Abstract: 【Aim】To ascertain the resistance status of Bradysia odoriphaga to ten insecticides, the potential risk of resistance of B. odoriphaga to cyromazine and the sublethal effects of cyromazine on B. odoriphaga. 【Methods】We determined the toxicity of 10 insecticides of 5 categories (neonicotinoids, pyrethroids, pyrroles, insectgrowthregulatorsandorganophosphates) to the 2nd instar larvae of B. odoriphaga from four regions including Puyang City in Henan Province, Bozhou City in Anhui Province, Tangshan City in Hebei Province, and Jining City in Shandong Province with the stomach-contact combination toxicity method. We observed the effects of sublethal concentrations (LC₁₅ and LC₃₀) of cyromazine on the larval duration, pupation rate, emergence rate and number of eggs laid per female of B. odoriphaga, and assessed the risk of resistance to cyromazine. We calculated the realized heritability (h²) of resistance of B. odoriphaga using Tabashnik’s method for threshold trait analysis and predicted the resistance development rates under different selection pressures based on the data of selection. 【Results】 Monitoring data demonstrated that the field populations of B. odoriphaga were susceptible or exhibited low-level resistance to cyromazine, hexaflumuron, chlorfluazuron and pyriproxyfen, and showed low to moderate levels of resistance to phoxim. All the monitored populations of B. odoriphaga showed low-level resistance to beta-cypermethrin. All field populations of B. odoriphaga were susceptible or developed low to moderate levels of resistance to imidacloprid, clothianidin and thiamethoxam. It would take 25.2, 20.7, 17.2, 14.4 and 11.4 generations, respectively, to develop 10-fold resistance to cyromazine in B. odoriphaga, under different selection pressures (mortality rates of 50%, 60%, 70%, 80% and 90%, respectively) when the realized heritability (h²) of resistance was 0.073. The emergence rates and numbers of eggs laid per female of F₀ and F₁ generations of B. odoriphaga were significantly reduced after exposure of the 2nd instar larvae to LC₁₅ and LC₃₀ of cyromazine. 【Conclusion】B. odoriphaga has low resistance risk to cyromazine. Cyromazine treatment at sublethal concentrations exhibits significant inhibitory effects on the pupation rate, emergence rate, and number of eggs laid per female of B. odoriphaga.

Key words: Bradysia odoriphaga, insecticide resistance monitoring, cyromazine, resistance risk, fitness cost