Overexpression of a cytochrome P450 and a UDP-glycosyltransferase is associated with imidacloprid resistance in the Colorado potato beetle, Leptinotarsa decemlineata

Role of CYP9E2 and a long non-coding RNA gene in resistance to a spinosad insecticide in the Colorado potato beetle, Leptinotarsa decemlineata

Spinosads are insecticides used to control insect pests, especially in organic farming where limited tools for pest management exist. However, resistance has developed to spinosads in economically important pests, including Colorado potato beetle (CPB), Leptinotarsa decemlineata. In this study, we used bioassays to determine spinosad sensitivity of two field populations of CPB, one from an organic farm exposed exclusively to spinosad and one from a conventional farm exposed to a variety of insecticides, and a reference insecticide naïve population. We found the field populations exhibited significant levels of resistance compared with the sensitive population. Then, we compared transcriptome profiles between the two field populations to identify genes associated primarily with spinosad resistance and found a cytochrome P450, CYP9E2, and a long non-coding RNA gene, lncRNA-2, were upregulated in the exclusively spinosad-exposed population. Knock-down of these two genes simultaneously in beetles of the spinosad-exposed population using RNA interference (RNAi) resulted in a significant increase in mortality when gene knock-down was followed by spinosad exposure, whereas single knock-downs of each gene produced smaller effects. In addition, knock-down of the lncRNA-2 gene individually resulted in significant reduction in CYP9E2 transcripts. Finally, in silico analysis using an RNA-RNA interaction tool revealed that CYP9E2 mRNA contains multiple binding sites for the lncRNA-2 transcript. Our results imply that CYP9E2 and lncRNA-2 jointly contribute to spinosad resistance in CPB, and lncRNA-2 is involved in regulation of CYP9E2 expression. These results provide evidence that metabolic resistance, driven by overexpression of CYP and lncRNA genes, contributes to spinosad resistance in CPB.

Six-year monitoring of pesticide resistance in the Colorado potato beetle (Leptinotarsa decemlineata Say) during a neonicotinoid restriction period

The Colorado potato beetle (CPB; Leptinotarsa decemlineata) is an important potato pest with known resistance to pyrethroids and organophosphates in Czechia. Decreased efficacy of neonicotinoids has been observed in last decade. After the restriction of using chlorpyrifos, thiacloprid and thiamethoxam by EU regulation, growers seek for information about the resistance of CPB to used insecticides and recommended antiresistant strategies. The development of CPB resistance to selected insecticides was evaluated in bioassays in 69 local populations from Czechia in 2017-2022 and in 2007-2022 in small plot experiments in Zabcice in South Moravia. The mortality in each subpopulation in the bioassays was evaluated at the field-recommended rates of insecticides to estimate the 50% and 90% lethal concentrations (LC50 and LC90, respectively). High levels of CPB resistance to lambda-cyhalothrin and chlorpyrifos were demonstrated throughout Czechia, without significant changes between years and regions. The average mortality after application of the field-recommended rate of lambda-cyhalothrin was influenced by temperature before larvae were sampled for bioassays and decreased with increasing temperature in June. Downwards trends in the LC90 values of chlorpyrifos and the average mortality after application of the field-recommended rate of acetamiprid in the bioassay were recorded over a 6-year period. The baseline LC50 value (with 95% confidence limit) of 0.04 mg/L of chlorantraniliprole was established for Czech populations of CPBs for the purpose of resistance monitoring in the next years. Widespread resistance to pyrethroids, organophosphates and neonicotinoids was demonstrated, and changes in anti-resistant strategies to control CPBs were discussed.

The impact of agrochemical pollutant mixtures on the selection of insecticide resistance in the malaria vector Anopheles gambiae: insights from experimental evolution and transcriptomics

BACKGROUND

There are several indications that pesticides used in agriculture contribute to the emergence and spread of resistance of mosquitoes to vector control insecticides. However, the impact of such an indirect selection pressure has rarely been quantified and the molecular mechanisms involved are still poorly characterized. In this context, experimental selection with different agrochemical mixtures was conducted in Anopheles gambiae. The multi-generational impact of agrochemicals on insecticide resistance was evaluated by phenotypic and molecular approaches.

