Pests
Yponomeuta malinellus Zeller - Apple Ermine Moth
Systematic position.
Class Insecta, order Lepidoptera, family Yponomeutidae, genus Yponomeuta. Vicarious species Yponomeuta orientalis Zagulajev causes harm to apple in the Far East.Synonym.
Hyponomeuta malinella Zell.Biological group.
It is an oligophagous pest of apple (Malus silvestris, M. domestica, M. praecox).Morphology and biology.
Forewings are white, with 12-16 black dots, located in three irregular rows; the top of available fine black speckles are visible at the wing apex (wingspan 16-22 mm). According to some references the moth does not differ externally from Yponomeuta padellus, other data differentiate the former species from the latter by a white fringe at the external margin of forewings. Hind-wings are ash-gray. Eggs are yellowish, flattened and elongate-ovate. Caterpillars of I-III instars are light yellow, with dark head, prothoracic scutellum, and thoracic legs; caterpillars of IV instar are yellow; caterpillars of the last instar are 13-16 mm long. Pupa orange-yellow in the beginning, later chartreuse; head dark-brown. Cocoons white, dense. Fertility of the moth reaches 150 eggs. Female lays eggs in groups (15-60 imprecated eggs in a batch) on branches of host plants near buds, covering the eggs with a shield formed by hardened slime. The shields are reddish in the beginning, later brownish. Eggs develop in 8-15 days. Caterpillars crawl from under the shield, penetrate into swollen buds, and then mine the top part of leaflets. After the first molt (after 10-12 days) they abandon mines and live openly. Caterpillars plait web nests, fastening leaves in twos; they gnaw around leaf plate or completely eat around leaves, leaving the main veins. Moving on to neighboring branches, they form colonies within web nests, containing to 200-300 caterpillars. Duration of larval stage (including wintering) is 300 to 320 days, and the period of active development in spring is 37-45 days. Duration of pupal development is 8-15 and sometimes 20 days. Pupation occurs in white dense opaque cocoons aggregated together in compact packs, each containing up to several hundred cocoons. Caterpillars of 1st instar winter under dense thick shield, in contrast to thin shield in Y. padellus. They hibernate at the approach of frost.Distribution.
This species lives in the central part and in the south of Western Europe. In the former USSR its natural (ancestral) area is limited to the European part (to the Leningrad Region in the north). The Apple Ermine was introduced into Transcaucasia, Kazakhstan, and Central Asia.Ecology.
This is a strictly monovoltine species. Caterpillars of 1st instar leave the shields in the 2nd half of April after transition of daily average temperature through 12 degrees C. Caterpillars usually exit from mines during the period of apple flowering. Dry and hot weather is favorable for the development of caterpillars. They pupate at the time of abscission of redundant seed-buds by apple trees. Moths fly from the end of June until the end of August. Life expectancy of the imagoes is 20-30 days; additional feeding is not necessary. In the afternoon they sit motionlessly, mainly on the lower side of leaves in the shade. Active flight begins right before twilight and lasts until dark. In 2 weeks after the exit the moths mate, and in 5-6 days the females start to lay eggs, finishing oviposition in the second half of July. In 8-15 days the caterpillars hatch, wintering under waterproof shields. The main entomophages for this species are Ageniaspis fuscicollis Dalm., Elasmus albipennis Thorns., Tetrastichus evonymellae Bche., etc.Economic significance.
This species develops on all species of apple, sometimes on pear. In the absence of control measures this species is a dangerous pest of horticulture, especially in steppe and forest-steppe areas. Caterpillars mine and eat around apple leaves. The damaged leaves are distinguished by brown tips. During mass reproduction the trees lose all leaves which results in the abscission of all seed-buds, and the remaining fruits decrease in size. There has been cases of the complete loss of fruits reported. General resistance of trees to adverse environmental conditions is reduced; e.g., their frost and drought resistance decrease. Because of the strong exhaustion of trees they do not produce fruit well the next year.Control measures.
Agronomical control measures: gathering and destruction of falling leaves in summer, removal and burning of web nests with caterpillars and pupae. Biological control measures: introduction of the parasite Ageniaspis fuscicollis, application of biological preparations. Chemical control measures: insecticide treatments (usually against a complex of harmful Lepidoptera) early in the spring, before bud blossoming and before exit of caterpillars from under shields, and also at the end of apple flowering, right after the falling of petals.With the absence of treatments against the complex of spring lepidopteran pests the Y. malinellus population is sometimes able to considerably exceed thresholds in some industrial orchards according to the following sources: Petrov (1958), Aleksidze (1983), Rilishkene & Zayanchkauskas (1984). The pest is mainly limited by control measures used against all early spring orchard pests; treatments against bud pests and Codling Moth also reduce the Y. malinellus population density.Reference citations:
Gershenzon Z.S. 1974. Family Yponomeutidae. In: Vasil.ev V.P., ed. Pests of agricultural crops and forest plantations. V. 2. Arthropods. Kiev: Urozhai. 245-250 p. (In Russian)Gershenzon Z.S. 1974. Yponomeutidae, Argyresthiidae. In: Puchkov V.G., ed. Fauna of Ukraine. V. 15(6). Kiev: Naukova Dumka. 132 p. (In Ukrainian)
Gershenzon Z.S. 1986. List of Yponomeutidae (Lepidoptera) of the USSR fauna. In: Gilyarov M.S., ed. Proceedings VEO. Lepidoptera of the USSR. V. 67. Leningrad: AN SSSR. 10-19 p. (In Russian)
Kurbanova D.D. 1967. Biology of Yponomeuta malinellus in Azerbaijan and its difference from Y. padellus. Zoologicheskii zhurnal, 46(4): 551-554. (In Russian)
Savkovskii P.P. 1976. Atlas of the pests of fruit and berry plants. Kiev: Urozhai. 207 p. (In Russian)
Sinev S.Yu. 1994. Family Yponomeutidae (Hyponomeutidae). In: Kuznetsov V.I., ed. Insects and mites - pests of agricultural plants. V. 3(1). Lepidoptera. St. Petersburg: Nauka. 247-254 p. (In Russian)
Vasil.ev V.P., Livshits I.Z. 1984. Pests of fruit crops. Moscow: Kolos. 399 p. (In Russian)