Prevalence and Diversity of Entomopathogenic Nematodes Spanning a Mean Annual Precipitation Gradient in Pastureland in Oklahoma

Abstract

Entomopathogenic nematodes in the families Steinernematidae and Heterorhabditidae are ubiquitous soil-dwelling obligate parasites of arthropods and are used commercially to suppress soil-dwelling insect pests in agricultural fields. Little is known about diversity of entomopathogenic nematodes in Oklahoma, which is home to 11 ecoregions, nine annual precipitation zones ranging from east to west, and seven soil orders. This study aimed to characterize entomopathogenic nematode communities inhabiting pastureland from different mean annual precipitation zones in Oklahoma. Soil physical parameters and weather data were used to characterize eight pastureland habitats. Soil samples were collected and native entomopathogenic nematodes were isolated using a common bioassay technique. Entomopathogenic nematodes were identified by PCR amplification of individual nuclear ribosomal its regions and sequencing. Six species of Steinernema in the Steinernematidae were isolated, including S. feltiae, S. texanum, S. glaseri., S. carpocapsae, and S. riobrave, and one population of Heterorhabditis bacteriophora in the Heterorhabditidae was recovered. Higher diversity and abundances of entomopathogenic nematodes were found in areas with higher precipitation levels. This study represents the first documentation of these species in OK and indicates a positive correlation between increased entomopathogenic nematodes prevalence as well as diversity and the increase in annual precipitation.