J.M. DiTomaso, The Regents of the University of California

J.M. DiTomaso, The Regents of the University of California

Tansy Ragwort


Longitarsus jacobaeae

Longitarsus jacobaeae, or the tansy ragwort flea beetle, is destructive in both the larval and adult stages. The adults emerge briefly in the spring and then rest during the hotter summer months. After fall rain storms, the adults again become active and begin mating in the fall.

The two established biotypes (Swiss and Italian) have different life cycles. The Italian strain lays eggs during October and November. The Swiss strain lays eggs in the spring and adults emerge from pupae in midsummer and immediately lay eggs that remain dormant during summer and fall finally hatching in the spring, beginning the life cycle anew.

The larvae of both biotypes hatch in approximately two weeks and feed on the roots of the target plant. Pupation occurs in the soil beginning in the spring for the Italian biotype and the fall for the Swiss biotype. The larval root feeding and adult defoliation combine to control up to 90% of the target plants over a six year period.

Redistribution efforts should be done using an insect-collecting vacuum on large rosettes after the first fall rains. Summer collections can also be done using sweep nets. It is best to release this agent in sunny pastures and in groups of 100 to 500.