Knockdown of the Nicotinic Acetylcholine Receptor β1 Subunit Decreases the Susceptibility to Five Neonicotinoid Insecticides in Whitefly (Bemisia tabaci)

Field-evolved resistance to nitenpyram is associated with fitness costs in whitefly

BACKGROUND

Elucidating fitness cost associated with field-evolved insect resistance to insecticide is of particular importance to current sustainable pest control. The global pest whitefly Bemisia tabaci has developed resistance to many members of neonicotinoids, but little is known about whitefly resistance to neonicotinoid nitenpyram and its associated fitness cost. Using insecticide bioassay and life-table approach, this study aims to investigate nitenpyram resistance status in field-collected whitefly populations, and to explore whether such resistance is accompanied by a fitness cost.

RESULTS

The bioassay results revealed that 14 of 29 whitefly populations displayed moderate to extremely high resistance to nitenpyram, demonstrating a widespread field-evolved resistance to nitenpyram. This field-evolved resistance in the whitefly has increased gradually over the past 3 years from 2021 to 2023. Further life-table study showed that two resistant whitefly populations exhibited longer developmental time, shorter lifespans of adult, and lower fecundity compared with the most susceptible population. The relative fitness cost of the two resistant populations was calculated as 0.69 and 0.56 by using net productive rate R0, which suggests that nitenpyram resistance comes with fitness cost in the whitefly, especially on reproduction.

CONCLUSION

Overall, these results represent field-evolved high resistance to nitenpyram in the whitefly. The existing fitness costs associated with nitenpyram resistance are helpful to propose a suitable strategy for sustainable control of whiteflies by rotation or mixture of insecticide with different modes of action. © 2024 Society of Chemical Industry.

Functional roles of nicotinic acetylcholine receptors in dinotefuran and flupyrimin toxicity and their sublethal effects on Sogatella furcifera (Hemiptera: Delphacidae)

Sogatella furcifera (Horváth) (Hemiptera: Delphacidae), a serious rice pest, has developed significant resistance to a wide range of pesticides. Neonicotinoid insecticides are currently the primary choice for controlling S. furcifera, yet their impact on the species remains poorly understood. In this study, we investigated the binding sites of a conventional insecticide (dinotefuran) and a novel insecticide (flupyrimin), and evaluated their sublethal effects on S. furcifera. Our results revealed that the LC50 of dinotefuran and flupyrimin were 2.51 mg/L and 2.80 mg/L in third-instar S. furcifera, respectively. RNA interference (RNAi) knockdown of S. furcifera nicotinic acetylcholine receptor (nAChR) alpha2 subunit (Sfα2) and S. furcifera nAChR beta1 subunit (Sfβ1) significantly reduced the susceptibility to dinotefuran by 18.7% and 16.8%, respectively, but had no effect on flupyrimin. Reproduction of the F0 and F1 generations was significantly inhibited by the LC25 of both dinotefuran and flupyrimin. In the dinotefuran treatment at LC25, the intrinsic growth rate (r) and finite growth rate (λ) were reduced to 0.15 and 0.16 days, respectively; the mean generation time (T) increased to 27.77 days, and the relative fitness was only 0.76 compared to the control. Additionally, the relative fitness (Rf) of the flupyrimin-treated group was reduced to 0.93 and 0.86 times that of the control group. The population dynamics of S. furcifera are significantly affected by both dinotefuran and flupyrimin, making these insecticides valuable tools for integrated pest management and the rational use of insecticides.

Dual mutations in the whitefly nicotinic acetylcholine receptor β1 subunit confer target-site resistance to multiple neonicotinoid insecticides

Neonicotinoid insecticides, which target insect nicotinic acetylcholine receptors (nAChRs), have been widely and intensively used to control the whitefly, Bemisia tabaci, a highly damaging, globally distributed, crop pest. This has inevitably led to the emergence of populations with resistance to neonicotinoids. However, to date, there have been no reports of target-site resistance involving mutation of B. tabaci nAChR genes. Here we characterize the nAChR subunit gene family of B. tabaci and identify dual mutations (A58T&R79E) in one of these genes (BTβ1) that confer resistance to multiple neonicotinoids. Transgenic D. melanogaster, where the native nAChR Dβ1 was replaced with BTβ1A58T&R79E, were significantly more resistant to neonicotinoids than flies where Dβ1 were replaced with the wildtype BTβ1 sequence, demonstrating the causal role of the mutations in resistance. The two mutations identified in this study replace two amino acids that are highly conserved in >200 insect species. Three-dimensional modelling suggests a molecular mechanism for this resistance, whereby A58T forms a hydrogen bond with the R79E side chain, which positions its negatively-charged carboxylate group to electrostatically repulse a neonicotinoid at the orthosteric site. Together these findings describe the first case of target-site resistance to neonicotinoids in B. tabaci and provide insight into the molecular determinants of neonicotinoid binding and selectivity.

The interaction of nicotinic acetylcholine receptor subunits Ldα3, Ldα8 and Ldβ1 with neonicotinoids in Colorado potato beetle, Leptinotarsa decemlineata

The Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say), is an extremely destructive notifiable quarantine pest. Over the last two decades, neonicotinoid insecticides, particularly thiamethoxam and imidacloprid, have been used to control it in Xinjiang, and local field populations have developed different levels of resistance in consequence. However, the contributions of nicotinic acetylcholine receptors (nAChRs) to neonicotinoid resistance are currently poorly understood in CPB. Previous studies have shown that nAChRα1, α3, α8 and β1 are major target subunits for neonicotinoids in some model and important agricultural insects including nAChRα1 subunit of L. decemlineata (Ldα1). In this study, the expression levels of Ldα3, Ldα8 and Ldβ1 following 72 h of treatments with median lethal doses of thiamethoxam and imidacloprid were compared using real-time quantitative PCR. These genes were then individually and simultaneously knocked down with Ldα1 by RNA interference (RNAi) using a double-stranded RNA (dsRNA) feeding method for six days to explore their roles in CPB susceptibility to imidacloprid and thiamethoxam. The results showed that the expressions of Ldα3, Ldα8 and Ldβ1 were significantly decreased by 36.99-74.89% after thiamethoxam and imidacloprid treatments, compared with the control. The significant downregulation of the target genes resulting from RNAi significantly reduced the mortality of adults exposed to thiamethoxam and imidacloprid by 34.53% -56.44% and 28.78%-43.93%, respectively. Furthermore, the adult survival rates were not affected by every dsRNA-feeding treatment, while the body weight of the test adults significantly deceased after four and six days of individual gene RNAi. This study showed that Ldα3, Ldα8 and Ldβ1 are down-regulated by thiamethoxam and imidacloprid and play important roles in the tolerance of CPB to neonicotinoids.