Location: Emerging Pests and Pathogens Research
2020 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
This is the final report for Project 8062-22000-020-00D which will end October 25, 2020.
Subobjective 1a. Characterize and quantify the effects of biotic and abiotic factors on efficacy of fungal pathogens applied against western flower thrips. Numerous tests with B. bassiana commercial strain GHA were conducted at constant 15, 20, 25, and 30 ºC, with all thrips exposed to the same dose of the pathogen. Results indicated that, under constant 25 degrees Celsius or daily fluctuating temperatures of 15–25 degrees Celsius, around 40 hours of high humidity was sufficient to support high levels of infection by biocontrol fungi. Greenhouse pest managers can apply this tactic by making spray applications during late afternoon and maintain high humidity conditions during a period comprising the subsequent night (when high humidity is most easily maintained), the next day (when maintenance of high humidity is most difficult), and the second night.
Subobjective 1b. Assess the potential of combining soil and foliar applications of fungi against westernflower thrips as a strategy to achieve acceptable levels of efficacy at reduced moisture levels. Soil drench applications of B. bassiana (Bb) strain GHA and another insect pathogenic fungus Metarhizium brunneum (Mb) commercial strain F-52 (active ingredient of the Met52® biopesticide) were investigated as alternatives/complements to foliar applications for control of western flower thrips in greenhouse ornamentals. Processing of thrips samples collected from flowering impatiens in 10 previously conducted tests (six tests of Bb and four of Mb) was completed in 2017. Tests showed that treatments by both pathogens provided equivalent levels of control, reducing total thrips populations on flowers by 32% and on foliage by 40% relative to spray carrier controls; respective reductions in populations of adult thrips were 40 and 52%. Though thrips control from these treatments is not adequate from the perspective of greenhouse pest management, the findings are encouraging in that the results were obtained under very low-humidity conditions found to render foliar applications almost completely ineffective. Drench or sprench applications of these insect-pathogenic fungi can thus be recommended as components of thrips integrated pest management programs.
Subobjective 2a. Determine effects of commercially available fungal biocontrol agents on Asian ambrosia beetles and their symbionts. The ambrosia beetle Xylosandrus germanus is an invasive pest attacking a wide range of host trees, including economically important orchard and nursery trees. The beetle is hard to control because of its cryptic habits, with only adult females found outside of beetle galleries under the bark during flights to search for new breeding sites. Research efforts to control this beetle conducted in collaboration with a scientist from Cornell University showed that entomopathogenic fungi B. bassiana and M. brunneum can be used to kill the females, and that infected females later produce fungal conidia than can also kill her progeny, sometimes up to 100% in the gallery. Laboratory in vitro assays also showed that the mycoparasitic fungus Trichoderma harzianum can be used to kill or suppress the fungal symbiont the beetle grows in their galleries for food (Castrillo et al. 2016). Complementary assays using beech logs showed that less than 50% of the females produced progeny due to sparse growth or absence of the symbiont in those treated with the mycoparasitic fungus, and due to death of female adults prior to laying eggs in those treated with insect pathogenic fungi (Castrillo et al. 2016). These results revealed multiple strategies to target these beetles in the field.
Subobjective 2b. Assess efficacy of commercially available entomopathogenic fungi for the walnut twig beetle. Thousand cankers disease (TCD), caused by the walnut twig beetle (WTB), Pityophthorus juglandis, and its associated fungal symbiont, Geosmithia morbida, is a deadly disease of the eastern black walnut, Juglans nigra. Few management options are available for preventing or reducing impact of TCD on black walnut trees. In collaboration with scientists at the University of Tennessee, the USDA Forest Service, and Cornell University, we evaluated the use of commercial strains M. brunneum F52 and B. bassiana GHA against WTB. Laboratory assays showed that WTB adults are readily susceptible to both fungi, with up to 90% of walnut twig beetles dying of fungal infection 4 days after exposure to these insect-pathogenic fungi (Castrillo et al. 2017). Field studies using commercially available products based on these fungi also showed more than 80% reduction in numbers of next generation beetles emerging from sprayed logs because of fewer beetle attacks and mortality among those that tunneled into the logs (Castrillo et al. 2017). These findings are the first to show an environmentally friendly option to target beetle populations and control thousand cankers disease in walnut trees.
Subobjective 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. The introduction of the coffee berry borer (CBB) to Hawaii Island threatens the productivity and quality of Kona coffee, one of the world's premier specialty coffees. In a collaboration with ARS scientists in Hilo, Hawaii, an area-wide project on the control of CBB in Hawaii was conducted from 2014 to 2018. Field efficacy studies on mycoinsecticides based on B. bassiana strain GHA in multiple farms at high and low elevations showed comparable results (Wraight et al. unpublished). Cumulative CBB mortality due to the fungus plateaued at 50-60% even after numerous sprays, and half rate applications were nearly as effective as full rates (Wraight et al. unpublished). Based on the results of this study several recommendations were made on the on the effective use of B. bassiana based mycoinsecticides in CBB control programs in Hawaii.
Subobjective 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. In collaboration with an ARS scientist in Ithaca, New York, a survey of naturally-occurring fungal pathogens associated with CBB in Hawaii identified three species: B. bassiana, Hirsutella eleutheratorum and M. anisopliae (Wraight et al. 2018a,b). The most common pathogen was B. bassiana sensu stricto, with multiple genotypes present (Castrillo et al. unpublished). These genotypes suggest a mix of those carried by CBB from other countries and those that are indigenous to Hawaii that "jumped" the beetle (Castrillo et al. unpublished). Based on the genotypic data, several strains of representative genotypes were selected for mass production and comparative virulence assays against laboratory-reared CBB. Results showed that while none of the naturally-occurring strains was more virulent than the commercial strain GHA, a few Hawaiian strains were as virulent (Wraight et al. unpublished). Further, observations on the sporulation habits of the more common indigenous genotypes revealed features that lend to better persistence and high epizootic potential (Wraight et al. 2018). These results suggest that these naturally-occurring B. bassiana could be more effective biocontrol agents than the commercially available strain GHA against CBB.
Subobjective 3a. Quantify EAB and parasitoid densities to determine whether establishment of EAB parasitoids has significant effects on EAB populations. The SY retired in October 2016.
Subobjective 3b. Determine impact of natural enemies released against emerald ash borer on ash health and survival. The SY retired in October 2016.
Accomplishments
