The horse-chestnut leaf miner (Cameraria ohridella) is a leaf-mining moth of the family Gracillariidae. The horse-chestnut leaf miner was first observed in North Macedonia in 1984, and was described as a new species in 1986. Its larvae are leaf miners on the common horse-chestnut (Aesculus hippocastanum). The horse-chestnut leafminer was first collected and inadvertently pressed in herbarium sheets by the botanist Theodor von Heldreich in central Greece in 1879.

Damage

thumb|left|Leaf miner damage

thumb|left|Leaf miner damage throughout the canopy

Cameraria ohridella causes significant damage, mainly late summer browning, to the appearance of horse-chestnut trees. Despite the poor appearance of these infested trees, there is no evidence that damage by the moth leads to tree death. Seed weight, photosynthetic storage and reproductive capacity may however be reduced. Trees survive repeated infestations and re-flush normally in the following year. It appears that most of the damage caused by the moth occurs too late in the growing season to greatly affect tree performance. The larva starts to pupate around four weeks after the egg hatches and, except when hibernating as a pupa in the mine, the adult emerges around two weeks later. In severe infestations, the mines of individuals can merge and almost the entire leaf area may be utilised. When this occurs it may lead to high moth mortality as the larvae compete for space and food. The moth is able to go through up to five generations each year, if the weather is hot and dry; on average in western Europe, the moth goes through three generations each year. The last generation of the year pupates for over six months so as to survive the winter. The pupae are extremely frost tolerant and have been recorded to survive temperatures as low as . This allows its populations to increase even after hard winters.

Distribution and dispersal

thumb|Distribution map (1984-2007)

Cameraria ohridella has now been found in Albania, Austria, Belgium, Belarus, Bosnia and Herzegovina, Bulgaria, Croatia, the Czech Republic, Denmark, England and Wales, Estonia, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Kosovo, Latvia, Liechtenstein, Lithuania, Luxembourg, Moldova, Montenegro, the Netherlands, North Macedonia, Poland, Serbia, Romania, Russia, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and Ukraine. Although horse-chestnut occurs naturally mostly above the contours

Origin and epidemiology

Cameraria ohridella was first noticed from outbreaks near Ohrid Lake, Yugoslavia in 1984, and was described as a new species by Deschka and Dimić in 1986. This Balkan origin is further documented by numerous herbarium samples that date back to 1879. but is not thought to pose such a strong risk to these species unlike to the common horse-chestnut. However, for biological control a highly specialist parasitoid still needs to be found.

Predators

thumb|A juvenile blue tit feeding on C. ohridella

thumb|Horse-chestnut leaf miner tree damage in Parma, Italy

A number of natural predators of the larval stages of C. ohridella have been recorded. Observations have shown that blue tits (Cyanistes caeruleus), great tits (Parus major) and marsh tits (Poecile palustris) feed on the larvae. Between them, three tit species are thought to prey on between 2 and 4% of the larvae. The southern oak bushcricket (Meconema meridionale) has also been found to prey on C. ohridella, consuming around 10 larvae per day. Overall the predation by the southern oak bushcricket is insignificant compared to that by birds however. Experiments with the predatory mite Euseius finlandicus, bush crickets (Phaneroptera sp.), ladybirds and lacewings found that none prey on C. ohridella.

Procedures

Inadvisably, trees can be removed, or better, leaves cleared and burned before adult emergence by the end of March. Use of the systemic insecticide imidacloprid A synthetic pheromone can be used to trap males, but effective control may be hard to thus achieve. In any case, infestation levels could diminish over time as Cameraria ohridella starts to recruit generalist members of the local parasitoid wasp community.

Projects

A number of projects have been launched to investigate the biology and biological control of Cameraria ohridella and its impact since 2001, for example, an EU-wide multidisciplinary project, CONTROCAM ("Control of Cameraria") and the HAM-CAM Project.

References

  • Taxon page for Cameraria ohridella Deschka & Dimic 1986. In: EOLspecies in English
  • HAMburger-CAMeraria-Projekt - Films Photos incl. REM in German
  • Cameraria Homepage in German and English
  • Czech Academy of Sciences Cameraria homepage in English
  • Forestry Commission Research page in English
  • Mactode Publications - Educational Resources on CD/DVD in English
  • HAMburger-CAMeraria-Projekt in German
  • Abstract of HAM-CAM-Projekt, 2003
  • BBC News report on infestation in Leicester, England, September 2010
  • BBC News report: Citizen science charts horse chestnut tree pest spread, 25 January 2014