Botanophila seneciella 
<<back to tansy ragwort
Common Name
Ragwort seed head fly
Weed Impacted
Larvae feed within seed heads of tansy ragwort, often destroying all of the developing seeds.
Agent Description
Adults look like small house flies. They are 5-7 mm (approx 3/16 to 1/4 in) long with reddish eyes. Larvae are creamy white maggots found within the seed heads.
Life Cycle
Adults emerge in the spring. Eggs are laid on young flower buds. Larvae hatch in April or May (later in higher elevations), and begin feeding within the buds. Mature larvae exit the flower in late summer to pupate and overwinter in the soil.
Field Identification
Presence of B. seneciella in the field can be determined by examining the contents of tansy seed heads in mid-summer.
Availability
These flies are widely distributed and are found at virtually every tansy ragwort infestation. Further redistribution is likely unnecessary.
Comments
While the impacts of B. seneciella are often overshadowed by those of the tansy ragwort flea beetle, Longitarsus jacobaeae, the flies may help reduce the spread of tansy where beetles have not established.
Using the Agent: Integrated Weed Management (IWM)
Biological control of tansy should be implemented only where infestations of tansy are large and eradication is not the primary goal. 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 Credits
Botanophila seneciella adult- Eric Coombs, Oregon Dept of Ag, bugwood.org http://www.insectimages.org/images/768x512/0023039.jpg
Botanophila seneciella larva - Eric Coombs, Oregon Dept of Ag, bugwood.org http://www.insectimages.org/images/768x512/0023040.jpg
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