Pests
Eriophyes pyri Pagenstecher. - Pearleaf Blister Mite
Systematic position.
Class Arachnida, order Acarina, suborder Tetrapodili, family Eriophyidae, genus Eriophyes.Biological group.
Pest of pear.Morphology and biology.
Body of adult mite is cylindrical, wormlike; the body color is white, changing to pinkish or light brown by autumn. Its size is 0.16-0.27 mm in length and 0.035-0.06 mm in width. Empodium has 4 beams, with 4 pairs of chetoids. Genital valve is 0.019 mm long, with 10-12 longitudinal costulae. Scutum is 0.03 mm long, triangular, devoid of projection over gnathosome. The medial costula is incomplete, while the admedial ones are clear, bent inward at the posterior scutum edge. Dorsal scutum is 0.023-0.025 mm long and 0.018-0.02 mm wide. Abdomen has 70.80 rings and micropapillae. Tergites and sternites are covered with rounded micropapillae, excluding 4-5 caudal half-rings, being smooth on the dorsal side. 86-96 tergites and 84-90 sternites are present. There are accessory chaetae being 0.007 mm long. Length of chelicerae is 0.017 mm, and length of rostrum is 0.02 mm. Legs of first pair are 0.027-0.029 mm long, and legs of second pair are 0.025-0.027 mm long. Fore tarsus is equal to fore tibia in length. Deutogynal females hibernate in buds, crowding by hundreds under first and second sheathing scales. Here they diapause, not feeding and not laying eggs even during temporary warming. Males play no significant role in Blister Pear Mite reproduction. After a short (2-3 days) feeding on buds, leaves, or fruits of pear, females start egg laying (in southern regions, the mites often inhabit fruits; while in central regions, they do it only when year is hot). Female fertility is 5 to 29 eggs. The egg is colorless, ellipsoid. Within the ranges of temperature of 10-17 and 18-26°C, development of eggs lasts 18-20 and 6-8 days, respectively; that of nymph stages (nymph I and II), 16 and 12 days, respectively. Therefore, the cycle is completed within 34-36 days in spring and within 18-20 days in summer. Adult females hibernate.Distribution.
The mite is ubiquitous, being found in all continents where pear grows. The area includes almost the entire European part of the former Soviet Union (Ukraine, Moldova, Belarus), the Caucasus (Georgia, Azerbaijan, Armenia), Kazakhstan, Middle Asia, Siberia and Altai Territory, Northern, Central and Western Europe, Bulgaria, Italy, Minor Asia, North America, Australia, North and South Africa, Australia.Ecology.
Major feeding plant of the Blister Pear Mite is the common pear Pyrus communis, as well as P. salicifolia, P. ussuriensis, P. nivalis, P. pyrastes, and P. sativa. Pest development is recorded also on some other rosaceous plants including apple (Malus domestica), quince (Cydonia oblonga), hawthorn (Crataegus), mountain ash (Sorbus aucuparia), cotoneaster (Mespilus spp.), etc. In spring, mites start activation in southern areas as early as at the end of February . in the beginning of May; i.e., long before bud blossoming, at bud warming to +9°C. When the average daily temperature reaches +10°C, the mites migrate to green part of scale (its lower part), where they feed on the bud juice. Females gradually move to the green part of scale and begin laying eggs. By the phase of green cone, nymphs I emerge from the eggs and migrate toward scale base, gradually moving to petioles of germ leaves. By this time, they transform to nymphs II and young females. Further they migrate to rolled-up leaflets and penetrate into the leaf plate parenchyma. At the places of mites' penetration, flat swellings are formed on both sides of the leaf, referred to as galls with well seen entrance hole on the lower part of the leaf. Pearleaf Blister Mite develops in 2-3 generations. In Georgia, it can produce 5 generations a year. Mites. migration to other trees occurs only with the help of extraneous agents such as wind, animals, human, and so on. The major role in Pearleaf Blister Mite dissemination belongs to humans, who carry the mite-infested plants from seedling farms when establishing new gardens. The pest densities are mainly downregulated by the predatory mites of the families Phytoseiidae, Tydeidae. The mite Typhlodromus rhenanus is registered in Moldova.Economic significance.
