Prevalence of naturally-occurring strains of Beauveria bassiana in populations of coffee berry borer Hypothenemus hampei on Hawai'i Island, with observations on coffee plant-H. hampei-B. bassiana interactions.
Beauveria bassiana (Bb) strain GHA is a major component of an areawide pest management program for coffee berry borer (CBB) in Hawai'i. Recent studies have aimed to provide comprehensive assessments of the efficacy of the Bb-spray component of these programs for economic analyses; however, evaluations have been complicated by activity of naturally-occurring strains of this pathogen infecting CBB. Investigations were therefore undertaken to characterize these strains, assess their natural epizootic potential, and account for their contribution to CBB population suppression. A number of field sites were encountered with no history of significant use of commercial Bb-based biopesticides and where strain GHA was not detectable. Sampling of these sites was conducted early in the coffee season. Greatest activity of wild-type Bb strains was observed on high-elevation farms (>500 m), where 24-42% of foundress beetles in green coffee berries were infected. In contrast, infection rates did not exceed 4% on farms at low elevations (<300 m). Rates of 23-29% infection, comparable to those on high-elevation farms, were recorded in a stand of feral coffee at 293 m elevation, but the coffee was completely shaded and ventilation restricted by a dense overstory of vegetation. Despite high activity of naturally-occurring Bb at some sites (primarily sites at high elevations with humid, moderate-temperature environments and dense pest populations), these fungi did not prevent CBB from exceeding the economic threshold for commercial spray applications. Nevertheless, the high natural epizootic potential of these fungal strains suggests strong potential for development as microbial biocontrol agents.