Abstract: To clarify the effects of sublethal concentration of imidacloprid on the ability of Orius similis to control Frankliniella occidentalis, the stomach toxicity method was used to treat O. similis, which was then fed F. occidentalis treated with two imidacloprid concentrations (LC₁₀ and LC₂₀) and water. The predation rate of O. similis on F. occidentalis under different treatments was measured. The functional response model was applied to explore the effects of imidacloprid on predation and prey searching ability. The results showed that the predation rate of O. similis on F. occidentalis was 18.4 individuals when both were treated with LC₁₀ imidacloprid, which was lower than that of O. similis or F. occidentalis treated with LC₁₀ imidacloprid at 18.6 and 19.4 individuals, respectively. The predation rate of O. similis on F. occidentalis was 20.9 individuals when treated with water. The functional response of O. similis treated with different concentrations of imidacloprid to F. occidentalis treated with the same concentration of imidacloprid, as well as to F. occidentalis treated with water, conformed to the Holling II type. The control efficiency (α/T_h) of adult female O. similis on F. occidentalis treated with both-concentrations of imidacloprid decreased with increasing imidacloprid concentration, with value of 32.38 and 25.65, respectively. Within a certain concentration range, the application of imidacloprid promoted the predation capacity of O. similis. The control efficiency of the 3-rd instar nymphs O. similis on F. occidentalis treated with LC₁₀ imidacloprid was 2.89 days higher than that of F. occidentalis treated with water. Imidacloprid affected the searching capacity of O. similis. The searching effects of adult female O. similis treated with two imidacloprid concentrations on F. occidentalis treated with the same concentration of imidacloprid decreased from 0.73 and 0.60 to 0.60 and 0.52, respectively. Overall, the application of imidacloprid inhibited the searching and predation efficiency of O. similis.

Key words: Orius similis, Frankliniella occidentalis, imidacloprid, predatory capacity