Adult whiteflies are are small sap-feeding insects between 1-3mm in length. Their bodies and wings are covered in a white waxy powder although there are species that have a dark grey covering, they are known as blackflies. Eggs are laid on the underside of leaves and the juvenile whiteflies resemble scale insect, they are also sap-feeders.

Whitefly on underside of foliar growth
Image: Whitefly on underside of new foliar growth.

Signs of Whitefly Infestation:

Yellowing of leaves.
Leaves falling off prematurely.

Damage Done by Whiteflies:

Severe infestations of whitefly will cause leaves to wilt, yellow and fall off prematurely.

Plants Attacked by Whitefly:

Mesembs
Leafy succulents - especially caudiciforms
Beans
Tomatoes

Treatment of Whiteflies:

Environmentally freindly:

For small infestations, remove flies by hand.
Make a loop of bright yellow electrical/insulation tape into a loop, sticky side on the outside, place it near to the infected plant. The white flies are attracted to the yellow colour and will get stuck onto the sticky tape.

Chemical:

Bifenthrin
Cyfluthrin
Deltamethrin
Diazinon
Fatty acids + pyrethrin
Malathion
Oleum
Permethrin
Phenothrin/tetramethrin
Pyriproxifen