the biological control of insects is the most safe and important way of control, it depends on mass rearing of parasitoid, but the ability of parasitoid become weaker after several generations of laboratory rearing. The aim of the present study was to determine the potential of Cotesia glomerata (L) in searching and responding when it's rearing on alternative hosts in laboratory Aporia crataegi(L),Pieris brassicae (L) and Galleria mellonella (L). The fertilized females showed a preference for host larvae that reared on then for the larvae Pieris brassicae (L), so the olfactory memory in C. glomerata (L) gets in larvae stage and continue until the emergence of adults and lay their eggs in their hosts which reared in more efficiently.