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

Adams, Rachael L.

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.

Keywords

Longitarsus jacobaeae; Coleoptera; Chrysomelidae; Senecio jacobaea; biological control; herbicides; Tordon®; Escort®; integrated weed management; non-target organism; toxicity; New Zealand

Date

1997

Type

Thesis

Access Rights

Digital thesis can be viewed by current staff and students of Lincoln University only. Print copy available for reading in Lincoln University Library.