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Rhinoncomimus latipes by J. Hough-Goldstein, Department of Entomology & Wildlife Ecology, University of Delaware, Newark, DE 19716
Appearance Adult weevils are about 2 mm long and are black when they first emerge, but become coated with an orange-brown substance apparently derived from plant sap after they have been feeding on P. perfoliata for several days. Weevils are typically found near the actively growing plant terminals. Feeding damage consists of characteristic small holes in leaves. Eggs are laid singly on the leaves, stems, or buds of P. perfoliata, and are yellowish, peanut-shaped, and covered with a small strip of frass. Larvae are rarely seen because they develop inside P. perfoliata stems, but scars or small holes are often visible on plants near nodes, where larvae have entered the stem or exited for pupation.
Habitat Rhinoncomimus latipes is found only on P. perfoliata, both in its native and introduced range. Persicaria perfoliata is primarily riparian in its native range in Asia. In North America it grows in full sun or partial shade, with typical habitats including roadsides, edges of woods, reforestation clear-cuts, utility rights-of-way, open meadows (if unmowed), and stream banks.
Pests attacked Host range studies in both China and North America have shown that this insect is extremely host-specific, with no egg-laying or larval survival on any plant species except P. perfoliata. Adult weevils feed minimally on several related Polygonaceae, but only under laboratory no-choice conditions.
Life cycle Adult weevils overwinter in the soil or leaf litter. They emerge in early spring when P. perfoliata seedlings are about 6 inches tall, and begin mating and laying eggs. Newly hatched larvae bore into the plant stem at nodes and feed internally. Once they are full grown, larvae crawl or drop out of the stem and pupate in the soil under the host plant. Adult weevils emerge from the soil about one week later, crawl up nearby stems and mate on the host plant, feed on its leaves, and initiate egg-laying. The complete R. latipes life cycle from egg to adult takes about one month, and at least three to four overlapping generations occur during the growing season in the mid-Atlantic region. Egg laying ceases between mid-August and mid-September, as weevils prepare for overwintering.
Relative effectiveness Although it is too soon for a complete assessment of the effectiveness of R. latipes in controlling mile-a-minute weed, initial indications are very positive. Weevils have overwintered and established at virtually all sites where they have been released, and P. perfoliata populations have declined substantially at many sites. Weevils disperse at a rate of more than 4 km per year after the first year of release. They locate both large and small mile-a-minute weed patches and establish new populations.
Pesticide susceptibility This weevil is susceptible to commonly used insecticides and thus should not be exposed to insecticidal sprays. It is not directly affected by commonly used herbicides, but larval development is indirectly affected by herbicides if the plant dies before larval feeding is completed.
Commercial availability Rhinoncomimus latipes has been reared since 2004 at the New Jersey Department of Agriculture Phillip Alampi Beneficial Insect Rearing Laboratory, Trenton, NJ, and the laboratory expects to begin selling the weevils in 2011. Weevils can also be collected from mile-a-minute plants where a population has established, by shaking the plant terminals into a large funnel with the small end inserted into a container. The adult weevils can then be transported to another mile-a-minute patch, as long as it is within the same state (otherwise a permit from USDA-APHIS is required).
References Ding JQ, Fu WD, Reardon R, Wu Y, Zhang GL (2004) Exploratory survey in China for potential insect biocontrol agents of mile-a-minute weed, Polygonum perfoliatum L., in Eastern USA. Biol Control 30:487-495
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