Table of Contents
- Epizootiology of insect diseases
- Spatial population structure of pathogens
- Biological control, especially using insect pathogens
- Microbial communities associated with wood-boring insects
Interests in our laboratory are multi-faceted, with questions ranging from molecular to cellular to organismal levels. Much of our work has focused on fungal diseases of insects associated with trees, especially lepidopteran larvae, coleopteran adults, and siricid wasps. Our current research systems include three non-natives: the Gypsy Moth (Lymantria dispar), a pest of oaks; the Asian Longhorned Beetle (Anoplophora glabripennis), which feeds on maples and other hardwoods; and Sirex noctilio and related conifer woodwasps. However, studies and fieldwork by the Hajek Lab are not restricted to these groups or the forest habitat.
I. Epizootiology of Insect Diseases
Epizootiology has been a primary focus of research in our laboratory, with explorations targeting many different aspects over the years. The model system that we have examined most extensively has been gypsy moth and the fungal pathogen Entomophaga maimaiga. Gypsy moth is an outbreak species that was introduced to North America from Europe in 1868-69 but is native across temperate Europe and Asia. Entomophaga maimaiga (Zygomycetes: Entomophthorales) was first found infecting gypsy moth in North America in 1989. The fungal pathogen since then has spread on its own and with a little help, causing high levels of infection in both high and low density gypsy moth populations. As a result, many credit E. maimaigawith now being the dominant natural enemy killing gypsy moth in North America — responsible for crashes in outbreak gypsy moth populations. Included in our years of studies have been spatial and temporal variability in host and pathogen, and the dynamics of host/pathogen interactions. On an ecological level, interactions of host and pathogen with the environment (e.g., host tree species, weather, types of soils, etc.) have been, and are presently being, explored.
Some Related Publications
Castrillo, L.A., L. Thomsen, P. Juneja, A.E. Hajek. 2007. Detection and quantification of Entomophaga maimaiga resting spores in forest soil using real-time PCR. Mycol. Res. 111: 324-331.
Hajek, A.E. 1999. Pathology and epizootiology of the Lepidoptera-specific mycopathogen Entomophaga maimaiga. Microbiol. & Molecul. Biol. Rev. 63: 814-835.
Hajek, A.E. 2001. Larval behavior in Lymantria dispar increases risk of fungal infection. Oecologia 126: 285-291.
Hajek, A.E., Tobin, P.C., Haynes, K.J. 2014 (online). Replacement of a dominant viral pathogen by a fungal pathogen does not alter the collapse of a regional forest insect outbreak. Oecologia. (in press) doi:10.1007/s00442-014-3164-7
Nielsen, C., M.G. Milgroom, A.E. Hajek. 2005. Genetic diversity in the gypsy moth fungal pathogen Entomophaga maimaiga from founder populations in North America and source populations in Asia. Mycol. Res. 109: 941-950.
Reilly, J.R., Hajek, A.E., Liebhold, A.M., Plymale, R.S. 2014. Impact of Entomophaga maimaiga (Entomophthorales: Entomophthoraceae) on outbreak gypsy moth populations (Lepidoptera: Erebidae): the role of weather. Environmental Entomology 43: 632-641.
II. Spatial Population Structure of Pathogens
If pathogen reservoirs have very aggregated distributions, areas of enemy-free space can occur. Without a dominant enemy locally present, hosts could escape and begin the increase that can escalate into development of an outbreak population. In the host/pathogen system comprising gypsy moth and the fungal pathogen Entomophaga maimaiga, populations of this obligate pathogen depend on the distribution of the host. Gypsy moth populations are in turn limited in distribution based on distributions of preferred host trees. In a simple world then, the fungal distribution could be expected to be identical to that of gypsy moth, but this is not the case; E. maimaiga distributions, at least sometimes, differ significantly from those of gypsy moth. Thus, areas with localized absence of infections by this pathogen may be responsible for recent episodes of defoliation caused by the gypsy moth. We are working to understand the relative importance of persistence of this fungus in local reservoirs, versus recolonization of sites through long-range dispersal of airborne conidia. We are also investigating how environmental factors including weather, soil type, and tree species influence the spatial population structure of E. maimaiga.
See the section above for some related publications.
