Two main species of White fly are recognized. Bemisia tabaci (cotton white-fly) and Trialeurodes vaporariorum (greenhouse white-fly). Both species are very harmful to a lot of culture crops.
White flies are no real flies (Diptera), but they belong to the order of Hemiptera. This insect is able to seriously damage plants by feeding on the leaves by sticking their feeding organ into the plant tissue and sucking up cell contents. This will cause growth reduction and it might cause defoliation. On top of this they excrete enormous amounts of “honeydew”. The whiteflies will take up such an enormous amount of sugars that they excrete so-called honeydew which is a source for food to several species of fungi. These fungi will cover the leaves and reduce the photosynthesis capacity. Another negative influence of the white fly on the plant is that the white fly can transmit viruses, like Tomato Yellow Leaf Curl Virus (TYLC) and Tomato Infectious Chlorosis Virus (TICV) can be transmitted by White flies.
The white-flies live mainly in close populations, they disperse only when the population of the white-flies on a plant becomes to big. The plague will start at the beginning on certain spots in the field. Later in time the white flies will disperse over the whole crop.
The white flies undergo a life cycle with certain stages. The first stage is egg, followed by the first, second, third and fourth stadium larvae and mature insect (adult). The eggs are laid at the lower surface of the leaves. The eggs are white and they have a size of about 0,25 mm. After 7 days they become black and hatch into first stadium larvae (mobile). This stadium develops through the different stages into a pupae. During this stage you can already see the red eye’s of the white flies. Eventually the adult will come out of the pupae. The adult starts feeding right away. The adults have two pairs of wings and are mainly found in the top of the plants. Female white flies start laying their eggs one of two days after they came out of the pupae. Till they mated the females only lay male eggs. After they mated, they are able to lay both male as female eggs. The plant species that is invaded by these white flies can determine how long a adult white fly lives and how many eggs a female can lay (1000-2500).
White fly can be treated for example with pesticides like: • Decis (deltamethrin) • Actellic (pirimifos-methyl) • Admire (imidacloprid) • Nomolt (teflubenzuron) • Methomex (methomyl) • Applaud (buprofezin) If possible it might be recommendable to use a natural enemy like Encarsia formosa. Start with biological control in an early stage, it the population needs time to settle in a crop. Work always conform the instructions on the package of the pesticide. Check with local authorities if you are allowed to use these pesticides.
For more information about it, please contact our professional advisory service in HORTICENTAR – Greenhouse training center.