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United States Department of Agriculture

Agricultural Research Service

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Location: Emerging Pests and Pathogens Research

2011 Annual Report

1a. Objectives (from AD-416)
1: Characterize fungal strains associated with insects (including insect pathogens and symbionts and plant pathogens vectored by insects) and develop methods to enable their rapid identification and tracking. 1a. Develop molecular assays to detect and quantify plant pathogenic oomycetes vectored by insects to verify transmission. 1b. Identify the primary fungal symbiont associated with Asian ambrosia beetles and assess the genetic diversity of these fungi from beetles in the eastern United States. 1c. Evaluate fungal delivery, establishment and persistence in target populations of invasive wood-boring beetles. 2: Determine and improve the effectiveness of fungi for use within integrated management systems for greenhouse, horticultural and landscape pests, including but not restricted to thrips, whiteflies, ambrosia beetles and emerald ash borer. 2a. Develop a biologically-based IPM program for western flower thrips infesting greenhouse crops. 2b. Compare the efficacy of Beauveria bassiana and Metarhizium anisopliae against the Q biotype of Bemesia tabaci. 2c. Develop available microbial control agents for management of Asian ambrosia beetles and their symbiotic fungi. 2d. Integrate pathogenic fungi with other biocontrol agents for emerald ash borer and evaluate non-target impacts.

1b. Approach (from AD-416)
The goals of this project are to integrate entomopathogenic fungi into management systems for selected insect pests of horticultural, nursery and landscape plants and to track fungal strains in these environments. The work comprises fundamental laboratory studies as well as applied greenhouse and field research. This project will develop basic information on the biology of fungal and oomycete pathogens associated with insects, their genetic and phenotypic variability, and their survival and transmission in greenhouse and field environments. Integration of fungal pathogens will be accomplished for management of key pests: a biologically based program will combine use of pathogens and predators for control of western flower thrips infesting greenhouse crops; efficacy of fungal pathogens will be determined for Bemisia whiteflies (B. tabaci Q biotype); microbial control agents will be developed for management of Asian ambrosia beetles; and a fungal mycoinsecticide will be integrated with other biocontrol agents used against emerald ash borer. Fungi used in the ways developed in this project will provide safe, effective biological alternatives to synthetic chemical insecticides and/or rotational partners for insecticide resistance management.

3. Progress Report
A robust and easily maintained laboratory colony of western flower thrips (Frankliniella occidentalis) was established on excised bean leaves. Insects from this colony were used in an extensive screening effort to identify fungal pathogens from the USDA-ARS collection of Entomopathogenic Fungal Cultures (ARSEF) with high virulence against key pests of greenhouse crops (see report of activities under Cooperative Research and Development Agreement project 1907-22000-019-12T). Thrips from the lab colony were also used to infest greenhouse research plots of potted impatiens for research aimed at development of a biologically based IPM program for western flower thrips. A number of greenhouse tests aimed at assessing efficacy of fungal pathogens (Beauveria and Metarhizium isolates) against western flower thrips and predatory midges (Aphidoletes aphidimyza) against green peach and foxglove aphids were conducted in 2011. Tests of promising fungal pathogens against thrips during summer were unsuccessful due to extraordinarily high thrips pressure from unknown sources (movements of migrating thrips into our greenhouses). We are currently in the process of sealing the research compartments against future invasions before resuming testing. A series of experiments were done to assess the impact of insect pathogenic fungi on Asian ambrosia beetles in the field. Small logs were attached to stakes in infested woodlots and then sprayed with a strain of Metarhizium brunneum. Survival of this fungus was high for 3 weeks. Beetle attack rate, survival, and reproduction were all significantly reduced versus controls. Emergence of adult progeny and establishment of M. brunneum within beetle galleries are currently being analyzed. Newly discovered infestations of the emerald ash borer in New York are being characterized so that an integrated plan for their management can be developed and implemented. Clusters of girdled trees serve as ‘sinks’ for concentrating beetle attack. Individual girdled trees used across a larger area help delimit the population. All trees used in 2010 have been felled and beetles quantified. For 2011, new clusters of girdled trees also serve as foci for release of hymenopterous parasitoids. In addition, predation, parasitism and disease incidence are being quantified at several sites. This work is being done in cooperation with researchers at several institutions.

