Cherry damage and the spatial distribution of European earwigs, (Forficula auricularia L.) in sweet cherry trees

Background: The European earwig, Forficula auricularia is an invasive insect pest found in many temperate regions of the world. Despite being well known predators, they are considered pests in sweet cherry though this has never been empirically tested. Our aim was to quantify the relationship between damaged cherry fruit and earwig population size, cherry bunch size and earwig distribution in cherry tree canopies in the cherry varieties Ron's Seedling, Lewis, Sweet Georgia, and Lapin.

Results: Significant differences in earwig damage type and frequency were observed between varieties with earwig exclusion significantly reducing damage by 21% in Lapin and 34% in Ron's Seedling. Earwigs were strongly aggregated within cherry bunches, with greater numbers and damage observed in larger bunch sizes in all varieties except Ron's Seedling where stem damage was independent of bunch size. In Ron's Seedling, cherry stems were 40x more likely to be damaged than Lewis stems and Lewis fruit two times more likely to be damaged than Ron's Seedling fruit. Sweet Georgia fruit were 4.5 times and stems 5 times more likely to be damaged than in Lapin. No predictive relationship between cherry damage levels and earwig numbers either within the tree canopies or within monitoring traps could be determined.

Conclusion: European earwigs may have a significant economic impact to sweet cherry production. The nature of this impact differs between cherry varieties and severity is strongly influenced by factors including bunch size. However, why damage differs between varieties remains unknown and warrants further investigation if the impact of earwigs to sweet cherry production is to be minimised.