Well, fullt adult delphax generally lose their spots and are quite easy to distinguish.
Also, male delphax have black on their first soft dorsal ray which is usually elongated further than the main dorsal spine.
c. agassizii and ambiacus are very difficult to distinguish because the patterning is so varied between them, so place of origin is the only reliable method.
I did think that agassizii had a rounder snout than ambiacus but apparantly not always the case!!
Every morning when I wake, I thank the Lord I'm Welsh!