Japanese Weevil
Coleoptera: Curculionidae, Pseudocneorhinus bifasciatus
Author: Eric R. Day, Director, Insect Identification Laboratory, Virginia Tech
Publication Number 444-624, Revised 2003
Plants Attacked
The Japanese weevil has a long list of hosts, but is especially found on cherry laurel, broad-leaved evergreens, pyracantha, privet, barberry, euonymus, and many others.
Description of Damage
Foliage is more or less chewed, beginning as marginal notches and increasing 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. 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 species.
Identification
The adults are a mottled, grayish, light brown. The bodies are more round and stubby than elongate as with many weevils. Although they feed in daytime, Japanese weevils frequently hide under leaves or in crotches and are not easily detected in light infestations. Larvae are legless, more or less C-shaped grubs in the soil, seldom seen or found. Japanese weevils, Pseudocneorhinus bifasciatu, are in the order Coleoptera and the family Curculionidae.
Life History
Little is known about the life history of this weevil. Adults are most frequently found first during mid to late June and continue to inhabit host plants and feed over several weeks or more. Presumably, they lay their eggs in the soil during midsummer and the larvae feed on plant roots until late the following spring. Adults cannot fly since the wing covers are fused together. There is one generation per year. Overwintering isdone by larvae in the ground.
Control
It is best to spray tree trunks, branches, and foliage during the second or third week of June, but trees can be treated whenever the weevils are seen. Products containing imidacloprid should provide effective control if applied as a soil drench just as growth starts in the spring.
Remarks
There are reports in the literature that populations have built up into the thousands on occasion. There are no recent records of such outbreaks, although light infestations are relatively common in the southeastern part of the state. The Japanese weevil is known to be equally abundant northward to and including Long Island, New York.
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