METHODS

Mosquito larvae were selected for 30 generations with three different agrochemical mixtures containing (i) insecticides, (ii) non-insecticides compounds, and (iii) both insecticide and non-insecticide compounds. Every five generations, the resistance of adults to deltamethrin and bendiocarb was monitored using bioassays. The frequencies of the kdr (L995F) and ace1 (G119S) target-site mutations were monitored every 10 generations. RNAseq was performed on all lines at generation 30 in order to identify gene transcription level variations and polymorphisms associated with each selection regime.

RESULTS

Larval selection with agrochemical mixtures did not affect bendiocarb resistance and did not select for ace1 mutation. Contrastingly, an increased deltamethrin resistance was observed in the three selected lines. Such increased resistance was not majorly associated with the presence of kdr L995F mutation in selected lines. RNA-seq identified 63 candidate resistance genes over-transcribed in at least one selected line. These include genes coding for detoxification enzymes or cuticular proteins previously associated with insecticide resistance, and other genes potentially associated with chemical stress response. Combining an allele frequency filtering with a Bayesian FST-based genome scan allowed to identify genes under selection across multiple genomic loci, supporting a multigenic adaptive response to agrochemical mixtures.

CONCLUSION

This study supports the role of agrochemical contaminants as a significant larval selection pressure favouring insecticide resistance in malaria vectors. Such selection pressures likely impact kdr mutations and detoxification enzymes, but also more generalist mechanisms such as cuticle resistance, which could potentially lead to cross-tolerance to unrelated insecticide compounds. Such indirect effect of global landscape pollution on mosquito resistance to public health insecticides deserves further attention since it can affect the nature and dynamics of resistance alleles circulating in malaria vectors and impact the efficacy of control vector strategies.

Adult mosquitoes of the sibling species Anopheles gambiae and Anopheles coluzzii exhibit contrasting patterns of susceptibility to four neonicotinoid insecticides along an urban-to-rural gradient in Yaoundé, Cameroon

BACKGROUND

Neonicotinoids are potential alternatives for controlling pyrethroid-resistant mosquitoes, but their efficacy against malaria vector populations of sub-Saharan Africa has yet to be investigated. The aim of the present study was to test the efficacy of four neonicotinoids against adult populations of the sibling species Anopheles gambiae and Anopheles coluzzii sampled along an urban-to-rural gradient.

METHODS

The lethal toxicity of three active ingredients for adults of two susceptible Anopheles strains was assessed using concentration-response assays, and their discriminating concentrations were calculated. The discriminating concentrations were then used to test the susceptibility of An. gambiae and An. coluzzii mosquitoes collected from urban, suburban and rural areas of Yaoundé, Cameroon, to acetamiprid, imidacloprid, clothianidin and thiamethoxam.

RESULTS

Lethal concentrations of neonicotinoids were relatively high suggesting that this class of insecticides has low toxicity against Anopheles mosquitoes. Reduced susceptibility to the four neonicotinoids tested was detected in An. gambiae populations collected from rural and suburban areas. By contrast, adults of An. coluzzii that occurred in urbanized settings were susceptible to neonicotinoids except acetamiprid for which 80% mortality was obtained within 72 h of insecticide exposure. The cytochrome inhibitor, piperonyl butoxide (PBO), significantly enhanced the activity of clothianidin and acetamiprid against An. gambiae mosquitoes.

CONCLUSIONS

These findings corroborate susceptibility profiles observed in larvae and highlight a significant variation in tolerance to neonicotinoids between An. gambiae and An. coluzzii populations from Yaoundé. Further studies are needed to disentangle the role of exposure to agricultural pesticides and of cross-resistance mechanisms in the development of neonicotinoid resistance in some Anopheles species.

