Natural occurrence of entomopathogens in Pacific Northwest nursery soils and their virulence to the black vine weevil, Otiorhynchus sulcatus (F.) (Coleoptera: Curculionidae)

The black vine weevil Otiorhynchus sulcatus (F.) is the primary insect pest of field and container-grown woody ornamentals in the Pacific Northwest (PNW). These studies were conducted to determine the natural occurrence of soil-borne entomopathogens in PNW nursery soils and determine their virulence to black vine weevil. Soil samples were collected July-September of 2002 from field-grown woody ornamental nursery stock in Oregon, Washington, and Idaho. Sample collection in each state took place in the major nursery production areas. A total of 280 samples was collected (Oregon, 170; Washington, 50; Idaho, 60). Entomopathogens were isolated using insect baiting (nematodes and fungi) as well as semiselective media (fungi). Bacillus thuringiensis Berliner was isolated through sodium acetate selection. Soil-borne entomopathogenic fungi occur widely throughout the major nursery production areas in the PNW. The entomopathogenic fungi Metarhizium anisopliae (Metchnikoff) Sorokin, Beauveria bassiana (Balsamo) Vuillemin, and Paecilomyces tenuipes (Peck) Samson were isolated. An entomopathogenic nematode (Steinernema oregonense Liu and Berry) and B. thuringiensis were also isolated. Of the 30 fungal isolates bioassayed, all but one was pathogenic to last-instar black vine weevil. None of the B. thuringiensis isolates collected were pathogenic to adult black vine weevil. The S. oregonense that were collected only infected a single black vine weevil larvae at 15 and 22degreesC. Pathogens collected from this soil survey will serve as a source of potential biological control agents for black vine weevil.