Hylobius transversovittatus 
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Common Name
Loosestrife root weevil
Weed Impacted
Hylobius transversovittatus attacks purple loosestrife (Lythrum salicaria). Adults feed on above-ground foliage and larvae feed within the roots (root mining), reducing the plant's stored reserves. Under host specificity tests, two native loosestrife species (Lythrum alatum and Decodon verticillatus) were used by the weevil; however, no nontarget effects have been reported from the field. Both plant species are native to eastern and midwestern states and are generally not found in the Pacific Northwest.
Insect Description
Adults are reddish-brown weevils, 8-12 mm (approximately 3/8 to 1/2 inch) long, with two rows of white spots (hair tufts) across the back. Larvae are cream-colored, brown- headed larvae found within the roots.
Life Cycle
Adults emerge in mid- to late summer after pupating in the root crown. Eggs are laid from June through August either in the soil or in stems just above the soil and hatch after 11 days. Larvae migrate and begin mining the roots, where they remain until the subsequent spring or summer. Occasionally, larval development can take two years.
Field Identification
Dead or dying loosestrife plants can indicate the presence of one or two loosestrife agents. If foliage is heavily fed upon with shot-hole type feeding, it likely indicates the presence of Galerucella spp. (see pictures of damage on webpage). Feeding by H. transversovittatus is generally not substantial enough to kill above-ground foliage, however larval feeding can cause stems to wilt. Confirmation of larval presence can be determined by digging up roots and dissecting them for larvae or frass (debris caused by insect). Hylobius transversovittatus adults feed nocturnally and can be very difficult to find; however, if multiple agents are present, weevils (H. transversovittatus and Nanophyes marmoratus) can be distinguished from non-weevils (Galerucella spp.) by the presence of a snout. Hylobius transversovittatus beetles can then be distinguished from N. marmoratus by their much larger size.
Availability
Hylobius transversovittatus is available for limited distribution and is currently reserved for sites not well controlled by Galerucella spp. Adults are collected in the spring and summer, reared from infested roots, or reared on semi-artificial diets. To inquire about availability and to request this biocontrol agent, please download, complete and submit this form.
Comments
Hylobius transversovittatus builds up populations and spreads more slowly than Galerucella spp., but by reducing root reserves, the weevil limits the plant’s ability to recover from Galerucella spp. damage. The additional use of the seed weevil, Nanophyes marmoratus, can reduce the amount of seed entering the system.
Using the Agent: Integrated Weed Management (IWM)
Hylobius transversovittatus can be used in combination with loosestrife leaf beetles (Galerucella spp.) and seed weevil (Nanophyes marmoratus). Releases should be made only where loosestrife infestations are large and immediate eradication is not the primary goal. Galerucella spp. should be released at all sites to determine whether establishment and effective management are possible using this agent.
Smaller populations of loosestrife can be hand-pulled, dug, or smothered. Mowing will likely only contribute to the spread of loosestrife, but when followed promptly by smothering, burning, or spraying, it may allow for more effective treatment. Repeated cultivation can help to weaken plants. If the seed weevil (N. marmoratus) is not present, flower heads can be removed to reduce seed production. Removal of plants or seed heads in satellite patches may be particularly effective in reducing the spread of purple loosestrife.
Burning will not control loosestrife, but it may promote earlier germination and help reduce the existing seed bank. Seedlings can then be pulled or sprayed.
Herbicides have been shown to reduce loosestrife; however, infestations often occur in or around environmentally sensitive areas (lakes, streams, wetlands, etc.) where herbicide treatment may not be an option. Consult with your county weed office, Extension office or an IWM practitioner to determine which herbicide treatments are safe and appropriate.
Physical, mechanical, and/or herbicide treatments should not be applied where insect agents are active. Using these measures in areas of release can be detrimental to the establishment and maintenance of strong agent populations.
Any treatment of loosestrife should include revegetation with native or other desirable plants. Revegetation promotes competition between plants, which can stress weeds and allow for more effective treatments. To learn more about revegetation and IWM, click here.
References
Coombs, E. M., J. K. Clark, G. L. Piper, and A. F. Cofrancesco, Jr. 2004. Biological Control of Invasive Plants in the United States. Western Society of Weed Science, Oregon State Univ. Press, Corvallis.
Wilson, L. M., M. Schwarzlaander, B. Blossey, and C. B. Randall. 2004. Biology and Biological Control of Purple Loosestrife. USDA Forest Service, FHTET-04-12.
Photo Credits
Hylobius transversovittatus adult - IWCP staff
Hylobius transversovittatus larva - Eric Coombs, Oregon Department of Agriculture, bugwood.org (insectimages.org), http://www.insectimages.org/images/768x512/1291018.jpg
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