Profile of the effects of a distinct precipitation gradient and land use practices on community composition of indigenous entomopathogenic nematodes (EPN) in Oklahoma

Entomopathogenic nematodes in the families Steinernematidae and Heterorhabditidae are obligate parasites of arthropods, exist naturally in soils worldwide, and have been used to suppress soil-dwelling insect pests. Little is known about EPN diversity within Oklahoma. Ranging from east to west, Oklahoma is home to 11 different ecoregions, 9 precipitation zones and 7 soil orders. This study aimed to characterize EPN communities throughout these diverse habitats. An additional objective of this study was to compare EPN communities in organic versus conventional beef and wheat production systems within the same ecoregion. A combination of bioassay technique and molecular identification was used to identify EPN species  . Soil samples were subjected to bioassay using G. mellonella to ascertain infection rates by EPN. EPN were identified, initially by infected G. mellonella symptoms. Based on these symptoms, appropriate primers were chosen to amplify regions of the ITS gene. These regions were then sequenced to confirm identification. The Heterorhabditis species of EPN identified included Heterorhabditis bacteriophora and H. georgiana. The Steinernema species of EPN identified included: Steinernema feltiae, S. texanum, and S. glaseri. S. feltiae was the most commonly encountered species across the state. Within the organic and conventional fields, overall infection rates were 2.38% in organic wheat, 1.63% in conventional wheat, 8.14% in organic pasture, and 7.26% in conventional pasture. This study showed a higher incidence of EPN in organic fields than conventional fields; pastures than agricultural fields; and a positive correlation with the increase in soil moisture as you move eastward across the state.