John Watkins
Abstract
This project was funded with the intent that possible biological controls could be found to control the population explosions of bark boring beetles. We hypothesized that due to the prevalence of beetle outbreaks in the West, we would find enough Agrilus liragus specimens to culture native entomopathogenic fungi. We hoped to sequence that fungi and hypothesized that there would be new species of pathogenic fungi that is specific to Agrilus liragus. Through our fieldwork we were not able to find sufficient numbers of Agrilus liragus to accomplish these goals. What we did find were high levels of the tree rotting fungus Phellinus tremulae at our study sites. We found that the prevalence of this fungus seem to have a strong correlation with altitude. More research is being done to further understand the environmental range of the fungus Phellinus tremulae.
Introduction
There is an alarming decline in the health of western forests, particularly with respect to the Aspen tree. It has been suggested that climate change is enabling explosive growth in the population of wood boring beetles, which in turn drives what is known as Sudden Aspen Decline (SAD). See, figure one.
While many factors contribute to SAD, some of the prevailing hypotheses suggest that a sudden change in climate is enabling an explosion of wood boring beetles, which has disrupted the delicate balance of ecological forces. I proposed a use of naturally occurring entomopathogenic fungi, fungi that selectively attack a host insect, as a bio-insecticide to help curb this insect explosion and restore the Aspen forests. The hope was that this would decrease the risk of wildfire, help to maintain the current levels of recreation and protect valuable watershed areas.
It is hypothesized that, due to climate change the population of the Bronze Poplar Borer (Agrilus Liragus) has increased to the point that its host species, the Quaking Aspens have entered an alarming decline (Worrall et al., 2008). Studies have shown that there has been a 32.2 % decline in the Aspen populations of stands surveyed in Nevada, Utah Idaho and western Wyoming, with another 30 % showing signs of moderate to heavy damage (Guyon & Hoffman, 2011). The bronze poplar borer has been found in 70.6% of all dead trees in affected areas in Idaho and in 53.7% of dead systems in Utah, which indicates that it is among the most important damage agent in Idaho systems. Indeed, in some systems Agrilus liragus appears to be the only significant agent of mortality (Guyon & Hoffman, 2011).
A novel approach, which has emerged in recent years, is the practical application of entomopathogenic fungi, fungi that causes disease in specific, target insect hosts. Hundreds of different types of fungi have coevolved with particular species of insects and, in many parts of the world, keep these insects in check.
There has been extensive research on the bark boring beetles that affect northern pine forests such as the Asian Longhorn Beetles and the Emerald Ash Borer (Shajahan et al. 2012). These studies have been carried out primarily by the United States Forest Service and its counterparts in Canada, New Zealand, Sweden, Norway, and Hungary. This research demonstrates an impressive 70-100% mortality of the beetles with the application of entomopathogenic fungi, particularly species such as, Beauveria bassiana and members of the genus Metarhizium (Popa et al. 2012). The appeal of this biological control approach is lost, however, with the use of potentially effective but non-native species of fungi. Thus, I hoped to characterize the naturally occurring pathogenic fungal communities associated with the Bronze Poplar Borers. Studies in Hungary had confirmed the effectiveness of this approach. Lackovic & Pernek (2012) found, for example that native fungal species were still capable of causing an 83% mortality. My hypothesis was that we would find naturally occurring entomopathogenic fungi within this community that will effectively serve as a biopesticide against the Bronze Poplar Borer.
Methods
Beetles were collected using funnel traps that were painted purple and green to mimic barney traps that have been successful against the closely related emerald ash borer in the Eastern United States. Four traps were built. Two were made of ten plastic funnels purchased from Wal Mart and painted green. One was made of eight funnels and painted purple and the other was eleven funnels and painted purple. At the bottom of the traps we taped 50 ml centrifuge tubes which were filled with 95% ethanol which acted as a killing agent. These traps were placed within dense Aspen stands off of Forest Trail 055 along the Alpine Loop Road near Sundance Utah at N 40.414582, W -111.607275. Traps were checked every 4 days through the month of July 2014. A trap used commercially for Japanese beetles (Bag-A-Bug by Spectracide) was placed along Squaw Peak road at N 40.302268, W -111.618057. It was left for two weeks during the month of July 2014.
Manual attempts at catching beetles along the Nebo loop road, Squaw Peak road and Alpine Loop Road using sweep nets as well as looking under the bark of dead aspens yielded no Agrilus liragus bettles.
The traps yielded an estimated 50 different insect species that included 150 different individuals. The majority of these individuals were of the order Hemiptera, Hymenoptera, Diptera and Coleoptera. Out of the 150 individuals only one Bronze Poplar Borer was collected.
