  The collective mode spectrum of the composite fermion state 1/3 filling
factor is evaluated. At zero momentum, the result coincides with the cyclotron
energy at the external magnetic field value, and not at the effective magnetic
field, in spite of the fact that only the former enters in the equations, thus,
the Kohn theorem is satisfied. Unexpectedly, in place of a magneto roton
minimum, the collective mode gets a treshold indicating the instability of the
mean field composite fermion state under the formation of crystalline
structures. However, the question about if if this outcome only appears within
the mean field approximation should be further considered.
