Twobanded Japanese Weevil

Plants Attacked

Twobanded Japanese weevil attacks a wide range of trees and shrubs in the landscape, but it is especially fond of cherry laurel, broad-leaved evergreens, pyracantha, privet, barberry, euonymus, and others. This weevil is an occasional pest of soybeans and vegetable in Virginia.

Description of Damage

Adult twobanded Japanese weevils are defoliators, chewing on leaves. Damage begins as marginal notches and increases to large rounded sections of the leaves being consumed. Holes are always cut inward from the margin, never in the inner part of the leaf. The larvae feed on roots of plants in the soil, but their habits are not well known, nor is the extent of the injury they produce. Injury is not distinguishable from that caused by black vine weevil, fullers rose beetle, and other similar species. 

Identification

Larvae of the twobanded Japanese weevil are small, legless, C-shaped grubs with a brown head capsule. They are seldom noticed.

The adults are a mottled, grayish, light brown. Often there is a broad gray band outlined in dark brown across the width of the wing covers (Fig. 1). Their bodies are stout and pear-shaped, with hair-like bristles on the head, legs, and wing covers (Fig. 2). The snout is relatively blunt and short for a weevil. Although they feed in daytime, Japanese weevils frequently hide under leaves or in crotches of limbs and are not easily detected in light infestations. The wing covers are fused together so adult weevils cannot fly. Movement of infested nursery stock is thought to transport this pest into new areas.

Coleoptera: Curculionidae, Pseudocneorhinus (Callirhopalus) bifasciatus (Roelofs) 

Life History

The life history of twobanded Japanese weevil has not been fully studied. Populations in the United States appear to be parthenogenetic as males are rarely found. Females lay their eggs in leaf folds made by folding over the edges of leaves on the host plant. Larvae hatch and drop to the soil, where they burrow to feed on the roots of host plants. Larvae overwinter in the soil, and emerge as adults in mid to late June. Adults feed and lay eggs until cooler weather in the fall; some adults may overwinter in leaf debris. There is one generation per year.

Control

Adults are diurnal feeders. They can be collected by placing a white sheet under the host plant and gently tapping the foliage to dislodge any adults present. Drown adults in soapy water, place in a freezer for several days, or destroy in another manner.

Spray the trunks, branches, and foliage of plants infested with twobanded Japanese weevils during the second or third week of June, when adults have emerged from the soil but have not laid many eggs yet. However, host trees and shrubs can be treated whenever the weevils are seen. See the Virginia Pest Management Guide for Home Grounds and Animals (PMG 456-018) for specific insecticide recommendations. Products containing imidacloprid should provide effective control if applied as a soil drench just as fresh plant growth starts in the spring.

Remarks

There are reports in the literature that populations of twobanded Japanese weevil occasionally built up into the thousands. There are no recent records of such outbreaks, although light infestations are relatively common in the southeastern part of Virginia. 

A closely related species, Pseudocneorhinus obesus, has recently been recognized in the eastern United States and is thought to have a life history similar to twobanded Japanese weevil.

Revised 

Theresa A. Dellinger, February 12, 2020.