The role of geography and host abundance in the distribution of parasitoids of an alien pest

Abstract

Chalcid wasps (Hymenoptera: Chalcidoidea) are probably the most effective and abundant parasitoids of the horse chestnut leaf miner (Cameraria ohridella), an alien pest in Europe that lacks specialized enemies. We studied how the species richness and abundance of chalcids are influenced by altitude, direction of an alien spread and host abundance ofC. ohridella. We quantified the numbers and species richness of chalcid wasps and the numbers ofC. ohridellathat emerged from horse chestnut (Aesculus hippocastanum) leaf litter samples collected from 35 sites in the Czech Republic. Species richness of chalcids, which was considered an indicator of the possible adaptation of parasitoids to this alien host, was unrelated toC. ohridellaabundance, direction of spread, or altitude. Chalcid abundance, which was considered an indicator of parasitism of the alien host, was strongly and positively related toC. ohridellaabundance. Chalcid abundance was negatively related to direction of spread and positively related, although in a non-linear manner, to altitude. The relationship of chalcid abundance with direction of spread and altitude was weaker than that withC. ohridellaabundance. The results provide evidence that biological control of the alien pestC. ohridellaby natural enemies might develop in the future.