Greenhouse whitefly (Trialeurodes vaporariorum) is a world wide insect pest affecting a wide selection of ornamentals and crop plants. Adult and larval stages of the insect feed on plant tissues which results in necrosis and plant deformities. Whitefly are vectors for some harmful plant virus and movement between plants by adults can lead to a spread of viruses within the Greenhouse or land.

Appearance and Biology
Adults are small (1.5mm) white, moth-like insects (Figure 1). Females can produces up to 250 eggs, laying an average of 10 eggs per day. Eggs are laid on the bottom surface of a leaf toward the top of a plant. After 1-2 days they will turn black in colour (Figure 2). Approximately 3 days later, a small larva will emerge with well developed legs and antennae. This first instar will move around the leaf looking for a suitable location to settle. Once a suitable feeding location is found the larva will settle and will stay in the same place for the duration of the 2nd to 4th instars (Figure 3). The 4th instar will pupate and between 4-6 days later an adult will emerge. Females live for about 60 days while males for about half this period. This is, however, temperature dependant.

Damage
Plant leaves are deformed and discoloured and plant growth may also be retarded due to whitefly feeding on the plant. Whitefly also excrete copious quantities of honeydew as they feed. Honeydew is a substrate for Sooty mould fungus which is black in colour. Development of Sooty mould on fruit and leaves can reduce crop value. The transmission of plant viruses across the crop negatively influences plant growth and vigour which turn result in lower yields.

Seasonal history
Due to artificial environments maintained in greenhouses whitefly has no real over-wintering period. However, the slight drop in temperature caused by seasonal change will result in the life cycle of whitefly being extended.

Control
Control of this pest is difficult as there has been a build up of resistance to many chemical insecticides. Effective control of this pest requires weekly applications of harsh pesticides. Various softer means of control have been considered, one of which is the introduction of the natural enemy of whitefly, the parasitic wasp Encarsia formosa. This wasp coupled with the use of Beauveria bassiana (a fungal control agent) leads to affective natural control of the pest in the absence of chemical applications.