Greenhouse and field experiments were used to determine the effect of soybean aphid feeding on SCN reproduction. The results of our experiments highlighted the importance of pest population density in determining the outcome of the interaction.

At extremely high aphid and SCN population densities (10x greater or more than those normally experienced in farm fields), aphid feeding actually decreases SCN reproduction. However, at population densities that commonly occurs in farmer fields, soybean aphid feeding increases SCN reproduction by 33% every generation. In Iowa, SCN can complete three to six generations each year so the 33% increase in reproduction we measured could occur for every generation that aphids are present in the farm field.

We also found that aphid colonization results in a rapid induction of defense signals in roots, but this signal disappears as aphid numbers increase on leaves, suggesting that the accumulation effector proteins from aphid saliva suppresses systemic defenses, and could explain increased SCN reproduction.

We also evaluated the ability of management tactics to mitigate the effect aphid feeding has on SCN reproduction. We discovered aphid populations as low as 90 aphids per plant could still increase SCN reproduction by 33%. In addition we discovered the soybean aphid resistance gene Rag1 was not able to mitigate the effect aphid feeding has on SCN reproduction. Therefore, management will need to focus on strategies that keep soybean aphid populations at very low densities (<90 aphids per plant) to manage the interaction. We are optimistic that a soybean aphid resistance gene pyramid (Rag1 + Rag2) could help with this interaction.