Progress 07/01/10 to 06/30/14
Outputs
OUTPUTS: Progress has been made with regard to our objectives to determine (1) if population genetic structure and composition of western pine beetle communities are predictable or variable across pine phytochemical phenotypes; and (2) if beetles and associated microbial communities locally adapt to host phytochemistry in a way that meaningfully impacts ecological performance of bark beetles, and the results have been disseminated by publications (listed in next section) and by scientific and public presentations. Information has also been incorporated into college forestry lectures at NAU. Results were presented at the Western Forest Insect Work Conference in Coeur D'alene, Idaho by Davis, T.S. and R.W. Hofstetter March 2012. The presentation was titled, The effects of tree chemistry and beetle chemical legacy on growth of a fungal mutualist. PARTICIPANTS: PI: Dr. Richard W. Hofstetter Student(s): Kasey Yturralde (2012-13), Thomas Seth Davis (2010-11) TARGET AUDIENCES: managers, foresters, and landowners PROJECT MODIFICATIONS: This project ended a year early due to quick research progression and findings
Impacts
The impact of bark beetle activity in the west is steadily increasing as a result of over-dense stands, drought stress, and increasing temperatures. Bark beetle outbreaks can rapidly shift forest structure and composition, and the magnitude of these disturbances can affect the rate of climate change. In light of this, ecosystem managers, foresters, and landowners can greatly benefit from reliable methods to reduce bark beetle abundances, prevent tree mortality, and accurately predict trends in beetle population dynamics. The spatial structure and variability of terpenoid-based phytochemical phenotypes of conifers influences beetle host selection and fecundity, and ultimately beetle population fluctuations. Association with mutualists is highly correlated with beetle performance. In these symbioses, beetles that feed on mutualistic fungi have higher survival, larger nitrogen budgets, and adults are larger and considerably more fecund. Mycophagy by teneral adults is also a requirement for reproduction in at least one species. However, beetles are typically associated with a varied microbial community including yeasts, bacteria, and opportunistic fungi The influence of these microbial communities on beetle population dynamics are almost entirely undstudied, and yeasts in particular appear to be extremely common associates of Dendroctonus bark beetles. Aside from a few studies, the functional ecology of yeast symbionts in Dendroctonus-microbe complexes is unknown. But, the few available studies suggest that yeasts have important functions in beetle-symbiont systems. From our results we proposed four testable roles of yeasts in beetle-microbe assemblages, including: (1) nutritional, (2) semiochemical, (3) protective, and (4) phytochemical detoxification. Yeasts are known to provide nutrients to other insects, but their potential nutritional benefit to bark beetles has not yet been investigated. In addition to directly affecting beetle nutrition, yeasts may indirectly affect nutrient acquisition by beetles through interactions with mycangial fungi. Yeasts enhanced the growth of one fungus, Ophiostoma montium, while suppressing the growth of the other, Grosmannia clavigera. Similarly, we found that volatile emissions from the yeast Ogataea pini (= Pichia pini) associated with D. brevicomis enhanced the growth of a mutualistic fungus while inhibiting the growth of an entomopathogenic fungus. Yeasts emissions may also act as semiochemicals in bark beetle systems. For example, yeast emissions influenced host habitat location by parasitoids and predators of bark beetles. Likewise, others have demonstrated that yeasts could oxidatively convert aggregation pheromones to anti-aggregation pheromones, indicating that trees heavily colonized by yeasts are unsuitable for beetle colonization. We found that tree vascular tissues inoculated with yeast (O. pini) had significantly different concentrations of several monoterpenes during the incipient stages of beetle colonization. Thus, there is evidence to support the functional roles of yeasts suggested above, but the examples are few and have not been tested extensively in any single beetle-microbe system.
Publications
- Cardoza, Y.J., R.W. Hofstetter and F.E. Vega. 2012. Chapter 8: Insect-associated microorganisms and their possible role in Outbreaks. In Insect Outbreaks Revisited (eds. P. Barbosa, D.K. Letourneau, A.A. Agrawal). Pages 155-174.
- Davis, T.S. and R.W. Hofstetter. 2010. Host-tree phytochemistry has non-additive effects on mycangial fungi isolated from Dendroctonus brevicomis. Abstract page 354 in The International Forestry Review. Proceedings of the XXII IUFRO World Congress, Seoul, Republic of Korea.
