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BACKGROUND: Fluralaner, a novel pesticide that targets the -aminobutyric acid (GABA) receptor (GABAR) subunit of resistant to dieldrin (RDL), exhibits strong potential to be an insecticide to control agricultural insect pests. However, the risk and action of fluralaner to economic insects, e.g., honeybee Apis mellifera Linnaeus, remains unclear. RESULTS:In this study, both oral and contact toxicity of fluralaner to honeybee were found to be 0.13 g adult -1 . Abamectin, dieldrin, ethiprole, -endosulfan, fipronil and fluralaner strongly inhibited the GABA-induced current in A. mellifera RDL (AmRDL), expressed in Xenopus laevis oocytes, with median inhibitory concentration (IC 50 ) values of 7.99, 868.1, 27.10, 412.0, 11.21 and 13.59 nM, respectively. The binding free energy and electrophysiological response of AmRDL and insecticides were opposite. The correlation values between toxicity (to A. mellifera) and binding free energy/electrophysiological inhibition (to AmRDL) were at a moderate level. CONCLUSION:In conclusion, we report for the first time the notable risk of fluralaner to honeybee in vivo and compared the actions of GABAR-targeted insecticides on the AmRDL receptor.

BACKGROUND Two‐spotted spider mite (TSSM), Tetranychus urticae Koch is a serious agricultural pest and has developed high levels of resistance to many acaricides. Hence, screening new acaricides is important in the control of TSSM. Fluralaner, a novel isoxazoline, has high activity against agricultural and ectoparasitic pests; however, little information is available about its effects on agricultural mites. Lethal and sublethal effects of fluralaner towards TSSM eggs and female adults were therefore evaluated in this study. RESULTS Fluralaner exhibited higher activity towards TSSM female adults (LC50, 0.49 mg L−1) compared with commercial acaricides including fenpyroximate, pyridaben and hexythiazox, and also excellent activity towards eggs (LC50, 0.36 mg L−1). The results of a sublethal effect study showed a significant reduction in the duration and fecundity of female adults with increases in the tested concentrations. The net reproductive rate (R0) decreased to 67.34 ± 3.96 and 50.29 ± 3.40 offspring per individual in LC10 and LC30 treatments compared with control (108.31 ± 7.61 offspring per individual). The intrinsic rate of increase (r) and finite rate of increase (λ) in the controls (0.30 and 1.36 d−1) were significantly higher than in the LC30 treatment (0.25 and 1.29 d−1); whereas, they were almost identical to values for the LC10 treatment. No change in mean generation time (T) was observed at sublethal concentrations treatments. CONCLUSION Our results demonstrated that fluralaner has high acaricidal activity and could be considered a potential acaricide for TSSM management. © 2019 Society of Chemical Industry

To generate an efficient tool used in Xenopus oocyte expression for in situ investigation of channel receptor expression, distribution and function, the C‐terminus of the honeybee (Apis mellifera L.) resistant to dieldrin (RDL) subunit was fused with *FP, including monomeric red, enhanced yellow or enhanced green fluorescent protein (referred to as mRFP, EYFP and EGFP, respectively). In the present study, all fused *FP‐AmRDLs could be visualized using fluorescence and laser confocal microscopy in cRNA‐injected oocytes. Fluorescence was distributed isotropically in the cellular membrane. The potencies of the agonist γ‐aminobutyric acid (GABA), but not β‐alanine, and the test antagonists (fipronil, flufiprole, dieldrin, α‐endosulfan, bifenazate and avermectin B1a) in the *FP‐AmRDL receptor did not significantly differ from that of the untagged receptor with two‐electrode voltage clamp detection. The half maximal effective concentrations (EC50s) of GABA in AmRDL, EGFP‐AmRDL, EYFP‐AmRDL and mRFP‐AmRDL receptors were 11.98, 12.61, 18.92 and 22.11 μM, respectively, and those of β‐alanine were 651.6, 629.6, 1643.0 and 2146.0 μM, respectively. Inhibition percentages of test antagonists against *FP‐AmRDL and AmRDL were not significantly different from each other. Overall, the consistency in functional properties between *FP‐AmRDL and AmRDL receptors makes pGH19‐*FP a promising tool for further in situ investigation of GABA receptors.