Mass loss of red supergiants ( RSG ) is important for the evolution of massive stars , but is not fully explained .
Several empirical prescriptions have been proposed , trying to express the mass-loss rate ( \dot { M } ) as a function of fundamental stellar parameters ( mass , luminosity , effective temperature ) .
Our goal is to test whether the de Jager et al .
( 1988 ) prescription , used in some stellar evolution models , is still valid in view of more recent mass-loss determinations .
By considering 40 Galactic RSGs presenting an infrared excess and an IRAS 60- \mu m flux larger than 2 Jy , and assuming a gas-to-dust mass ratio of 200 , it is found that that the de Jager rate agrees within a factor 4 with most \dot { M } estimates based on the 60- \mu m signal .
It is also in agreement with 6 of the only 8 Galactic RSGs for which \dot { M } can be measured more directly through observations of the circumstellar gas .
The two objects that do not follow the de Jager prescription ( by an order of magnitude ) are \mu Cep and NML Cyg .
We have also considered the RSGs of the Magellanic Clouds .
Thanks to the works of Groenewegen et al .
( 2009 ) and Bonanos et al .
( 2010 ) , we find that the RSGs of the Small Magellanic Cloud have mass-loss rates consistent with the de Jager rate scaled by ( Z / Z _ { \sun } ) ^ { \alpha } , where Z is the metallicity and \alpha is 0.7 .
The situation is less clear for the RSGs of the Large Magellanic Cloud .
In particular , for L > 1.6 \times 10 ^ { 5 } L _ { \odot } , one finds numerous RSGs ( except WOH-G64 ) having \dot { M } significantly smaller than the de Jager rate and indicating that \dot { M } would no longer increase with L .
Before this odd situation is confirmed through further analysis of LMC RSGs , we suggest to keep the de Jager prescription unchanged at solar metallicity in the stellar evolutionary models and to apply a ( Z / Z _ { \sun } ) ^ { 0.7 } dependence .