Characterization and functional analysis of UDP-glycosyltransferases reveal their contribution to phytochemical flavone tolerance in Spodoptera litura

Efficient detoxification is the key factor for phytophagous insect to adapt to phytochemicals. However, the role of uridine diphosphate (UDP)-glycosyltransferases (UGTs) in insect anti-defense to phytochemical flavone is largely unknown. In this study, 52 UGT genes were identified in Spodoptera litura and they presented evident gene duplication. UGT played a crucial part in larval tolerance to flavone because the enzyme activity and transcriptional level of 77 % UGT members were remarkably upregulated by flavone administration and suppression of UGT enzyme activity and gene expressions significantly increased larval susceptibility to flavone. Bacteria coexpressing UGTs had high survival rates under flavone treatment and flavone was dramatically metabolized by UGT recombinant cells, which indicated the involvement of UGTs in flavone detoxification. What's more, ecdysone pathway was activated by flavone. Topical application of 20-hydroxyecdysone highly upregulated UGT enzyme activity and more than half of UGT expressions. The effects were opposite when ecdysone receptor (EcR) and ultraspiracle (USP)-mediated ecdysone signaling pathway was inhibited. Furtherly, promoter reporter assays of 5 UGT genes showed that their transcription activities were notably increased by cotransfection with EcR and USP. In consequence, this study suggested that UGTs were involved in flavone detoxification and their transcriptional expressions were regulated by ecdysone pathway.

Gene expression plasticity facilitates different host feeding in Ips sexdentatus (Coleoptera: Curculionidae: Scolytinae)

Host shift is ecologically advantageous and a crucial driver for herbivore insect speciation. Insects on the non-native host obtain enemy-free space and confront reduced competition, but they must adapt to survive. Such signatures of adaptations can often be detected at the gene expression level. It is astonishing how bark beetles cope with distinct chemical environments while feeding on various conifers. Hence, we aim to disentangle the six-toothed bark beetle (Ips sexdentatus) response against two different conifer defences upon host shift (Scots pine to Norway spruce). We conducted bioassay and metabolomic analysis followed by RNA-seq experiments to comprehend the beetle's ability to surpass two different terpene-based conifer defence systems. Beetle growth rate and fecundity were increased when reared exclusively on spruce logs (alternative host) compared to pine logs (native host). Comparative gene expression analysis identified differentially expressed genes (DEGs) related to digestion, detoxification, transporter activity, growth, signalling, and stress response in the spruce-feeding beetle gut. Transporter genes were highly abundant during spruce feeding, suggesting they could play a role in pumping a wide variety of endogenous and xenobiotic compounds or allelochemicals out. Trehalose transporter (TRET) is also up-regulated in the spruce-fed beetle gut to maintain homeostasis and stress tolerance. RT-qPCR and enzymatic assays further corroborated some of our findings. Taken together, the transcriptional plasticity of key physiological genes plays a crucial role after the host shift and provides vital clues for the adaptive potential of bark beetles on different conifer hosts.

Silencing the rhythm gene AgCLK-1 reduced feeding of Aphis gossypii

The cotton aphid Aphis gossypii Glover is an important cotton pest, and means of controlling this insect is a primary research focus. Although biological rhythm is an important mechanism that regulates numerous insect processes and activities, its role in cotton aphid has not been elucidated. In the present study, four highly-expressed circadian rhythm genes were selected from the cotton aphid genome database and their physicochemical properties and protein structures were analyzed. These genes were in the Takeout, Timeless, and Timeless interacting-related families, and the corresponding proteins contained highly-conserved Swis and TIMELESS domains. Gene expression analysis at multiple developmental stages revealed differing expression patterns between the four genes. AgCLK-1 had the highest relative expression of the four, especially during the nymph period. Silencing AgCLK-1 caused a significant refusal of the cotton aphids to feed at 1, 3, and 5 d of treatment. These results demonstrated that AgCLK-1 played a key role in regulating the feeding behavior of cotton aphid. This new functional understanding provides novel insights into cotton aphid biology and suggests new targeting strategies for agricultural pest control.

