The pales weevil can be a very serious pest of seedling pines in forests, ornamental nurseries, and Christmas tree plantations in the eastern United States and parts of Canada. Adult beetles cause injury to their host plants when they feed on the bark of twigs and small branches. Adults are approximately 1/4 inch in length with noticeable "snouts", black to reddish brown, with small patches of yellow/white on the head and elytra (hardened wings). Beetles will chew a series of small holes in the bark; if there are not enough beetles attacking the host, the tree may be able to fill and heal these holes with resin/pitch. If the population is heavy enough, these holes will be excavated by the adult beetles enough to turn into patches of missing bark, which may eventually lead to entire branches or seedlings to be stripped of their bark. (Most or all of the bark is removed, and crystalized, white resin may cover these areas.) Adult beetle feeding occurs primarily at night; if disturbed, the weevils will drop to the ground and play dead. Adult beetles hide in sheltered areas during the day. On larger host plants, the feeding from the adults will be found on the ends of branches or on small twigs. On small twigs where girdling occurs, needles will die and turn red/brown, producing a flagging symptom. The overwintering life stage of the pales weevil are the adults who hide at the soil surface or in the leaf litter. Activity resumes in the spring with warming temperatures, typically by late April and early June (in warmer climates, adult activity can occur year-round). Adult beetles are particularly attracted to freshly cut stumps, where egg laying will preferentially occur on the roots. Females burrow to find the root in the soil, chew notches in the root, and lay eggs in groups of 1-3. Eggs are pearly white, slightly oblong, and rounded at the ends and approximately 1 mm. long. Eggs hatch and the larvae tunnel the roots as they pass through 5-6 instars. Mature larvae are approximately 1/2 inch in length. Larvae (immatures) are legless, white/cream colored, with brown, hardened head capsules. Once mature, larvae plug their tunnel and pupate in a chamber in the bark or sapwood that looks similar to a chip cocoon created by the white pine weevil. Pupation occurs by September, adults emerge, feed, and prepare to overwinter. Adults of this species are capable of living through two winters in some locations. (Historical records from Petersham, MA and Boston, MA report adult activity as late as November 18 and December 1, respectively (Peirson, 1921).)
Tender bark of seedling white pine and other conifers up to 18 ft. tall may be fed upon by this insect. Adult beetles may also feed on the twigs of larger pines. Adult pales weevils are attracted to freshly cut pine stumps and sawdust. The pales weevil can be a very serious pest of young pines. Often not as serious of a pest in ornamental landscapes, thanks to the lack of breeding material available (a benefit of sanitation measures in managed landscapes). Entire twigs, small branches, or seedlings may be stripped of their bark by this insect, leaving behind "criss-crossed ridges". 3-4 year old white pine seedlings were historically reported to be killed by this insect in as little as a few days. Twigs of larger branches that become girdled may suffer needle mortality, leading to red/brown flagging.
Monitoring for this insect can occur from April to October. Search flagged branches for the presence of adults or stripped areas of bark. Stumps can be destructively sampled to look for evidence of larval feeding or chip cocoons from pupation.
Removing and destroying cut stumps or debris of susceptible hosts may help discourage adult attraction, settlement, and egg laying in those locations. Areas where pines were harvested should not be replanted with seedlings for up to two years post-harvest to avoid attracting this insect to those seedlings.
Historical records indicate that "parasitic Diptera (flies) and Hymenoptera (wasps) have been found in the vicinity of logs and stumps where pales weevils have been breeding". Some native birds feed on the adult beetles, but are not heavily predated upon since beetles are primarily active at night. Woodpeckers will feed on the larvae. Moles have also been observed in the area where adult activity is reported on stumps, presumably feeding on the adult weevils. A fungus, which needs ample moisture to be effective, has been reported from pales weevils. The fungus, Sporotrichum globuliferum, will kill adult beetles (Peirson, 1921). Metarrhizium anisopliae will also infect pales weevils. Neoaplectana spp. nematodes will infect the 6th instar larvae and pupae of the pales weevil (Thomas, 1970).
Azadirachtin (larvae) (NL)
Beauveria bassiana (NL)
Bifenthrin (NL)
Chlorpyrifos (N)
Cyantraniliprole (NL)
Entomopathogenic nematodes (L)
Flonicamid+cyclaniliprole (N)
Imidacloprid (L)
Isaria (paecilomyces) fumosoroseus (larvae) (NL)
Metarhizium anisopliae (robertii) (NL)
Neem oil (NL)
Permethrin (L)
Tau-fluvalinate (NL)
Active ingredients that may be applied systemically include: azadirachtin (injection, soil drench), cyantraniliprole (soil drench, soil injection), Metarhizium anisopliae (robertii) (soil drench), and neem oil (soil drench).
Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.
When used in a nursery setting, chlorpyrifos is for quarantine use only.
Note: Beginning July 1, 2022, neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.
