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Pine Root Collar Weevil

Jennifer C. Girón Duque, University of Puerto Rico, Bugwood.org
Hylobius radicis Buchanan - Adult(s)      Pine root collar weevil is found throughout the north central and northeastern regions of the United States and in southeastern Canada. It primarily attacks Scots, red, jack, Austrian and eastern white pine.

Weevils require two years to complete their entire life cycle. They lay eggs from early May to early September on the root collar of living trees or in the soil surrounding the root collar. Each female adult will lay 10 to 70 eggs in one season. Eggs hatch in 7 to 17 days, depending on temperature. Larvae are small (up to 1 cm long) whitish grubs. Larvae burrow into the inner bark (cambium) of the root collar and large roots, and feed until the weather turns cold in autumn. During the winter, larvae are inactive and are protected from cold temperatures in galleries under the bark or in tunnels in the soil. As the soil warms in the spring, larvae resume feeding. Pupation occurs in chip cocoons made of sawdustlike frass; they are found in the soil near the root collar or, occasionally, under the bark. Adult weevils emerge in 30 to 40 days.

Adult weevils feed on the bark of live pine tree shoots until autumn, then overwinter in the litter or in bark crevices at the base of trees. Adult weevils often live and continue to feed and reproduce for two more years. Up to three overlapping generations of pine root collar weevil may occur on the same host tree. Adult weevils are not strong fliers and frequently move only a short distance to attack a new host tree.

Weevils are sensitive to light and temperature. Most adults feed during evening hours when temperatures are cool. Weevil adults spend the day resting at the base of the tree, venturing up to the canopy only on cool, overcast days. However, when pines are grown in shade, beneath other trees, or in dense stands, conditions are often too cool for pine lot collar weevil populations to build. Trees growing in open sunlight in Christmas tree fields or young plantations are most susceptible to pine root collar weevil.

DAMAGE

The principal injury to trees is caused by larvae feeding below ground in the root collar, root crown and large roots. Small trees (less than 4 inches in diameter) can be killed in a single year by as few as two to five larvae. Larger trees may harbor several larvae and may be repeatedly attacked each year. Soil and bark near the root collar of infested trees becomes black and soaked with pitch see figure 1 (37 K). Trees are weakenedat ground level and may fall over or die within one to four years of the first attack. When trees are girdled, the entire canopy fades from green to yellow to red. Larger trees that have been partially girdled have low growth rates see figure 2 (32 K) and are more susceptible to windthrow and secondary pests see figure 3 (48 K).

Feeding by adult weevils girdles small shoots and branches, causing them to die and "flag" or turn red. Weevil feeding can be distinguished from other pest damage by the gnawed wounded area, often covered with pitch, located at the base of the dead shoot.
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