The dual role of earwigs (Dermaptera) in winter grain crops in Australia.
Earwigs have been observed as an irregular pest of increasing concern to farmers growing canola and other winter grain crops in Australia over the past decade. In this study, we tested how abiotic and biotic factors influence the feeding behaviour of earwigs. Studies were conducted with two Australian native species, Labidura truncata and Nala lividipes, and the introduced European earwig, Forficula auricularia. We constructed field-based exclusion plots that prevented F. auricularia from moving in or out of a small area of canola. We monitored F. auricularia activity and the feeding damage to canola plants throughout the winter growing season. In the laboratory, we established microcosms containing crop seedlings, as well as aphids as an alternate food source, to examine the feeding behaviour of all three species. The native earwigs L. truncata and N. lividipes did not cause feeding damage to canola or wheat but were found to actively consume aphids when present. We conclude that these species are unlikely to cause significant (economic levels) of pest damage in a field environment. In the microcosm trial, F. auricularia caused considerable damage to canola seedlings and readily consumed aphids. Forficula auricularia also caused feeding damage to canola seedlings early in the winter growing season in the field trial. However, by the end of the season, F. auricularia presence was associated with increased canola biomass. Furthermore, F. auricularia did not damage canola until all nearby aphids were consumed. Together, our field and laboratory studies suggest F. auricularia can be an important predator of aphid pests in canola, indicating a dual role of this species as both a pest and a beneficial species in winter grain systems.