The mechanisms of metabolic resistance to pyrethroids and neonicotinoids fade away without selection pressure in the tarnished plant bug Lygus lineolaris

BACKGROUND

Heavy selection pressure prompted the development of resistance in a serious cotton pest tarnished plant bug (TPB), Lygus Lineolaris in the mid-southern United States. Conversely, a laboratory resistant TPB strain lost its resistance to five pyrethroids and two neonicotinoids after 36 generations without exposure to any insecticide. It is worthwhile to examine why the resistance diminished in this population and determine whether the resistance fade away has practical value for insecticide resistance management in TPB populations.

RESULTS

A field-collected resistant TPB population in July (Field-R1) exhibited 3.90-14.37-fold resistance to five pyrethroids and two neonicotinoids, while another field-collected TPB population in April (Field-R2) showed much lower levels of resistance (0.84-3.78-fold) due to the absence of selection pressure. Interestingly, after 36 generations without exposure to insecticide, the resistance levels in the same population [laboratory resistant strain (Lab-R)] significantly decreased to 0.80-2.09-fold. The use of detoxification enzyme inhibitors had synergistic effects on permethrin, bifenthrin and imidacloprid in resistant populations of Lygus lineolaris. The synergism was more pronounced in Field-R2 than laboratory susceptible (Lab-S) and Lab-R TPB population. Moreover, esterase, glutathione S-transferase (GST), and cytochrome P450-monooxygenases (P450) enzyme activities increased significantly by approximately 1.92-, 1.43-, and 1.44-fold in Field-R1, respectively, and 1.38-fold increased P450 enzyme activities in Field-R2 TPB population, compared to the Lab-S TPB. In contrast, the three enzyme activities in the Lab-R strain were not significantly elevated anymore relative to the Lab-S population. Additionally, Field-R1 TPB showed elevated expression levels of certain esterase, GST and P450 genes, respectively, while Field-R2 TPB overexpressed only P450 genes. The elevation of these gene expression levels in Lab-R expectedly diminished to levels close to those of the Lab-S TPB populations.

CONCLUSION

Our results indicated that the major mechanism of resistance in TPB populations was metabolic detoxification, and the resistance development was likely conferred by increased gene expressions of esterase, GST, and P450 genes, the fadeaway of the resistance may be caused by reversing the overexpression of esterase, GST and P450. Without pesticide selection, resistant gene (esterase, GST, P450s) frequencies declined, and detoxification enzyme activities returned to Lab-S level, which resulted in the recovery of the susceptibility in the resistant TPB populations. Therefore, pest's self-purging of insecticide resistance becomes strategically desirable for managing resistance in pest populations. Published 2023. This article is a U.S. Government work and is in the public domain in the USA.

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.

Chlorpyrifos and chlorfenapyr resistance in Spodoptera frugiperda (Lepidoptera: Noctuidae) relies on UDP-glucuronosyltransferases

Fall armyworm, Spodoptera frugiperda (J. E. Smith), has become an important agricultural pest worldwide. S. frugiperda is mainly controlled by the chemical insecticides, whereas the frequent application of insecticides would result in the resistance development. Insect uridine diphosphate-glucuronosyltransferases (UGTs), as phase II metabolism enzymes, play vital roles in the breakdown of endobiotic and xenobiotics. In this study, 42 UGT genes were identified by RNA-seq, including 29 UGT genes were elevated compared to the susceptible population, and the transcript levels of 3 UGTs (UGT40F20, UGT40R18, and UGT40D17) were increased by more than 2.0-fold in the field populations. Expression pattern analysis revealed that S. frugiperda UGT40F20, UGT40R18, and UGT40D17 were increased by 6.34-, 4.26-, and 8.28-fold, compared the susceptible populations, respectively. The expression of UGT40D17, UGT40F20, and UGT40R18 was affected after exposure to phenobarbital, chlorpyrifos, chlorfenapyr, sulfinpyrazone, and 5-nitrouracil. The induced expression of UGT genes may have improved UGT enzymatic activity, while the inhibition of UGTs genes expression may decreased UGT enzymatic activity. Sulfinpyrazone, and 5-nitrouracil, significantly increased the toxicity of chlorpyrifos and chlorfenapyr, as well as phenobarbital significantly reduced the toxicity of chlorpyrifos and chlorfenapyr against the susceptible populations and field populations of S. frugiperda. The suppression of UGTs (UGT40D17, UGT40F20, and UGT40R18) significantly increased the insensitivity of the field populations to chlorpyrifos and chlorfenapyr. These findings strongly supported our viewpoint that UGTs may play a critical role in insecticide detoxification. This study provides a scientific basis for the management of S. frugiperda.

