Whiteflies slip through greenhouse mesh too fine for their own predators
Aleyrodidae—the sole family in Aleyrodoidea—are tiny hemipterans that usually suck from leaf undersides. Most sport wingspans under 3 mm and bodies 1–2 mm long, so small that greenhouse control is awkward. Adults typically carry seven-segmented antennae like other mobile sternorrhynchans.
More than 1,550 species of whitefly have been described, all in Aleyrodidae, the only family in its superfamily and a cousin of the jumping plant lice within Sternorrhyncha. Older books spell the family "Aleurodidae," a junior synonym that is formally incorrect. The root is the Greek aleurodes, "floury," after the fine wax powder that dusts most species, though not all are white: the citrus blackfly, Aleurocanthus woglumi, is slate black.
Most measure 1 to 2 mm with wingspans under 3 mm, and that tininess is their shield in glasshouses. Only extremely fine mesh keeps them out, and they can pass through screens that block their natural enemies, so populations inside can explode unchecked. A few tropical "giant whiteflies" pass 5 mm, and oddly, in some of them males are far bigger than females. Adults of both sexes have two pairs of working wings with drastically reduced veins, often a single unbranched one. The compound eyes are pinched in the middle, and the degree of pinching separates genera: a single facet links the halves in Bemisia, while in Trialeurodes they are fully split.
Only the first larval stage walks; once its stylets are sunk into the phloem it stays put, and its legs wither after the first moult. The last instar stops feeding and turns into a pupa inside its own hardened skin, a stage that blurs the usual line between nymphs and larvae. Males come from unfertilised eggs, and a female can mate with her own sons to produce daughters. The family dates back to the Jurassic.
Feeding itself is not the main harm. Masses of honeydew breed sooty mould and can foul cotton harvests, saliva injures plants, and above all a small minority of species spread viruses. Bemisia tabaci and its relatives carry cassava mosaic, tomato yellow leaf curl and other begomoviruses; the tomato disease, found in Florida in 1997, is the worst, and the insect carries nearly 60 others. Losses run to hundreds of millions of dollars a year, and fast-evolving pesticide resistance pushes growers toward biological control.
Source: Whitefly
