There are over 180 known species of Polydrusus weevil, four of which are native to the United States. Two non-native, introduced species of weevil in the genus Polydrusus are potential pests of ornamentals, urban street trees, and occasionally fruit crops. Both Polydrusus formosus and P. impressifrons were introduced into North America from Europe in the early 1900's. Both are found in the northeastern United States. Adult weevils of these two species feed on the leaves and buds of some hardwood and fruit trees. Adult weevils of P. formosus are slightly bigger (0.2-0.27 inches) than P. impressifrons (0.15-0.22 inches). Both have a brilliant green, iridescent color, with subtle differences to the black markings on the elytra (hardened wing covers). In both species, a single generation per year is known in New England. Adults emerge from the soil by late May/early June and feed on host plant buds or leaves through August. In southern New England, adult activity may be particularly noticeable from June to July during the daytime. Adult female weevils lay groups of tiny, white, cylindrical eggs on the surface of the soil beneath host plants or in the cracks and crevices of the bark. Females may lay anywhere from 800-2,000 eggs in their lifetime. Eggs hatch, and the larvae (immature weevils) feed on the roots of their host plants. They overwinter in this life stage and pupate the following spring before emerging again as adult weevils.
Adult weevil feeding causes damage to host plant leaves and buds. On larger trees and shrubs, feeding from these insects is typically rarely noticeable. Young trees are the most susceptible to feeding by these weevils, and may on occasion suffer noticeable feeding damage. Larval feeding on host plant roots is not known or thought to cause significant damage to the trees or shrubs.
Visually monitor for the presence of adult weevils on susceptible host plants, particularly between June and July.
If large numbers of adult weevils are present on young trees, hand picking and destroying or dropping them into a can of soapy water can help mechanically reduce the population on younger, smaller host plants.
A parasitoid wasp in the family Braconidae (Diospilus polydrusi) was introduced into North America in an attempt to kill the eggs of Polydrusus formosus.
Azadirachtin (NL)
Beauveria bassiana (NL)
Bifenthrin (NL)
Cyantraniliprole (NL)
Entomopathogenic nematodes (L)
Flonicamid+cyclaniliprole (N)
Isaria (paecilomyces) fumosoroseus
Metarhizium anisopliae (robertii) (NL)
Neem oil (NL)
Permethrin (L)
Tau-fluvalinate (NL)
Chemical management of these weevils may not be necessary. It is typically not needed on larger, mature trees or shrubs. Smaller, young trees or new plantings may need to be monitored in areas where these insects have historically or recently been active.
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.
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.
