Whiteflies

Whiteflies are small, soft-bodied insects related to aphids and scale, though the winged adults resemble tiny moths more than flies. Adults are 1–2 mm long with a pale yellow body covered in a white, powdery wax that coats two pairs of wings held roof-like over the body. Several species occur in Australian production settings, including greenhouse whitefly, silverleaf whitefly and sweetpotato whitefly, which differ slightly in wing shape and host preference but cause similar damage.

Immature stages are found on the underside of leaves and are far less mobile than adults. After hatching, a flat, oval, semi-transparent to pale green crawler (the first instar) settles and becomes a scale-like nymph that flattens against the leaf surface, losing legs and antennae function. These nymphs are 0.3–0.8 mm, translucent to yellowish, and moult through several stages before pupating into a slightly raised, oval case from which the winged adult emerges. Eggs are minute, spindle-shaped and laid in small groups or circular patterns on leaf undersides, often pale yellow turning grey before hatching.

Whiteflies are present across most of Australia, with populations building rapidly in warm, humid conditions typical of late spring through autumn, and persisting year-round in glasshouses and warm coastal regions. They feed on a very wide range of ornamental, vegetable and nursery crops, and several species are also known to transmit plant viruses.

Populations can increase quickly because of short generation times and high fecundity, and heavy infestations are difficult to manage once established. Effective management relies on regular monitoring of leaf undersides, use of yellow sticky traps to track adult activity, encouraging or introducing biological control agents such as parasitic wasps and predatory bugs, and avoiding conditions that favour rapid buildup, such as overcrowded, water-stressed or over-fertilised crops. Removing heavily infested foliage and controlling weed hosts around production areas also helps reduce carryover populations between crops.