Stable co-evolutionary relationships between species can result in the loss of autonomous synthesis of essential nutrients when these can be obtained from the ecological partner. Parasitoid insects obtain the majority of their nutrients from their host, and contain multiple, independently-evolved lineages that do not increase their adult lipid reserves despite feeding on a surplus of dietary sugars, although some parasitoid species in these lineages were found to have reactivated adult lipogenesis. Several clades within the parasitoid insects have lost the parasitoid lifestyle and switched to either a predatory or a phytophagous lifestyle. Here, we test whether adult lipid accumulation is reactivated in two species that independently evolved a phytophagous lifestyle from parasitoid ancestors. The larvae of Megastigmus aculeatus (Hymenoptera: Chalcidoidea: Torymidae) and Bruchophagus platypterus (Hymenoptera: Chalcidoidea: Eurytomidae) obligatorily feed on seeds of specific plants. Seeds of wild host plants were collected and the emerging wasps were tested for their lipogenic abilities by comparing their lipid content upon emergence and after feeding on sugar. The lipid content of both species after ad libitum access to sugars was equal to or lower than at emergence, indicating lack of lipogenesis. Therefore the secondary switch to phytophagy was not associated with recovery of lipid accumulation in these species. We discuss these results in relation to the lipid content of the host seeds and the reversibility of the lipid accumulation phenotype. We infer that the close relationship between seed-feeding insects and their hosts allow the seed-feeders to rely on a predictable amount of lipids in their diet which relaxes the need for autonomous lipid synthesis.