Survey of rhizosphere associated entomopathogenic fungi on small fruits and Christmas trees in the Willamette Valley, OR

Graduation date: 2010The entomopathogenic fungi Metarhizium anisopliae and Beauveria bassiana are commercially available as microbial control agents for the black vine weevil, Otiorhynchus sulcatus (F.) (Coleoptera: Curculionidae), the key root-feeding insect pest in Pacific Northwest small fruits and ornamentals. Understanding habitat selection is critical to improve the efficacy, persistence and cost of these fungi as microbial insecticides. This study sought to determine the prevalence of Metarhizium and Beauveria spp. in the rhizosphere of strawberry, blueberry, grape and Christmas tree crops in the Willamette Valley of Oregon. Entomopathogenic fungi were assigned to thirteen phylogenetic species based on molecular phylogenetic criteria. Four species of Metarhizium were isolated including M. brunneum, M. guizhouense, M. robertsii, and M. pemphigi. Nine Beauveria species were isolated including, Beauveria brongniartii, an undescribed species referred to as Clade C and seven morphologically cryptic phylogenetic species of B. bassiana. Strawberries and blueberries were significantly associated with M. brunneum and Christmas trees with M. guizhouense and M. robertsii. Grapes were significantly associated with B. bassiana phylogenetic species Bbas-16. All of the Metarhizium isolates screened were pathogenic to O. sulcatus larvae in laboratory bioassays but only M. brunneum and M. robertsii caused significant levels of infection. The study results suggest that certain species of Metarhizium and Beauveria are significantly associated with the strawberry, blueberry and Christmas tree rhizosphere and could potentially provide better pest control for O. sulcatus