Effects of tillage practices on entomopathogenic nematodes in a corn agroecosystem Leah C. Millar * and Mary E. Barbercheck Department of Entomology, North Carolina State University, Raleigh, NC 27695-7634, USA Received 28 February 2001; accepted 20 March 2002 Abstract Cultural practices such as tillage affect soil abiotic and biotic factors, which in turn may affect the survival and activity of en- tomopathogenic nematodes. We investigated the relative sensitivity of an inundatively applied nematode species, Steinernema riobrave (Texas), and two endemic nematode species, Steinernema carpocapsae and Heterorhabditis bacteriophora,totillagepractices in no-till and conventional-till corn near Goldsboro, North Carolina. Two baiting methods using Galleria mellonella, one conducted in the laboratory and the other in the field, were used to evaluate the nematodes in terms of infected insects and nematode per- sistence. H. bacteriophora, which was only rarely detected, was not significantly affected by tillage. Tillage had a significant negative effect on the detection of S. carpocapsae and a significant positive effect on the detection of S. riobrave. The nematodes’ dissimilar sensitivities to tillage may be partly explained by differences in environmental tolerances and differences in tendencies to disperse deeper in the soil profile. Ó 2002 Elsevier Science (USA). All rights reserved. Keywords: Steinernema riobrave; Steinernema carpocapsae; Heterorhabditis bacteriophora; Entomopathogenic nematode; Biological control; Tillage effects 1. Introduction The use of entomopathogenic nematodes in the families Steinernematidae and Heterorhabditidae as in- undatively applied biological control agents against soil insect pests is rapidly expanding. However, field trials using these nematodes as biological control agents have often yielded highly variable results (Georgis and Gau- gler, 1991) and this has been attributed in part to the lack of understanding of their biology in natural and agricultural ecosystems. Knowledge of the effects of soil environmental factors on entomopathogenic nematodes is needed to select the most appropriate species for op- timal insect pest management. The efficacy of entomo- pathogenic nematodes, as with other biological control agents, can be affected by various abiotic and biotic factors. These factors can include soil texture, temper- ature, moisture, and nematode natural enemies (Kaya and Gaugler, 1993). Cultural practices such as tillage affect soil abiotic and biotic factors. For example, reduced tillage en- hances soil microbial diversity (Hassink et al., 1991; Lupwayi et al., 1998), nematode diversity (Freckman and Ettema, 1993), and soil arthropod diversity (House and Alzugaray, 1989). Soil under reduced tillage has lower temperatures and higher soil moisture levels compared to conventional tillage regimes (Sprague and Triplett, 1986), which may favor the development of disease in soil insect populations (Sloderbeck and Yeargan, 1983). Soil moisture is considered an impor- tant factor in influencing the infectivity of entomo- pathogenic nematodes (Kaya, 1990). Hence, reduced tillage has been suggested as a method of conserving entomopathogenic nematodes (Brust, 1991). The detec- tion of endemic Heterorhabditis bacteriophora Poinar was higher in no-till (NT) compared to conventional-till (CT) in corn (Brust, 1991). Hummel (2000) found a greater percentage of bait insects infected with endemic Steinernema carpocapsae (Weiser) (Fletcher strain) in Biological Control 25 (2002) 1–11 www.academicpress.com * Corresponding author. Present address: USDA-APHIS, Raleigh Plant Protection Center, 1017 Main Campus Dr., Suite 2500, Raleigh, NC 27606-5202, USA. Fax: +919-513-1995. E-mail address: leah.c.millar@aphis.usda.gov (L.C. Millar). 1049-9644/02/$ - see front matter Ó 2002 Elsevier Science (USA). All rights reserved. PII:S1049-9644(02)00042-7