Project Reconsidered
This project was based on the hypothesis that large numbers of Agrilus liragus could be captured and sequenced. Because entomopathogenic fungi is only found on a small percentage of individuals, one beetle collected over an entire month of trapping was not sufficient to justify the continuation of the project and the goals of the project had to be reassessed.
Introduction
While collecting for Agrilus liragus, we noticed that a high percentage of the trees along the Alpine Loop road were infected with the fungus Phellinus tremulae. As a tree rotter, this fungus feeds on the heartwood of the tree and will eventually cause mortality. In certain areas, our surveys found that up to 45% of the trees were infected with the fungus and would face mortality. We decided that it merited further research and decided to first conduct surveys to determine how wide the fungus had spread.
Methods
Sites were located along the Alpine Loop in Provo Utah, the Nebo loop outside of Nephi Utah, the Little Cottonwood Canyon Road outside of Sandy Utah, and the Big Cottonwood Canyon Road outside of Brighton Utah. Individual stands were surveyed at the following locations. Along the Alpine Loop stands were surveyed at 6854 ft, 7150 ft, 7607 ft, 8044 ft, 7978 ft, 7632 ft, 7134 ft, and 6780 ft. Along the Nebo loop stands were surveyed at 6760 ft, 7360 ft, 7951 ft, 8820 ft, 9287 ft, 8826 ft, 7914 ft, and 7254 ft. In the Little Cottonwood Canyon stands were surveyed at 5726 ft, and 6907 ft. In the Big Cottonwood Canyon stands were surveyed at 7002 ft, 7282 ft, 7522 ft, 8051 ft, and 8056 ft. At each stand of aspens we conducted straight line surveys where we counted between 68 and 150 trees. We recorded how many of those trees exhibited the sporocarps of Phellinus tremulae and how many did not. The identification was done visually.
Results
Using chi-squared analysis, we determined that there was a significant differences in the prevalence of disease through the stands. On the north side of Mt. Nebo, the P-value was < 0.00001 meaning that at p>0.05 there was a significant change in the incidence of disease across the stands at different elevations. This was also the case on the southern slope of the Alpine loop where the p-value among the stands was 0.000598 as well as on the northern slope where the p-value was 0.021518. In the Big Cottonwood Canyon, there was also a significant difference between stands and the p-value was < 0.00001. On the south side of Mt. Nebo, the p-value was 0.369469 so there was no significant change in the incidence of disease between the stands which were at different elevations. This was also the case in the Little Cottonwood Canyon where the p-value was 0.990058. General trend lines show that across all of the sites, there is a correlation between the altitude at which the trees are found and the prevalence of the fungi within the stands.
Discussion
Further analysis on why there is an apparent gradient influencing the colonization of Phellinus tremulae, is still being conducted and this project is not yet complete. We are currently testing several hypotheses. While we are confident that elevation is having an impact on the colonization of the fungus, we do not know which factors are at play. We imagine that the dryness of the south side of Mt. Nebo may have reduced the fitness of Phellinus tremulae and caused the high p-value. We are also exploring the possibility that the temperature may be affecting the fitness of Phellinus tremulae and are designing an experiment that will allow us to better understand how temperature influences the growth. This will require several more months of testing and analysis before we can come up with a complete report for the project.
Scholarly Sources
Guyon, J., J. Hoffman. 2011. Survey of aspen dieback in the intermountain region. USDA Forest Service.
Lackovic N., Pernek M. 2012. Mogucnost primjene entomopatogene gljive Beauveri Bassiana Za Suzbijanje Jasenove Pipe (STEREONYCHUS FRAXINI), trans- (POSSIBILITY OF USING ENTOMOPATHOGENIC FUNGI BEAUVERIA BASSIANA FOR CONTROLLING THE ASH WEEVIL (STEREONYCHUS FRAXINI) Radovi (Hrvat. šumar. inst.) 44(2): 101-111
Popa V., Déziel E., Lavallée R., Bauce E. and Guertin C. 2012, The complex symbiotic relationships of bark beetles with microorganisms: a potential practical approach for biological control in forestry. Pest. Manag. Sci., 68: 963–975
Shajahan Johny, George Kyei-Poku, Debbie Gauthier, Kees van Frankenhuyzen, Peter J. Krell. 2012., Characterization and virulence of Beauveria spp. recovered from emerald ash borer in southwestern Ontario, Canada. Journal of Invertebrate Pathology, 111: 41-49.
Worrall James J., Leanne Egeland, Thomas Eager, Roy A. Mask, Erik W. Johnson, Philip A. Kemp, Wayne D. Shepperd. 2008. Rapid mortality of Populus tremuloides in southwestern Colorado, USA, Forest Ecology and Management 255: 686-696.