European earwig (Forficula auricularia) responses to understory treatments in organic and conventional peach orchards of northern Utah

European earwig populations were monitored in response to 11 orchard-floor, nutrient, and weed- management treatments established in two peach orchards (0.48 and 0.40 ha ) in the western arid production region of northern Utah.  Earwigs are of interest due to their abundance in the peach system and diverse functional role; they are both herbivorous pests and beneficial predators. Adults and nymphs were sampled with cardboard refuge-traps weekly from May through October in 2010 and 2011. Seasonal abundance differed by date and was parabolic in shape; densities peaked in early August just before peach harvest. Populations were greater in 2011 and treatment effects were more evident. Legume alleyway treatments, opposed to grass, enhanced earwig populations and had the most marked effect throughout the study. Additionally, adults were greater in plots with commercial NPK fertilizer than compost and in plots with straw mulches and living cover-crops in the tree-rows than in those with tillage or weed fabric. Nymphs were also abundant in living cover-crops but differed from adults in that they were negatively influenced by straw mulch and were not affected by fertilizer type. These results suggest that available nutrients (from fertilizers and legumes) and refuge (from structure of cover crops and mulches) positively influenced earwig densities. Legume alleyways increased tree trunk cross-sectional area and overall arthropod diversity in plots, but impacts of earwig herbivory on peach fruits and predation on pests in the system must be considered in the overall cost and benefit analyses of peach orchard understory treatments.