Susceptibility, resistance risk and sublethal effect to fenmezoditiaz, a novel mesoionic insecticide, in the brown...

The brown planthopper (Nilaparvata lugens) has developed resistance to commonly used insecticides in Asia. Fenmezoditiaz, a novel mesoionic chemical insecticide, was designed to control piercing-sucking pests, especially N. lugens. In this study, the current susceptibility, risk assessment and sublethal effect of N. lugens to fenmezoditiaz was determined. Fenmezoditiaz showed high activity against N. lugens (the susceptibility baseline of LC₅₀ was 0.045 mg/L) and was susceptible to all field populations (resistance ratio = 0.7 to 1.7-fold). Meanwhile, the field populations showed resistance to four other insecticides. The susceptible strain was artificially selected with fenmezoditiaz for 16 generations and resulted in an 8.0-fold increase in LC₅₀. With the realized heritability (h² = 0.105), the projected resistance development (100-fold) would be expected after 20.4 generations under a 90 % selection pressure every generation. The fecundity for sublethal doses (LC₁₅ and LC₃₀) of fenmezoditiaz (83.6 and 80.8 eggs/female) was significantly less than those of the control (127.8 eggs/female). This sublethal effect could persist into the F₁ generation, resulting in a significant decrease in population. Additionally, six P450 genes were significantly down-regulated in sublethal treatment and resistance selection strains. These findings provided theoretical assistance for the control of N. lugens in the field and revealed that fenmezoditiaz could represent a candidate for N. lugens.