Cytochrome P450 CYP6DB3 was involved in thiamethoxam and imidacloprid resistance in Bemisia tabaci Q (Hemiptera: Aleyrodidae)

High level resistance for a variety of insecticides has emerged in Bemisia tabaci, a globally notorious insect. Neonicotinoid insecticides have been applied widely to control B. tabaci. Whether a differentially expressed gene CYP6DB3 discovered from transcriptome data of B. tabaci is involved in the resistance to neonicotinoid insecticides remains unclear. In the study, CYP6DB3 expression was significantly up-regulated in both thiamethoxam- and imidacloprid-resistant strains relative to the susceptive strains. We also found that CYP6DB3 expression was up-regulated after B. tabaci adults were exposed to thiamethoxam and imidacloprid. Moreover, knocking down CYP6DB3 expression via feeding corresponding dsRNA significantly reduced CYP6DB3 mRNA levels by 34.1%. Silencing CYP6DB3 expression increased the sensitivity of B. tabaci Q adults against both thiamethoxam and imidacloprid. Overexpression of CYP6DB3 gene reduced the toxicity of imidacloprid and thiamethoxam to transgenic D. melanogaster. In addition, metabolic studies showed that CYP6DB3 can metabolize 24.41% imidacloprid in vitro. Collectively, these results strongly support that CYP6DB3 plays an important role in the resistance of B. tabaci Q to imidacloprid and thiamethoxam. This work will facilitate a deeper insight into the part of cytochrome P450s in the evolution of insecticide resistance and provide a theoretical basis for the development of new integrated pest resistance management.

UGT2B13 and UGT2C1 are involved in lambda-cyhalothrin resistance in Rhopalosiphum padi

Uridine diphosphate-glucuronosyltransferases (UGTs) are major multifunctional detoxification phase II enzymes involved in the metabolic detoxification of xenobiotics. However, their roles in insecticides resistance are still unclear. In this study, we identified two UGTs genes (UGT2B13 and UGT2C1) in Rhopalosiphum padi, a serious insect pest of wheat worldwide. Bioassays results showed that the resistance ratio of R. padi resistance strain (LC-R) to lambda-cyhalothrin (LC) was 2963.8 fold. The roles of UGT2B13 and UGT2C1 in lambda-cyhalothrin resistance were evaluated. Results indicated that the UGTs contents were significantly increased in the LC resistant strain of R. padi. UGT2B13 and UGT2C1 were significantly overexpressed in the LC-R strain. Transcription levels of UGT2B13 and UGT2C1 were relatively higher in the gut of LC-R strain. RNA interference (RNAi) of UGT2B13 or UGT2C1 significantly decreased the UGTs contents of the LC-R aphids and increased mortality of R. padi exposure to the LC50 concentration of LC. This study provides a new view that UGTs are involved in LC resistance of R. padi. The findings will promote further work to detailed the functions of UGTs in the metabolism resistance of insects to insecticides.

Leveraging RNA Interference to Impact Insecticide Resistance in the Colorado Potato Beetle, Leptinotarsa decemlineata

The Colorado potato beetle, Leptinotarsa decemlineata Say, is a potato pest that can cause important economic losses to the potato industry worldwide. Diverse strategies have been deployed to target this insect such as biological control, crop rotation, and a variety of insecticides. Regarding the latter, this pest has demonstrated impressive abilities to develop resistance against the compounds used to regulate its spread. Substantial work has been conducted to better characterize the molecular signatures underlying this resistance, with the overarching objective of leveraging this information for the development of novel approaches, including RNAi-based techniques, to limit the damage associated with this insect. This review first describes the various strategies utilized to control L. decemlineata and highlights different examples of reported cases of resistances against insecticides for this insect. The molecular leads identified as potential players modulating insecticide resistance as well as the growing interest towards the use of RNAi aimed at these leads as part of novel means to control the impact of L. decemlineata are described subsequently. Finally, select advantages and limitations of RNAi are addressed to better assess the potential of this technology in the broader context of insecticide resistance for pest management.

