SYSTEM-WIDE STUDY OF WOOLLY APPLE APHID
Orpet, Robert John
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Woolly apple aphid, Eriosoma lanigerum (Hausmann), is an increasingly important pest in apple orchards worldwide and is difficult to manage with currently available tactics. To address the need for new knowledge and tactics to manage this pest, I conducted studies on the potential effects of physical control tactics, biological control, and factors related to differences in organic versus conventional management. I found that preventing woolly apple aphid movement from tree roots to canopies did not influence their aboveground population dynamics, suggesting limited utility of using physical barriers to block this movement. In a video-recording experiment I collected evidence that predation by coccinellid larvae could decrease woolly apple aphids populations, but coccinellids had a relatively narrow window of seasonal activity. Earwigs (Forficula auricularia L.) in the same study appeared to be effective generalist predators which could prevent low-density woolly apple aphid populations from increasing. I conducted an earwig augmentation experiment at four different orchards and confirmed that greater earwig abundance results in lower and more stable woolly apple aphid populations and I found no evidence that earwigs damaged apples. Molecular gut content analysis of earwigs further demonstrated that they are effective predators of low-density aphid populations, as woolly apple aphid DNA was detected in their guts even during periods when woolly apple aphids were rare. In a two-year observational study of 20 organically or conventionally managed orchards I found no correlation between woolly apple aphids with spray programs, soil quality, tree nitrogen, or natural enemy communities. Moreover, conventional and organic orchards were generally similar in these factors. Interviews I conducted with pest management decision-makers highlighted that a range of practices are used in conventional and organic orchards and these management styles may not represent a distinct dichotomy. I suggest greater attention to earwigs in integrated pest management programs could reduce incidence of woolly apple aphid outbreaks, and that conventional and organic apple orchards in central Washington are often managed similarly.