Life cycle, population dynamics

• Adults Colomerus vitis pass the winter as overwintering females (not diapausant), under the bark, buds near or at the base of the shoots.

• As soon as the buds swell , the phytoptes progress towards them where they begin to prick the young leaf outlines through the scales. The galls are then visible on the young tissue that develops. The adults reproduce in it, laying their eggs as early as mid-April. The populations of phytoptes are concentrated on the first leaves at the base of the twigs, all the more so as the climatic conditions are unfavorable to the growth of the vine (temperature> 10 ° C). The "first cycle" of this mite ends as soon as twig growth intensifies.
  During the summer , the “second cycle” begins with the stopping of vegetation. The leaves then become more and more contaminated until the end of the vegetative period. On the one hand, the “migrant” individuals from the base move towards the apices; on the other hand, the phases of moving step by step cause "partial migrations" by leaps of 2 leaves. These migrations persist in particular thanks to the development of axillary shoots triggered by trimming. These inter-hearts become an important place of multiplication.

• When the leaves fall in autumn, some of the adult phytoptes will have gained the winter buds. The hardening of the epidermis of old leaves (thickening of cell membranes and formation of cork in attacked cells) leads to this winter migration. However, a large part of the populations persists on the other leaves at all stages of development, from egg to adult. Only the overwintering adults will tolerate the first frosts.

• In the end, there are up to 7 generations which follow one another and which can be observed on the foliage.

• Synoptic of the development of Colomerus vitis on vines (figure 1)