Sustainable Agriculture Fact Sheet April 2020
Crop: Apples
Need: Discovering whether earwigs are pest, neutral or beneficial insects in apple orchards
States: Washington
Background: Woolly apple aphids are a serious pest in apple orchards and are difficult to control with current insecticides. However, beneficial insect predators can control wooly apple aphids.
The Problem: A few studies have suggested that European earwigs could suppress woolly apple aphids, but many Washington apple growers were skeptical or unaware of those findings. Because earwigs are only active at night their feeding behavior is rarely observed. Earwigs are also often found in cracks in damaged fruit, leading some growers to believe they cause crop damage. However, entomologists know earwigs are attracted to tight spaces and suspected they might seek refuge in damaged fruit, but not cause the damage. Some growers apply insecticides to control earwigs, which could be unnecessary or even counterproductive if earwigs provide beneficial services to growers.
The Research: Entomology graduate student Robert Orpet at the Washington State University manipulated earwig populations in sections of different orchards to measure whether the insects provided positive benefits by controlling wooly apple aphid populations or negative effects by damaging fruit.
He also examined the gut content of earwigs to document what they ate, and conducted more than a dozen in-depth interviews with growers and pest managers to document their knowledge and opinions about earwigs. His findings:
*It is possible to manipulate earwig populations. In some experimental sections, Orpet removed earwigs and in others he augmented them.
The sections with higher earwig populations had lower woolly apple aphid densities. Earwigs are a predator of the woolly apply aphid, and Orpet even got great night-vision video showing an earwig completely descimating an aphid colony. See video.
*Fruit damage was similar between the high-earwig sections (2.2%) and the low earwig areas (2.0%), “These results provide no evidence that earwigs increased damage to apples.”
The stomach content analysis backed up the raw numbers, showing woolly apple aphids were a sought-after food source even when their population densities were low. Earwigs also ate many other types of insects as well, which has biological control advantages because earwig populations wouldn’t necessarily fluctuate with the aphid population.
The Impact: We predict that fewer orchardists will target earwigs with insecticide sprays after hearing the results of this project. Others may modify their pesticide programs to conserve earwigs, resulting in better aphid control. A reduction in pesticide use has potential environmental, human health benefits, economic benefits. Because of the 1-year duration of the project, we do not yet know how this project has affected sustainability, but more than 10 orchard managers have contacted Robert Orpet for advice on earwig population establishment and augmentation, and most of the interviewees in this project indicated they gained knowledge and were interested in the potential benefits of earwigs in conversation after the formal interview.
Links:
Journal of Integrated Pest Management article
More information: Robert Orpet, Washington State University, robert.orpet@wsu.edu, 847-337-4480