Vertebrate females exposed to pathogens transfer specific antibodies to their offspring, providing them with a temporary protection during the time required for their immune system to mature. Invertebrates lack the antibodies that vertebrate females transfer to their offspring. However, maternal transfer of immunity, also referred to as “trans-generational immune priming” (TGIP), occurs in invertebrates too, suggesting that it has to be achieved by other, yet unknown, mechanisms. Evidences of TGIP in invertebrates are largely phenomenological and await the elucidation of the underlying mechanisms as well as its evolutionary and ecological implications. So far, TGIP in invertebrates has been probably best described in the mealworm beetle, Tenebrio molitor (Coleopteran, Tenebrionidae) in terms of both immunological and fitness consequences for the offspring through various developmental stages. T. molitor females subjected to a bacterially based benign immune challenge produce eggs and larvae that contain high antibacterial activity and adult offspring with an increased concentration of circulating immune cells. Such an investment into offspring immunity is variable among females. It constrains the female immune responsiveness and fecundity and slows down the growth rate of the offspring. Yet the physiological and molecular mechanisms through which TGIP is achieved are not known. Furthermore, it is not known whether variation among females in investment into TGIP has a genetic basis. If so, variation may be maintained by genetic constrains with other life history traits and selective pressures imposed by parasite persistence from one generation to the next. In this project, we aim to study TGIP in T. molitor through the investigation of its underlying mechanism(s) and effects at the physiological and molecular levels. We will use several complementary methodologies, including proteomics and transcriptomics to identify the main immune effectors and immune genes associated to TGIP, microscopy to determine the site of their production and functional approaches to experimentally validate their importance in this phenomenon. We will also investigate the source of variation in TGIP among females through the estimation of its genetic variance and covariance with life-history traits of the mother and her offspring in order to understand the conditions of its evolution and its maintenance in natural populations. The outcome of such a study will provide unprecedented advances on the functional aspects of TGIP as well as on its ecology and evolution in invertebrate systems.