Interactions Between Soil Invertebrates and Entomopathogenic Nematodes in No-till and Conventional-till Corn in North Carolina.

Abstract

The conservation of naturally-occurring biological control agents, such as entomopathogenic nematodes (EPN), of soil-dwelling pests in agriculture may decrease the need for chemical pesticides, result in economic savings, promote a safer environment for both farm workers and native wildlife, and protect groundwater and surface water run-off. Thorough evaluation of abiotic and biotic interactions between EPN and the soil community and environment are important to assess both impacts to EPN populations and potential impacts on soil fauna resulting from the introduction of EPN.

Two experiments were conducted to evaluate the response of soil fauna to the application of EPN to the soil in no-till and conventional-till corn. Each experiment used a different application method (Bait experiment = EPN delivered via infected insect cadaver, Inundation experiment = EPN delivered in aqueous solution). Both experiments were designed as a stripped split split plot over four blocks. Each experiment was repeated on 6 different dates. Variables included: 4 blocks x 2 tillage regimes x 2 sampling times x 5 treatments. The treatments included: three nematode species treatments Heterorhabditis bacteriophora (CEFS strain), Steinernema riobrave (commercially available but does not naturally occur in NC), and Steinernema carpocapsae (CEFS strain) and two control treatments, water and soil for inundation, and water and a dead insect control for bait. Response of soil fauna was measured at the levels of abundance (large traditional taxonomic affiliations of soil invertebrates), diversity, and community composition based on the finest level of taxonomic identification of invertebrates collected.

Responses of soil fauna differed between the two application methods. Experimental factors, including sampling date and time, tillage regime, and blocks significantly affected abundance, diversity and community composition of soil invertebrates in both experiments. Significant changes in abundance of individual soil invertebrate taxa due to the effect of nematode treatment were found in both experiments. Both positive responses and negative responses, were detected in various taxonomic categories. And, large taxonomic groupings of invertebrates exhibited responses that differed significantly from the responses of individual taxa within those large groupings.