Rabdophaga rigidae isn't in Ron's book. R. salicisbatatus is the only integral stem gall for Rabdophaga on willow described. What are the differences between R. rigidae and R. salicisbatatus? Or I wonder if R. salicisbatatus is a synonym. There doesn't seem to be much about that species online.

Definitely not synonymous. R. rigidae galls are hard and terminal; "monothalamous, subglobular to tapered, 1-3 cm long, and 0.5-1.0 cm wide. . . A few leaves often begin to grow beyond the gall but soon die." R. salicisbatatas galls are "very large, soft" twig swellings, "sometimes resembling a potato in shape. . . variable but usually polythalamous and bulging abruptly out of the twig." (1) Gagné's illustrations for this species show a non-terminal gall that apparently doesn't kill the twig beyond it.

If we just look at the monothalamous vs polythalamous part, this gall is monothalamous, and Ron's book does mention that R. salicisbatatas is polythalamous.

The drawing he has looks similar to the gall I photographed. It seems he should have included R. rigidae in the book!

I will have to find more of these galls and cut them open and see if I can find both species and be clear on the differences.... Would like to find some that are polythalamous; maybe those will be clearly different in their appearance.

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