There are three strains of this species established in the U.S. They are morphologically identical but differ in their life cycle. Oval shaped eggs are less than 1 mm in diameter. They are white turning orange with maturity. Larvae are small white grubs approximately 1-4 mm long. The final of three instars has a brown head capsule. Pupae found in the soil are white and 2-4 mm long. Adult beetles are of similar size, light-brown or coppery in color, with large hindlegs.
Shot hole feeding patterns on tansy ragwort leaves, particularly in rosette stage in late summer or autumn can indicate adult presence. There is a native flea beetle that also feeds on tansy ragwort but the shot holes are smaller and more common during the spring and early summer. Larvae may also be found in the root crown in early summer, however, beetles are very small and jump when disturbed.
Of the three strains present in the U.S., the Italian CAD (cold-adapted) and Swiss strains are more tolerant of higher elevation sites and cold winters than the coastal Italian CPNW (Coastal Pacific Northwest). The Italian strain overwinters as either eggs or larvae. Larvae begin feeding on or with in roots in the spring, return to soil to pupate in the summer and emerge as adults in late summer. These adults continue feeding on foliage and lay eggs in late summer early fall on lower leaves or near the soil. Beetles from the Swiss strain overwinter as eggs laid the previous summer on tansy ragwort rosettes. Larvae hatch in the spring and initially feed on leaf petioles prior to burrowing into the root crown. Mature larvae pupate in the soil in late spring early summer. Adults then emerge in late summer and spend 2-3 weeks feeding on foliage before laying eggs. Adults are present until heavy frosts.
Larval feeding on roots can reduce plant energy storage, impact reproduction and cause death. Adult foliar feeding reduces photosynthesis as well as water and nutrient transport. In drought stressed plants, this damage can lead to plant death.
Both the CPNW and Swiss strains are available in Montana. The CAD strain is difficult to collect and therefore not as readily available. We have seen good establishment of the Swiss strains where it has been released but it doesn’t appear that the CPNW strain establishes in Montana. If you are interested in obtaining these insects view the biocontrol vendor list for options.
This biocontrol agent is very effective at reducing established infestations of tansy ragwort. Research in Oregon showed a 90% reduction in flowering plants six years after biocontrol introduction. The flea beetle appears to be just as effective in Montana as it is in Oregon. The Swiss and Italian CAD strains are more tolerant of higher elevation sites. This biocontrol works well with Tyria jacobaeae.
Using the Agent
Adult beetles can be collected using a sweep net or insect vacuum. Italian CAD and Swiss strains are best collected in late summer. A sieve might help to sort beetles from debris collected along with beetles. At least 200 beetles should be released on sites where no beetles are established. Establishment can be monitored by observing plant foliage for shot hole feeding or looking for adult beetles the following summer after release.
Biocontrols should be used on sites where infestations are heavy and immediate eradication is not the primary goal. Where the biocontrol is well-established other physical, chemical or mechanical control methods should be avoided so as not to interfere with insect populations.
For more information on control methods and herbicide recommendations contact your local weed district or Extension Service.
Winston, R., C.B. Randall, R. D. Clerck-Floate, A. McClay, J. Andreas, M. Schwarzlander. May 2014. Field Guide for the Biological Control of Weeds in the Northwest. http://www.ibiocontrol.org/westernweeds.pdf
Washington State University Integrated Weed Control Project. Biological Control Agents. Accessed February 9, 2017. http://invasives.wsu.edu/biological/longitarsusjacobaeae.htm