apices of the T are joined by additional sutures thus forming a 'trap-door.' Pupal cases from which parasites have emerged can be recognized by an irregular circular hole which is chewed by the emerging parasite.

The white powdery wax that covers the body of most species in this family is secreted from abdominal glands after the adult has emerged from its pupal case. Some species have dark spots on the wings, although these may not develop until a few hours after emergence, and a few species are not white. The Citrus Blackfly, Aleurocanthus woglumi, has black wings and little wax, and several species of Aleurodicinae have patterned wings. An undescribed species of Dialeurodes on coffee in southern Nigeria has red wings,
and Bemisia giffardi has very pale yellow wings (Mound and Halsey 1978).

click to view life cycle diagram

The generic classification of the Aleyrodidae is based on the structure of the fourth larval instar, the so-called pupal case, not on the structure of adults. This has the great advantage that since the pupal cases are sessile it is possible to collect and identify host plants with the insects. Unfortunately some polyphagous whitefly species vary in the appearance of their pupal cases depending on the form of the host plant cuticle on which they develop. This variation has caused a significant amount of misidentification, and so deductions from host plant associations must always be approached with caution." (Mound and Halsey 1978).

"Morphologically the aleyrodids seem to be degenerate psyllids, although ecologically they are the tropical equivalent of aphids--opportunist insects with transient populations. The feeding apparatus is similar to that of the other Sternorryncha, but in contrast to psyllids the antennae have fewer segments and the forewings fewer veins" (Mound and Halsey 1978).

Significantly, Russell (1957) found that many species of whitefly had been misidentified, and re-classified two genera and twelve Bemisia species as B. tabaci (Gennadius).
Morphological differentiation of pupae is one of the better methods for determining identity of species (Martin and others 2000). However, molecular analysis is the only effective means of confirming the identity of genetic variants or subspecies of B. tabaci (Brown 2000, Brown and others 1995, Frohlich and others 1999, Rosell and others 1997).

"Martin (1987) produced an identification guide to common whitefly pest species of the world, which can be used to distinguish B. tabaci from other whiteflies (although for this particular identification it is necessary to work through the entire key to reach B. tabaci). Bohmer (1989) gave details of how to separate B. tabaci and Trialeurodes vaporariorum (Westwood), the two common European glasshouse whitefly pests (Cock 1993). Caballero (1994), using photographs of pupae, developed a reference key of whiteflies in Central American, and Gill (no date) developed a similar key for whiteflies common to California.

Presently, three whitefly species, B. tabaci, T. vaporariorum (West.), or T. abutiloneus (Haldeman), are known to be vectors of plant viruses, while B. tabaci is the most important, having been associated with more than 100 viral diseases in the tropics and subtropics (Nault, 1997).

T. vaporariorum is polyphagous and found nearly worldwide because it inhabits greenhouses as well as field crops. It transmits criniviruses (Beet pseudo-yellows virus, Potato yellow vein virus, Tomato infectious chlorosis virus and Tomato chlorosis virus) and potyviruses (Brown and Czosnek 2001).

T. abutiloneus is the only reported whitefly vector of Dioda vein chlorosis virus (Brown and Czosnek 2001).

Two species within the Bemisia genera, B. afer and B. tabaci contain several species, variants or biotypes. The B. afer group includes B. berbericola and B. tuberculata, while the tabaci complex includes only tabaci and graminus as well as several biotypes (Gill 1994): the Jatropha (Bird 1957), Sida (Bird 1957), 'A' (Costa and Brown 1991), 'B' (Costa and Brown 1991) (also known as B. argentifolii Bellows and Perring), and 'Q,' among others (Bedford and others 1994; Costa and others 1993; Guirao and others 1997). "The first known record for B. tabaci in Hawaii was a collection made in 1982. While these specimens have not been located, a collection made in California from Hawaii in 1984 is available for study, and these specimens agree morphologically with [the B biotype] (Gill 1994). The 'B' biotype was soon thereafter recognized in greenhouse and field crops in Arizona, Florida, California, and Texas; and is rapidly infesting areas in both the New and Old Worlds. (Gill 1992 and 1994).

