  We present IRAC/MIPS Spitzer observations of intermediate-mass stars in the 5
Myr old Lambda Orionis cluster. In a representative sample of stars earlier
than F5 (29 stars), we find a population of 9 stars with a varying degree of
moderate 24um excess comparable to those produced by debris disks in older
stellar groups. As expected in debris disks systems, those stars do not exhibit
emission lines in their optical spectra. We also include in our study the star
HD 245185, a known Herbig Ae object which displays excesses in all Spitzer
bands and shows emission lines in its spectrum. We compare the disk population
in the Lambda Orionis cluster with the disk census in other stellar groups
studied using similar methods to detect and characterize their disks and
spanning a range of ages from 3 Myr to 10 Myr. We find that for stellar groups
of 5 Myr or older the observed disk frequency in intermediate mass stars (with
spectral types from late B to early F) is higher than in low mass stars (with
spectral types K and M). This is in contradiction with the observed trend for
primordial disks evolution, in which stars with higher stellar masses dissipate
their primordial disks faster. At 3 Myr the observed disk frequency in
intermediate mass stars is still lower than for low mass stars indicating that
second generation dusty disks start to dominate the disk population at 5 Myr
for intermediate mass stars. This result agrees with recent models of evolution
of solids in the region of the disk where icy objects form (>30 AU), which
suggest that at 5-10 Myr collisions start to produce large amount of dust
during the transition from runaway to oligarchic growth (reaching sizes of ~500
km) and then dust production peaks at 10-30 Myr, when objects reach their
maximum sizes (>1000 km)
