Problem type: Insect

Name of problem: Whitefly

Plant name(s): Flowering and foliage house plants as well as greenhouse-grown ornamentals and vegetables

Symptoms / Characteristics:
Symptomatic leaves appear speckled or bleached, eventually turning yellow and wilting. Whiteflies use their needle-like mouthparts to pierce succulent plant tissues and extract the sap. The damage caused by a single whitefly is insignificant but whiteflies usually exist in masses. The cumulative effect can be detrimental to plant health. Like many other sap-sucking insects, whiteflies excrete a sticky substance known as honeydew that gives the leaves a glossy appearance and can facilitate the development of harmful sooty mold fungi. The honeydew may also attract other types of insects, especially ants. Whiteflies also act as insect vectors, aiding in the transmission of viruses from one plant to another.

Adults are white, winged, moth-like insects that reach a mature length of only 2 mm. They typically reside on the leaf undersides and fly into a cloud of white around the plant whenever the leaves are disturbed. Hundreds of tiny, almost microscopic, eggs are laid on the leaf undersides. The eggs are light yellow at first and turn dark grey with maturity. Tiny, oval, scale-like nymphs emerge within ten days. During the crawler phase, the nymphs move around the plant in search of potential feeding sites. Once an appropriate site is located the nymph pierces the plant tissue and commences feeding, where it remains stationary until maturity. Immobile nymphs resemble mealybugs.

Control / Preventions:
Whiteflies are usually introduced by bringing infested plants into the home. Carefully inspect plants before purchase to ensure that they are insect-free. Minor infestations may be dealt with by gently washing the plants in warm, soapy water. This will help to eliminate eggs and larvae but will not be effective against the quick-flying adults. Therefore, this treatment is best performed in isolation of other plants to ensure that the adults don't fly onto another host.

Whiteflies are particularly attracted to the color yellow. Placing yellow sticky traps immediately next to an infested plant is an ideal way to attract and trap the adults. Upon disturbance, the adults will fly off the plant leaves and land on the yellow surface. Repeated disturbances will effectively reduce insect populations below harmful levels, providing the traps remain in place long enough to trap subsequent adult generations.

Whitefly eggs and larvae are resistant to most chemical controls and at any given time, an infested plant may harbor eggs, larvae and adults. Repeated chemical applications (on a weekly basis) may be necessary in order to eliminate subsequent adult generations. Predatory and parasitic insects may be used to control whiteflies in a greenhouse. Encarsia formosa is a parasitic wasp that is commonly used for the biological control of whiteflies.