The impact of entomopathogenic nematode applications on mortality of codling moth larvae on the orchard floor

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

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

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Entomopathogenic nematodes are tiny parasites of insects that can be applied in a water mixture and can kill their hosts within only a few hours after infection. The codling moth (Cydia Pomonella [L.]) is a serious pest of apples worldwide and is of critical concern in organic apple production. Codling moth larvae pupate and overwinter in silk cocoons in soil surface litter and under the bark on tree trunks or branches. Entomopathogenic nematodes have potential for management targeting codling moth larvae since they actively search out hosts in protected locations. We have been evaluating the entomopathogenic nematodes species, Steinernema feltiae (Filipjev), at three Michigan organic apple orchards to test its effectiveness for codling moth management. Our previous research indicated that nematode applications were more effective in orchards planted with smooth-barked tree varieties, presumably because the codling moth larvae in these orchards are forced to overwinter on the ground where they may be more susceptible to infection by entomopathogenic nematodes. This study was designed to test the hypothesis that codling moth larvae in cocoons on the ground are more susceptible to nematode sprays than those in other locations in the orchard. We found that nematodes applied with a backpack sprayer were able to successfully infect codling moth larvae in a variety of locations in the orchard. However, larvae that were in cocoons under wooden shelters on the soil surface did not exhibit increased infection in nematode treated plots compared to those in untreated plots. This result implies that entomopathogenic nematodes may need to be applied at higher rates to kill codling moth larvae in cocoons on the orchard floor in smooth barked orchards with dense undergrowth.