The effects of two herbicides against the biological control agent, the ragwort flea beetle (Longitarsus jacobaea (Waterhouse))

Abstract

The toxicity of two herbicides, Tordon® and Escort®, was tested against adult and larval ragwort flea beetles (Longitarsus jacobaeae) (Waterhouse) [Coleoptera: Chrysomelidae] by topical application under laboratory conditions. No concentration of Escort® was toxic to adult ragwort flea beetles when topically applied. The highest mortality rate of 74% was found with the simulated field rate of Tordon® (500 ml/100L of water) using the Potter tower method.

The effects of Escort® and Tordon® to adult and larval ragwort flea beetles settled on plants before spraying was investigated, under outdoor and shade-house conditions. Less than 20% mortality occurred at all concentrations of both herbicides. Further investigations of possible sub-lethal effects by the two herbicides on the fecundity of the ragwort flea beetle revealed no significant effects on oviposition rate or post-treatment oviposition period. Investigations of the possible sub-lethal effects of the two herbicides on ragwort flea beetle larval head capsule width and mortality showed no conclusive evidence that the two herbicides had any significant effect.