Linden gall mite (Phytoptus tillae)
Pest description and crop damage A very tiny mite that causes red to greenish galls on leaves. Damage is seldom serious.
No controls are registered.
For more information
Johnson, W.T. and H.H. Lyon (1991), Insects That Feed on Trees and Shrubs, 2nd ed., Cornell University Press (p. 482-488).