Toxicity of Flonicamid to Diaphorina citri (Hemiptera: Liviidae) and Its Identification and Expression of Kir Channel Genes

Flonicamid is a selective insecticide effective against piercing-sucking insects. Although its molecular target has been identified in other species, the specific effects and detailed mechanism of action in <i>Diaphorina citri</i> Kuwayama remain poorly understood. In this study, we determined that the LC₅₀ of flonicamid for <i>D. citri</i> adults was 16.6 mg AI L^-1 after 4 days of exposure. To explore the relevant mechanisms, the treatments with acetone and with 20 mg AI L^-1 flonicamid for 96 h were collected as samples for RNA-Seq. The analysis of the transcriptomes revealed 345 differentially expressed genes (DEGs) in <i>D. citri</i> adults subjected to different treatments. Among these DEGs, we focused on the inward-rectifying potassium (Kir) channel genes, which have been extensively studied as potential targets of flonicamid. Three Kir subunit genes (<i>Dckir1</i>, <i>Dckir2</i>, <i>Dckir3</i>) in <i>D. citri</i> were successfully cloned and identified. Furthermore, the expression profiles of these <i>DcKirs</i> were investigated using RT-qPCR and showed that their expression significantly increased after <i>D. citri</i> eclosion to adulthood, particularly for <i>DcKir3</i>. The <i>DcKirs</i> were predominantly expressed in gut tissues, with <i>DcKir1</i> and <i>DcKir2</i> exhibiting high expression levels in the hindgut and midgut, respectively, while <i>DcKir3</i> showing high expression in the midgut and Malpighian tubules. This study provides insights into the potential roles of Kir subunits in <i>D. citri</i> and enhances our understanding of the physiological effects of flonicamid in this pest.