Beyond biotypes: Aphis glycines (Hemiptera: Aphididae) biology and the durability of aphid-resistant soybean

In North America, Aphis glycines, is capable of reducing soybean yields by as much as 40%. The management of A. glycines has relied heavily on the use of broad-spectrum insecticides that can be detrimental to both the pest and natural enemies that are present in soybean at the time of application. An alternative management strategy for A. glycines is the use of aphid-resistant soybean that contain Rag genes. The presence of three virulent A. glycines biotypes (i.e., able to overcome aphid-resistance genes) in the US however raises the question about the durability and practicality of Rag genes. Here I examined the potential interactions that may be occurring between both virulent and avirulent A. glycines on soybean, and whether fitness costs exist for virulent biotypes. I also evaluated whether the use of an interspersed refuge strategy for resistant and susceptible soybean would manage A. glycines populations, and determined their impact on natural enemies present in soybean. Our results demonstrate that a virulent A. glycines biotype is capable of obviating the resistance gene in soybean; therefore, making the plant a suitable host for both an avirulent and virulent biotype. This effect occurs in the absence of the virulent biotype for up to a period of five days. Fitness costs were present for all virulent biotypes that have been discovered. An interspersed refuge strategy reduces A. glycines populations, and has minimal impacts on natural enemies present in soybean. Future research will need to investigate the mechanism responsible for the obviation of resistance effect. Work should also be conducted to determine the durability of Rag genes when a refuge in a bag approach is used.