Defoliating Weevils
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Hagle, S.K; S. Tunnock; K.E. Gibson; and C.J. Gilligan. 1987. Field Guide to Diseases and Insect Pests of Idaho and Montana Forests. U.S. Department of Agriculture, Forest Service. State and Private Forestry, Northern Region. Missoula, Montana. Reprint 1990. Publication Number R1-89-54.
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Hosts
Lodgepole pine and ponderosa pine. May feed on other species of pines and Douglas-fir.
Distribution
Probably found throughout host ranges.
Damage
Adults puncture holes in current needles (fig. 132) and through needle sheaths. Dried up portions of the needles are blown off by wind or broken off by rain and snow. Chunks of needles may be eaten leaving a saw-toothed edge (fig. 133). Larvae may feed on roots.
Identification
Magdalis adults are black and may be seen puncturing holes in new needles from late June through August. They are about one-fourth inch long, and have prominent curved beaks. Eggs are laid on twigs in late August. Larvae feed on cambium and wood tissue beneath the bark. Scythropus, known as the elegant weevil, is broad nosed and scale covered. It is metallic blue-green, gold, brass, or bronze colored and about one-fourth inch long fig. 134). Habits for both weevils are similar, except that Magdalis more often feeds on fresh slash than does Scythropus.
Similar damages
Damage of the two species may be confused, but Scythropus feeds by puncturing needles whereas Magdalis removes chunks of needles. Adults are distinct. Adult feeding damage on needles could be mistaken for other defoliation – such as that caused by pine sawflies.
References
- Anonymous. 1982. For. Insect & disease identification and management. USDA For. Serv.,Northern Region; Idaho Dept. of Lands, Insect and Disease Control; Montana Dept. of State Lands, Division of Forestry. 192 p.
- Furniss, R. L., and V. M. Carolin. 1977. Western For. Insects. USDA Forest Serv., Misc. pub. 1339, 654 p., illus.
