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The horse-chestnut leafminer Cameraria ohridella Deschka and Dimić, 1986 is a small species of leaf-mining moth in the family Gracillariidae. This species would probably have remained obscure but for its recent dramatic rise into public prominence as a result of a spectacular process of biological invasion in the past 25 years. The basic information given on this page marks the first quarter century of biological invasion of this species, since the first records reported within the type series information (i.e. 8-14 July, 1984). The moth's type locality is 6 km. south of Ohrid (Lake Ohrid) in Macedonia at 705 m. elevation, as reported in the original description (https://www.orleans.inra.fr/content/download/2649/47277/version/1/file/Deschka+and+Dimic+1986+Cameraria+ohridella.pdf). This species has been found to be present as early stages in numerous herbarium collections of native horse-chestnut in Albania and Greece going back to 1879 (Lees et al. 2011). The species has come to wide public recognition in many countries only in the last decade owing to the extreme browning it causes to the white flowered, Common Horse-chestnut tree Aesculus hippocastanum L. (hereafter “horse-chestnut”).
It is relevant to understand the history of this tree species in Europe. This tree derives its latin and common names in several languages from the use of its seeds or their extracts for prevention of equine pulmonary heart disease, coughs or parasites, a practice that dates back to such use in the Ottaman empire centered in Istanbul, which included the Balkans (Lack, 2000; 2002). This tree has been widely planted in European parks and cities since the 1570-80s (it was introduced to Paris around 1615: Augustin, 2005). By 1581, the "Castanea equina" had been introduced to Vienna from Istanbul by Karl Clusius, probably as a present from the Turkish Ambassador David Ungnad Graf von Weissenfels, and likely as a living tree (Lack, 2000). Leaf samples were earlier (1563) sent to Ulysse Aldrovandi in Bologna. In 1795-1798, the tree was first discovered growing naturally in the Pindus Mountains of Greece by English botanist John Hawkins, although it had been widely supposed to be of north Indian origin, as reflected in the French common name "Marronnier d'Inde" (Lack, 2000).
The fact then that the appearance of C. ohridella (and indeed the genus Cameraria) in much of Western Europe has been so recent and dramatic, without earlier detection by entomologists, had made its origin a far greater mystery than that of its hostplant. It was originally thought to be a relict species in the Balkans (Deschka and Dimić, 1986; Pschorn-Walcher, 1994; Grabenweger and Grill, 2000), where the horse-chestnut is considered to be a relict from the Tertiary period (Xiang et al., 1998; Avtzis et al., 2007; Harris et al., 2009). A more recent hypothesis (Hellrigl, 1998; 2001) was that the moth is an example of a sudden host plant shift to horse-chestnut, probably from maple or sycamore (Acer spp.), maybe combined with long distance translocation (Kenis et al., 2006; but see also under Origin). Another hypothesis was that this species may have originated in North America (e.g. Kenis et al., 2005), but this was not considered likely, despite the high Cameraria diversity in this region (52 out of 74 described species: Grabenweger and Grill, 2000; de Prins and de Prins, 2005), because of the lack of close relatives of Old World species in the New World and the good knowledge of the North American fauna (Kumata, 1963; Pschorn-Walcher, 1997). The finding of larvae and pupae in the conspicuous mines of this species on herbarium specimens that were collected in remote parts of the southern Balkans by some of the earliest botanical explorations of the region, for example by Theodor Heldreich whose distributed botanical duplicates (from an 1879 collection) contained the earliest known caterpillars of the species (Lees et al. 2011), rules out these hypotheses and clearly shows a Balkan origin for a moth, whose genus was also not previously known to occur in Europe..