Background: The sweet potato weevil, Cylas formicarius, is the most serious pest of sweet potato worldwide. The molecular mechanism of sex pheromone recognition in C. formicarius has not been reported. Odorant-binding proteins (OBPs) play a critical role in selectively binding and transporting pheromones or other odors to the surface of olfactory receptor neurons through the aqueous sensillar lymph, therefore the function of sweet potato OBPs is worth studying. Results: Herein, the CforOBP1-3 genes encoding three classical OBPs were cloned in C. formicarius by reverse transcriptionpolymerase chain reaction. Phylogenetic analysis showed that CforOBP1-3 were homologous genes, but the relationship between CforOBP2 and CforOBP3 was closest among the three genes. In addition, real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR) assays demonstrated that the expression of CforOBP1 was higher in the antennae and legs of female and male insects, while CforOBP2 and CforOBP3 were mainly expressed in the antennae of male insects. The fluorescent competitive binding assay results indicated that CforOBP1-3 had strong binding affinities to sex pheromones and other tested ligands. Finally, the mRNA expression of CforOBP1-3 was successfully inhibited by RNA interference, and in vivo behavioral experiments showed that CforOBP1-3-deficient C. formicarius was partly anosmic and lost some of its ability to locate sex pheromones and host plant volatiles. Conclusion: These results suggested that CforOBP1 was shown to be involved in the process of weevils feeding and finding sweet potato, and CforOBP2-3 were mainly involved in the mating behavior of adult male weevils.

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