Abstract
The insect chemosensory system plays an important role in many aspects of insects’ behaviors necessary for their survival. Despite the complexity of this system, an increasing number of studies have begun to understand its structure and function in different insect species. Nonetheless, the chemosensory system in the orange spiny whitefly Aleurocanthus spiniferus, as one of the most destructive insect pests of citrus in tropical Asia, has not been investigated yet. In this study, the sensillum types, morphologies and distributions of the male and female antennae of A. spiniferus were characterized using scanning electron microscopy. In both sexes, six different sensilla types were observed: trichodea sensilla, chaetica sensilla, microtrichia sensilla, coeloconic sensilla, basiconic sensilla, and finger-like sensilla. Moreover, we identified a total of 48 chemosensory genes, including 5 odorant-binding proteins (OBPs), 12 chemosensory proteins (CSPs), 3 sensory neuron membrane proteins (SNMPs), 6 odorant receptors (ORs), 8 gustatory receptors (GRs), and 14 ionotropic receptors (IRs) using transcriptome data analysis. Tissue-specific transcriptome analysis of these genes showed predominantly expression in the head (including antennae), whereas CSPs were broadly expressed in both head (including the antennae) and body tissue of adult A. spiniferus. In addition, the expression profiling of selected chemosensory genes at different developmental stages was examined by quantitative real time-PCR which was mapped to the transcriptome. We found that the majority of these genes were highly expressed in adults, while AspiORco, AspiGR1, AspiGR2, and AspiIR4 genes were only detected in the pupal stage. Together, this study provides a basis for future chemosensory and genomic studies in A. spiniferus and closely related species. Furthermore, this study not only provides insights for further research on the molecular mechanisms of A. spiniferus-plant interactions but also provides extensive potential targets for pest control.
Highlights
In insects, the chemosensory system is extremely critical for detecting and discriminating specific chemical signals in the environment necessary for their survival and reproduction (Hallem et al, 2006; Knolhoff and Heckel, 2014; Kang et al, 2020)
Chaetae sensilla presented on the scape and pedicel female A. spiniferus, while it was found on the pedicel and flagellum (Figure 1C and Table 1)
Based on the transcriptome results, we found that all of odorant-binding proteins (OBPs) and sensory neuron membrane proteins (SNMPs), and major of odorant receptors (ORs) and ionotropic receptors (IRs) were more considerably expressed in head than in bodies (Figure 9A)
Summary
The chemosensory system is extremely critical for detecting and discriminating specific chemical signals in the environment necessary for their survival and reproduction (Hallem et al, 2006; Knolhoff and Heckel, 2014; Kang et al, 2020). The insect peripheral chemosensory system comprises odorant receptors (ORs), gustatory receptors (GRs), ionotropic receptors (IRs), odorant binding proteins (OBPs), chemosensory proteins (CSPs), and sensory neuron membrane proteins (SNMPs) (Fleischer et al, 2018; Sun et al, 2020; Liu et al, 2021). These protein families have been identified from a large number of insect species, they still remain unidentified from several insect species. Odorant binding proteins are small soluble olfactory proteins which are thought to be responsible for transporting hydrophobic odor molecules through the sensillum lymph to odorant receptors, which are housed on the dendritic membrane of olfactory sensory neurons (Wang et al, 2020; Tian et al, 2021). ApisOBP3 and SaveOBP7 showed a high binding affinity with aphid alarm pheromone, (E)-betafarnesene, whereas, ApisOBP1, ApisOBP3, ApisOBP8, ApisOBP7, and SaveOBP7 showed a high binding affinity with plant volatiles (Qiao et al, 2009; Zhong et al, 2012)
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