Inhibitory Effect of Fluralaner on GABA Receptor Subunit RDL of Bactrocera dorsalis

<i>Bactrocera dorsalis</i> (Hendel) (Diptera: Tephritidae), a highly destructive pest, affects fruits and vegetables globally, leading to significant economic losses. As a homomeric subunit of γ-aminobutyric acid (GABA) receptors, RDL plays a crucial role in various physiological activities in insects. However, functional characterization of RDL from <i>B. dorsalis</i> has not yet been elucidated. Here, we cloned the <i>Rdl</i> gene from <i>B. dorsalis</i>, <i>BdRdl</i>, and investigated the expression pattern of <i>BdRdl</i>. The results showed that <i>BdRdl</i> was highly expressed in pupae and the heads of male and female adults. Also, we characterized the BdRDL in <i>Xenopus oocytes</i> through two-electrode voltage clamping. It turned out that the inward current of BdRDL induced by GABA was followed in a dose-dependent manner with a median effective concentration (EC₅₀) of 2.4 × 10^-4 M. Additionally, we determined the mode action of fluralaner, a new insecticide, on BdRDL in oocytes. We found that fluralaner significantly inhibited the currents induced by GABA, suggesting that fluralaner worked as an antagonist of BdRDL. Furthermore, we found that fluralaner exhibited a comparable insecticidal activity to avermectin against <i>B. dorsalis</i> adults. Lastly, the modeling and molecular docking predicted that fluralaner interacted with RDL via hydrogen bonds. Our results not only characterized the RDL of <i>B. dorsalis</i>, but also revealed that fluralaner works as an antagonist of BdRDL and could be used as an effective strategy for <i>B. dorsalis</i> control.