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Progress 01/01/11 to 12/31/11
Outputs
OUTPUTS: Progress has been made with regard to our objectives are to determine (1) if population genetic structure and composition of western pine beetle communities are predictable or variable across pine phytochemical phenotypes; and (2) if beetles and associated microbial communities locally adapt to host phytochemistry in a way that meaningfully impacts ecological performance of bark beetles, and the results have been disseminated by publications (listed in next section) and by scientific and public presentations. Information has also be incorporated into college forestry lectures at NAU. Results were presented Entomological Society of America, Reno, November 2011 by Davis, T.S. and R.W. Hofstetter title Reciprocal interactions between the bark beetle associated yeast Ogataea pini and host plant phytochemistry and at the North America Forest Insect Work Conference. Portland, Oregon May 2011 by Davis, T.S. and R.W. Hofstetter. The presentation was titled, Reciprocal interactions between a bark-beetle associated yeast and host pine phytochemisty. PARTICIPANTS: PI: Dr. Richard W. Hofstetter Student(s): Kasey Yturralde, Thomas Seth Davis (2010-11) TARGET AUDIENCES: Ecosystem managers, foresters, and landowners can greatly benefit from reliable methods to reduce bark beetle abundances, prevent tree mortality, and accurately predict trends in beetle population dynamics. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
The impact of bark beetle activity in the west is steadily increasing as a result of over-dense stands, drought stress, and increasing temperatures. Bark beetle outbreaks can rapidly shift forest structure and composition, and the magnitude of these disturbances can affect the rate of climate change. The spatial structure and variability of terpenoid-based phytochemical phenotypes of conifers influences beetle host selection and fecundity, and ultimately beetle population fluctuations. Association with mutualists is highly correlated with beetle performance. However, beetles are typically associated with a varied microbial community (other than mutualist fungi) including yeasts, bacteria, and opportunistic fungi The influence of these microbial communities on beetle population dynamics are almost entirely undstudied, and yeasts in particular appear to be extremely common associates of Dendroctonus bark beetles Aside from a few studies (e.g., Hunt and Borden 1990, Adams et al 2008, Rivera et al 2009, Davis et al 2011a, Davis et al 2011b), the functional ecology of yeast symbionts in Dendroctonus-microbe complexes is unknown. Furthermore, nearly all studies investigating beetle-microbe associations fall short of addressing the actual impacts of symbionts on beetle population dynamics. But, the few available studies suggest that yeasts have important functions in beetle-symbiont systems. From our results we proposed four testable roles of yeasts in beetle-microbe assemblages, including: (1) nutritional, (2) semiochemical, (3) protective, and (4) phytochemical detoxification. Yeasts are known to provide nutrients to other insects, but their potential nutritional benefit to bark beetles has not yet been investigated. In addition to directly affecting beetle nutrition, yeasts may indirectly affect nutrient acquisition by beetles through interactions with mycangial fungi. For example, others found that several yeast species had significant effects on the growth of two mutualist fungi associated with D. ponderosae. Yeasts enhanced the growth of one fungus, Ophiostoma montium, while suppressing the growth of the other, Grosmannia clavigera. Similarly, we found that volatile emissions from the yeast Ogataea pini (= Pichia pini) associated with D. brevicomis enhanced the growth of a mutualistic fungus while inhibiting the growth of an entomopathogenic fungus. Yeasts emissions may also act as semiochemicals in bark beetle systems. For example, yeast emissions influenced host habitat location by parasitoids and predators of bark beetles. Likewise, others have demonstrated that yeasts could oxidatively convert aggregation pheromones to anti-aggregation pheromones, indicating that trees heavily colonized by yeasts are unsuitable for beetle colonization. We found that tree vascular tissues inoculated with yeast (O. pini) had significantly different concentrations of several monoterpenes during the incipient stages of beetle colonization. Thus, there is evidence to support the functional roles of yeasts suggested above, but the examples are few and have not been tested extensively in any single beetle-microbe system.
Publications
- 1. Davis, T.S. and R.W. Hofstetter. 2012. Plant secondary chemistry mediates the performance of a nutritional symbiont associated with a tree-killing herbivore. Ecology 93(2): 421-429.
- 2. Davis, T., K. Jarvis, K. Parise and R. Hofstetter. 2011. Oleoresin exudation rate increases and viscosity declines following a fire event in a ponderosa pine ecosystem. Journal of the Arizona-Nevada Academy of Science 43(1): 6-11.
- 3. Davis, T.S., R.W. Hofstetter, J.T. Foster, N.E. Foote, and P. Keim. 2011. Interactions between the yeast Ogataea pini and filamentous fungi associated with the western pine beetle. Microbial Ecology 61: 626-634.
- 4. Davis, T.S. and R.W. Hofstetter. 2011. Oleoresin chemistry mediates oviposition behavior and fecundity of a tree-killing bark beetle. Journal of Chemical Ecology 37: 1177-1183.
- 5. Davis, T.S. and R.W. Hofstetter. 2011. Reciprocal interactions between the bark-beetle associated yeast Ogataea pini and host plant phytochemistry. Mycologia 103(6): 1201-1207.
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