  Periodic comets of different dynamical groups with orbits at 2 - 5 AU still
occasionally active. The observed dust activity of such objects can be
connected with processes of water ice sublimation (MBCs) or crystallization of
amorphous water ice (QHCs) as well as with external causes. No connections of
cometary flares with cyclic variations of solar activity indexes were found.
But some individual solar flares can affect the brightness of comets. Cometary
objects in the main asteroid belt have a lower statistic of flares than comets
at orbits like quasi-Hilda objects.
