When Jassids are on the menu trout will single them out amongst other food items.
There seems to be a symbiotic relationship between Jassids and ants and they live in harmony. Co-existing seems advantageous to both. Perhaps they protect each other, help keep their nests clean? Secretions from the Jassids are of interest to the ants on sappy gum trees such as manor gums and others.
Image credits: Gary France