BACKGROUND AND PURPOSE Ionotropic GABA receptors (GABARs) in insects are the major inhibitory receptor and common targets in insecticides for pest control. Due to their high spatiotemporal resolution, the photopharmacological ligands have been developed in vertebrates, but only a few in insect yet. EXPERIMENTAL APPOACH In this study, two types of photoswitchable ligands (PCLs) by incorporating photoswitch azobenzene or dithienylethene into the antagonist, fipronil (FIP) generated the DTFIPs (DTFIP1 and DTFIP2) and ABFIPs (p-, m-, and o-ABFIP). Their photomodulation was measured by mosquito larval behavior, and the potential action mechanism of them was explored by two-electrode voltage clamp (TEVC) technique in vitro. KEY RESULTS DTFIP1 and m-ABFIP exhibited biggest difference of insecticidal activity between unirradiated and irradiated formation, and allowed for optical control of insect locomotors activity in swimming. The TEVC assay results indicted m-ABFIP and DTFIP1 enable optical control over the homomeric RDL-type GABAR, which is achieved by regulating the chloride channel of insect resistance to RDL-type GABAR by photoisomerization. CONSLUSION AND IMPLICATIONS Our results suggested that PCLs provide an alternative and precise tool for studying insect ionotropic GABARs and GABA-dependent behavior.

BACKGROUND AND PURPOSE Fluralaner is a novel isoxazoline insecticide with broad insect spectrum, and mainly acts on the insect GABA receptor with unique binding action, but its molecular interaction with insect GABA receptor has not been deeply identified on molecular level according to its selectivity between target (insect) and non-target (mammal) organisms. EXPERIMENTAL APPOACH The potential binding residues (I258T and L275I in TM1; V288I, M298N, G303N and A304S in TM2; G3’M/S, A327S, G336N, M338I and A339F in TM3; M473V and I477D in TM4) were predicted by SYBYL-X 2.1 software, and verified respectively by the site-directed mutagenesis and two-electrode voltage clamp (TEVC) technique. KEY RESULTS In the 11 predicted amino acids, the G3’M has the strongest ability to reduce the sensitivity of recombinant rice stem borer RDL homomeric channel to fluralaner. Compared with the wild-type (WT)-RDL, the G3’M mutation almost completely abolish the binding of fluralaner and avermectin, but not fipronil on recombinant homomeric channel of RDL from several orders of insects in vitro. In addition, the M3’G on rat Mus musculus β2 improved the sensitivity of recombinant heteromeric Mmα1β2-M3’G channel to fluralaner. Our results demonstrated that the glycine at the third position of TM3 determines the action of fluralaner and should be the binding site of fluralaner with RDL. CONCLUSION AND IMPLICATIONS These results would contribute to understanding the molecular interaction of fluralaner with RDL homomeric channel and may be used to guide future modification of isoxazolines to achieve highly selective control of pests with minimal effects on non-targeted organisms.