First report of pine wilt in Colorado, USA.
The pinewood nematode, Bursaphelenchus xylophilus, is native to North America and primarily subsists in declining or dead native conifers as a fungivore. However, the nematode causes a lethal wilt of several widely planted exotic pine species, including Scots (Pinus sylvestris) and Austrian (Pinus nigra) pines, in the USA. Pine wilt is now widely distributed in the Great Plains, but has not previously been reported in the Rocky Mountain region. In autumn 2006, in Larimer and Weld counties in Colorado, USA, a Scots pine exhibited symptoms consistent with pine wilt. Nematodes extracted from the trees were identified as B. xylophilus based on morphological characteristics. No additional confirmations were made until 2011 when two Scots pines located in Denver County and one from Weld County were confirmed with pine wilt. In 2012, pine wilt was identified in a total of 7 Austrian pines from Arapahoe, Boulder, Douglas, and Jefferson counties, from one Scots pine in Prowers County, and from one Scots pine in Mesa County located 400 km to the west and on the western side of the Continental Divide. Average summer temperatures in 2012 were the warmest on record along the eastern Front Range of the Rocky Mountains, and may have contributed to the increase in pine wilt observations. In 2013, during a slightly cooler summer, two Austrian pines and one mugo (Pinus mugo) pine from Jefferson County and three Scots pines from Mesa and Arapahoe counties were also diagnosed with pine wilt. This is thought to be the first report of pine wilt in Colorado.