SELECTION OF DWARF MISTLETOE–INFECTED PONDEROSA PINES BY IPS SPECIES (COLEOPTERA: SCOLYTIDAE) IN NORTHERN ARIZONA

Abstract

In 2002 a bark beetle epidemic severely impacted ponderosa pine (Pinus ponderosa Douglas ex C. Lawson.) forests in northern Arizona. Ponderosa pine mortality occurred over approximately 211,000 ha statewide (USDA 2002). Ips spp. (Ips pini Lecontei and I. lecontei Swaine, Coleoptera: Scolytidae) predominated within infestations and accounted for approximately 99% or about 208,000 infested hectares statewide (McMillin 2003, S.C. Kenaley personal communication). High rates of infestation and tree mortality occurred within the Coconino (24,400 ha), Prescott (30,600 ha), and Tonto National Forests (27,000 ha). In the Tonto National Forest alone, 47% of the ponderosa pine forest type was infested, and many stands had mortality rates of 80%‐90%. Western pine beetle (Dendroctonus brevicomis Leconte), roundheaded pine beetle (Dendroctonus adjunctunus Blandford), and mountain pine beetle (Dendroctonus ponderosae Hopkins) have also been detected within infested areas in northern Arizona, but these bark beetle populations have not yet reached epidemic levels. In many areas where bark beetle infestations occurred, ponderosa pine mortality was greatest in areas infested with southwestern dwarf mistletoe (Arceuthobium vaginatum