Turning a Pest into a Natural Enemy: Removing Earwigs from Stone Fruit and Releasing Them in Pome Fruit Enhances Pest Control

Simple Summary Biological control, which is the use of natural enemies to regulate crop pests, is considered a key aspect of integrated pest management. In pome fruit (apple and pear) crops of the northwestern United States, the European earwig Forficula auricularia (L.) sensu lato may provide a unique opportunity for augmentative biological control. While this generalist omnivore is a direct pest in stone fruit crops like cherries and peaches, it is a beneficial predator in apple and pear crops. In these crops, it feeds on two key pests, the woolly apple aphid and pear psylla, respectively, and rarely damages fruit. Here, we tested a two-way strategy to reduce fruit damage by removing earwigs from crops where they are pests and releasing earwigs into orchards where they can help control pest populations. We found that mass-trapping earwigs in stone fruit orchards did not significantly reduce earwig numbers or fruit injury; however, this was a relatively easy and practical method for collecting thousands of individuals for augmentative release in pome fruit orchards. Two mass releases (once annually) of earwigs helped control key pests in pears and apples, such as pear psylla and woolly apple aphids, by the second year. We did not find evidence of a reduction in other pests, such as mites and other aphid species. Finally, we found that earwig releases can be useful in establishing their populations in orchards where they are absent or rarely found, potentially providing increased pest control over multiple seasons.Abstract The European earwig Forficula auricularia (L.) (Dermaptera: Forficulidae) is an omnivorous insect that is considered a minor pest of stone fruit and a key predator of pests in pome fruit orchards. In many pome fruit orchards, earwigs are absent or in low abundance due to broad-spectrum spray programs and the slow recolonization rate of earwigs. Orchards in transition to organic or "selective" conventional programs often struggle to achieve effective levels of biological control, and thus, may benefit from inoculating earwigs to expedite their re-establishment. In a two-year study, we evaluated the potential for mass trapping earwigs from stone fruit using rolled cardboard traps to reduce fruit damage and provide earwigs for augmentation in pome fruit. We also tested whether a single mass release or five releases (on alternating weeks) of the same total number of earwigs in apples and pears reduced pests relative to plots where no releases occurred. Mass trapping did not decrease earwig abundance or substantially reduce fruit damage in stone fruit orchards. However, trapping was an efficient method for providing earwigs for augmentation. Earwig abundances were only increased in orchards where earwigs were previously low or absent; however, multiple orchards with varying prior levels of earwigs exhibited reductions in key pests (woolly apple aphid and pear psylla). For some other pests evaluated, plots with mass releases of earwigs had a slight trend in overall lower pest density when compared with control plots. A strategy for moving earwigs out of stone fruit orchards and into pome fruit orchards could be an effective method for augmenting orchard predator populations.