Whiteflies

Adult whiteflies are tiny, winged insects covered in a fine white wax, usually resting on the undersides of leaves. Immature stages (nymphs) are flattened, oval, and scale-like, ranging from translucent to pale yellow, and remain fixed in place while feeding on the underside of leaves.

• Adults fly up in a small cloud when infested foliage is disturbed
• Sticky honeydew on leaves and surfaces below, often with black sooty mould growing on it
• Yellowing, wilting, or reduced vigour under heavy, sustained infestation
• Pale, flattened nymphs and cast skins visible on the undersides of leaves

Eggs are laid on the undersides of leaves, often anchored by a short stalk and sometimes arranged in a circular or arc-shaped pattern. After hatching, a brief mobile "crawler" stage settles to begin feeding, after which the nymph passes through several flattened, immobile instars before a final non-feeding stage that precedes adult emergence.

In warm climates and protected environments such as greenhouses, generations overlap continuously, so all life stages may be present at once and populations can persist without a clear seasonal gap.

Direct feeding by large whitefly populations can weaken plants, cause yellowing, and reduce vigour. Honeydew excreted during feeding coats leaves and fruit, and the sooty mould that grows on it can further reduce photosynthesis and lower produce quality. For many crops, however, the greatest economic impact comes from the plant viruses that some whitefly species transmit while feeding.

Whiteflies attack a very broad range of host crops. Notable hosts include tomato, potato, and soybean, alongside many other vegetables and ornamentals, with the specific pest species and dominant biotype varying by region and cropping system.

Regular scouting for whiteflies focuses on the undersides of leaves and on field or greenhouse margins, where colonization often begins, so that trends can be tracked before populations become difficult to manage.

• Yellow sticky traps placed within the canopy to catch flying adults
• Inspection of leaf undersides for eggs, nymphs, and cast skins
• Gently disturbing foliage to observe adults flushing into flight
• Prioritizing field edges or greenhouse entry points where infestations often start

Whitefly management, like that of other sap-feeding pests, relies on combining several tactics within an integrated pest management approach rather than a single control method.

• Conserve natural enemies such as parasitic wasps, predatory beetles, and lacewings
• Avoid excessive nitrogen fertilization, which can encourage lush growth attractive to whiteflies
• Use reflective mulches or fine screening in greenhouses to reduce colonization where practical
• Remove heavily infested crop residues and manage weeds that can host whiteflies between crops
• Monitor with traps and leaf inspection, and use local thresholds to guide any intervention