BACKGROUND Chemosensory proteins (CSPs) play important roles in chemical communication, but their precise physiological functions are still unclear. Cylas formicarius is the most serious pest attacking sweet potato around the world. At present, there is no effective way to control this pest. RESULTS Our results showed that CforCSP1, 5 and 6 genes were highly expressed in the antennae of both sexes of C. formicarius. In addition, results from a fluorescence competitive binding assay showed that the CforCSP1, 5 and 6 proteins had high binding affinities for 17 plant volatiles including eight host plant volatiles. This indicated that the three proteins may be involved in the detection of host plant volatiles. Furthermore, results from four‐arm olfactometer bioassays showed that there was a significant tendency for C. formicarius to be attracted to eucalyptol, β‐carotene, benzaldehyde, vanillin and phenethyl alcohol, while it was repelled by β‐ionone. Finally, the levels of expression of the three CforCSPs in C. formicarius were successfully inhibited by RNA interference (RNAi). Behavioral experiments showed that CforCSP1, 5 and 6‐deficient C. formicarius were partly anosmic to β‐cyclocitral, benzaldehyde, octyl aldehyde, and β‐ionone and exhibited a reduced ability to locate the host plant volatiles β‐carotene and vanillin. CONCLUSION Our data suggest that CforCSP1, 5 and 6 likely are involved in the chemical communication between C. formicarius and host plant volatiles, which may play pivotal roles in oviposition and feeding site preferences. More importantly, these results could provide information for the development of monitoring and push‐pull strategies for the control of C. formicarius. © 2021 Society of Chemical Industry.

Cylas formicarius is one of the most important pests of sweet potato worldwide, causing considerable ecological and economic damage. To improve the effect of comprehensive management and understanding of genetic mechanisms, the genetic functions of C. formicarius have been the subject of intensive study. Using Illumina and PacBio sequencing, we obtained a chromosome-level genome assembly of adult weevils from lines inbred for 15 generations. The high-quality assembly obtained had a size of 338.84 Mb, with contig and scaffold N50 values of 14.97 Mb and 34.23 Mb, respectively. In total, 157.51 Mb of repeat sequences and 11,907 protein-coding genes were predicted. A total of 337.06 Mb of genomic sequences was located on the 11 chromosomes, and the sequence length that could be used to determine the sequence and direction accounted for 99.03% of the total length of the associated chromosome. Comparative genomic analysis showed that C. formicarius was sister to Dendroctonus ponderosae, and C. formicarius diverged from D. ponderosae approximately 138.89 million years ago (Mya). Many important gene families that were expanded in the C. formicarius genome were involved in the chemosensory system. In an in-depth study, the binding assay results indicated that CforOBP4-6 had strong binding affinities for sex pheromones and other ligands. Overall, the high-quality C. formicarius genome provides a valuable resource to reveal the molecular ecological basis, genetic mechanism and evolutionary process of major agricultural pests, deepen the understanding of environmental adaptability and apparent plasticity, and provide new ideas and new technologies for ecologically sustainable pest control.