Trialeurodes vaporariorum and Bemisia tabaci have 3 developmental stages that take place on the underside of zucchini leaflets: egg, 4 larval stages, and adults. The duration of the complete cycle (figure 1) varies according to the temperature. It fluctuates for T. vaporariorum from less than 20 days at 27 ° C to more than 40 days at 14 ° C (more than 50 days for B. tabaci ).

• Forms of conservation and / or alternative hosts

These insects do not have a stage suitable for the winter phase. They only survive if their hosts do not die. Note that the eggs can be subjected to temperatures below 0 ° C for several days. These whiteflies are easily maintained on many cultivated hosts, but also on various weeds, which should therefore be removed carefully.

• Stages of development

The eggs (Figures 2-1 and 2) (Figures 2 and 3) are mostly deposited on the underside of the leaflets at the apex. White in color, they are oval and have a diameter of 0.25 mm. In the days following the laying, they turn dark. Between 7 and 10 days later, the hatch larvae (figures 2-3) (figures 4 and 5); these, oval and flat, measure 0.3 mm and have well-developed antennae and legs. Losing these later, they are motionless and feed with their rostrum. The second instar larvae are flattened, transparent and measure 0.37 mm. The third and fourth instar larvae are quite comparable (Figures 2-4 and 5), but with respective lengths of 0.51 and 0.73 mm. In the last larval stage, the insect secretes wax. It is when its red eyes appear that it is referred to as a puparium (Figure 2-6) (Figure 6). Subsequently, the whitefly develops and takes on a white tint. The adults (figure 4-7) (figures 7 and 8) have 2 pairs of wings, their size different according to the sex: 1.1 mm for females and 0.9 mm for males. The body and wings are coated with a characteristic white waxy powder. Slight morphological criteria (which can be consulted in the table below) make it possible to differentiate the two insects. The larvae and adults, often present on the underside of the blade, feed through their rostrum which acts as a suction pump. The excess sugar in the sap is released in the form of honeydew, especially by the large larvae.
 

 

• Dispersion in culture

Concentrated on a few plants at the start of an infestation, the adults easily fly around the greenhouse and disperse as plant sizes and temperatures increase. The wide distribution of plants of horticultural species in particular has largely contributed to the dissemination of B. tabaci throughout the world.

• Favorable development conditions

These insects appreciate mild temperatures and summer shelter conditions. Their lifespan is between 10 and 20 days on tomato; of course, it fluctuates according to the temperatures. B. tabaci , which does not survive temperatures below 0 ° C, has higher thermal requirements than T. vaporariorum .

Last change : 04/19/21