NATURAL OCCURRENCES OF ENTOMOPATHOGENS IN PACIFIC NORTHWEST NURSERY SOILS AND THEIR VIRULENCE TO THE BLACK VINE WEEVIL OTIORHYNCHUS SULCATUS F. (COLEOPTERA: CURCULIONIDAE)

Authors: Bruck, Denny

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/11/2004
Publication Date: 10/1/2004
Citation: Bruck, D.J. 2004. Natural occurrences of entomopathogens in Pacific Northwest nursery soils and their virulence to the black vine weevil Otiorhynchus sulcatus F. (Coleoptera: Curculionidae). Environmental Entomology. 33(5): 1335-1343.

Interpretive Summary: The Black vine weevil (BVW) is the primary insect pest of field and container-grown woody ornamentals in the Pacific Northwest. These studies were conducted to determine the natural occurrence of soil-borne insect infecting pathogens (fungi, nematodes, bacteria) in Pacific Northwest nursery soils as well as determine their virulence to BVW. Soil samples were collected July - September of 2002 from field-grown woody ornamental nursery stock in OR, WA and ID. Sample collection in each state took place in the major nursery production areas (OR - Willamette Valley, WA - Puget Trough, ID - Treasure Valley). There were a total of 280 samples collected in all (OR - 170, WA - 50, ID - 60). Results indicate that soil-borne fungi occur widely throughout the major nursery production areas in the Pacific Northwest. The most prominent fungus isolated was Metarhizium anisopliae (Metchnikoff) Sorokin followed by Beauveria bassiana (Balsamo) Vuillemin and Paecilomyces tenuipes (Peck) Samson. Metarhizium anisopliae was isolated from over 75% of the nurseries sampled in the Pacific Northwest. However, the occurrence of insect infecting nematodes (Steinernema oregonense Liu and Berry, 1 location) and the bacteria Bacillus thuringiensis (3 locations) were very low. All but one of the 30 fungal isolates tested for their ability to kill last instar BVW were lethal. None of B. thuringiensis isolates or the nematode collected was infective. Based on the results of this survey, it is apparent that fungi are the most prevalent, and in this case infective, BVW natural pathogen.

Technical Abstract: The Black vine weevil (BVW) Otiorhynchus sulcatus F. is the primary insect pest of field and container-grown woody ornamentals in the Pacific Northwest. These studies were conducted to determine the natural occurrence of soil-borne entomopathogens in Pacific Northwest nursery soils as well as determine their virulence to BVW. Soil samples were collected July - September of 2002 from field-grown woody ornamental nursery stock in OR, WA and ID. Sample collection in each state took place in the major nursery production areas (OR - Willamette Valley, WA - Puget Trough, ID - Treasure Valley). There were a total of 280 samples collected (OR - 170, WA - 50, ID - 60). Entomopathogens were isolated using Galleria baiting (nematodes and fungi) as well as selective media (fungi). Bacillus thuringiensis Berliner was isolated via sodium acetate selection. Results indicate that soil-borne entomopathogenic fungi occur widely throughout the major nursery production areas in the Pacific Northwest. The most prominent fungus isolated was Metarhizium anisopliae (Metchnikoff) Sorokin followed by Beauveria bassiana (Balsamo) Vuillemin and Paecilomyces tenuipes (Peck) Samson. Metarhizium anisopliae was isolated from over 75% of the nurseries sampled in the Pacific Northwest. However, the occurrence of entomopathogenic nematodes (Steinernema oregonense Liu and Berry, 1 location) and Bacillus thuringiensis (3 locations) were very low. All but one of the 30 fungal isolates bioassayed against last instar BVW was infective. None of B. thuringiensis isolates or the nematode collected were efficacious towards BVW. Based on the results of this survey, it is apparent that fungi are the most prevalent, effective, pathogen BVW would encounter in the field.