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Simple Summary: Ophraella communa Lesage is a specific biological control agent of the invasive weed Ambrosia artemisiifolia L. Understanding the molecular mechanism by which O. communa recognizes A. artemisiifolia will help improve its bio-control effect. Odorant-binding proteins (OBPs) play a vital role in insect olfactory perception. In this study, the sequence and expression characteristics of OcomOBP7 were analyzed. We obtained the pure protein of OcomOBP7 by prokaryotic expression and purification, and its binding characteristics were analyzed using a fluorescence competitive binding assay. Finally, we verified the function of OcomOBP7 in vivo using RNAi combined with an electroantennography (EAG) assay. The results showed that the binding ability of OcomOBP7 was broad-spectrum and was involved in the host plant localization of O. communa. The olfactory system plays a key role in various insect behaviors, and odorant-binding proteins participate in the first step of the olfactory process. Ophraella communa Lesage is an oligophagous phytophagous insect that is a specific biological control agent for Ambrosia artemisiifolia L. The leaf beetle must identify and locate A. artemisiifolia through olfaction; however, its odorant-binding protein (OBP) function has not yet been reported. In this study, OcomOBP7 was cloned, and its tissue expression profile and binding ability were analyzed using RT-qPCR and fluorescence binding assays, respectively. Sequence analysis demonstrated that OcomOBP7 belongs to the classical OBP family. The RT-qPCR results showed that OcomOBP7 was specifically expressed in the antennae, indicating that OcomOBP7 may be involved in chemical communication. The fluorescence binding assay showed that OcomOBP7 has an extensive binding ability to alkenes. The electroantennography experiments showed that O. communa antennal response to α-pinene and ocimene decreased significantly after interference because the two odors specifically bound to OcomOBP7. In summary, α-pinene and ocimene are odorant ligands corresponding to OcomOBP7, indicating that OcomOBP7 is involved in the chemical recognition of A. artemisiifolia. Our study lays a theoretical foundation for research into O. communa attractants, which is helpful for the better biological control of A. artemisiifolia by O. communa. [ABSTRACT FROM AUTHOR]

Simple Summary: Leaf beetle Ophraella communa is considered an effective biocontrol agent against the common ragweed Ambrosia artemisiifolia. However, there are no studies that assess the antennal sensilla and chemosensory proteins expression profiles of O. communa. In this study, the types and morphology of sensilla on the antennae were examined by scanning electron microscopy (SEM). The results showed that there are six types of sensilla (sensilla trichodea, sensilla chaetica, sensilla basiconica, sensilla styloconica, sensilla coeloconica, and Böhm bristles) distributed on the antennae. We also found that the expression levels of five chemosensory proteins in male and female antennae were higher than those in other tissues by quantitative real-time polymerase chain reaction. Our results lay the foundation for interpreting the olfactory functions of adult O. communa. Ophraella communa is an efficient biocontrol agent used against the invasive weed Ambrosia artemisiifolia. It is an herbivorous insect that feeds on specific plants; the olfactory functions of this insects plays an important role in their search for host plants. There are no reports on O. communa sensilla types, morphology, or chemosensory protein (CSP) genes. In this study, we observed the external structure and distribution of antennal sensilla in adult O. communa antennae by scanning electron microscopy; moreover, we cloned 11 CSPs (CSP1–CSP11) and elucidated their tissue-expression profiles using quantitative real-time polymerase chain reaction. Six types of sensilla were identified: sensilla trichodea (including two subtypes), sensilla chaetica, sensilla basiconica (including two subtypes), sensilla styloconica, sensilla coeloconica, and Böhm bristles. Both male and female antennae had all six types of sensilla, and no sexual dimorphism was noted in sensillar types or distribution. We also found that the expression levels of CSP2, CSP3, CSP4, CSP6, and CSP7 in male and female antennae were higher than those in other tissues, which suggests that these five CSPs may be related to olfactory function in O. communa. Ultimately, our results lay the foundation for interpreting the olfactory functions of adult O. communa. [ABSTRACT FROM AUTHOR]