Fitness Cost of the Field-Evolved Resistance to Sulfoxaflor and Multi-Insecticide Resistance of the Wheat Aphid Sitobion miscanthi (Takahashi)

SIMPLE SUMMARY: Pest control mainly relies on the use of chemical insecticides, whereas insecticide resistance is problematic for the effective management of insect pests. Sulfoxaflor is a new sulfoximine insecticide. The wheat aphid Sitobion miscanthi is one of the most important pests adversely affecting wheat cultivation. We obtained an S. miscanthi field population highly resistant to sulfoxaflor, despite this insecticide not having been widely and continuously used for control of wheat aphids in China. The understanding of the cross-resistance or multi-resistance spectrum and fitness cost caused by insecticide resistance is important for selecting suitable insecticides to integratively manage insecticide resistance. Our findings suggest that the S. miscanthi population that is highly resistant to sulfoxaflor had moderate resistance to two pyrethroid insecticides, which was accompanied by severely adverse biological fitness. The study provides valuable information regarding the rational use of pesticides and may be relevant for exploring new mechanisms of insecticide resistance. ABSTRACT: Sulfoxaflor belongs to a new class of insecticides that is effective against many sap-feeding pests. In this study on Sitobion miscanthi (Takahashi) (i.e., the predominant wheat pest), a highly sulfoxaflor-resistant (SulR) population was obtained from a field. Its resistance to the other seven insecticides and its biological fitness were analyzed using a leaf-dip method and a two-sex life table approach, respectively. Compared with the relatively susceptible (SS) population, the SulR population was highly resistant to sulfoxaflor, with a relative insecticide resistance ratio (RR) of 199.8 and was moderately resistant to beta-cypermethrin (RR = 14.5) and bifenthrin (RR = 42.1) but exhibited low resistance to chlorpyrifos (RR = 5.7). Additionally, the SulR population had a relative fitness of 0.73, with a significantly prolonged developmental period as well as a lower survival rate and poorer reproductive performance than the SS population. In conclusion, our results suggest that S. miscanthi populations that are highly resistant to sulfoxaflor exist in the field. The possibility that insects may develop multi-resistance between sulfoxaflor and pyrethroids is a concern. Furthermore, the high sulfoxaflor resistance of S. miscanthi was accompanied by a considerable fitness cost. The study data may be useful for improving the rational use of insecticides and for exploring novel insecticide resistance mechanisms.