As far as the Slate Drake and the Gray Drake Mayflies are concerned,there seems to be some debate as to what genus that the larger Gray or Slate colored mayflies we come across on the Lower Yuba really are. The concensus is that they are Drakes. Are they the genus Siphlonurus or are they the genus Isonychia? I’m not an entomologist so the best I can do is research.ccording to the information in the book “Flyfishers Guide to Northern California” put together by Seth Norman, the chapter authored by our local Ralph Wood, states that they are Gray Drakes or Siphlonurus occidentalis. Hogan Brown has remarked that there is a minor Isonychia hatch on the Lower Yuba . . .
