Pales weevil, Hylobius pales, and pitch-eating weevil, Pachylobius picivorus, are commonly referred to as “pine regeneration weevils” because of the damage they cause to pine seedlings during the regeneration of a pine stand.
Adults of each species commonly feed on the cambium (growth-tissue) of year-old seedlings but will feed on older seedlings and saplings.
Weevil problems in Texas usually aren’t widespread and tend to be localized on scattered tracts. But, when large population buildups occur, up to 80% of seedlings can be lost.
Weevils are wide, hard-shelled beetles characterized by a rigid and prominent snout with tiny chewing mouthparts at the tip. Pales weevil and pitch-eating weevil are very similar in appearance. Adults are black or dark brown, and usually speckled with white markings. They are ¼ to ⅓ of an inch long.
The larvae of both species are white, legless, around ¼ of an inch long, and have a dark brown head capsule. Pupae are white and possess the typical weevil mouthparts. Eggs are very small and white.
Impact
Adult weevils typically eat patches of bark anywhere on the stem, branches, and primary roots of year old and older seedlings. With a moderate population of weevils present, feeding may be extensive enough to girdle the stem and/or root collar causing a seedling to quickly wither and die.
If weevils are overabundant, they may remove all bark, leaving a seedling with green needles, which later turn red, and a white stem. Examination of pine stumps and large roots in the area may reveal larvae, pupae, or oval shaped, nest-like, pupal cells.
On sandy sites, the weevils may burrow into the soil to feed on and below the root collar. In this situation, seedlings may die with no observable above-ground signs of damage. Below-ground feeding is rare on clay soils.
Life cycle
The weevil life cycle is six to eight weeks from egg to death. They cause most damage in March and April, but some may occur in the fall.
Adults are attracted to the odor of freshly cut pine stumps, scorched pines, or dying trees, and feed on tender bark of nearby seedlings. They deposit their eggs in the root bark of stumps and trees.
Larvae hatch in one to two weeks, and feed primarily in the root system. They leave a series of tunnels, known as galleries, which are left packed with wood shavings and end at a shallow fibrous-covered pupal cell in the sapwood.
The pupa stage is two to four weeks, depending on the temperature, before an adult weevil emerges from the cell. New adults may feed on seedlings before flying to other cutover or recently burned stands.
Control
In forestry applications, the most practical and inexpensive method of control is to delay planting for six to nine months following harvest. Consider:
- If no pine has been cut from an area to be planted, there will be no weevil problem.
- If a pine stand is cut before June 1 and the area is planted during the following winter, there will be no weevil problem.
- If three cords of pine/acre or less are cut from an area or pushed down during site preparation after June 1, losses should be less than 5% if the area is planted during the following winter.
- If five to 10 cords per acre of pine are cut or pushed down during site preparation, losses may be up to 25% if the area is planted the following winter.
- If over 10 cords of pulpwood or 5,000 board feet of sawtimber are cut or pushed down during site preparation after June 1, use treated seedlings or plant seedlings next year.
If you must plant less than six months after harvest, seedlings treated in a nursery with the insecticide Arctic® (permethrin) should be used. Arctic® can also be applied after planting.
In residential areas, you should hand pick and destroy weevils or spray selected trees with Arctic®. Always follow label directions.