Context : The determination of lithium abundances in stars of young clusters have shown that they deplete Li by different degrees during their pre-main sequence phase .
Beryllium abundances are complementary to the lithium ones , and can help tracing the mixing processes in the stellar interiors .

Aims : Our aim is to derive beryllium abundances in a sample of G- and K-type stars of two young pre-main sequence open clusters , IC 2391 and IC 2602 .
The Be abundances are used to investigate the mixing of internal material in these stars .
The reliability of the Be lines as abundance indicators in low-temperatures is also investigated in detail .

Methods : We derived Be abundances from high-resolution , high signal-to-noise UVES/VLT spectra using spectrum synthesis and model atmospheres .
Atmospheric parameters and other elemental abundances are adopted from a previous work .

Results : The sample stars have masses in the range between 0.80 \leq M / M _ { \odot } \leq 1.20 .
They have been shown to differ in lithium abundance by about 0.60 dex , with lower A ( Li ) in cooler and lower mass stars .
Here , we find that all the stars have the same Be abundance within the uncertainties .
These observations show that the Be abundance is not affected by the mixing events in the pre-main sequence , in this mass range , in agreement with the expectation of evolutionary models .
A comparison with Be abundances in older clusters shows that , contrary to the models , cool stars deplete Be during their main-sequence lifetime , confirming what has been previously suggested in the literature .

Conclusions :