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Title: Earthworms enhance soil health and may also assist in improving biological insect pest suppression in pecans

item Shapiro Ilan, David
item BROWN, IAN - Georgia Southwestern State University

Submitted to: Pecan Grower
Publication Type: Trade Journal
Publication Acceptance Date: 12/11/2013
Publication Date: 1/10/2014
Citation: Shapiro Ilan, D.I., Brown, I. 2014. Earthworms enhance soil health and may also assist in improving biological insect pest suppression in pecans. Pecan Grower. 25(3)26-35.

Interpretive Summary: Earthworms improve soil quality through aeration, increasing nutrient availability and breaking down and distributing organic matter. In this study we discovered that earthworms can also have another beneficial quality: earthworms may serve as phoretic hosts to insect-killing nematodes and fungi. The earthworms carry the nematodes and fungi through the soil and thereby assist in dispersing these biological control agents. The earthworm-mediated dispersal of biological control agents can lead to improved insect pest suppression. Specifically, in our laboratory and greenhouse experiments earthworms (night crawlers, Lumbricus terrestris) enhanced dispersal of the entomopathogenic (insect-killing) fungus, Beauveria bassiana, and the entomopathogenic nematode, Steinernema carpocapsae. Furthermore, the increased nematode dispersal led to improved suppression of pecan weevil larvae.

Technical Abstract: Prior research indicated that earthworms may serve as phoretic hosts to entomopathogenic nematodes. Therefore, we hypothesized that biocontrol efficacy of entomopathogenic nematodes could be enhanced in the presence of earthworms based on increased nematode dispersal through the soil. We also hypothesized that earthworms may serve as phoretic hosts to other entomopathogens, such as entomopathogenic fungi. Our results indicated that earthworm presence improved the ability of Steinernema carpocapsae (Sal strain) to control Curculio caryae below the soil surface. Additionally, S. carpocapsae (All strain) only caused significant C. caryae suppression relative to the controls in the presence of earthworms. Beauveria bassiana dispersal was enhanced by earthworm presence. The fungus was carried through soil by the earthworm; conidia recovered from the earthworm casts remained viable and was pathogenic to Galleria mellonella. Earthworms and other phoretic hosts may assist in dispersal of entomopathogenic nematode and fungal populations in various ecosystems and thereby assist in regulation of insect pests. Additionally, it may be conceivable to combine the application of earthworms with entomopathogens to achieve enhanced levels of inundative or inoculative biocontrol.