Nanophyes marmoratus
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Common Name
Loosestrife seed weevil
Weed Impacted
Larvae and adults impact purple loosestrife by feeding on unopened flower buds. Flower buds with larval feeding damage usually abort and fail to produce seeds. Adults also feed on developing leaves, further weakening plants by interfering with photosynthesis.
Insect Description
Adults are very small, dark reddish-brown weevils, 2 to 2.5 mm (approximately 1/16 to 3/32 inch) long, with a long snout and light-colored markings on the back. Larvae are small, whitish grubs found feeding within the flower bud.
Life Cycle
Overwintered adults appear on plants in mid-May and feed on developing leaves near the shoot tips, moving later to feed on young flower buds. Females lay eggs from June to September inside the immature buds. Larvae feed on petals, ovaries, and other structures in unopened buds. A single larva completes development inside a single bud. Pupation occurs within a chamber formed inside the infested bud.
Field Identification
Several insect agents have been released for control of purple loosestrife. In the field, weevils (N. marmoratus and Hylobius transversovittatus) can be distinguished from non-weevils (Galerucella spp.) by the presence of long snouts. Nanophyes marmoratus is much smaller than H. transversovittatus and may need to be shaken from the plants onto a light-colored sheet in order to be observed. Galerucella spp. are generally more common than either of the weevils. Feeding damage is distinguished by shot-hole type feeding damage to the upper leaves of the plant and the larval emergence holes in unopened dead flowers (see picture).
Availability
This beetle is available in Washington, Idaho, Oregon, and several other states. Adults are collected in late spring and throughout the summer. To inquire about availability and to request this biocontrol agent, please download, complete and submit this form.
Comments
Nanophyes marmoratus does best at sites where Galerucella spp. has not established. However, if Galerucella spp. is present, N. marmoratus can be used to reduce seed production in those plants that are still able to flower. It may not build to large numbers but will likely persist at low densities.
Using the Agent: Integrated Weed Management (IWM)
All three purple loosestrife biocontrol agents can be used in conjunction with one another. Nanophyes marmoratus can be used well in combination with Hylobius transversovittatus, but will not build to large numbers where Galerucella spp. is abundant. Releases should be made only at sites where loosestrife infestations are large and immediate eradication of the weed is not the primary objective.
Smaller populations of purple 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. Removal of plants or seed heads in satellite patches may be particularly effective in reducing the spread of purple loosestrife.
Burning will not control purple 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 purple loosestrife; however, infestations often occur in or around environmentally sensitive areas (lakes, streams, wetlands, etc.) where treatments 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 purple 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. Schwarzlaender, B. Blossey, and C. B. Randall. 2004. Biology and Biological Control of Purple Loosestrife. USDA Forest Service, FHTET-04-12.
Photo Credit
Nanophyes marmoratus adults - Eric Coombs, Oregon Department of Agriculture, bugwood.org (insectimages.org), http://www.insectimages.org/images/768x512/0021100.jpg
Nanophyes marmoratus emergence hole - IWCP staff
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