REFERENCES CITED

Bedford ID, Markham PG, Brown JK, Rosell RC. (1994). Geminivirus transmission and biological characterization of whitefly (Bemisia tabaci) biotypes from different world regions. Annals of Applied Biology 125: 311-325.

Brown JK. (2000). Molecular markers for the identification and global tracking of whitefly vector-begomovirus complexes. Virus Research 71:233-260.

Brown JK, Czosnek H. (2001). Whitefly transmitted viruses. Advances in Botanical Research, NY: Academic, 65-100.

Brown JK, Frohlich D, Rosell R. (1995). The sweetpotato/silverleaf whiteflies: biotypes
of Bemisia tabaci (Genn.), or a species complex? Annual Review of Entomology 40: 511-534.

Caballero R. (1994). Clave de campo para immaduros de moscas blancas de Centroamerica (Homoptera: Aleyrodidae). Escuela Agricola Panamericana, Zamorano, Honduras, 4p.

Cock MJW. (1993) Bemisia tabaci, an update 1986-1992 on the cotton whitefly with an annotated bibliography. CAB IIBC, Silwood Park, UK, 78p.

Costa HS, Brown JK. (1991). Variation in biological characteristics and in esterase patterns among populations of Bemisia tabaci (Genn.) and the association of one population with silverleaf symptom development. Entomologia experimentalia et applicata 61:211-219.

Costa HS, Brown JK, Sivasupramaniam S, Bird J. (1993). Regional distribution, insecticide resistance, and reciprocal crosses between the `A' and `B' biotypes of Bemisia tabaci. Insect Science and Application 14:127-138.

Frohlich D, Torres-Jerez I, Bedford ID, Markham PG, Brown JK. (1999). A phylogeographic analysis of the Bemisia tabaci species complex based on mitochondrial DNA markers. Molecular Ecology 8:1593-1602.

Gill RJ. (1994). A preliminary report on the World species of Bemisia and its congeners, with an analysis of environmentally driven morphology shifts and their effects on the stability of the species. Unpublished.

Gill RJ. (1992.) A review of the sweet potato whitefly in southern California. Pan-Pacific Entomologist 68:144-152.

Gill RJ. (1990). The morphology of whiteflies. In: Gerling D (Editor) Whiteflies: their bionomics, pest status, and management. Andover, Hants, UK: Intercept: 13-46.

Gill RJ. (no date) Color-photo and host keys to California whiteflies. State of California, Department of Food and Agriculture.

Guirao P, Beitia F, Cenis JL. (1997). Biotype determination of Spanish populations of Bemisia tabaci (Hemiptera: Aleyrodidae). Bulletin of Entomological Research 87: 587-593.

Martin JH, D Mifsud and C Rapidsarda. (2000). The whiteflies (Hemiptera: Aleyrodidae) of Europe and the Mediterranean Basin. Bulletin of Entomological Research 90: 407-448.

Mound LA, Halsey SH. (1978). Whitefly of the world: A systematic catalogue of the Aleyrodidae (Homoptera) with host plant and natural enemy data. British Museum (Natural History): Chichester. 329p.

Nault, L. (1997). Arthropod transmission of plant viruses: a new synthesis. Annals of the Entomological Society of America 90: 521-541.

Rosell, RC, Bedford, ID, Frohlich DR, Gill RJ, Brown JK, Markham PG. (1997). Analysis of morphological variation in distinct populations of Bemisia tabaci (Homoptera: Aleyrodidae). Annals of the Entomological Society of America 90: 575-589.

Russell LM. (1957). Synonyms of Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae). Bulletin of the Brooklyn Entomological Society 52: 122-1123.