You may use, as an example, Shannon index and/or the Simpson diversity

thank you very much! I was doubtful on Shannon because of the intraspecificity of the case, but I guess that considering the life stage as a specie, would fit anyway? Am I right?

Thats an excellent question Guido. I followed here just to see if any of the colleagues could help on this too. By definition the Brillouin diversity index would better fit for the intraespecifc case but in practice few ecologists used because Brillouin index is less familiar than the Shannon index.