Soil Invertebrate Biodiversity under Contrasting Orchard Management Regimens in Michigan

Graduate Student Final Report – Ceres Trust Research Grant

Graduate Student: Nathaniel J. Walton, Michigan State University Department of Entomology

Major Professor:  Dr. Matt Grieshop, Michigan State University Department of Entomology

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Healthy soil contains a diversity of microorganisms that perform essential functions such as aeration, decomposition, and biological control of crop pests. Entomopathogenic nematodes (EPNs) are tiny insect parasites that can be applied with water using conventional sprayers and can kill their insect hosts within only a few hours after infection.  The codling moth (Cydia Pomonella [L.]) is a serious insect pest of apples worldwide and is of critical concern in organic apple production. Codling moth larvae pupate and overwinter in silk cocoons in soil litter and on tree trunks or branches.  EPNs have potential for management targeting codling moth larvae since they actively search out hosts in protected locations. National Organic Program (NOP) approved formulations of EPNs are available for management of a variety of pests. We have been evaluating the EPN species, Steinernema feltiae (Filipjev) at three Michigan organic apple orchards to determine its impact on the orchard soil arthropod community. EPNs are already present in most soils, so applications that augment natural populations could have a variety of impacts on other soil microorganisms. Mites and springtails for example, can feed on nematodes and might benefit from an EPN application. However, other organisms such as beetle larvae are susceptible to EPN infection and could be harmed by EPNs.  To date we have found little evidence of any impact of EPN applications on soil ecology in organic orchards.  EPN applications had no impact on overall soil arthropod abundance and diversity within organic orchards. Organic orchards also had consistently higher soil arthropod abundance compared to paired conventional orchards, independent of EPN treatment.  Indices of arthropod diversity did not differ significantly between orchard management types (organic vs. conventional).

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