Erschoviella musculana
(Asian walnut moth)

In Central Asia, outbreaks of E. musculana occur in valley and mountain forests and orchards up to an altitude of 1900-2100 m.

E. musculana is considered as a serious walnut pest in many southern countries of the former USSR. It is very likely to be able to establish in the many European and Mediterranean countries of the south and east of the Europe where its host plants are important nut trees.

In valleys and on southern slopes of mountains at altitudes of 1100-1300 m, the mass flight of the first generation of E. musculana usually occurs from the beginning of April until the end of May. The mass flight of the second generation occurs in June-July. The mass flight of the third generation occurs in August. At higher altitudes (1700-1900 m), the pest develops only two generations per year. In this case, the first generation flies in May and the second at the beginning of August. Above 1900 m, the pest develops only one generation per year and the flight is from the end of May until June. Adults feed on nectar and live for 21 days. The female lays 30-120 eggs, usually two or three together on young nuts (often where two nuts are touching) or on buds of one-year-old shoots of walnut. Neonate caterpillars usually enter the young nut through the petiole and feed there. After finishing one nut, a caterpillar passes into another and continues to feed. Infested nuts usually contains one caterpillar but it is possible to find nuts with two, and even three, caterpillars. The caterpillar moults four times. Development takes 25-40 days. When leaving the fruit before pupation, the caterpillar makes a round emergence hole, which is much larger than the entrance hole and is not filled with excrement. Caterpillars of the autumn generation cannot enter the nut, and so feed only in the pericarp. Caterpillars also often feed in the centre of young one-year-old shoots and even in leaf axils; this happens more often during years of low harvest of nuts. In this case, the entrance hole (usually at the base of leaf petiole) is also small and filled with excrement (easily seen from outside), whereas the round emergence hole (usually in the terminal bud) is much larger and free from excrement. Caterpillars usually spend all their life inside nuts and shoots, and they leave them only to find a place for pupation. They usually pupate in deep cracks in the bark or under loose bark in the butt part of the trunk up to several metres above the soil. It is possible sometimes to find large aggregations of cocoons (up to 170 specimens) in some refuges (usually under loose bark). Caterpillars of the first two generations may also pupate in the grass or on branches. Pupal development takes about 10 days. The pest overwinters at the larva or pupal stage inside the cocoon (Vassiliev, 1912; Degtyareva, 1964; Makhnovskii, 1955, 1970; Dzhaparov, 1990).

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Possibilities for control of the pest are very limited. During almost all its life cycle, it is well protected against chemical and bacterial treatments. On young trees, trapping bands are used against pest caterpillars. Removing and destruction of fallen fruits may give good results. It is also possible to destroy aggregations of pest pupae under loose bark (Degtyareva, 1964; Makhnovskii, 1970; Dzhaparov, 1990).

The natural enemies of E. musculana may play an important role in regulation of its populations. Sixteen species belonging to Ichneumonidae, Braconidae, Pteromalidae, Torymidae, Trichogrammatidae, Carabidae, Raphidiidae and Formicidae are recorded as parasitoids and predators of the pest. The most frequent of these are Trichogramma sp. and Pimpla instigator. Sometimes, caterpillars are infected by the bacterium Bacillus thuringiensis or the fungus Beauveria bassiana (Degtyareva, 1964; Dzhaparov, 1990).

Phytosanitary Measures

E. musculana was added in 2003 to the EPPO A2 action list, and endangered EPPO countries are thus recommended to regulate it as a quarantine pest. Since the risk of introduction of E. musculana with fruits, cut branches or wood appears low enough to be acceptable, phytosanitary measures need concern only plants for planting of Juglans spp. Freedom from the pest can be ensured by a pre-export inspection.