Grapevine - Biological cycle

Biological cycle

Daktulosphaira vitifoliae has a complex life cycle that fluctuates depending on the species of Vitis parasitized. On American species, the insect reveals 2 phases during its cycle: an epigeal or aerial phase, and another hypogea or root. On Vitis vinifiera , its entire cycle, which is less complex, is perpetuated in the hypogeal form on the roots; training of sexed adults is very rare.

The epigeal cycle takes place on the aerial organs of the vine, in particular on the non-lignified organs of the plant. The foundresses hatch winter eggs in early spring. They colonize the apical leaves via their upper surface and the edge of the blade, and form galls. The first larval instar is mobile, light yellow in color and conical in shape. Throughout her life, the founder will lay 550 to 600 yellow eggs (figure 1) with a smooth or reticulated surface.

From these eggs gallicole hatch neogallicoles-gallicoles , that is to say individuals forming new galls. Three to 5 generations will follow one another per year without interruption. For 3 weeks, the female adult lays hundreds of eggs, but the fertility rate will decline over generations. The first generation appears 4 to 5 weeks after the appearance of the galls formed by the founder. During their movement, the young larvae can be blown away, which greatly contributes to their dissemination. An increasing rate of individuals will migrate to the roots with each generation. The larvae that leave the maternal galls to migrate to the roots are called neogallikoles-radicoles . The hypogeal cycle takes place at the level of the roots, the individuals are then called radicoles.

The root larvae settle on the root system all the better when the soil is rich in clay. The larvae attach themselves to the root and develop until the adult stage, during which the female will lay about a hundred eggs. The number of eggs laid will subsequently decrease over the generations. There are 6 to 7 generations of root crops in France in general. Gradually, some of the larvae migrate to the soil surface to colonize the foliage, either directly or by wind diffusion.

As winter approaches, young ranchers become winterers able to withstand the harsh winter conditions. Some will first give rise to the pre-nymphs, nymphs and nymphoids that precede the winged forms, which will emerge from the ground and represent the perfect winged and colonizing form. There are 2 types of winged shapes:
- the andropares which lay small eggs males.
- the gynopares producing female eggs large. The laying will take place under the leaves or on the bark. These eggs will give the sexual forms. After fertilization, females will lay a single winter egg fixed by a peduncle in the crevices of the bark. In the spring, the egg will hatch to give an parthogenetic founder wingless of the epigeal cycle.