Two-Marked Treehoppers can be a pest. They weaken plants with their consistent feeding from the stems and leaves. This leads to browning and death. The treehopper can also secrete a sweet sticky substance called honeydew. This attracts other insects and can promote mold growth that looks like a black soot or ash.
Popultions of Two-Marked Treehoppers are host specific, yet each seems to feed on a different plant making interactions between populations a bit complicated. They are able to travel to other areas and if they encounter another Two-Marked Treehopper that has always fed from a different plant, the likelihood of the two reproducing greatly diminishes. It's not impossible that the two will mate, just less probable than if a male and female on the same diet would meet.
Additional references: University of Missouri, Department of Biological Sciences 2008 (McNett and Cocroft)