The actions of neonicotinoid insecticides on nicotinic acetylcholine subunits Ldα1 and Ldα8 of Leptinotarsa decemlineata and assembled receptors

The insect nicotinic acetylcholine receptor (nAChR) is a pentameric channel protein and also a target for neonicotinoids. There are few reported studies on the molecular interactions of Leptinotarsa decemlineata nAChRs with neonicotinoids. In this study, we analyzed the response of acetylcholine and neonicotinoids (thiamethoxam [TMX], imidacloprid [IMI], and clothianidin [CLO]) on hybrid receptors constructed by nAChR alpha 1 and alpha 8 subunits of L. decemlineata (Ld alpha 1 and Ld alpha 8) co-expressed with rat beta 2 subunit (r beta 2) at different capped RNA (cRNA) ratios in Xenopus oocytes. In addition, we evaluated the expression changes of Ld alpha 1 and Ld alpha 8 after median lethal dose of TMX treatment for 72 h by quantitative polymerase chain reaction (qPCR). The resulting functional nAChRs Ld alpha 1/r beta 2 and Ld alpha 1/Ld alpha 8/r beta 2 showed different pharmacological characteristics. The neonicotinoids tested showed lower agonist affinity on Ld alpha 1/Ld alpha 8/r beta 2 compared to Ld alpha 1/r beta 2 at same ratios of subunit cRNAs. The sensitivities of neonicotinoids tested for Ld alpha 1/r beta 2 and Ld alpha 1/Ld alpha 8/r beta 2 at cRNA ratios of 5:1, 1:1 and 5:5:1, 1:1:1, respectively, were lower than those for nAChRs at ratios of 1:5 and 1:1:5, respectively, whereas the values of maximum response (I-max) varied. For Ld alpha 1/Ld alpha 8/r beta 2, a reduction of Lda8 cRNA resulted in increased sensitivity to IMI and decreased sensitivity to TMX. The expression of Ld alpha 1 and Ld alpha 8 significantly decreased in adults by 82.12% and 47.02%, respectively, while Ld alpha 8 was significantly upregulated by 2.44 times in 4th instar larvae after exposure to TMX. We infer that Ld alpha 1 and Ld alpha 8 together play an important role in the sensitivity of L. decemlineata to neonicotinoids.

Automated summary

This study analyzed the molecular interactions between Ld alpha 1 and Ld alpha 8 subunits of L. decemlineata nAChRs and neonicotinoids, and found that Ld alpha 1 and Ld alpha 8 play an important role in the sensitivity to neonicotinoids.