  We present a study of 15 new brown dwarfs belonging to the $\sim7$ Myr old 25
Orionis group and Orion OB1a sub-association with spectral types between M6 and
M9 and estimated masses between $\sim0.07$M$_\odot$ and $\sim0.01$ M$_\odot$.
By comparing them through a Bayesian method with low mass stars ($0.8\lesssim$
M/M$_\odot\lesssim0.1$) from previous works in the 25 Orionis group, we found
statistically significant differences in the number fraction of classical T
Tauri stars, weak T Tauri stars, class II, evolved discs and purely
photospheric emitters at both sides of the sub-stellar mass limit. Particularly
we found a fraction of $3.9^{+2.4}_{-1.6}~\%$ low mass stars classified as CTTS
and class II or evolved discs, against a fraction of $33.3^{+10.8}_{-9.8}~\%$
in the sub-stellar mass domain. Our results support the suggested scenario in
which the dissipation of discs is less efficient for decreasing mass of the
central object.
