Diversity of arthropods and entomopathogenic nematodes in conventional and conservation till in Maryland cropping systems

Conservation tillage regimes in agriculture, increasingly important for managing nutrient losses to watersheds, can be associated with increased pest insect outbreaks. Entomopathogenic nematodes (EPN) are widespread, potent generalist insect predators, but endemic diversity, spatial distributions, and capacity to regulate pest populations are poorly known. Over two years, we surveyed communities of soil-dwelling insects and EPN in replicated, paired tilled and no-till field corn (Zea mays) and soy (Glycine max) plots at five experimental stations in Maryland. The objectives were to characterize the soil invertebrate communities at these sites, and to test the prediction that conservation tillage favors enhanced diversity and abundance of arthropods and nematodes. Arthropods were collected with standardized vacuum sampling of surface litter followed by Tullgren extraction, and by sifting of soils and hand collection in the field. EPN were isolated with bioassays of soil cores, and identified with molecular techniques (RFLP and sequencing of the internal transcribed spacer (ITS) region of the ribosomal DNA repeat region). Soil temperature was higher and moisture was lower in conventional tillage. No arthropod orders were more abundant in conventional till, but predominantly predaceous taxa, such as spiders (Araneae), centipedes (Chilopoda) and ants (Hymenoptera: Formicidae), were more abundant with higher richness in conservation till. Overall, prevalence of EPN doubled in conservation tillage (mean 0.17 ± 0.04 S.E. vs. 0.08 ± 0.02). This effect was consistent at 4 of 5 sites, and the treatment effect intensified from spring to late season. These data suggest that increased local arthropod numbers with conservation tillage can be accompanied by enhanced function of diverse natural enemies.