The Pearleaf Blister Mite damages most severely seedling farms and young gardens. In seedlings injured by the mite, bark is hardly scaled off during bud grafting, and grafted buds do not survive. Moreover, it causes mass leaf drying in seedling farms and young gardens, sharply hampering the physiological state of plants. In fruit-producing gardens, the mite damages also flowerbuds, ovaries and fruits, provoking their decease and falling out during strong infestation. Due to the hidden way of life, even the intensive treatments hardly make its harmfulness economically insensible. Control measures include chemical sprayings of trees just prior to and during budding, as well as flowerbud denudation. In order to prevent dissemination of the Pearleaf Blister Mite, the seedling and breeding farms should be located at 300 to 500 m or more from the infested plantings. Grafts for inoculation must be cut off from the healthy, mite-free trees only. Vital importance for the Pearleaf Blister Mite control belongs to the usage of resistant pear varieties and to performing the actions favoring the increase of cell juice osmotic pressure in the pear leaves (such as application of increased manure dosages, and so on).Reference citations:
Bagdasaryan, A.T. 1981. Eriophyidae acarines of fruit trees and shrubs in Armenia. Erevan: Izdatel'stvo AN Armyanskoi SSR. 202 p. (in Russian).Busuiok, M.N. 1988. Resistance of pear-trees varieties to pearleaf blister mite. In: Gulii, V.V., ed. Agricultural cultures protection from diseases, pests and weeds in conditions of MSSR (Collection of scientific proceeding). Kishinev: Kishinev agricultural institute, p. 14-19 (in Russian).
Cherkezova, S.R. 2001. Herbivorous acarines. In: Khvostova, I.V. & Makarova, E.V., ed. System-forming ecological factors and criteria of zones of sustainable development of fruit growing in Northern Caucasus. Krasnodar: Northern Caucasus Research Institute for Orchard and Grape Growing, p. 108-111 (in Russian).
Man'ko, I.F. 1958. Pearleaf blister mite and pest control in conditions of BSSR. In: Al'smik, P.I., ed. Collection of proceeding. Minsk: Institute of fruit growing, vegetable-growing and potatoes, 11: 109-114 (in Russian).
Minder, I.F. 1957. Materials on biology of pearleaf blister mite (Eriophyes pyri Pgst.). Zoologicheskii zhurnal 36 (7): 1007-1015 (in Russian).
Prokof.ev, M.A. 1987. Orchard protection from pests in Siberia. Moscow: Rossel.khozizdat, 239 p. (in Russian).
Shvanderov, F.A. 1979. Tetrapod mites (Acarina, Eriophyoidea) on pear. In: Shaldybin, L.S., ed. Fauna, systematics, biology and ecology of helminthes and their intermediate hosts (Republic collection of proceeding). Gor.kii: Gor'kii State Pedagogical institute, p. 109-117 (in Russian).
Sokolov, L.M. 1960. Pearleaf blister mite (Eriophyes pyri Pgst.) and its control measures under conditions of Michurin area of Tambov region. Zoologicheskii zhurnal 39 (4): 521-526 (in Russian).
Vasil.ev, V.P. & Livshits, I.Z. 1984. Pests of fruit cultures. Pearleaf blister mite (Eriophyes pyri Pgst.). Moscow: Kolos, p. 47-49 (in Russian).
Vereshchagina, V.V. 1965. Pearleaf blister mite. Zashchita rastenii ot vreditelei i boleznei 1: 37-38 (in Russian).
Vereshchagina, V.V., Mikhailyuk, I.B. 1972. Pests of pear-tree. Zashchita rastenii 6: 59 (in Russian).
Zotsenko, L.N. 1958. Pests and pathology of fruit culture. In: Kosov, V.V. & Polyakov, I.Ya., eds. Forecast of appearance and survey of pests and diseases of agricultural crops. Moscow: Minsel.khoz, p. 452 (in Russian).