TU43/CU33/1.36/Patch 13, TU45/CU34/1.37/Patch 14
Survival. Difficulty is hard.
I placed a row of silverfish-stoneblocks in creative and mined it in survival with a Looting 3 pick axe, diamond. Not one silverfish spawned. I tried a diamond regular pick axe and the same result.
No cobble spawned as expected.
gt. ariana gaming