Since the 1990s, the negative ecological and economic impacts of the native plant leafy spurge Euphorbia esula L. (Euphorbiaceae), have increased in the floodplains of Val de Saône (France). Growing in dense patches, this latex-rich plant is toxic to cattle and when present in cut hay reduces the profitability of annually mowed grasslands. This economic loss has resulted in land use changes, such as shifting mowed pastures into intensive agricultural (corn) and forestry (poplar) practices. In a prior study, we proposed the implementation of an integrated pest management (IPM) program, based on modification of traditional agricultural practices occurring in the Val de Saône, for controlling weediness of leafy spurge. In this study, we compare the effect of traditional management versus this IPM program on the biology of two principal insect herbivores present in the Val de Saône, Oberea erythrocephala (Coleoptera: Cerambycidae) and Spurgia euphorbiae (Diptera: Cecidomyiidae). Traditional mowing takes place between mid-June and early July and appears to have an impact on the biology of the two insects. It occurs during the reproductive period of O. erythrocephala and eliminates the stems that are required for oviposition. Avoiding the mowing of spurge patches, as recommended in the IPM, should enhance O. erythrocephala populations. Mowing also kills shoots that harbor S. euphorbiae galls and so precludes the development of late summer generations of this midge.