THE DUAL ROLE OF THE EUROPEAN EARWIG IN TEMPERATE TREE FRUIT ORCHARDS

Aldo Hanel

doi:10.7273/000006534

The European earwig, Forficula auricularia L., is an omnivorous generalist insect commonly found in agricultural ecosystems. In temperate tree fruit crops, earwigs are considered a pest in stone fruit, but are a key natural enemy in pome fruit. While in stone fruit (e.g., cherries, peaches), earwigs can damage the fruit and cause economic damage, in pome fruit (e.g., apples, pears), earwigs rarely damage the fruit and feed on multiple key pests, such as codling moth, pear psylla, and woolly apple aphids. This dissertation explores ways to develop and implement a trap-and-move strategy for earwigs in tree fruit in order to reduce damage in stone fruit while improving pest control in pome fruit. In the first chapter, I present a systematic review on augmentation biological control in temperate tree fruit crops and vineyards. I highlight how orchards, as perennial crops, offer an ideal system for biological control to thrive. However, growers still lack key information to adopt such strategies, including the rates and timing of biocontrol agent releases, and the cost-benefit of releases compared to conventional pesticide programs. In the second chapter, I explored possible improvements to corrugated cardboard traps, the standard way to monitor and trap earwigs. Standard cardboard traps, without any additional components or enhancement, were the best way to mass trap and remove earwigs from stone fruit orchards in the Pacific Northwest, USA. In the third chapter, I tested a trap-and-move protocol for earwigs, moving earwigs from stone fruit to pome fruit orchards. Removing earwigs from stone fruit did not reduce their abundance or possible fruit damage over two years but provided large amounts of earwigs for releases in pome fruit. Earwig augmentation in apples and pears improved suppression of woolly apple aphids and pear psylla in the second year of releases. To further improve successful earwig augmentation and conservation in pome fruit, in the fourth chapter, I investigated the nontarget effects of pesticides commonly used in orchards on earwigs. Currently used selective insecticides were mostly harmless to earwigs, except spinetoram, and to a lesser extent, spinosad. Herbicides, particularly paraquat and glufosinate, were also acutely toxic to earwigs, and their use should be avoided or carefully planned. Lastly, in the fifth chapter, I investigated earwig diet through gut content analysis using universal barcoded primers. There were no sequence reads for other natural enemies or pests in earwigs’ guts, likely due to earwig DNA having a higher affinity for the primers used. This was noticeable as possible prey DNA was only detected at unrealistic amounts of prey:earwig DNA in our positive controls. However, I found multiple sequence reads for the earwig parasitoid Triarthria setipennis in earwigs from all three crops, highlighting their distribution and presence throughout the season. The results presented in this thesis provide tree fruit growers in the Pacific Northwest with a new tool to improve sustainable pest control while reducing the use of harmful pesticides.

THE DUAL ROLE OF THE EUROPEAN EARWIG IN TEMPERATE TREE FRUIT ORCHARDS

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