AbstractThe olive fruit fly,Bactrocera oleae, is the most destructive pest of olive orchards worldwide. The monophagous larva has the unique capability of feeding on olive mesocarp, coping with high levels of phenolic compounds and utilizing non-hydrolyzed proteins present, particularly in the unripe, green olives. On the molecular level, the interaction betweenB. oleaeand olives has not been investigated as yet. Nevertheless, it has been associated with the gut obligate symbiotic bacteriumCandidatus Erwinia dacicola. Here, we used aB.oleaemicroarray to analyze the gene expression of larvae during their development in artificial diet, unripe (green) and ripe (black) olives. The expression profiles ofCa. E. dacicolawere analyzed in parallel, using the Illumina platform. Several genes were found overexpressed in the olive fly larvae when feeding in green olives. Among these, a number of genes encoding detoxification and digestive enzymes, indicating a potential association with the ability ofB. oleaeto cope with green olives. In addition, a number of biological processes seem to be activated inCa. E. dacicoladuring the development of larvae in olives, with the most notable being the activation of amino-acid metabolism.