The twobanded Japanese weevil was first detected in the United States in 1914 near Philadelphia, PA and has since spread throughout New England and other parts of the US. It is native to China, Japan, Korea, Mongolia, and eastern Siberia (Wheeler and Boyd 2004). Weevils feed during the daytime and are camouflaged by their color (light to dark brown with mottled bands of color on the elytra) and easily missed when looked for due to their small size (approximately 0.24 inch long). The adult weevil is pear-shaped with a short, blunt snout. If disturbed, the adult weevils will drop to the ground and play dead in self defense. Adult weevils have fused elytra (hardened wings) and as such are unable to fly. Dispersal of this insect is thought to occur relatively slowly by their own movement. The life cycle of this insect includes adults, eggs, and larvae all being capable of overwintering in the leaf litter and debris beneath their host plants. Overwintered adults remain inactive until warm spring temperatures allow, by approximately April (New York). Once the adults begin their activity, they crawl to their host plants to begin feeding. Rapid spring growth of the host plant may obscure the damage being caused by the feeding adult weevils. By approximately mid-May, the adult weevils begin their egg laying which can last through the summer months. All adult weevils in the United States are female and lay viable eggs without mating. (Males have been reported in the literature in China.) The tiny white eggs are laid inside pod-like structures inside a folded leaf margin. Each pod can contain 1-9 eggs. Female fecundity may change depending upon the host plant on which she is feeding. Females were found with 355 eggs when feeding on multiflora rose vs. 7 eggs on mountain laurel (Maer 1983). Once ready to hatch from the egg, the larva (immature) falls to the ground beneath the infested host plant where it will spend time in the soil. The specifics about the larval portion of this insect's life cycle are not yet fully understood by science. White, legless larvae are 0.30 - 0.33 in long when fully mature. Larvae and pupae are reported from depths of at least 9 inches in the soil (Allen, 1959). A single generation occurs per year.
New leaves and shoots are particularly injured by the feeding of the twobanded Japanese weevil on its hosts. The adult weevils will chew notches in host plant leaves until only the leaf midvein is left behind. Weevil pressure on a single shrub can be heavy - 265 adult twobanded Japanese weevils were once reported from a single spirea (Johnson and Lyon, 1991). The damage to the host plant may be confused for that of weevils in the genus Otiorhynchus, including the black vine weevil (O. sulcatus). Further research is needed to determine the extent of larval feeding on host plant roots and subsequent damage to those areas. Privet and forsythia are known hosts for twobanded Japanese weevil larvae. Adult feeding on host plant leaves (particularly the inner and new foliage) is thought to be the most damaging life stage of this insect. Foliar damage is evident by late summer with adults being most abundant by September.
Adults of the twobanded Japanese weevil may be monitored for from approximately mid-May to September. Because they are active during the daytime, they may be sampled for using the cultural management techniques suggested below. Beginning in the early spring, visually scout susceptible host plants, focusing on new growth on the inner parts of the plant. Look for chewed notches from the host plant leaves, or leaves defoliated down to the midvein. Search plants with a declining appearance first.
Because the twobanded Japanese weevil feeds during the daytime, collection of the adults on heavily infested host plants is possible. Lay a white cloth or other material on the ground beneath the plant. Be careful not to jar the plant before the cloth is spread on the ground beneath. Shake the shrub vigorously to disturb the beetles, which will lead to them dropping from the host plant to "play dead". The weevils can then be collected from the cloth and dropped into a container of soapy water.
Natural enemies of the twobanded Japanese weevil are not fully understood at this time.
Azadirachtin (NL)
Beauveria bassiana (NL)
Bifenthrin (NL)
Cyantraniliprole (NL)
Entomopathogenic nematodes (L)
Isaria (paecilomyces) fumosoroseus
Metarhizium anisopliae (robertii) (NL)
Neem Oil (NL)
Permethrin (L)
Tau-fluvalinate (NL)
Chemical management of the twobanded Japanese weevil may be difficult. Contact insecticides target the active adults. Larvae and pupae are protected within the soil.
Active ingredients that may be applied systemically include: 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.
