--- - "\nAdults females of P. hospiton only lay eggs on \nFerula communis and larvae only feed on the same plant. The different pattern of activity of GRNs evoked by plant saps allows both females and larvae to discriminate among them (accepting ferula as host and rejecting fennel and carrot) thus strengthening the theory that the peripheral taste sensitivity plays a key role in host acceptance or rejection, and in the discrimination process between host and nonhost plants.\n\n\n\n\n\n\nAbstract\nThe Lepidopteran Papilio hospiton uses only plants belonging to the Apiaceae and the Rutaceae families as hosts. Both adult females and larvae are equipped with gustatory receptor neurons (GRNs) capable of detecting sugars, bitters and salts, thus providing information for evaluating the chemical composition of the plant. Since the activation of these neurons may affect insect behavior, the aim of this study were: (a) to study the gustatory sensitivity of both females and larvae to the sap of two Apiaceae, \nFoeniculum vulgare (fennel) and \nDaucus carota (carrot), that are not used as host plants; (b) to cross‐compare the spike activity evoked from these two plants with that evoked by \nFerula communis (ferula), the host plant preferred by ovipositing females of \nP. hospiton and where the larvae perform best; (c) finally, to confirm that the gustatory system can provide the central nervous system with the necessary information to evaluate differences between plant saps. The results show that: (a) fennel and carrot both evoke a higher neural activity from the bitter‐sensitive neurons and lower from the sugar‐sensitive neurons with respect to ferula, in both adult females and larvae; (b) on the basis of the different patterns of neural activity generated in tarsal, lateral and medial sensilla by fennel and carrot versus ferula, both adult and larvae possess enough information to discriminate among these plants; (c) adult females of \nP. hospiton lay eggs where the larvae have the greatest growth success and this confirms the importance of taste sensitivity in host plants selection." - 'Archives of Insect Biochemistry and Physiology, EarlyView. '