Location: Emerging Pests and Pathogens Research
2019 Annual Report
Objectives
Objective 1: Integrate mycoinsecticides to manage selected insect pests of greenhouse crops, including, but not limited to, soil and foliar treatments for thrips control and for optimizing abiotic conditions. (NP304, Component 3, Problem Statement 3A2)
Subobjectives:
1a. Characterize and quantify the effects of biotic and abiotic factors on efficacy of fungal pathogens applied against western flower thrips.
1b. Assess the potential of combining soil and foliar applications of fungi against western flower thrips as a strategy to achieve acceptable levels of efficacy at reduced moisture levels.
Objective 2: Characterize pest microbial associates and determine the efficacy of microbial control agents to manage insect pests, including, but not limited to, Asian ambrosia beetles, walnut twig beetle, and coffee berry borer.
Subobjectives:
2a. Determine effects of commercially available fungal biocontrol agents on Asian ambrosia beetles and their symbionts.
2b. Assess efficacy of commercially available entomopathogenic fungi for the walnut twig beetle.
2c. Assess efficacy of Beauveria bassiana against coffee berry borer in the Kona coffee-growing region on the island of Hawaii; determine best practices for effective deployment of this pathogen as one component of an area wide IPM program.
2d. Characterize the indigenous isolates of Beauveria infecting coffee berry borer in Hawaii and determine the roles of these pathogens in natural suppression of this insect pest.
Objective 3: Determine the impact of natural enemies, such as parasitic wasps and microbial biopesticides, introduced for management of emerald ash borer.
Subobjectives:
3a. Quantify EAB and parasitoid densities to determine whether establishment of EAB parasitoids has significant effects on EAB populations.
3b. Determine impact of natural enemies released against emerald ash borer on ash health and survival.
Approach
The goals of this project are to integrate entomopathogenic fungi into management systems for insect pests of greenhouse ornamental and vegetable crops and insect pests of trees in nursery, field, and natural settings and to track fungal strains in these environments. The work comprises fundamental laboratory studies as well as applied field and greenhouse research. This project will develop basic information on the biology of fungal pathogens associated with insects, their genetic and phenotypic variability, and their activity and persistence in field and greenhouse environments. Integration of fungal pathogens will be accomplished for management of key pests. Studies will identify minimal ambient moisture requirements for effective deployment of fungal pathogens against western flower thrips infesting greenhouse crops. Microbial control agents will be developed for management of Asian ambrosia beetles and walnut twig beetle. Application methods and strategies will be developed for optimal use of fungi against coffee berry borer in the Kona coffee districts of Hawaii. Parasitoid releases for management of emerald ash borer will be evaluated for their impact on their host and the resulting impacts on ash health and regeneration. Biological control agents used in the ways developed in this project will provide safe, effective biological alternatives to synthetic chemical insecticides or as rotational partners for insecticide resistance management.
Progress Report
Objective 2c. Field research by ARS scientists from Ithaca, New York, and in collaboration with researchers from ARS in Hilo, Hawaii, and the University of Hawaii, Hilo, aimed at assessing efficacy of spray applications of Beauveria bassiana-based biopesticide against coffee berry borer (CBB) was completed in September 2017. Data collected during four field seasons (2014–2017) in the South Kona and Kau coffee growing districts of Hawaii Island are being analyzed for publication. Objective 2d. Studies aimed at genetic and biological characterization of wild strains of the fungus B. bassiana collected from Hawaiian coffee fields has been completed. Isolates of B. bassiana from over 8000 adult female CBB were initially screened morphologically to differentiate the commercial strain B. bassiana GHA from those indigenous to the sampled coffee farms and feral sites. Of these, over 150 indigenous isolates, representatives of different morphovars detected, were selected and characterized molecularly by sequencing two genes. All were identified as B. bassiana sensu stricto, and data also revealed multiple genotypes associated with CBB. The most common genotype was found at multiple sites on Hawaii Island (including at epizootic levels on an organic farm), one site on Oahu, from other insect hosts, and from a collection made prior to CBB detection. One hundred and fifty strains representing all major genotypes detected have been accessioned to the ARS Collection of Entomopathogenic Fungal Cultures (ARSEF). Seventeen strains representing distinct genotypes were selected for bioassays against laboratory-reared CBB adults, with strain GHA as the standard. Most of the Hawaiian strains exhibited virulence comparable to GHA; none were significantly more virulent. A number of these strains also showed mass-production potential equal to, or greater than, strain GHA. In our field studies, the Hawaiian strains also exhibited a greater capacity for persistence and natural spread in CBB populations than strain GHA, and in view of these numerous positive attributes, we conclude that these fungi are strong candidates for commercial development as biocontrol agents. Additional testing would be required, however, to determine if these fungi possess other key attributes of strain GHA, including activity against a broad range of insect pests and exceptional stability (shelf life) following production and formulation.
Accomplishments
1. Identification of coffee berry borer (CBB) collected in Hawaiian coffee. This fungus was first reported from CBB from Columbia in 1993, and again in 2007, but isolation and further identification studies were unsuccessful. Researchers from ARS-Ithaca, New York, ARS-Hilo, Hawaii, and the University of Hawaii, Hilo, Hawaii, collected CBB infected with the fungus (Hirsutella) fitting the same description and successfully cultured the Hawaiian strain and conducted molecular analysis. Results identified it as a member of the citriformis group. Our publication reports the first account of isolation, in vitro culture, genetic characterization and host transmission of this fungal pathogen. A culture of the fungus has been accessioned to ARSEF.
Review Publications
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.
Clifton, E., Castrillo, L.A., Gryganski, A., Hajek, A.E. 2019. Native fungal pathogens drive collapse of a new invasive herbivore. Proceedings of the National Academy of Sciences. 116:9178-9180. https://doi.org/10.1073/pnas.1903579116.
Hajek, A.E., Steinkraus, D.C., Castrillo, L.A. 2018. Sleeping beauties: Horizontal transmission by Entomophthoralean Fungi via resting spores. Insects. 9(3). https://doi.org/10.3390/insects9030102.
