Longitarsus jacobaeae 
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Common Name
Tansy ragwort flea beetle
Weed Impacted
This beetle attacks tansy ragwort. Both larvae and adults are destructive to plants. Larvae feed on and within roots (root mining), destroying the host plant’s stored energy reserves. Adults feed on leaves, inhibiting photosynthesis and impairing the plant’s ability to replenish its energy stores. Larval root mining and heavy feeding by adults on rosette (ground-level) leaves in the fall and winter often results in plant death in the spring, when plants begin to produce new shoots and buds.
Insect Description
Adults are small, golden-brown or coppery-colored beetles, 2-4 mm (approx. 1/16 to 1/8 in) long, with enlarged hindlegs for hopping. Larvae are small, slender, white grubs found on or in the roots.
Life Cycle
There are two strains of this beetle in the field, one an Italian strain and the other a Swiss strain. Italian-strain adults emerge in the spring and rest in summer, becoming active after rainstorms. These beetles mate and lay eggs in October and November. The Swiss-strain beetles emerge in mid-summer and immediately begin to feed, mate, and lay eggs that will remain dormant through the summer and fall and hatch the following spring. Eggs are laid on ragwort plants near the bases of rosettes or on the ground next to the plants. Eggs hatch after about two weeks and young larvae move to begin feeding both on and within the roots. Pupation occurs in the soil.
Field Identification
The presence of L. jacobaeae in the field can be indicated by the classic, “shot-hole” type feeding damage made by adult beetles in tansy leaves.
Availability
This beetle is readily available in Washington, Oregon, Montana, and California. Adult beetles are typically collected in October and November. To inquire about availability and to request this biocontrol agent, please download, complete and submit this form.
Comments
L. jacobaeae has been a highly successful biological control agent, repeatedly demonstrating outstanding control of tansy ragwort. In Oregon, the 90% control of flowering plants was achieved within six years of release. At many sites, no flowering plants have been observed in several years, and any weed resurgences have generally been controlled by L. jacobaeae within one or two years after being reported. The Swiss-strain of the beetle is currently showing some potential at higher-elevation sites in eastern Washington and Oregon, where previous releases of the Italian strain have failed to establish.
Using the Agent: Integrated Weed Management (IWM)
L. jacobaeae should only be released where infestations of tansy are large and immediate eradication is not a primary objective. Smaller, satellite populations of the weed can be hand-pulled, dug, or sprayed. Consult with your county weed office, Extension office or an IWM practitioner to determine which herbicide treatments are safe and appropriate.
Mowing will not control tansy and can actually worsen the problems associated with the weed; livestock may be unable to avoid the smaller plants mixed among grasses and so be poisoned. Sheep, however, can feed on tansy with no harmful effects, and intensive grazing by sheep can provide good control. Repeated cultivation can also weaken tansy.
Physical, mechanical, and/or chemical 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 tansy should include revegetation with native or other desirable plants. Revegetation promotes competition between plants, which can stress weeds and allow for more effective treatment. 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.
Mitich, L. M. 1995. Tansy Ragwort. Weed Technology 9(2): 402-404.
Photo Credit
Longitarsus jacobaeae - IWCP staff
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