Taxonomy

Cameraria ohridella is a small moth. Adults are around 3.5mm in forewing length. They are orange-brown in colour and have:

• a basal white longitudinal streak
• 4 whitish, bent or interrupted fasciae edged in black
• greyish brown hindwings, long-fringed
• orange-tufted head
• antennae over 4/5 forewing length
• legs with equal white and black bands

Larvae are also small - up to 5.5mm long.

The moth’s leaf mines are easily recognised as multiple, conspicuous whitish yellow and brown blotches on the surface of horse-chestnut leaves and cause significant browning towards the end of the summer.

Evolution

The origin of this moth is a far greater mystery than that of its host plant. C. ohridella, and the genus Cameraria, has only recently made a dramatic appearance in much of western Europe.

In the Balkans, the host plant, the horse-chestnut is thought to be a relict species, which was first found growing naturally in Greece in 1795 (Deschka and Dimić, 1986; Pschorn-Walcher, 1994; Grabenweger and Grill, 2000) from the Tertiary period (Xiang et al., 1998; Avtzis et al., 2007; Harris et al., 2009).

C. ohridella has been hypothesized to also originate in the Balkans, where it forms a relict population as the only known European Cameraria (Dimić and Deschka, 1986; Grabenwager and Grill, 2000; Pschorn-Walcher, 1994).

The work of Valade et al (2009) has shown that a southern Balkan origin is far more likely than alternative hypotheses that suggest:

• it originated in east Asia, perhaps China, where Acer and Aesculus-feeding relatives are known to exist (Grabenwager and Grill, 2000; Kenis et al, 2005)
• that the moth was an example of a sudden host plant shift to horse-chestnut from maples or sycamores (Hellrigl, 1998; 2001) perhaps combined with long distance translocation (Kenis et al, 2006)

Indeed, the recent analysis of mtDNA and microsatellites by Valade et al 2009 showed a reduction in genetic diversity of C. ohridella populations sampled from artificial habitats - such as planted trees in public parks and gardens - across Europe, compared to C. ohridella sampled in natural stands of horse-chestnuts in the southern Balkans.

These findings suggest the hypothesis that the European populations of C. ohridella living on relict horse-chestnut populations in the southern Balkans may have been biogeographically isolated until the advent of modern road infrastructure and transport mechanisms.

Look-alikes

The adults closely resemble some species of Phyllonorycter, but the larvae can be distinguished by reduced legs. The pupae can be distinguished by the absence of cremastral hooks, and the presence of strong spinoid setae in the first to fifth abdominal segments (de Prins et al, 2003).