European earwig Forficula auricularia L. (Dermaptera: Forficulidae) responses to understory treatments in organic and conventional peach orchards of northern Utah

The European earwig, Forficula auricularia L., is of interest in peach systems due to its abundance and diverse functional role; it is both a frugivorous pest and beneficial predator. The justification and protocol for earwig pest management in organic peach systems has not been established, and is a potential limitation to adoption of organic practices.  Manipulation of orchard understory vegetation is a strategy that can reduce external inputs for weed and nutrient management, a real plus in organic systems, and may influence earwig population densities and phenology. We studied earwig populations in 11 understory treatments in organic and conventional peach systems in northern Utah. Earwigs were sampled weekly with cardboard refuge-traps from May through October in 2010 to 2012. Tree growth and weed pressure were also monitored. Earwig seasonal abundance differed by year, was parabolic, and peaked in early August just before peach harvest. Earwig trap-catch was significantly higher in legume alleyways, relative to grass; in commercial NPK fertilizer, in contrast to compost; and in straw mulch and living cover-crops in the tree-rows, as opposed to those with tillage, weed fabric, or paper mulch. Tree growth was greatest in treatments with NPK fertilizer and legume alleyways. Tillage, weed fabric, and paper mulch significantly reduced weeds. Our results suggest that high available nutrients and refuge positively influenced earwig densities. The benefit of earwig population management via understory treatments has wide ranging possibilities; however, additional research into harm vs. benefit of earwigs in peach orchards is needed.