We show that curvature induced particle production at reheating generates adiabatic dark matter if there are non-minimally coupled spectator scalars weakly coupled to visible matter .
The observed dark matter abundance implies an upper bound on spectator masses m and non-minimal coupling values \xi .
For example , assuming quadratic inflation , instant reheating and a single spectator scalar with only gravitational couplings , the observed dark matter abundance is obtained for m \sim 0.1 GeV and \xi \sim 1 .
Larger mass and coupling values of the spectator are excluded as they would lead to overproduction of dark matter .