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Whiteflies

Also known as Greenhouse whitefly (Trialeurodes vaporariorum), Silverleaf or sweetpotato whitefly (Bemisia tabaci), Aleyrodidae

PestHarmful
Greenhouse whitefly (Trialeurodes vaporariorum) Photo: Dr. Guido Bohne · CC BY-SA 4.0

In short

Whiteflies are tiny sap-sucking insects with white, waxy wings that flutter up in a cloud when a plant is disturbed. Their flat, scale-like nymphs feed on leaf undersides, covering the plant in honeydew and sooty mould, and some species spread plant viruses.

How it looks

Adults have yellowish bodies and four whitish wings dusted with mealy white wax; species differ in details such as how the wings are held (the silverleaf whitefly holds its wings slightly tilted towards the surface). Tiny oblong eggs are laid on leaf undersides. The first nymphal stage, the crawler, moves briefly before settling; later nymphs are flat, oval, wingless, with no visible legs, and look like pale scale insects stuck to the underside of the leaf.

Signs

A cloud of white adults when the plant is shaken; yellowing, drying or falling leaves; sticky honeydew and black sooty mould. The silverleaf whitefly can also cause distortion, discolouration or silvering. Adults alone rarely cause serious damage unless they are spreading a virus.

Life cycle

Egg, four nymphal stages (only the first moves) and winged adult. Development is fast in warm conditions, and in warm regions they breed all year round.

What favours it

Warm conditions, greenhouses and dusty conditions favour them; with no cold season, breeding is continuous.

Prevention

  • Check the undersides of leaves on new plants and quarantine them.
  • Hang yellow sticky traps to catch adults early.
  • Avoid dusty conditions, keep greenhouses ventilated and remove unwanted plants and weeds that act as hosts.
  • Protect natural enemies by avoiding broad-spectrum sprays.

Treatment

Start with the first step and move down only if the problem persists.

  1. Remove heavily infested leaves and hose adults off with water.
  2. Use yellow sticky traps to reduce adults as well as monitor them; you may need as many as one trap for every two large plants.
  3. Introduce the parasitoid wasp Encarsia formosa early in an infestation; the predatory bug Macrolophus pygmaeus and predatory mites are other options, and lacewings help too.
  4. Spray insecticidal soap or neem oil with thorough coverage of leaf undersides, repeating as directed; follow the product label.
  5. Systemic insecticides such as the neonicotinoid class harm natural enemies; use only as a last resort and follow the product label.

Pros and cons

Cons

  • Honeydew and sooty mould make plants sticky and dirty.
  • Some species transmit plant viruses.
  • Adult whiteflies can carry broad mites from plant to plant.

Look-alikes

Soft scale crawlers and young scales
Scales are domed or waxy bumps on stems and veins, and there are no white-winged adults.
Mealybugs
Wingless, mobile and covered in powdery wax with filaments.

Affected plants

Many vegetables and greenhouse and indoor ornamentals. Whiteflies are rarely a problem on orchids.

Sources

  1. Whiteflies — UC IPM Pest Notes
  2. Indoor plants: sap-feeding insects — RHS
  3. Orchid Insect and Mite Pests in South Florida (ENY2114) — UF/IFAS
  4. Managing Broad Mites on Greenhouse Crops — UConn IPM

Written in our own words from these sources. Check a product label before using any treatment.