The effects of orchard-floor management on the density, dispersal, and distribution of European earwigs (Dermaptera: Forficulidae) in peach orchards of northern Utah

The economic importance of the European earwig Forficula auricularia L. in Utah peach orchards has been recognized but remains ambiguous due to the insect’s dynamic feeding behaviors (i.e., beneficial predator and pest herbivore). Local growers are requesting appropriate integrated pest management (IPM) programs that either promote or discourage earwigs.  Earwigs inhabit the orchard floor and its manipulation is a prospective IPM tool. Density, dispersal, and distribution of earwig populations in eleven orchard-floor treatments were monitored using refuge trap and capture-mark-recapture experiments. The treatments represented the industry standard or alternative approaches to managing ground vegetation and fertilization. On 67 trapping dates from 2010 to 2012, 60,787 earwigs were captured in 6,450 refuge traps. An average of 619 (± 71) earwigs were caught each day and increased each year at a rate of 272 earwigs per day, without evidence of density dependence. In 2012, 2,350 earwigs were marked on the elytra with color-coded paint dots, released throughout the orchard, and recaptured every other day (26.4 ± 1.3% recapture rate). Earwig movement was not biased in any particular direction, such as along or across tree rows, and it did not differ between sexes. Orchard-floor treatments that provided high refuge space and nutrients positively influenced abundance. Legume plots provided the greatest number of earwigs (presumably due to its high refuge and nitrogen availability). Abundance was the lowest, and emigration was greatest, in tillage treatments (presumably due to low refuge and food resources), making it the preferred treatment for reducing earwig herbivory.