Date of this Version
The increased use of thiamethoxam seed treatments for controlling target pests such as the bean leaf beetle, Cerotoma trifurcata (Forster), suggests the need for methods to measure and monitor the development of resistance to these insecticides. Overwintering and F1 bean leaf beetles were collected from alfalfa and soybean fields and used in early growth stage soybean studies to measure toxicity of thiamethoxam both in greenhouse experiments and laboratory bioassays involving exposure to treated foliage. Lethal and sub-lethal effects were detected in both greenhouse and lab bioassays. Lethal concentrations determined from laboratory assays were compared with residues determined from field grown plants that were sampled through the early vegetative stages.
Results of these studies show that thiamethoxam is highly active against adult bean leaf beetles. Commercial rates and bioassay concentrations of thiamethoxam provide effective control causing lethal and sublethal effects. The quantification of insecticide levels in soybean leaves from new nodes over time indicate that thiamethoxam provides control at early vegetative growth stages, but insecticide concentrations fall off as the plant grows and insecticide available for uptake becomes limited. These results provide a foundation for resistance monitoring and detection.
Advisors: Thomas E. Hunt and Blair D. Siegfried