www.csfs.colostate.edu QUICK GUIDE SERIES FM 2014-1 Spruce Beetle

• Main Authors: An Agent, Subalpine Change
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2014
• Subjects: Newfoundland; Alaska
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.666.6114; http://csfs.colostate.edu/pdfs/Spruce-Beetle-QuickGuide-FM2014-1.pdf

The spruce beetle is a native species in Colorado’s spruce forest ecosystem. Endemic populations are always present, and epidemics are a natural part of the changing forest. There usually are long intervals between such events as insect and disease epidemics and wildfires, giving spruce forests time to regenerate. Prior to their occurrence, the potential impacts of these natural disturbances can be reduced through proactive forest management. The spruce beetle (Dendroctonus rufipennis) is responsible for the death of more spruce trees in North America than any other natural agent. Spruce beetle populations range from Alaska and Newfoundland to as far south as Arizona and New Mexico. The subalpine Engelmann spruce is the primary host tree, but the beetles will infest any spruce tree species within their geographical range, including blue spruce. In Colorado, the beetles are most commonly observed in high-elevation spruce forests above 9,000 feet. At endemic or low population levels, spruce beetles generally infest only downed trees. However, as spruce beetle population levels in downed trees increase, usually following an avalanche or windthrow event – a high-wind event that topples trees over a large area – the beetles also will infest live standing trees. Spruce beetles prefer large (16 inches in diameter or greater), mature and over-mature spruce trees in slow-growing, spruce-dominated stands. However, at epidemic levels, or when large-scale, rapid population increases occur, spruce beetles may attack trees as small as 3 inches in diameter. Attacks also have been observed in krummholz – trees near timberline that exhibit stunted growth due to harsh conditions. Life History Spruce beetles have a life cycle of one to three years, and a two-year life cycle is the most common. Adult spruce beetles usually are dark brown to black with reddish-brown or black wing covers. They are cylindrical in shape and Figure 1. Engelmann spruce trees infested with spruce beetles on Spring Creek Pass.