  By using a reductive perturbation method, we derive from Maxwell-Bloch
equations a cubic generalized Kadomtsev-Petviashvili equation for ultrashort
spatiotemporal optical pulse propagation in cubic (Kerr-like) media without the
use of the slowly varying envelope approximation. We calculate the collapse
threshold for the propagation of few-cycle spatiotemporal pulses described by
the generic cubic generalized Kadomtsev-Petviashvili equation by a direct
numerical method and compare it to analytic results based on a rigorous virial
theorem. Besides, typical evolution of the spectrum (integrated over the
transverse spatial coordinate) is given and a strongly asymmetric spectral
broadening of ultrashort spatiotemporal pulses during collapse is evidenced.
