Effects of single and mixed infections of Bean pod mottle virus and Soybean mosaic virus on host-plant chemistry and host–vector interactions

Co-infection by vector-borne plant viruses is common, yet few studies have explored the effects of mixed infections on host-plant phenotypes or plant–vector interactions. We documented the effects of single and mixed infection by Bean pod mottle virus (BPMV) and Soybean mosaic virus (SMV) on key biochemical plant traits and the behaviour and performance of virus vectors (BPMV: Epilachna varivestis, SMV: Aphis glycines) in order to understand how virus-induced changes in plant phenotypes might influence (i) the acquisition and transmission of each virus by its respective vector in single infections, (ii) the likelihood of secondary infection for plants singly infected with either virus and (iii) the implications of co-infection for virus transmission by vectors. Single infection by either BPMV or SMV increased host-plant palatability for E. varivestis, potentially enhancing vector acquisition of BPMV from BPMV-infected plants as well as the risk of secondary BPMV infection in plants infected with SMV. However, co-infected plants were no more palatable to beetle vectors than mock-inoculated plants. BPMV infection had minimal impacts on A. glycines. SMV infection reduced A. glycines population growth, but increased aphid feeding preferences for infected plants, a pattern likely not conducive to the (non-persistent) transmission of SMV. Co-infection eliminated the negative effects of single SMV infection on aphid population growth, and aphids exhibited a feeding preference for co-infected (relative to mock-inoculated) plants. Our results demonstrate that virus effects on host phenotype and vector behaviour can be modified by the presence of a co-infecting virus, with potentially important implications for disease transmission.