Whiteflies are easily distinguished from other pests because of their distinctive behaviour and appearance. The adults are white and moth-like and are just over 1mm long, their wings and bodies are covered with powdery wax. Whitefly usually remain hidden on the undersides of leaves and in growing tips where they suck the sap of the host. When disturbed they flutter around in a characteristic and noticeable way. The small, flat, oval nymphs, often called scales, also inhabit the undersides of the leaves where they too suck sap. The nymphs are colourless and virtually transparent until they pupate into thicker, white, wax-covered pupae. There are several species of whitefly outdoors — during the summer these may include the 

glasshouse whitefly (Trialeurodes vaporariorum) that is a major pest of nearly all glasshouse plants including chrysanthemum. The main symptoms are yellowing and mottling of the foliage followed by stunting, wilting and death if the plants are heavily infested. Sooty moulds and specks of honeydew that the larvae excrete over the leaves make the plants unsightly and impact commercial value. By the time that these symptoms are apparent the plants will already be colonised by several generations of whitefly. 

The glasshouse whitefly generally reproduces by parthenogenesis, from eggs laid erect in circular groups on the underside of smooth leaves but are more scattered on hairy leaves. Each female lays about 200—250 eggs at a rate of about eight per day during a life span of 3—6 weeks. The eggs are yellowish when laid but become black within 2—3 days; the incubation period is nine days at 21 °C. 

Pale green, flattish larvae hatch from the eggs. They are active for a few days but then settle down and remain motionless until they mature. These immobile stages are called ‘scales’. Like aphids and scale insects, they feed by means of stylets which are inserted in the tissues of the plant to take up sap. Before becoming adult, a whitefly passes through four stages, the last of which corre­sponds to the pupal stage of other insects. The duration of the immature stages varies with temperature; at 21 °C it is about 18 days. Thus the total period from egg to adult at this temperature is about 27 days. The whitefly hibernate over winter on any plants until the following season.

Controls
Amateur Products: 
Pyrethrum - derived from the flowers of Tanacetum cinerariifolium 8 products from various manufacturers 
Fatty Acids - derived from plant and animal oils. 5 products from various manufacturers. Plant Extracts - a mixture of long chain polymers and surfactants that block the breathing pores. 5 products from 3 manufacturers.
Synthetic pyrethroid compounds containing Bifenthrin: Several products including combined insecticide and fungicide e.g rose clear 
Systemic action - Imidacloprid - Provado 

Professional Products: 
Imidacloprid. - Admire, Intercept. - also for aphids, leaf miner 
Deltamethrin.- Decis - also for leaf miner, caterpillars. Inc tortrix. 
Acetamiprid - Gazelle - also for aphids 
Spiromesifen - Oberon - also for red spider 
Thiacloprid - Calypso - also aphids, capsids, thrips, Western flower thrips, 
Teflubenzuron - Nemolt - also for caterpillers

Biological Control
The white fly predator Encarsia formosa  gives excellent control of whitefly on greenhouse plants but not so well on chrysanthemums because they are often in the greenhouse when the temperatures are too low for the Encarsia to function properly.  However, whitefly is normally a pest of chrysanthemums when they are housed in mixed greenhouses with other plants that occupy the greenhouse full time. Encarsia will give quite good control in this sort situation.