SummaryIn insects, specialized feeding on the phloem sap (containing mainly the sugar sucrose) has evolved only in some hemipteran lineages. This feeding behavior requires an ability to locate feeding sites buried deeply within the plant tissue. To determine the molecular mechanism involved, we hypothesized that the phloem-feeding whiteflyBemisia tabacirelies on gustatory receptor (GR)-mediated sugar sensing. We first conducted choice assays, which indicated thatB. tabaciadults consistently choose diets containing higher sucrose concentrations. Next, we identified fourGRgenes in theB. tabacigenome. One of them,BtabGR1, displayed significant sucrose specificity when expressed inXenopusoocytes. Silencing ofBtabGR1significantly interfered with the ability ofB. tabaciadults to discriminate between non-phloem and phloem concentrations of sucrose. These findings suggest that in phloem feeders, sugar sensing by sugar receptors might allow tracking an increasing gradient of sucrose concentrations in the leaf, leading eventually to the location of the feeding site.