Predator complex of the horse chestnut leafminer <i>Cameraria ohridella</i>: identification and impact assessment

Abstract

Abstract: The control of Cameraria ohridella Deschka and Dimic (Lepidoptera, Gracillariidae) by natural enemies in Europe is poor. Thus, in the past 15 years epidemic population densities of the moth regularly caused a continuous pre‐mature defoliation of horse chestnut trees, Aesculus hippocastanum L.. Whereas several studies investigated the parasitoid complex of the leafminer and revealed its inefficiency, only little is known about the predators of C. ohridella . The aim of this study was to identify the predator complex in European horse chestnut stands by visual observations and exposure experiments and to assess the impact of different predator guilds on C. ohridella populations by an exclusion experiment. Of all potential predators observed, only blue tits, Parus caeruleus L., great tits, Parus major L., marsh tits, Parus palustris L. and the southern oak bushcricket Meconema meridionale (Costa) were found to prey on the pre‐imaginal leafminer stages. Bushcrickets have to our knowledge never before been recorded preying on leafminers; moreover M. meridionale showed a measurable negative impact on the C. ohridella population. However, birds seem to be of greater importance as predators of C. ohridella than arthropods. Predation rates of birds ranged from 2 to 4% of leafminer populations, which is of the same order of magnitude as published parasitism rates. We conclude that the augmentation of tit densities, for example via nesting boxes in chestnut trees, should be considered as a component of an integrated control strategy against the horse chestnut leafminer.