Gardening glossary
Whitefly
Whiteflies (family Aleyrodidae) are not true flies but are more closely related to aphids and scale. Adults are 1 to 2 mm long with two pairs of wings dusted in a waxy white coating that gives them their name. Despite the resemblance to tiny moths, they are sap-sucking phloem feeders. The two most common pest species are the greenhouse whitefly (Trialeurodes vaporariorum) and the silverleaf or sweetpotato whitefly (Bemisia tabaci).
Eggs are laid in arcs or circles on the undersides of leaves and hatch into flat, scale-like nymphs called crawlers. Crawlers settle, lose their legs, and feed in place for several weeks before pupating and emerging as winged adults. Because three life stages overlap on the same leaf, treatment must be repeated to catch each new wave of adults.
Feeding damage causes leaves to yellow, dry, and drop, and like aphids, whiteflies excrete copious honeydew that supports sooty mold. Bemisia tabaci is a serious vector of begomoviruses including tomato yellow leaf curl virus, which can devastate tomato, pepper, bean, and cassava crops.
To diagnose, gently shake the plant and watch for a small cloud of white insects rising from the foliage, then settling back on leaf undersides. Yellow sticky cards hung at canopy height trap adults and confirm presence. Treatment combines weekly sprays of insecticidal soap or neem oil aimed at leaf undersides, removal of heavily infested lower leaves, and biological control with Encarsia formosa parasitic wasps in protected growing environments. Reflective mulch deters them from settling on outdoor vegetable crops.