The qualitative effects of moderate P1 control are dependent on interspecific interactions between P1 and P2. “Moderate control” is 50% of the level of chemotherapeutic control required for elimination. Interactions can be synergistic (+) or antagonistic (˗) and can occur at different stages of the transmission cycle (the left interaction symbol denotes host susceptibility to heterologous infection, and, the right symbol is fecundity of heterologous adult parasites following infection establishment). Where the polarity of these interactions does not affect qualitative behaviour, the interaction is left blank. The prevalence of P1 and P2 before and after moderate P1 control is represented by the circle size, and the prevalence of co-infection by the amount of intersection. Where P2 fails to persist, it is represented by a point. To exemplify the link between this conceptual figure and the corresponding simulation results, the purely synergistic scenario (top interaction) corresponds to half way across the x-axis of Figure 3Div, and the purely antagonistic scenario (second from top interaction) corresponds to half way across the x-axis of Figure 3Ai.