This project aims to develop biological control methods using parasitoid Microhymenoptera against aphids in several crop productions. Two complementary methods are investigated: 1) increasing the numbers of naturally occurring parasitoids using strips of herbaceous vegetation at the edges of fields, 2) by mass release. Moreover, we study 1) the influence of host specificity on demography, 2) the characterisation of parasitoid populations and analyses of genetic variation using RAPD-PCR, 3) the co-evolution of tritrophic systems (plant - aphid - natural enemies), 4) the capability to survive cold and the modelling of winter survival. Finaly we aim to develop an artificial diet for parasitoid rearing.