The glasshouse whitefly Trialeurodes vaporariorum and the tobacco whitefly Bemisia tabaci are major pests of many vegetable and ornamental crops. Due to its high resistance to most insecticides, the tobacco whitefly poses a particular threat to many crops.
The whitefly goes through six stages, namely egg, first, second, third and fourth larval stage (which develops into a pupa) and adult. The adult whiteflies can usually be found in the top of the plant and on the underside of young leaves, where they deposit their eggs. When shaking infested plants, adults will first fly, then return to the underside of the leaves. The larvae are found on the underside of young leaves; pupae are found on the oldest leaves. Larvae of Bemisia tabaci can occur on both young and old leaves.
- Bigger larvae in particular secrete honeydew whilst feeding, on which sooty moulds develop. Also larvae produce large amounts of wax on and around their dorsal surface. These substances soil the crop and reduce production.
- Both adult whiteflies and larvae extract food from the plant. This influences the plant's physiological processes, and can cause growth reduction.
- Viruses may also be transmitted.