Toxicity of Nine Insecticides to Frankliniella occidentalis and Frankliniella intonsa under the Environment of Elevated CO₂ Concentration

Purpose To compare the toxicity differences of nine insecticides to Frankliniella occidentalis and F. intonsa under two CO₂ volume fractions, providing theoretical guidance for field control of thrips under the environment of elevated CO₂ in the future.

Methods The toxicity of nine insecticides to F. occidentalis and F. intonsa of female, male adults and 2nd instar nymph under 400 μL/L and 800 μL/L CO₂ conditions were determined by soaking method.

Results Under 800 μL/L CO₂ condition, the LC₅₀ values of fiflonil for female, male adults and 2nd instar nymphs of F. occidentalis were 0.401, 0.337 and 0.261 mg/L, respectively, which were 0.82 times, 0.94 times and 0.73 times of those under the 400 μL/L CO₂ condition, respectively; the LC₅₀ values of fiflonil for female, male adults and 2nd instar nymphs of F. intonsa were 0.381, 0.263 and 0.219 mg/L, respectively, which were 0.82 times, 0.87 times and 0.78 times of those under the 400 μL/L CO₂ condition, respectively. Under the two CO₂ concentrations, the toxicity of nine insecticides to F. occidentalis and F. intonsa were as follows: fipronil>phoxim>abamectin>thiamethoxam>carbosulfan>lambda-cyhalothrin>bifenthrin>deltamethrin>chlorantraniliprole, and the sensitivity of both thrips to insecticides was in the order of 2nd instar nymphs>male adults>female adults.

Conclusion Elevated CO₂ increases the sensitivity of F. intonsa and F. occidentalis to nine insecticides, and the former stronger than that of latter. Fipronil is the most effective insecticide against two species and can be recommended insecticide for field control.