III. Biological Control, Especially Using Insect Pathogens
Work in our laboratory has focused on biological control of invasive species, but studies in the lab are not solely restricted to invasives. Also, we have principally worked with fungal pathogens. There are over 700 species of fungal pathogens infecting insects and mites, and several of these have been developed as microbial insecticides in numerous countries. We have conducted studies with how to preserve fungal pathogens, how to grow them inside and outside of hosts to produce specific fungal stages, and how to apply them in the field for pest control.
A. Asian Longhorned Beetle
We are studying the feasibility of fungal pathogens to control the invasive Asian longhorned beetle. This potentially major pest of hardwood trees in forests and city plantings is a recent immigrant, with populations found in New York, Massachusetts, Ohio, and believed to be eradicated from Illinois, and New Jersey. We have worked with the entomopathogenic fungi Metarhizium and Beauveria (Hyphomycetes), using an application method originally developed in Japan for control of closely related beetles. Fiber bands covered in infective fungal spores (conidia) are placed around tree trunks where adult Asian longhorned beetles contact them when wandering during their normal prematurational development period. We are also investigating the potential for applying pathogenic fungi in various spray application mixtures directly onto tree bark.
For further details, and publications list, see Research on ALB (under Hajek Lab Research in menu across the top of this page).
B. Gypsy Moth
Fungi in the Entomophthorales can be virulent pathogens, causing rapid epizootics in host populations, but they have seldom been exploited for control, in part because they are difficult to mass produce and apply successfully. Our studies have shown that E. maimaiga resting spores are the best stage to release for gypsy moth control, and we can produce these spores within hosts or in culture media. We are currently conducting studies on resting spore dormancy in order to develop methods to ensure that resting spores being released for gypsy moth control will germinate that season.
Some Related Publications
Hajek, A.E., A.E. Burke, C. Nielsen, J.J. Hannam, L.S. Bauer. 2008. Nondormancy in Entomophaga maimaiga azygospores: effects of isolate and cold exposure. Mycologia 100: 833-842.
Hajek, A.E., J.S. Strazanac, M.M Wheeler, F. Vermeylen, L. Butler. 2004. Persistence of the fungal pathogen Entomophaga maimaiga and its impact on native Lymantriidae. Biol. Contr. 30: 466-471.
Reilly, J.R., A.E. Hajek. 2007. Density-dependent resistance of the gypsy moth, Lymantria dispar to its nucleopolyhedrovirus, and the consequences for population dynamics. Oecologia 154: 691-701.
Solter, L.F., A.E. Hajek. 2008. Control of gypsy moth, Lymantria dispar, in North America since 1878. In: A.E. Hajek, T.R. Glare & M. O’Callaghan (eds.) Use of Microbes for Control and Eradication of Invasive Arthropods. Springer, Dordrecht, NL.
IV. Microbial Communities Associated with Wood-Boring Insects
We are interested in the microbial symbionts associated with wood-boring insects, and a current project involves the fungal strains associated with the invasive woodwasp, Sirex noctilio, in North America. Sirex noctilio, a European woodwasp that attacks pines, is an invasive pest that was first trapped in New York State in 2004. In the Southern Hemisphere this invasive species has destroyed up to 80% of a pine plantation in as little as two years. As of 2008 S. noctilio was found in areas across the state of New York, and also in Michigan, Pennsylvania, and Vermont. This wasp carries a symbiotic wood rot fungus (Amylostereum areolatum) that the ovipositing female injects into the tree, and the wasp larvae subsequently feed on rotting wood. Successful biological control programs have been developed in the Southern Hemisphere, where this wasp has been introduced, using parasitic nematodes (Deladenus siricidicola). However, in North America there are several other native woodwasp species in the same woodwasp family. Our research focuses on woodwasp species and their associated fungi, both within and outside regions where S. noctilio is present. DNA from different strains of Amylostereum are being sequenced to determine taxonomic relationships and the specificity of each fungal strain to each woodwasp species. The potential effect of the parasitic nematodes on the native Sirex species and other non-target insects is also being examined, toward evaluating environmental impacts that might occur due to releasing the nematode for S. noctilio control. We have also investigated which parasitoid species are presently associated with S. noctilio in northeastern forests.
For updated details through 2018 on these research areas and publications from the Hajek Lab, see Sirex/Deladenus/Amylostereum Research (under Hajek Lab Research in the menu across the top).