Abstract
Lepidopteran insects are mostly monophagous or oligophagous. Female butterflies distinguish their host plants by detecting a combination of specific phytochemicals through the gustatory sensilla densely distributed on their foreleg tarsi, thereby ensuring oviposition on appropriate host plants. In this study, to gain insight into the molecular mechanism underlying host plant recognition by the gustatory sensilla, using Asian swallowtail, Papilio xuthus, we focused on a family of small soluble ligand-binding molecules, odorant-binding proteins (OBPs), and found that three OBP genes showed enriched expression in the foreleg tarsus. Multicolor fluorescence in situ hybridization analyses demonstrated the coexpression of these three OBP genes at the bases of the foreleg gustatory sensilla. Further analyses on other appendages revealed that PxutOBP3 was exclusively expressed in the tissues which could have direct contact with the leaf surface, suggesting that this OBP gene specifically plays an important role in phytochemicals perception.
Highlights
Most phytophagous insects utilize a limited range of host plants [1, 2]
We previously demonstrated that the foreleg gustatory sensilla housed at least three types of gustatory receptor neurons which were tuned for five oviposition stimulants [11], and identified PxutGr1 as a receptor gene for one of the oviposition stimulants, synephrine [12]
Most of the odorant-binding proteins (OBPs) genes were clustered on the genome; 38 genes resided on only six scaffolds, each of which had 4–11 OBP genes (Figure 1, Supplementary Data Sheet 2, and Supplementary Figure 1)
Summary
Most phytophagous (plant-feeding) insects utilize a limited range of host plants [1, 2]. For these monophagous and oligophagous insect species, precise discrimination of right host plants is fundamentally important [3, 4]. In Lepidoptera, because of low mobility of larvae, host plant selection is mainly executed by female adults during oviposition [5]. P. xuthus larvae feed exclusively on Rutaceae plants, whereas adults suck floral nectar and no longer feed on leaves [8, 9]. A complete set of oviposition stimulants for P. xuthus, composed of 10 compounds in the Rutaceae leaves, has been identified [10]. It has been argued that chemoreceptors and
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