In herbivorous insects, food selection depends on sensitivity to specific chemical stimuli from host-plants as well as to secondary metabolites (bitter) and to sugars (phagostimulatory). Bitter compounds are noxious, unpalatable or both and evoke an aversive feeding response. Instead, sugars and sugar alcohols play a critical role in determining and enhancing the palatability of foods. We assumed that peripheral taste sensitivity may be related to the width of the host selection. Our model consists of two closely phylogenetically related Papilionid species exhibiting a difference in host plant choice: Papilio hospiton and Papilio machaon. The spike activity of the lateral and medial maxillary styloconic taste sensilla was recorded following stimulation with several carbohydrates, nicotine and NaCl, with the aim of characterizing their gustatory receptor neurons and of comparing their response patterns in the light of their different acceptability in feeding behaviour. The results show that: a) each sensillum houses phagostimulant and phagodeterrent cells; b) the spike activity of the gustatory neurons in response to different taste stimuli is higher in P. hospiton than in P. machaon; c) sugar solutions inhibit the spike activity of the deterrent and salt cells, and the suppression is higher in P. machaon than in P. hospiton. In conclusion, we propose that the different balance between the phagostimulant and phagodeterrent inputs from GRNs of maxillary sensilla may contribute in determining the difference in food choice and host range.

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The Mediterranean fruit fly, Ceratitis capitata (Wiedemann, 1824; Diptera: Tephritidae), is a polyphagous pest in horticulture, mainly targeting Citrus fruits. Natural essential and fixed oils are currently under investigation for their broad-spectrum in pest control. To gain better knowledge about medfly behavior and biochemistry, we examined with behavioral and biochemical assays, the effects on C. capitata from six natural fixed oils obtained from vegetable (five) or animal (one) matrices using the ecofriendly supercritical CO 2 extraction. Oils were obtained at 250/300 bar and 40°C from the seeds of Laurus nobilis and Citrus paradisi, the fruits of Myristica fragrans and Pistacia terebinthus, wheat germ, and mullet roes (marine oil). Behavioral experiments were performed by means of twochoice tests to analyze the oil attractant effect compared with control (water or standard diet). The fatty acid composition of oils and the total lipid and fatty acid profile of medflies were characterized by chromatographic techniques. Behavioral bioassays showed that fixed oil obtained from M. fragrans (nutmeg butter) was more attractive than other oils. Medflies fed (24 hr) on marine oil showed significant changes in the total lipid and fatty acid profile induced by oil ingestion without toxic effects. However, 56% mortality was observed in insects fed on M. fragrans oil and no biochemical changes ascribable to oil ingestion were detected in the medflies that survived. Our results advance Arch. Insect Biochem. Physiol. 2018;99:e21508. wileyonlinelibrary.com/journal/arch

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