|Scientific Name||Trialeurodes vaporariorum Westwood 1856|
|Common Names||English: Glasshouse whitefly; German: Weisse Fliege; Spanish: Mosca blanca de las hortalizas; French: Aleurode des serres; Italian: Aleirode delle serre; Dutch: Witte vlieg|
Adults look like small moths, are about 1.5 mm (0.058 inch) long, and have pale yellow wings, powdered with white wax. At rest, these are held flat, giving the insect a triangular appearance - in contrast to the otherwise similar-looking Bemisia tabaci, which folds its wings alongside its body and is smaller. In flight, the wings of T. vaporariorum span up to 5 mm (0.19 inch).
The nymphs are usually pale green, sometimes yellow or brown,flat-oval shaped and up to 0.8 mm (0.03 inch) long.
The nymphs and adults of whitefly suck plant sap from the phloem. Due to their often very large numbers (2,000 individuals and more per leaf are not uncommon), the loss of nutrients can lead to growth deformation, yield reduction, wilting of leaves, and in extreme cases the death of the plant.
At least the same amount of injury again is caused by honeydew. As is typical for phloem-feeding insects, whiteflies have to ingest a lot of plant sap, because they need the proteins and amino acids that are contained only in low concentrations, in contrast to the rather large amount of carbohydrates. So they excrete the excess liquid, with most of the sugars still in it, as honeydew. This can be produced in copious amounts (literally dropping from the leaves) and it will cover all plant surfaces beneath the feeding sites with a sticky film, which will serve as a substrate for sooty molds that interfere with photosynthesis and render fruits unmarketable.
While T. vaporariorum is less important as a vector than B. tabaci, it does transmit some viruses of the Crinivirus type that can cause significant damage, and its importance in this respect has increased during the last years.
Each female lays about 2-7 eggs per day, inserting them into slits in epidermal cells or into stomata, mostly on the undersides of leaves. On smooth leaves, it arranges them in a circular pattern, whereas on hairy ones, they are distributed irregularly.
About one week after oviposition, the first instar nymphs hatch. Being mobile, they are called 'crawlers'. As soon as they have successfully inserted their stylets into a suitable phloem vessel, they become sessile for the rest of their development, which comprises three more instars, the last of which eventually transforms into a pupa. The larva stops feeding and its outer appearance changes. It develops long wax filaments around its margins, changes its color and form, becoming more 'box-shaped' . The duration of this stage is 3-9 days: the whole nymphal development may last 9-18 days. The adults live about 3-6 weeks, during which time each female may lay several hundred eggs. Reproduction is almost always parthenogenetic. Under favorable conditions, the whole life cycle can be completed in 3-4 weeks.
For oviposition, the youngest parts of the plant are preferred, so most adults settle there. The distribution of the different life stages on fast-growing plants frequently shows a certain stratification effect due to the alternating mobile and sessile phases.
Additional Crop Information
T. vaporariorum probably has the most comprehensive host range of all insect pests. It includes about 800 species. Besides vegetables, the most threatened crops in glasshouses are ornamentals.
T. vaporariorum originates from Central America, but is nowadays found worldwide. It is originally a (sub-)tropical species and, although it can even withstand slight frost for a short time, it is only found in glasshouses in cold climates, at least during the winter. It was accidentally introduced to Europe in the middle of the 19th century.
It is considered the most harmful insect pest in greenhouses. However, during recent years, it has also gained importance as a pest of field-grown vegetables.
Integrated Crop Management
Careful monitoring is essential for all management strategies. Proper hygiene can at least delay outbreaks. Meticulously check all plants and materials that are brought into the greenhouse.
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