A number of native bark beetles can cause tree mortality in western forests and urban environments. These insects have co-evolved over thousands of years with their host trees and are an integral part of forest ecosystems. Bark beetles help shape forest structure and composition and influence forest productivity and biogeochemical cycling (i.e., the movement of elements through the ecosystem). They also play important roles in providing habitat for many wildlife species, arthropods (e.g., insects and millipedes), and a great diversity of fungi. Under certain circumstances bark beetles can come in conflict with land managing objectives, whether for a forester or a homeowner, and tree mortality can become problematic.
Researchers are working through a long list of questions about how bark beetles affect ecosystems, from changes to scenery to changes in quality and quantity of water flowing from infected watersheds. Bark beetle infestations create patches of forest that have trees of various ages, densities, species, and successional stages. This variation helps keep the forests healthy. Researchers are looking at ways to connect bark beetle activity with landscape patterns so they can better understand the beetle’s ecological role.
Bark beetles are causing a significant change to western forest scenic landscapes. Scientists are pursuing several lines of research that address the negative effects of beetles and help us understand the beetle’s positive influences.
Impact of management on beetle outbreaks: Research suggests that practices such as forest thinning can help mitigate extensive tree mortality caused by bark beetles. However, most studies addressing vegetation management have been conducted on small plots, areas where even-aged management is practiced and in limited forest types. It is also not well understood what levels of insect populations can simply overwhelm managed stands.
Interactions between bark beetles and forest fires: Fire can injure trees and change the volatile emissions of conifers, a process that often increases the trees’ susceptibility to some bark beetles. Bark beetles can also change the forest environment by influencing forest structure and transforming fuels. Overall, wildfire risk following beetle outbreaks, although not well understood, might depend on interactions with several factors. Some of these include weather and climatic patterns, forest type and tree cover type, site characteristics, changes in forest structure, time since mortality, and past management history.
Effects of climate change on beetle biology and outbreaks: Beetle outbreaks are coinciding with increased winter temperatures and changing precipitation patterns. Climate change affects bark beetles by altering their development and temperature-induced mortality. Climate change may also affect trees’ defense mechanisms against bark beetle attacks.
Use of semiochemical, substances that insects produce and use to communicate and regulate the attack process in a tree, to mitigate attacks: Many bark beetles produce aggregation chemicals, or pheromones, that concentrate insect populations on an infected tree in an effort to overcome tree defenses. When a tree is fully colonized by the beetles, an anti-aggregation pheromone is released to prevent additional attacks on the tree. This is a way for the insects to reduce competition for resources. Scientists have identified many of these chemicals and studies are being conducted to examine their effectiveness in managing insect populations. Scientists also continue to test insecticides that can be used to prevent trees from being attacked by the bark beetles.
|Bark Beetle Species||Scientific Name||Primary Host Trees||Scientific Name|
|Mountain pine beetle||Dendroctonus ponderosae||Ponderosa pine
|Spruce beetle||Dendroctonus rufipennis||Engelmann Spruce||Picea engelmannii|
|Douglas-fir beetle||Dendroctonus pseudotsugae||Douglas-fir||Pseudotsuga menziesii|
|Pinyon ips||Ips confusus||Pinon pine||Pinus edulis|
|Pine engravers||Ips spp. (various species)||Pines and other conifers||various|
|Western balsam bark beetle||Dryocoetes confusus||Subalpine fir||Abies lasiocarpa|
Fettig, Christopher J.; DeGomez, Tom E.; Gibson, Kenneth E.; Dabney, Christopher P.; Borys, Robert R. 2006. Effectiveness of permethrin plus-C (Masterline®) and carbaryl (Sevin SL®) for protecting individual, high-value pines from bark beetle attack. Arboriculture & Urban Forestry 32(5):247-252.
Witcosky, Jeff. 2009. Will the Mountain Pine Beetle Epidemic Spread from Lodgepole Pine into Ponderosa Pine along the Northern Front Range Counties of Colorado?. Report to the Joint Ecology Working Group. 30 p.
Negrón, José F.; Popp, John B. 2004. Probability of Ponderosa Pine Infestation by Mountain Pine Beetle in the Colorado Front Range. Forest Ecology and Management 191:17-27.