4. Accomplishments
1. Studies reveal limited ability of fungus gnat larvae to vector root rot diseases. Fungus gnat larvae are commonly associated with diseased plants, and it has long been speculated that they are important vectors of Pythium root-rot pathogens. Previous lab studies based on Petri dish assays have revealed that fungus gnat larvae readily ingest Pythium spores and that ingested spores can survive passage through the gut and produce high rates of plant infection; however, little is known of the potentially for fungus gnat larvae to transmit Pythium under greenhouse conditions. Collaborative studies completed by ARS researchers at Ithaca, NY, and Cornell University researchers revealed that vectoring of Pythium to geranium seedlings was highly variable, depending on the type of substrate supporting the plant and the strain of Pythium fed to the fungus gnat larvae. A highly virulent strain of Pythium was readily transmitted to geranium seedlings rooted on wet paper in Petri dishes, but transmission was more than 10-fold lower to seedlings growing in a commercial peat-based potting medium. In addition, fungus gnat larvae were not able to transmit all strains of Pythium. Our findings indicate that these insects are less efficient vectors of Pythium pathogens than previously believed and will be useful to researchers developing IPM strategies for greenhouse pest and disease management.

2. Management tools developed for Phytophthora diseases in floral crops Phytophthora surveys of production facilities in North Carolina over the past 10 years by researchers at North Carolina State University, with recent support and collaboration of ARS researchers at Ithaca, NY, have identified the most important Phytophthora species attacking floriculture crops and determined that many strains of these pathogens are insensitive to the most widely used fungicide, mefenoxam (Subdue MAXX). Therefore, newer fungicides are needed for disease control. Tests with several promising new products were conducted with gerbera daisy infected with mefenoxam-insensitive isolates of P. drechsleri. Effective disease control was achieved with a number of these products and product combinations. These findings have identified new materials for fungicide rotation schemes and are contributing to the reduction of disease losses in floriculture across the United States.

3. Efficacy of aphid midge limited against mixed aphid infestations. Simultaneous outbreaks of multiple aphid pests such as green peach aphid and foxglove aphid is a common occurrence in mixed floriculture crops in northeastern USA greenhouses, and biological control programs are complicated by lack of a single effective control agent. The aphid midge, Aphidoletes aphidimyza, could potentially fill this niche; the midge larvae are generalist predators, and application costs are comparable to those of other commonly used natural enemies. Greenhouse studies completed by collaborating Cornell University and ARS researchers at Ithaca, NY, assessed the potential of this insect to control mixed infestations of these aphids on pansy. The aphids exhibited markedly different behaviors in the greenhouse, with green peach aphids colonizing primarily the top leaves of the pansy plants and foxglove aphids favoring the lower leaves. Midges released into greenhouses infested with both aphids laid nearly all of their eggs among green peach aphids in the tops of the plants, ignoring foxglove aphids on the lower leaves. These findings demonstrate a low potential for this natural enemy to control mixed aphid infestations. Identification of this problem has contributed to development of more effective IPM programs.

4. Insect-pathogenic fungi used to control Asian ambrosia beetles. Asian ambrosia beetles are serious pests of nursery and landscape trees. Beetles cause both cosmetic and systemic damage and are difficult to control. ARS researchers at Ithaca, NY, tested three commercially available strains of insect-pathogenic fungi against field-collected and laboratory-reared Xylosandrus germanus beetles. Among the three commercial fungal strains tested, Beauveria bassiana Naturalis and Metarhizium brunneum F52 were more virulent than B. bassiana GHA. The researchers also found that beetle inoculation with fungal spores did not affect the usual way in which beetles invade their host substrate, but did result in fewer beetles successfully excavating chambers within the diet and producing offspring. The number of offspring produced was also reduced and infection was observed among larvae, pupae and adult progeny. These results demonstrate that exposure to available microbial control agents can have a significant impact on beetle success. The use of these strains can be a vital component of an integrated beetle management program.

Review Publications
Castrillo, L., Griggs, M., Ranger, C.M., Reding, M.E., Vandenberg, J.D. 2011. Virulence of Beauveria bassiana and Metarhizium anisopliae (Ascomycota: Hypocreales) commercial strains against adult Xylosandrus germanus (Coleoptera: Scolytidae) and impact on brood. Biological Control. 58(2):121-126.

Faria, M., Hajek, A.E., Wraight, S.P. 2009. Imbibitional damage in conidia of the entomopathogenic fungi Beauveria bassiana, Metarhizium anisopliae, and Metarhizium acridum. Biological Control. 51:346-354.

Faria, M., Hotchkiss, J.H., Hajek, A.E., Wraight, S.P. 2010. Debilitation in conidia of the entomopathogenic fungi Beauveria and Metarhizium anisopliae and implications with respect to viability determinations and mycopesticide quality assessments. Journal of Invertebrate Pathology. 105(1):74-83.

Last Modified: 06/21/2017
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