Tracking origins of invasive herbivores through herbaria and archival DNA: the case of the horse-chestnut leaf miner

Determining the native geographic range or origin of alien invasive species is crucial to developing invasive species management strategies. However, the necessary historical dimension is often lacking. The origin of the highly invasive horse-chestnut leaf-mining moth Cameraria ohridella has been controversial since the insect was first described in 1986 in Europe. Here, we reveal that herbarium collections across Europe indicate a Balkan origin for C ohridella. We successfully amplified nuclear DNA and mitochondrial DNA barcode fragments from larvae pressed within leaves of herbarium samples collected as early as 1879. These archival sequences confirm an identity of C ohridella and set back its history in Europe by more than a century. The herbarium samples uncovered previously unknown mitochondrial haplotypes and locally undocumented alleles, showing local outbreaks of C ohridella back to at least 1961 and dynamic frequency changes that may be associated with road development. This case history demonstrates that herbaria are greatly underutilized in studies of insect-plant interactions, herbivore biodiversity, and invasive species' origins.