Impacts of host plant resistance on Pandora neoaphidis, a fungal pathogen of soybean aphid

Since the introduction of the soybean aphid, Aphis glycines Matsumura, from Asia, insecticide use in soybean has increased 130-fold in the North Central US. Development of aphid-resistant soybean varieties is one management tactic which may decrease reliance on insecticides. Exploring potential non-target impacts of such resistance will be an important step in incorporating host plant resistance into soybean aphid pest management programs. In field experiments in 2009 and 2010, we investigated potential impacts of Rag1 aphid resistant soybean on a fungal pathogen of soybean aphid, Pandora neoaphidis, via open plot and cage studies at two field sites in Minnesota. In both years of open plot studies at Rosemount, MN, Rag1 resistant soybean experienced lower aphid pressure and aphid disease prevalence compared to a non-resistant isoline. However, in cage studies at Becker, MN, in 2009, when aphid densities were equivalent in both resistant and non-resistant treatments, and in 2010, when resistance significantly decreased aphid densities in cages, Rag1 resistance had no impact on aphid disease prevalence. These results support the conclusion that the observed decrease in aphid disease prevalence in Rag1 soybean was likely due to the lower aphid density in these plots. Our data confirm that aphids on resistant plants can reach a high enough density to allow P. neoaphidis establishment. Thus, the incorporation of host plant resistance into soybean aphid management programs is compatible with the action of P. neoaphidis.