Challenging a mutualism paradigm: Do bark beetles need fungi?

Northern Arizona University, Flagstaff AZ

Investigators

Abstract

In the last 10 years, an estimated 47 million ha of forest have been affected by bark beetle driven tree mortality in the western U.S. and Canada. It has long been thought that a mutualism between bark beetles and their closely associated fungi is the key reason these insects are so successful. Both beetles and their fungi require tree death for success; however, despite considerable study, controversy remains about the importance of each individual agent in causing tree mortality and whether the association is a true mutualism. Clearly fungi benefit from the association by gaining transport to a new host but the benefit to the beetle is less clear. The fungi are variously thought to benefit the beetles by assisting in depleting tree defense, disrupting water conduction in the tree, and/or providing nutrient supplementation to the beetles themselves. Due to the almost ubiquitous presence of fungi with the beetles it has been virtually impossible to truly separate the action of the two agents. This project will investigate the impact of fungicide on tree physiology and the potential effectiveness of fungicide at reducing the growth of bark beetle-associated fungi at the whole tree level. In addition, this project will examine the impact of fungicide on bark beetle activity/success. If fungicide proves to be effective at stopping or slowing fungal growth, with minimal impacts on tree function and beetle activity, bark beetle researchers will be able to investigate the respective role of each agent in tree mortality and ultimately the impact of fungi on beetle success. This will have broad implications for informing our understanding of the nature of bark beetle/fungus relationships. This project also has potential impacts for mitigating future tree mortality from bark beetles.