Adult white pine weevils overwinter in the leaf litter or other sheltered areas nearby host plants. Adults are approximately 1/4 inch long, oval, brown, with two white spots on the back of the wing covers, and a long "snout". In the spring, the adult weevils crawl or fly to the leaders of suitable host trees where they mate in pairs that may gather in groups. Females dig a round hole in the bark to create a cavity into which she deposits 1-5 tiny eggs. Each hole is then filled with a plug of chewed bark. Hundreds of white pine weevil eggs may be deposited by multiple females in a single leader. Eggs hatch and larvae (3/4 inch long, C-shaped, white with a brown head, and legless) feed in the bark, tunneling and killing the previous season's leader. The current year's growth will occur during this time of feeding, which causes it to droop, producing bent terminal ends known as "shepherd's crooks". Larvae bore into the wood and create pupal chambers (chip cocoons) made of chewed wood and bark. New generation adults leave the host plant by the late summer and feed on twigs before finding sheltered areas within which they overwinter. Research in British Columbia indicates that some adult white pine weevils can live up to 4 years (Johnson and Lyon, 1991)!
The white pine weevil is capable of killing the top 2 to 3-year's growth. This can be seriously disfiguring to the tree, but typically does not kill the entire plant. Trees, however, are known to become crooked or "limby" (for example, "cabbage trees") as a result of repeated terminal mortality. In the case of bushy "cabbage" trees such as white pine with repeated weevil attack, some may find this aesthetically attractive. In the case of the production of timber from eastern white pine, weevil attack can be seriously economically damaging. Branch tips may have small, round exit holes from emerging adults and pitch flow from these holes. Bark can be peeled back to reveal tunneling, frass, chip cocoons, larvae, or adult weevils. Terminal branches may flag and die, or stunt and bend to form "shepherd's crooks".
Search for weevils and signs of weevil damage on the terminal 12 inches of host plants from March through May. Infested terminals may begin to flag by June.
Before June, but after adult emergence in the spring, remove and destroy flagging or crooked leaders on small trees. Prune out and destroy any infested terminals. Affected trees can be pruned and staked to regain single leader dominance. Trees in sunny locations are more apt to be attacked.
Natural enemies of the white pine weevil are not thought to provide adequate management of damaging populations of this insect in managed landscapes where they have become a problem. Predators and parasitoids of this insect are known in the literature. This includes but is not limited to the following parasitoids: Allodorus crassigaster (Braconidae), Bracon pini (Braconidae), Coeloides pissodis (Braconidae), Dolichomitus terebrans (Ichneumonidae), Eubazus strigiterum (Braconidae), Eurytoma picea (Eurytomidae), Eurytoma pissodis (Eurytomidae), and Rhopalicus pulchripennis (Pteromalidae) and the following predators: Lonchaea corticis (Diptera) and Rhizophagus grandis (Coleoptera) (Invasive Species Compendium; CABI).
Abamectin (NL)
Azadirachtin (NL)
Beauveria bassiana (NL)
Bifenthrin (NL)
Entomopathogenic nematodes (L)
Isaria (paecilomyces) fumosoroseus (larvae) (NL)
Metarhizium anisopliae (robertii) (NL)
Neem Oil (NL)
Tau-fluvalinate (NL)
Thorough coverage on terminals of white, Scotch, and Japanese black pines. Also Norway and white spruce. If trees are heavily infested in an area, contact insecticides can be applied in March or April, as soon as adult white pine weevils become active from their overwintering shelters (between 7-58 GDD's and when daytime temperatures are 50°F or above). This is best completed when adults start feeding again, but before females begin to lay eggs.
Must manage the adult female prior to egg laying. Overwinters as adult in leaf litter. Rarely kills trees but causes host to develop multiple leaders. Adults active in early April in southern New England.
Active ingredients that may be applied systemically include: Abamectin (injection), azadirachtin (injection, 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.
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.
