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Hylobius transversovittatus
(Coleoptera: Curculionidae)

This native European weevil was introduced in 1992 as part of a 5-15 year program to control purple loosestrife, an exotic weed infesting North American wetlands. Release sites were New York, Pennsylvania, Maryland, Virginia, Minnesota, Oregon, Washington state in the United States, and sites in Canada. Since 1992, releases have been made in Ohio, Indiana, Illinois, Iowa, Michigan, Wisconsin, South Dakota, Colorado and Montana. Colonization of these introduced populations appears to have been successful.

Appearance

The Hylobius transversovittatus adult is about 13 mm long and 6 mm wide, is dark brown and has two rows of white tufted hairs across its body. Its thorax and head taper to an elongate, curved proboscis. Eggs are oval and whitish, about 1.4 mm long and 1 mm wide.

Habitat

Purple loosestrife is a weed species in wetlands over much of temperate North America, and the aim of the introduction program of H. transversovittatus is to locate the releases so that this weevil will be able to easily colonize and spread. Currently, purple loosestrife exists in large, monotypic stands throughout the northeastern U.S. and southeastern Canada, the Midwestern U.S., and in isolated locales in the western U.S. and southwestern Canada. Irrigation systems provide conduits for its spread in dry areas.

Pests Attacked

H. transversovittatus is considered host-specific to purple loosestrife (Lythrum salicaria). Before introduction of H. transversovittatus to North America, approximately 50 native plants, including some closely related to purple loosestrife, were tested for susceptibility to this weevil. Only two, swamp loosestrife (Decodon verticillatus) and winged loosestrife (Lythrum alatum), were potential hosts, and under field conditions in Europe, it was determined that H. transversovittatus, if given a choice, avoided the North American natives.

Life Cycle

Adults emerge in the spring from soil or soil litter and feed at night on the new leaves of purple loosestrife. Evidence of their feeding is seen along leaf edges. Peak activity is from June to August, although their reclusive, nocturnal patterns make them difficult to observe. Adults may live for several years. The egg laying phase lasts two to three months, with one to three eggs being laid each day and deposited singly into the stem or the soil near a root. A female can produce approximately 200 eggs each year. The larvae mine to the roots where they feed on root tissue. Larvae develop in 1-2 years. Mature larvae form a pupation chamber in the upper part of the root from which they emerge as adults between July and October. Larvae hibernate in different stages of maturity.

Relative Effectiveness

In Europe, there are several insects which act together to control purple loosestrife. As a result, only small, scattered stands of the plant exist. The current program includes the introduction of this Hylobius species, two species of the beetle Galerucella, and the planned release of two flower-feeding beetle species which are also specific to purple loosestrife. It is predicted that upon establishment of these species, North American purple loosestrife will be reduced by 90% over approximately 90% of its present range.

These weevils will not prosper on plants growing in high water areas and in shade.

Pesticide Susceptibility

Early indications are that H. transversovittatus is highly susceptible to pesticides; exposure should be strictly avoided.

Conservation

Although beetles and larvae can survive submergence for a few days or weeks, experiments have shown that excessive flooding will eventually prove fatal to larvae and restrict adult access to the plant. Best sites should be at least 5-10 acres and free of standing water most of the year. The optimum condition is ground water 1-3 inches below the surface.

Commercial Availability

Not available commercially at this time.

Acknowledgments

Thanks to Richard Malecki and Bernd Blossey for providing information and photographs for this section.

References

Blossey, B. (1993) Herbivory below ground and biological weed control: life history of a root-boring weevil on purple loosestrife. Oecologia, 94: 380-387.

Blossey, B., Schroeder, D., Hight, S.D., Malecki, R.A. (1994) Host specificity and environmental impact of the weevil Hylobius transversovittatus, a biological control agent of purple loosestrife (Lythrum salicaria), Weed Sci., 42: 128-133.

Kok, L.T., McAvoy, T.J., Malecki, R.A., Hight, S.D., Drea, J.J., and Coulson, J.R. (1992) Host specificity tests of Hylobius transversovittatus Goeze (Coleoptera: Curculionidae), a potential biological control agent of purple loosestrife, Lythrum salicaria L. (Lythraceae). Bio. Control, 2: 1-8.

Malecki, R.A., Blossey, B., Hight, S.D., Schroeder, D., Kok, L.T., Coulson, J.R. (1993) Biological control of purple loosestrife: a case for using insects as control agents, after rigorous screening, and for integrating release strategies with research. BioSci., 43: 680-686.

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