Chemosensory protein 8 confers thiamethoxam resistance in Diaphorina citri

The Asian citrus psyllid (Diaphorina citri) serves as the primary vector of the bacterium Candidatus Liberibacter asiaticus (CLas), which is responsible for causing citrus Huanglongbing. Neonicotinoid pesticides such as thiamethoxam are frequently utilized for D. citri management worldwide, but their use have resulted in considerable development of insecticide resistance within D. citri populations. Recent reports have revealed that chemosensory proteins (CSPs)-mediated resistance represents a novel insecticide resistance mechanism in insects. In this finding, we found that exposure to thiamethoxam at different concentrations resulted in significant upregulation of transcriptional levels of DcitCSP8 by 2.41, 2.24 and 1.74-fold respectively. The expression profiles among different tissues showed that DcitCSP8 highly occurred in the legs and wings, and its expression being significantly induced by thiamethoxam with 2.40-fold increase specifically in the legs. The purified recombinant protein DcitCSP8, derived from Escherichia coli expression, present strong in vitro binding affinity (Ki = 4.74 μM) to thiamethoxam. Furthermore, the nanocarrier star polycation (SPc) was used to enhance silencing efficiency, resulting in a significant reduction of DcitCSP8 by 85.37% and 91.80% at 24 and 48 h post application of SPc + ds DcitCSP8. Knockdown of DcitCSP8 transcription significantly increased the susceptibility of D. citri adults in response to thiamethoxam, while reinjection of DcitCSP8 protein could restore the resistance in DcitCSP8-silenced individuals. Our findings highlight the association between DcitCSP8 and thiamethoxam resistance via high binding affinity that mitigates toxicity in D. citri, shedding light on CSP-mediated insecticide resistance and potentially contributing to the development of novel strategies targeting CSPs for managing resistance in D. citri.