Combining the cinnabar moth (Tyria jacobaeae) and the ragwort flea beetle (Longitarsus jacobaeae) for control of ragwort (Senecio jacobaea): an experimental analysis.
A field experiment conducted in Oregon tested the independent and combined effects of Tyria jacobaeae and Longitarsus jacobaeae on ragwort (Senecio jacobaea). Both species feed on different stages of the host plant and at different times of the year, and were introduced to North America as biological control agents. L jacobaeae alone reduced vegetative ragwort densities by 95% and flower production by 39%, compared with plants in control (untreated) plots. Damage by T. jacobaeae was simulated by removing all leaves and capitula from generative plants, but plants were able to regenerate some of the foliage and flowers. The treatment ultimately reduced capitulum production by 77% and the number of achenes per capitulum by 15%. Damage by L. jacobaeae reduced the ability of flowering plants to compensate for defoliation to the extent that capitulum production was reduced by 98% and no viable achenes were produced. These findings supported the strategy of introducing complementary enemies which attack different stages and at different times, thereby reducing the number of individual life stages and temporal refuges for the host.