Glasshouse whitefly
The glasshouse whitefly (Trialeurodes vaporariorum) is a species of tropical origin (from Brazil or South Mexico). Nowadays it is a wide spread pest of agricultural and flower-ornamental crops (more than 300 plant species) in outdoor planting and glass-covered ground. The largest number is observed near greenhouse enterprises where the pest survives winters. The glasshouse whitefly is an agent of numerous virus infections. In many countries it is recognized as a quarantine pest.
Biology. Life cycle.
The body is 1.0–1.5 mm in length, yellowish, oblong, covered with a white meal waxen coating. The antennae are 7-segmented. The first 2 segments are spherical, others are thin and long. The last segment ends with a thorn-like hair. There are compound and simple eyes. Two pairs of white wings are covered with a waxen coating. In dormant state they are folded plainly over the back side of an abdomen. The legs are long and thin, the tarsus (paw) is 2-segmented with 2 claws.
The female lays 10–20 eggs in clumps on a leaf underside. They are attached to a leaf with a stemlet. The larvae emerged from the eggs are oval and flat. They have 3 pairs of legs and move on leaves during several hours. Then the larva sticks to a leaf. Larva stage takes 10–14 days. Within this period the larvae molt twice. The larvae of 2nd and 3rd ages have rudimental legs and antennae, therefore they lose motility. The larva of 4th age is known as a puparium is oval, convex, green-light with a belting bend. It has 5–8 long waxen filaments, several pairs of big hillocks on a back and a range of papilla-shaped glands at the edge of a body. The winged individuals emerge in 13–15 days. The female lives about 30 days and lays 85–130 eggs. The full development duration of one generation at a temperature of 21–23°C is 23–29 days.
Life mode of the insect
The insect multiplies in a greenhouse all the year and reproduces 10–12 generations. Particularly they are numerous in summer months. So far as the larvae need in a large quantity of aminoacids for active growth they consume a lot of plant sap. This sap contains the surplus of sugars. It is excreted in form of sugary wastes on which sooty fungi develop. Immediately after flying out of a puparium an adult whitefly begins feeding and mating. The fertilized female lays eggs, and individuals of both the sexes emerge from them. If the mating doesn't take place there emerge males from the laid eggs only. Usually sex ratio in a progeny is 1:1. In hot period the number of the males increases. The pest is unpretentious to hydrothermal conditions (temperature, air humidity). It is the most active and harmful in spring-summer period. The larvae and the imago usually inhabit leaf undersides of various plants. They prefer moist and shade places.
Symptoms of injuries
Sucking out cell sap the pest causes yellowing of leaves. Sooty fungi settling sugary excretions deteriorate the assimilatory ability of leaves and the ornamental value of plants.
