| Douglas fir twig weevil |
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Order: Coleoptera
Family: Curculionidae
Scientific name: Cylindrocopturus furnissi (Buchanan G.)
Common name: Douglas fir twig weevil (DFTW)
Identification
Adults: Tiny brown weevil with light colored mottling on legs and body, approximately 3.0 mm in length.
Larvae: White to yellowish in color, up to 4.0 mm in length (white when young, becoming more yellowish as the larvae mature).
Damage: Douglas fir seedlings may exhibit deformation of branches and poor growth causing economic loss to grower. Damage is usually inconspicuous on older trees. To identify the presence of DFTW in Christmas trees, concentrate on dead or dying twigs near the top of the tree, especially the larger diameter branch stubs left after pruning. On the lower part of the tree it is necessary to look for branch stubs among the foliage. Look for 1 mm diameter adult weevil exit holes. Stems suspected of current or previous weevil infestation should be cut lengthwise and opened. Look in the area between the inner bark and the wood for evidence of larvae, frass, tunnels, and exit holes. Some tunnels may extend into the pith. Look carefully for whitish larvae feeding in bark and pith. Damage is greatest in drought years and on dry sites. Christmas trees that are growing under stress conditions (dry or water-logged soils, nutrient deficits, air pollution) may be more susceptible to attack. Shearing or pruning in August and September acts to remove many of the infested branches.
Impacts: Mexico treats DFTW as a quarantine actionable pest and has established a low tolerance level for the weevil. Christmas trees infested with DFTW larvae during inspection by Mexican officials at the Ports of Entry are subject to on site judgment as to the pest risk level. Excessive levels will be rejected or subject to treatment at growers’ expense. The Oregon Department of Agriculture Christmas tree program staff will notify each grower whether or not Douglas fir twig weevil was detected, after inspecting Christmas tree fields. Fields with pest levels exceeding allowable certification levels will NOT be eligible for certification.
Host plants: Primarily Douglas fir (Pseudotsuga menziesii), but also can attack Noble fir (Abies procera) in stress conditions.
Distribution: Throughout the native range of Douglas fir in coastal British Columbia and western Washington, western Oregon and western California (Furniss 1942.)
Biology and Life cycle: Adults emerge from Douglas fir twigs beginning in early to mid-June and continuing through early August. Adults feed on tender twigs for about a month before preparing small punctures in the bark of 1-3 year-old twigs in which eggs are deposited. Eggs hatch after a few days and larvae bore through the outer bark into the underlying inner bark and cambial region. Larvae form feeding galleries in the cambial region between the bark and wood of the branch. Feeding continues from late summer through the following spring. Maturing larvae may tunnel through the wood into the pith region. Larvae of all sizes overwinter in infested branches. After a period of spring feeding, larvae pupate during May and June. Some adults may overwinter on the tree and resume egg laying in the spring. One generation occurs each year.
Prepared by:
• Randy Vial, Oregon Department of Agriculture, Horticulturist
• Jack DeAngelis, Oregon State University, Extension Entomologist
• David Overhulser, Oregon Department of Forestry, Entomologist
Photo credits:
DFTW adult: Ken Gray Image Courtesy of Oregon State University
DFTW larva: USDA Forest Service, Ogden Archives, www.forestryimages.org
DFTW damage: Oregon Department of Agriculture
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