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Phyllonorycter robiniella Clemens
Lepidoptera: Gracillariidae
Has 3 overlapping generations per year (VI-X.). Monophagous on Robinia. The white caterpillars make oval blotch mines on the underside of the leaves. The mine never crosses the midrib. Regularly -particularly if the population density is high- more than one mine can be found on a leaf. These mines often merge each other and therefore sometimes even 15 larvae can be found in one mine. The fully grown larvae pupate in oval, white cocoons within the mine. Native to North America, found there throughout the natural range of Robinia pseudoacacia. It was accidentally introduced to Europe and first reported near Basel, Switzerland, in 1983. Later, it was also reported in France, Germany, Italy (1988), Austria (1989) and Slovakia (1992). It spread gradually through Austria, reaching NW Hungary. Mines were first observed in the autumn 1996. The rate of spread increased significantly after reaching Hungary. In 2 years it had practically invaded the whole country, a distance of ca. 500km in a West to East direction. The fast spread of this species (and also Parectopa robiniella) on black locust, is a phenomenon unique to Hungary because black locust is found throughout the whole country, comprising about 365,000 hectares, 21,6 % of the forested area. It causes the same type of damage as Parectopa robiniella - early leaf fall in mid-summer. The long-term impact of the chronic defoliation is as yet unknown but likely will significantly decrease the locust's productivity. These two species often occur together, but mines of the Phyllonorycter's first generation appear a few weeks prior (early June) to mines of Parectopa. In 2002 this species damaged ca. 11000 hectares of locust forests in Hungary. Unlike in case of Parectopa, the native parasitoids seem to "learn" this invading species and can cause mentionable mortality. The most significant parasitoid species are the braconid Pholetesor nanus (its pupa can be seen near the Phllonorycter pupa on the photo) and the eulophid Pediobius saulius.
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