Thiamethoxam, bifenthrin, and flonicamid resistance in Schizaphis graminum and associated fitness costs

The green bug, Schizaphis graminum Rondani (Hemiptera: Aphididae), is a major pest of wheat plants through direct feeding and indirectly by transmitting several viruses around the world. Insecticides including thiamethoxam, bifenthrin, and flonicamid, are widely used to control this pest. However, indiscriminate chemical applications cause resistance in several insect pests, including aphids. In the current study, we investigated the evolution of thiamethoxam, bifenthrin, and flonicamid resistance in S. graminum after continuous selection pressure. Furthermore, we assessed the fitness of all resistant strains compared to susceptible strains using the age-stage, two-sex life table method. Thiamethoxam, bifenthrin, and flonicamid-resistant strains were evolved with 38.57, 28.67, and 21.31-fold resistance after selection for over ten generations. Life table analysis showed that all resistant strains had significantly reduced adult longevity, fecundity, and reproductive days, and an increased total pre-reproductive period compared to susceptible aphids. In addition, the key demographic parameters such as the intrinsic rate of increase (r) and the net reproductive rate (R0) were substantially reduced in the resistant S. graminum populations. These findings provide in-depth information about the risk of insecticide resistance evolution and the associated fitness costs in S. graminum.