Prevalence of naturally-occurring strains of Beauveria bassiana in populations of coffee berry borer Hypothenemus hampei on Hawaii Island, with observations on coffee plant-H. hampei-B. bassiana interactions

Authors: Wraight, Stephen; GALAINI-WRAIGHT, SANDRA - University Of Hawaii; Howes, Rebecca; Castrillo, Louela; CARRUTHERS, RAYMOND - University Of Hawaii; SMITH, ROBERT - Smithfarms; Matsumoto Brower, Tracie; Keith, Lisa

Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/10/2018
Publication Date: 7/11/2018
Citation: Wraight, S.P., Galaini-Wraight, S., Howes, R.L., Castrillo, L.A., Carruthers, R.I., Smith, R.H., Matsumoto Brower, T.K., Keith, L.M. 2018. Prevalence of naturally-occurring strains of Beauveria bassiana in populations of coffee berry borer Hypothenemus hampei on Hawaii Island, with observations on coffee plant-H. hampei-B. bassiana interactions. Journal of Invertebrate Pathology. https://doi.org/10.1016/j.jip.2018.07.008.
DOI: https://doi.org/10.1016/j.jip.2018.07.008

Interpretive Summary: Use of Beauveria bassiana (Bb) strain GHA is a major component of an areawide pest management program for coffee berry borer (CBB) in Hawaii. Studies have included detailed assessments of the efficacy of spray applications of this fungal pathogen (the only Bb strain registered for use in Hawaii); however, evaluations have been complicated by activity of a diverse assemblage of naturally-occurring strains of Bb infecting CBB. During studies to characterize these strains and account for their contribution to CBB population suppression and enable more accurate assessments of commercial strain GHA efficacy, 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 to assess the natural pest-control potential of these fungi. Greatest activity of wild-type Bb strains was observed on high-elevation coffee farms (less than or equal to 550 meters), where 24–42% of foundress beetles in green berries were infected. In contrast, infection/mortality rates did not exceed 4% on farms at low elevations (less than 200 meters). Rates of 23–29% infection, comparable to those on high elevation farms, were recorded in a stand of feral coffee at 290 meter elevation, but the coffee was completely shaded and ventilation restricted by a dense overstory of mango and albizia trees. Despite high levels of Bb activity at some sites, the naturally-occurring pathogens did not prevent pest populations from exceeding economic thresholds for commercial spray applications. Nevertheless, the high natural capacity of these fungi to infect CBB and spread in CBB populations suggests strong potential for development as microbial biocontrol agents.

Technical Abstract: Use of Beauveria bassiana (Bb) strain GHA is a major component of an areawide pest management program for coffee berry borer (CBB) in Hawaii. Studies have included detailed assessments of the efficacy of spray applications of this fungal pathogen (the only Bb strain registered for use in Hawaii); however, evaluations have been complicated by activity of a diverse assemblage of naturally-occurring strains of Bb infecting CBB. During studies to characterize these strains and account for their contribution to CBB population suppression and enable more accurate assessments of commercial strain GHA efficacy, 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 to assess the natural pest-control potential of these fungi. Greatest activity of wild-type Bb strains was observed on high-elevation coffee farms (= 550 m), where 24–42% of foundress beetles in green berries were infected. In contrast, infection/mortality rates did not exceed 4% on farms at low elevations (< 200 m). Rates of 23–29% infection, comparable to those on high elevation farms, were recorded in a stand of feral coffee at 290 m elevation, but the coffee was completely shaded and ventilation restricted by a dense overstory of mango and albizia trees. Despite high levels of Bb activity at some sites, the naturally-occurring pathogens did not prevent pest populations from exceeding economic thresholds for commercial spray applications. Nevertheless, the high natural epizootic potential of these fungi suggests strong potential for development as microbial biocontrol agents.