The vine phylloxera Daktulosphaira vitifoliae (Fitch, 1856) (Hemiptera: Phylloxeridae) is a small insect (0,8mm to 1,2mm long), similar to an aphid, that feeds on vine roots and leaves. The hemiptera is native to North America, but it became a pest of economic importance at the end of the 19th century, when it was introduced in Europe and spread rapidly in the main producing countries, decimating wine vineyards. V. vinifera. This occurred because at that time vine plants were cultivated as free plants.
By attacking the roots of V. vinifera (radical form), the insect causes two characteristic symptoms: nodosities and tuberosities. Nodosities occur in the non-lignified tissue of the plant, near the tips of the rootlets, forming hook-like structures (Figure 1). Tuberosities occur in lignified parts of the root, and permanent feeding on these roots can lead to the gradual decline of plants associated with the presence of pathogens present in the soil, due to injuries caused at the sites of stylet insertion during feeding (Figure 2).
In the aerial part, (gallicola form) phylloxera forms structures known as galls (Figure 3) that form mainly on young leaves. Among the symptoms arising from the formation of these galls on the leaves, leaf distortion, necrosis and early defoliation stand out. The gallicola form reaches high populations only in American vines, requiring control in rootstock nurseries and in some years in the aerial part of hybrid cultivars, where it causes a reduction in branch production. Additionally, in new plantings, the insect prevents plant development, making them physiologically more susceptible to biotic and abiotic stresses. Furthermore, the large amount of galls reduces the plants' photosynthetic capacity, reducing the concentration of carbohydrates, reducing the potential for formation of the graft callus during the seedling production stage. Canopy cultivars, hybrids such as BRS Lorena and BRS Bibiana, have demonstrated susceptibility to the gallcolour form of phylloxera, making it necessary to apply insecticides in vineyards in situations of high infestation.
In Brazil, phylloxera has been found in practically all wine-growing regions of the country. Coexistence with the insect, without the negative repercussions observed in other countries, has been attributed to the intensive cultivation of vine cultivars of American origin such as Isabel, Bordo, Concord and Niágara, which host the pest in the roots, but tolerate its attack. In cultivars of V. vinifera The gallicolous form (aerial part) generally does not occur, with only the radiculous form, which remains for the winter period in the nodosities and tuberosities produced.
Soil textural properties, particularly the ratio of sand to clay content, is an important factor affecting the establishment, development and population dispersal of phylloxera. In general, sandy soils minimize pest infestation.
Phylloxera has a complex biological cycle, including sexual, asexual, winged and apterous (wingless) reproductive forms. In spring, through the winter eggs deposited in the rhytidome (outer layer of the bark) of the vine by the apterous sexual forms, the first instar nymphs hatch, which will colonize the new leaves of the vine of American origin and form the first galls. Each gallicultural female can oviposit hundreds of eggs, reproducing parthenogenetically inside the gall (Figure 3). Later, depending on climatic conditions, new chicken females may emerge from these eggs, which will complete several generations on the leaves, or radicular females, which migrate to the soil and develop in the root system, causing knots in young expanding roots or tuberosities in roots. lignified.
At the end of the summer, some eggs of radicular females give rise to winged forms, which emerge from the soil and migrate to the woody parts of the plant (Figure 4). These winged insects oviposit two types of eggs: a smaller one that gives rise to wingless males and a larger one, which gives rise to wingless females. After mating, these apterous forms restart the cycle by ovipositing winter eggs (one per female). In some cases, an alternative route may occur where sexual forms (male egg and female egg) are produced by chicken females. The “fundatrix” (winter egg) is oviposited in the rhytidome of plants, remaining in hibernating form during the winter. Alternatively, in addition to the winter egg, the first instar nymphs may hibernate, while the other stages of development do not survive the cold.
In the roots, the eggs have an incubation period of six days under ideal temperature conditions (22ºC to 26°C), with 90% viability. First instar nymphs are active and can move between roots to establish new feeding points. When the insect moults to the second instar, the gallicolous and radicular forms of phylloxera tend to feed at a fixed point. There are four instars that precede the adult phase, completing this phase in less than a week.
In Brazil, under creation vitro carried out on lignified Cabernet Sauvignon roots, the eggs have an incubation period of 5 ± 0,36 days with 100% viability. The insect goes through four instars, the first being longest, with an average duration of 10,72 ± 0,41 days, the second, third and fourth instars having 1,71 ± 0,06, 1,50 ± 0,06 and 1,57 ± 0,05 days, respectively (Figure 5). Under ideal conditions, (25°C, 70% humidity in the dark) adults on excised roots survive for one month to two months, ovipositing around nine eggs per female daily, with an average of 207,79 ± 11,98 eggs/ female throughout life.
Chemical control of phylloxera, when present in the roots, has not been recommended because, in general, the rootstock species used are resistant to insect attack. The control of the gallicultural form, in fields of rootstock matrices or in new plantings of rootstocks for subsequent grafting, has been carried out from the appearance of the first galls. For canopy cultivars, such as BRS Lorena and BRS Bibiana, the application of insecticides in the vineyards is necessary in situations of high infestation. Insecticides that are effective in controlling the insect are imidacloprid, thiamethoxam, pyrethroids and more recently flupyradifurone.
It is necessary to be aware of the possibility of the appearance of phytophagous mites as a result of the sequential application of broad-spectrum insecticides that cause an imbalance in the population of natural enemies, contributing to the emergence of secondary pests.
Simone Andzeiewski and Daniel Bernardi, UFPel; Marcos Botton, Embrapa Grape and Wine
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