We describe Spitzer IRAC and MIPS observations of the nearby 25 Myr-old open cluster NGC 2232 .
Combining these data with ROSAT All-Sky Survey observations , proper motions , and optical photometry/spectroscopy , we construct a list of highly probable cluster members .
We identify 1 A-type star , HD 45435 , with definite excess emission at 4.5–24 \mu m indicative of debris from terrestrial planet formation .
We also identify 2–4 late-type stars with possible 8 \mu m excesses , and 8 early-type stars with definite 24 \mu m excesses .
Constraints on the dust luminosity and temperature suggest that the detected excesses are produced by debris disks .
From our sample of B and A stars , stellar rotation appears correlated with 24 \mu m excess , a result expected if massive primordial disks evolve into massive debris disks .
To explore the evolution of the frequency and magnitude of debris around A-type stars , we combine our results with data for other young clusters .
The frequency of debris disks around A-type stars appears to increase from \sim 25 % at 5 Myr to \sim 50–60 % at 20–25 Myr .
Older A-type stars have smaller debris disk frequencies : \sim 20 % at 50–100 Myr .
For these ages , the typical level of debris emission rises from 5–20 Myr and then declines .
Because 24 \mu m dust emission probes icy planet formation around A-type stars , our results suggest that the frequency of icy planet formation is \eta _ { i } \gtrsim 0.5–0.6 .
Thus , most A-type stars ( \approx 1.5–3 M _ { \odot } ) produce icy planets .