Exploration of the microbial control options for the management of sod webworm, Chrystoteuchia topiara (Zeller), in Oregon grass seed production systems

The larvae of cranberry girdler or subterranean sod webworm Chrysoteuchia topiaria Zeller (Lepidoptera: Crambidae) inflict damage to the plant roots leading to the poor fall regrowth and ultimately reduced yields in cool-season grass seed production systems. As soil-dwelling insect species, larvae are continuously exposed to a wide range of subterranean pathogenic organisms; identifying these organisms and determining their impact would contribute to the development of biological control. The main aim of this study was to survey to determine what native EPN species occur in grass seed fields and to test if they can offer effective control against sod webworms. Soil samples were collected during a field survey at biweekly intervals during March-May 2021 in 22 commercial grass seed fields in western Oregon. Isolation of EPNs was performed using insect baiting techniques using commercially available waxworm larvae, Galleria mellonella Linnaeus (Lepidoptera: Pyralidae). Out of 88 composite samples (440 single point samples); nematodes were recovered from 22 samples. Three different EPN isolates were identified using molecular tools. BLASTn analyses indicated that the most predominated Oregon EPN isolate (Oregon_WV-3) were conspecific to an unidentified EPN isolate N6734 from Nebraska Cornfields (GenBank accession: MK754228) with up to 100% identity of the partial sequence of the cytochrome oxidase subunit 1 (cox1) gene and other two isolates being conspecific to Steinernema and Oschieus sp. Results of the lab infectivity trials using three native OR isolates and commercial EPN products against black cutworm larvae were promising.