Collection, isolation, in vitro culture, and laboratory transmission of Hirsutella eleutheratorum (Hypocreales: Ophiocordycipitaceae) from coffee berry borer on Hawaii Island

Authors: Wraight, Stephen; WRAIGHT-GALAINI, SANDRA - University Of Hawaii; Castrillo, Louela; Griggs, Michael; Keith, Lisa; Matsumoto Brower, Tracie

Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/6/2018
Publication Date: 8/7/2018
Citation: Wraight, S.P., Wraight-Galaini, S., Castrillo, L.A., Griggs, M., Keith, L.M., Matsumoto Brower, T.K. 2018. Collection, isolation, in vitro culture, and laboratory transmission of Hirsutella eleutheratorum (Hypocreales: Ophiocordycipitaceae) from coffee berry borer on Hawaii Island. Journal of Invertebrate Pathology. 157:53-66. https://doi.org/10.1016/j.jip.2018.08.002.
DOI: https://doi.org/10.1016/j.jip.2018.08.002

Interpretive Summary: The insect pathogenic fungus Hirsutella eleutheratorum was first identified as a pathogen of coffee berry borer (CBB)in Colombia in 1992. Since then there has been only one additional report of the fungus on CBB which was also from Colombia. All attempts at laboratory culture of the Colombian strains of the fungus were unsuccessful. During the 2016–2017 coffee seasons on the island of Hawaii, extensive sampling of CBB populations was conducted in coffee fields treated with the common fungal pathogen Beauveria bassiana and in untreated fields. Among the samples collected from two high-elevation sites in the district of South Kona were rare findings of adult CBB infected with a fungal pathogen fitting the description of H. eleutheratorum, most notably producing spores on long, filamentous structures protruding from many points on the killed beetle. The fungus was readily isolated from freshly-killed CBB and cultured on potato dextrose agar. In the laboratory, adult CBB exposed to fungus-killed beetles or to cultures of the fungus succumbed to infection within 10–15 days. To our knowledge, this is the first record of H. eleutheratorum from coffee berry borer in Hawaii and the first account of successful isolation, culture, and host-to-host transfer of this pathogen. Unfortunately, rates of infection by this fungus were very low (less than 1%) in all CBB populations sampled, and the pathogen had no significant impact on pest populations. This was the case even under field conditions supporting high levels of infection by the fungus B. bassiana. Though an interesting pathogen of CBB in Hawaii, these observations indicate that H. eleutheratorum has little potential for development as a biological control agent.

Technical Abstract: The insect pathogenic fungus Hirsutella eleutheratorum was first identified as a pathogen of coffee berry borer Hypothenemus hampei (CBB) in Colombia in 1993; all attempts at isolation and culture of the pathogen were unsuccessful. Since 1993 there have been few additional reports of the fungus on CBB, (all were from South America), and no additional attempts at isolation. During the 2016 and 2017 coffee production seasons on the island of Hawaii, extensive sampling of CBB populations was conducted in coffee fields treated with Beauveria bassiana-based biopesticides and in untreated fields. Among the samples collected from two high-elevation sites in the district of South Kona were rare findings of adult foundress CBB infected with a species of Hirsutella fitting the description of H. eleutheratorum. Prevalence of the pathogen was, in all cases, very low (less than 1%), having no significant impact on pest populations, even under conditions supporting epizootics of Beauveria bassiana. The fungus was readily isolated from freshly-killed CBB and cultured on potato dextrose agar (PDA). Molecular characterization identified the fungus as a member of the Hirsutells citriformis clade, which includes species recently placed in the genus Ophiocordyceps. In the laboratory, adult CBB exposed to fungus-killed beetles or to PDA cultures of the fungus succumbed to infection within 10–15 days. Under high-humidity laboratory conditions, the fungus emerged from the killed host and produced long, conidia-bearing synnemata characteristic of the species. To our knowledge, this is the first record of H. eleutheratorum from CBB in Hawaii and the first account of successful isolation, in vitro culture, host-to-host, and culture-to-host transfer of this fungal pathogen.