Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/26/2016
Publication Date: 11/1/2016
Citation: Unruh, T.R., Miliczky, E., Horton, D.R., Thomsen Archer, K.L., Rehfield-Ray, L.M., Jones, V. 2016. Gut content analysis of arthropod predators of codling moth in Washington apple orchards. Biological Control. 102:85-92. Interpretive Summary: Apples pears and walnuts are important fruits and nuts for both consumption in the United States and for export to trading partners. The key pest of these products is the codling moth, the proverbial worm in the apple. Since 1991, control of codling moth has relied on mating disruption supplemented with several pesticide applications, and by the natural biological control provided by beneficial predators. Multiple studies by ARS and Land Grant entomologists have demonstrated that organic production, where pesticide use is minimal, increases the abundance of beneficial predators of insect pests. However, these studies do not identify which beneficial predators and spiders feed on key pest such as codling moth and are important in pest suppression. To identify important arthropod predators of codling moth, USDA ARS scientists and a Washington State University collaborator have evaluated 18 families of spiders and predatory insects by molecular gut content analysis to determine the rate at which they attack the codling. We found that nine percent of 2591 predator specimens evaluated had eaten codling moth within the past three days or less and that three groups were especially important predators: a large complex of spiders (15 genera), the predatory ground beetles (two species), and the European earwig. Our results identify these predators as important candidates for conservation and enhancement through continued use of pheromone-based mating disruption and judicious timing and use of minimally disruptive insecticides such as used in organic production. Following this model will also reduce problems with maximum pesticide residue limits facing growers that export these commodities.
Technical Abstract: More than 70% of pome fruits in the USA are produced in central Washington State. The codling moth, Cydia pomonella (L.) is consistently the most damaging pest. We used polymerase chain reaction (PCR) to amplify codling moth DNA in 2591 field-collected arthropod predators to estimate predation in seven apple orchards over a four-year period. Predators were captured by hand, with beat trays, pitfall traps or cardboard bands, which encompassed the tree canopy, orchard soil surface and cryptic habitats. PCR of homogenates from excised guts or from whole bodies showed that 8.9 % of the specimens were positive for codling moth DNA. Spiders, including 24 genera from 12 families, two carabid beetle species and the European earwig, Forficula auricularia (L), accounted for 87% of specimens and were 8.3 %, 8.4 % and 14.7 % positive for codling moth, respectively. PCR products from 87 of the 230 specimens that were positive for codling moth based on melt curves and band size in gels were sequenced and 100% showed a 99-100% match with codling moth COI nucleotide reference sequences in GenBank. Homogenates of adult earwigs or their excised guts or their daily accumulations of feces were used as DNA templates to measure digestion rates; adults showed a half-life of 3.7 days and feces showed a half-life of 3.6 days. Pterostichus melanarius (Illiger) showed a digestion half-life of 4.4 days. Increased understanding of which predators most often feed on codling moth may help guide evolving pest management programs in Washington apples.