Update: European Earwig Biology
and Management in Peach Orchards
Cardboard traps tied to lower peach trunks catch hundreds of adult and juvenile earwigs, and serve as a monitoring tool.
The European earwig has been known to occur in Utah since the 1930s, and has become a ubiquitous pest and predator in many plant systems. The primary concern in fruit crops is that earwigs chew directly into fruits near harvest-time causing substantial crop loss. However, earwigs also prey upon small, soft-bodied insects such as caterpillars and aphids, providing pest management services through biological control. Thus, in an attempt to balance the “good and bad” of earwigs, we are studying their biology and optimal timing for fruit protection in peach orchards.
Small rolls of one-sided corrugated cardboard (corrugation turned inward, 4-inch wide strips) tied to the base of tree trunks and scaffold limbs were efficient traps for monitoring earwigs. On average, more earwigs were caught in traps placed on lower peach tree trunks than scaffold limbs. However, trap catch by location varied with earwig life stage and time of season. Overwintered adults and summer nymphs (juveniles), active from May through mid-July, were caught in higher numbers in lower trunk traps while summer adults, active from mid-July through September, were equally present in trunk and limb traps. The attraction of ripening fruit in the canopy later in the summer is a likely cause for the change in behavior of summer adults. We have documented two summer generations of European earwig in northern Utah. The second generation is small, and occurs in August and September during the period when peach fruits ripen.
Branches enclosed in a "cage" revealed that earwigs help reduce aphid population, and do not prefer to feed on fruits until they have softened, just before or at maturity.
We investigated the timing of leaf- and fruit-feeding by caging earwigs on peach shoots. Adults and nymphs fed on both leaves and fruit. The majority of leaf-feeding occurred in July and August, and slowed down as shoot growth terminated and leaves hardened off. The first fruit injury was observed in mid-July, but levels were low. The majority of fruit-feeding occurred in August and September when fruits softened as they neared maturity, and was greatest in September. Few second-generation nymphs were active late in the season.
To evaluate biological control services of earwigs, we caged adults on shoots infested by green peach aphid during May and June (see image, next page). Aphid densities were significantly less on shoots with earwigs as compared to shoots without earwigs. Differences occurred within one week after earwigs were added to aphid-infested shoots, and continued for up to 3 weeks.
To protect fruit from earwig feeding near harvest, a primary control tactic is application of insecticides. Studies were undertaken to determine the efficacy of conventional and organic insecticides, and effect of application timing.
Two applications of various insecticides applied to peaches 4 and 2 weeks before harvest showed that Warrior and Success were the most effective options for earwig control in 2012. In 2011, Success was the most effective (data not shown).
In a 2011 trial, insecticides were applied only once, about 4 weeks before harvest. The conventional formulation of spinosad (Success) was the most effective in protecting fruit, while the organic formulation of spinosad (Entrust), carbaryl (Sevin), and lambda-cyhalothrin (Warrior*) were intermediate, and all were better than the untreated control. Numbers of earwigs caught in trunk traps were reduced for up to 2 weeks in only the two spinosad treatments as compared to the others.
Results differed somewhat in a 2012 trial where Warrior* was the most effective insecticide. We found that using it once 4 weeks before harvest was just as effective as using it twice, at 4 and 2 weeks before harvest. Success, Sevin, and indoxacarb (Avaunt*) were intermediate in fruit protection. Two applications of Success and Avaunt were more effective than one application in reducing earwig counts. In conclusion, all insecticides reduced fruit injury. Spinosad showed consistent efficacy in both years while Warrior performed better in the second year. The efficacy of spinosad was enhanced when it was applied two times at about 4 and 2 weeks before harvest.
This research was supported by the USDA Organic Agriculture Research and Extension Initiative, the Utah Department of Agriculture Specialty Crop Block Grant Program, and the Utah Agricultural Experiment Station. Look for research updates in upcoming fruit industry meetings, gardening classes, and publications.
*Registered for commercial orchard use only
-Diane Alston, Entomologist and Andrew Tebeau, PhD student in Dept. of Biology, USU