Horticulture/Trialeurodes vaporariorum

Trialeurodes vaporariorum, commonly known as the glasshouse or greenhouse whitefly inhabits the world’s temperate regions. It is a primary insect pest of many fruit, vegetable and ornamental crops, frequently being found in glasshouses and other protected horticultural environments. Adults are 1-2 mm in length, with yellowish bodies and four wax-coated wings held near parallel to the leaf surface.

Symptoms and Signs
All life-stages apart from eggs and pupae cause crop damage through direct feeding, inserting their stylet into leaf veins and extracting nourishment from the phloem sap. As a by-product of feeding, honeydew is excreted and that alone can be a second, major source of damage. The third and potentially most harmful characteristic is the ability of adults to transmit several plant viruses. The crop hosts principally affected are vegetables such as cucurbits, potatoes and tomatoes, although a range of other crop and non-crop plants including weed species are susceptible, and can therefore harbour the infection.

Ecology
Females are capable of mating less than 24 hours after emergence and most frequently lay their eggs on the undersides of leaves. Eggs are pale yellow in colour, before turning grey prior to hatching. Newly hatched larvae, often known as crawlers, are the only mobile immature life-stage. During the first and second larval instars, the appearance is that of a pale yellow/translucent, flat scale which can be difficult to distinguish with the naked eye. During the fourth and final immature life-stage (the pupa), compound eyes and other body tissues become visible as the larvae thicken and rise from the leaf-surface.

Host plants
Greenhouse whiteflies feed on a wide range of plants, including plants in the following genera:
 * ../Aster/
 * ../Brassica/
 * ../Camellia/
 * ../Cercis/
 * ../Cucumis/
 * ../Dahlia/
 * ../Hydrangea/
 * ../Ilex/ (Holly)
 * ../Ipomoea/
 * ../Lactuca/ (Lettuce)
 * ../Lilium/
 * ../Lonicera/
 * ../Lycopersicon/
 * ../Ocimum/
 * ../Rhododendron/ (Rhododendron, Azalea)
 * ../Salvia/ (Sage)
 * ../Verbena/

Control
Effective control has been provided for many years through the release of beneficial insects, such as the aphelinid parasitoid, ../Encarsia formosa/. If required, integrated pest management strategies can incorporate applications of selective chemical insecticides that complement these natural enemies. For the majority of outdoor crops chemicals are still the most widely used method of control.