Inoculation and conservation of the biocontrol agent European earwig in Washington pear orchards

Abstract

European earwig, Forficula auricularia L. sensu lato (Dermaptera: Forficulidae), is a univoltine, resident, omnivorous species and a beneficial predator in pome fruit orchards. Here, three methods were used to investigate pear (Pyrus communis L., Rosaceae) orchard inoculation with European earwig for biocontrol of pear psylla, Cacopsylla pyricola (Foerster) (Hemiptera: Psyllidae), in Washington State, USA. The first method was earwig inoculation experiments. In a first experiment (2019–2020), each of three orchards had one inoculation and one control plot. In a second experiment (2020–2021), there were four inoculation and four control plots in each of the same three orchards. In both experiments, earwigs persisted during the year of inoculation, but earwigs were nearly absent the following season at two orchards that used conventional broad-spectrum pesticides. At the third orchard, which excluded broad-spectrum pesticides under an integrated pest management (IPM) program, earwigs became abundant in year two of the second experiment. The second method was case studies. In the first of two case studies, during 2016, 2017, 2022, and 2023, in half of the integrated orchard from above, conventional broad-spectrum sprays were used. Earwig populations became low in the conventional half. In the second case study, earwigs became abundant after inoculation of an integrated orchard by the grower. Earwigs spread to the edge of the orchard in year two and spilled into a neighboring orchard in years three and four. The third method was an observational study of 36 pear orchards over 5 years. Earwigs were rarely found in conventionally sprayed orchards, and earwigs increased each additional year integrated management was used. The findings suggest conventional pear spray programs in Washington nearly eradicate earwigs, but populations can recover under integrated management with natural dispersal from refuges or with inoculative releases.