Calepitrimerus vitis
Calepitrimerus vitis
The eriophid mite or bronze acariosis (Calepitrimerus vitis Nalepa, 1905) is a small arachnid belonging to the Eriophyidae family.
Systematic –
From a systematic point of view it belongs to:
Eukaryota domain,
Kingdom Animalia,
Subkingdom Eumetazoa,
Superphylum Protostomia,
Phylum Arthropoda,
Subphylum Chelicerata,
Class Arachnida,
Order Prostigmata,
Superfamily Eriophyoidea,
Eriophyidae family,
Genus Calepitrimerus,
Species C. vitis.
The term is basionym:
– Phyllocoptes vitis Nalepa, 1905.
Geographic Distribution and Habitat –
Calepitrimerus vitis is the mite that causes vine acariosis, present in France since 1950. This parasite is widespread throughout the wine-growing area, especially in the northern areas where budding is more difficult at the beginning of the season; rarer in the south. It is especially harmful to young vines which are more sensitive than older ones.
Morphology –
Calepitrimerus vitis is a very small mite which, like all eriophids, has only two pairs of legs.
The adult female measures 0.15 mm while the males (few in number) are smaller.
Aptitude and biological cycle –
Calepitrimerus vitis has sexual and/or parthenogenic reproduction.
To feed, the mite pierces plant tissues with a stylet made of needle-like chelicerae. The yellow-brownish wintering females (called deutogynes) spend the winter in colonies of 5-100 individuals under the first dark perula of the buds, more rarely in the down. Gems in positions 6–9 are often the most affected. Females can also be observed in the folds of the annual shoots and under the bark of 2-3 year old wood, where sometimes there are thousands of them. When budding they invade the first 5 leaves. The following generations, white-cream in colour, subsequently honey (protogynous), progressively colonize the young leaves, since their formation. The axillary buds are also infested.
In temperate climates, 4 generations follow one another over the course of the season, which can become 7–10 in warmer areas or years. Egg incubation lasts 8–10 days and development to adulthood takes 7 to 10 days. The first generation of protogynous females appears at the end of May, while the deutogynous ones appear from August, but especially in autumn when they reach their wintering places.
As for damage, slow growth of the vine favors it in spring. The buds do not germinate, or only late. If shoots form, they remain stunted; the internodes are short and often zigzag.
The leaves remain small, curled up into a spoon shape. In severe cases, the vegetation freezes, the bunches abort, drip or develop into tendrils, the leaves darken and fall. Due to the development of secondary buds the vegetation becomes bushy. If the attack is weak, the axis of the shoot remains normal, but the leaves are bullous and more or less deformed. In transparency, yellowish punctuations are visible, often confluent near the petiole or scattered heterogeneously on the edge. There are no, or few, necrotic areas visible to the naked eye. In June the main leaves still show these stippling and there may be some deformations. Be careful not to confuse these symptoms with those of excoriosis or eutipiosis, or with damage from thrips or herbicides (glyphosate).
In summer the upper side of the leaves that are well exposed to the sun progressively darkens, while the lower side remains a patinated grey-white colour. When the damage is severe, the entire leaf is colored with a reddish-brown hue with bronze reflections, hence the name bronze acariosis. However, the photosynthetic activity of these leaves is not reduced. Some bunches darken, at least in part, and undergo more or less pronounced dripping.
After the death of the affected epidermal cells, some acini split. The entire stump, or the entire plot, can turn dark, while the new leaves in the upper part of the vegetation show the symptoms of spring acariosis: deformations, blistering and yellowish stippling.
Ecological Role –
Calepitrimerus vitis is an arachnid described by Alfred Nalepa in 1905.
To verify the infestation of this mite, checks must be carried out. Quantitative controls of the overwintering populations in the buds are carried out in the laboratory with the washing-immersion method. The sample must have from 10 to 20 shoots, depending on the size of the plot. To weigh the alternation of density from one organ to another, two successive buds must be taken for each strain taken.
The irregularity of the distribution makes it difficult to set a precise tolerance threshold. Starting from 5 mites on average per bud, the plot must be monitored in spring and, if necessary, treated. Attacks are generally assessed as serious starting from 15–20 mites on average per bud, which often corresponds to the presence of significant populations under the bark.
In summer the leaf tolerates 50 to 100 mites without damage. During the season, monitoring the symptoms will allow you to decide, depending on their severity, whether to intervene immediately for curative purposes or whether to wait until the following year. It is necessary to monitor the young plantations (from the 1st to the 4th leaf) and the vineyards adjacent to the attacked plots, since these eriophids are transported with the plants, by the wind and by human activity.
Natural antagonists and control These eriophids are preyed upon by various mites and some insects. A sufficient number of typhlodromes can keep populations at a weak level.
If necessary, young vines should be treated during the 2nd or 3rd year, before introducing these predators.
In the event of a significant attack, it is advisable to treat the following year, at budding.
If the pressure is weak, early desuckering favors the rapid development of the shoots and is sufficient to avoid stunting of growth. In case of growth arrest, a specific acaricide can be applied.
Summer treatments are useless.
It should be underlined that the greatest problems occur during vegetative growth and at the end of summer. The cause of the unwelcome return, however, is linked to the alteration of the biological balance of the vineyard habitat: before intervening it is better to verify the correctness of the diagnosis.
In vineyards which in the previous season showed attacks by Calepitrimerus vitis, having reached the phenological phase of budding (leaf buds), it will be advisable to intervene with the specific acaricides biphenazate or abamectin.
Alternatively, but with caution to avoid any phytotoxicity effects, products that are also permitted in organic farming can be used such as with potassium salts of fatty acids, mineral oil and sulphur.
The latter could be preferred if it was necessary to intervene against powdery mildew in this period. The symptoms of the attack of the acariosis agent (deformed shoots that tend to dry out, shortened and “zig zag” internodes) can be confused with viral diseases and vice versa. Therefore, it is always advisable that the diagnosis is confirmed by a specialized laboratory (observation under the microscope of a technician with an “expert eye” is enough) to avoid unnecessary treatments. Furthermore, it will be possible to intervene against acariosis even in the middle of summer, if satisfactory results have not been obtained during budding or if at this stage it has not been possible to diagnose the C. vitis infestation.
Guido Bissanti
Sources
– Wikipedia, the free encyclopedia.
– GBIF, the Global Biodiversity Information Facility.
– Laffi f., 1983. Mites of agricultural interest. Cooperativa Libraria Universitaria Editrice. Bologna.