The neonicotinoid insecticide imidacloprid has unexpected effects on the growth and development of soil amoebae

Neonicotinoid pesticides are the most widely used insecticides worldwide and have become a global environmental issue. Previous studies have shown that imidacloprid, the most used neonicotinoid, can negatively affect a wide range of organisms, including non-target insects, fish, invertebrates, and mammals. Imidacloprid can also accumulate and persist in soils, posing threats to the terrestrial ecosystem. However, we know little about one ecologically important group of organisms, the single-celled soil protists. In this study, we used a soil amoeba, Dictyostelium discoideum, to test whether and how imidacloprid affects the growth and development of soil amoebae. We provide the first empirical evidence that environmental concentrations of imidacloprid negatively impact the fitness and development of soil amoebae. In addition, the adverse effects did not show a dose-response relationship with increased imidacloprid concentrations, where no significant difference was observed among the treatment groups. Further transcriptome analyses showed that imidacloprid affected amoeba's key DEGs related to phagocytosis, cell division, morphogenesis, and cytochrome P450. Moreover, soil amoebae show both conserved and novel transcriptional responses to imidacloprid. In conclusion, this study has expanded the non-target list of imidacloprid from animals and plants to single-celled protists, and we believe the impact of neonicotinoid pesticides on the microbiome is significantly underestimated and deserves more studies.

RNAi-mediated silencing of AccCYP6k1 revealed its role in the metabolic detoxification of Apis cerana cerana

Insect cytochrome P450 monooxygenases (P450s or CYPs) perform important functions in the metabolic detoxification of both endogenous and exogenous substrates. However, the mechanism of action of the P450 genes in bees is unclear. In this study, we investigated the effects of AccCYP6k1 on the metabolism and detoxification of Apis cerana cerana. Spatiotemporal expression profiling revealed that the expression of AccCYP6k1 was the highest in foragers (A15) and was mainly expressed in the leg, midgut and head. RT-qPCR results showed that AccCYP6k1 exhibited different expression patterns following exposure to xenobiotics. In addition, silencing AccCYP6k1 increased the pesticides sensitivity and affected the detoxification system and antioxidant process of A. cerana cerana. In brief, the induced expression of AccCYP6k1 is related to the resistance of A. cerana cerana, while knockdown AccCYP6k1 affect the pesticides resistance and metabolic detoxification system of A. cerana cerana. These findings not only support the theoretical basis of metabolic detoxification in bees but also provide a better understanding of P450-mediated resistance to pesticides in insects.

Cytochrome P450 gene CYP6BQ8 mediates terpinen-4-ol susceptibility in the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

Cytochrome P450 proteins (CYPs) in insects can encode various detoxification enzymes and catabolize heterologous substances, conferring tolerance to insecticides. This study describes the identification of a P450 gene (CYP6BQ8) from Tribolium castaneum (Herbst) and investigation of its spatiotemporal expression profile and potential role in the detoxification of terpinen-4-ol, a component of plant essential oils. The developmental expression profile showed that TcCYP6BQ8 expression was relatively higher in early- and late-larval stages of T. castaneum compared with other developmental stages. Tissue expression profiles showed that TcCYP6BQ8 was mainly expressed in the head and integument of both larvae and adults. The expression profiling of TcCYP6BQ8 in developmental stages and tissues is closely related to the detoxification of heterologous substances. TcCYP6BQ8 expression was significantly induced after exposure to terpinen-4-ol, and RNA interference against TcCYP6BQ8 increased terpinen-4-ol-induced larval mortality from 47.78 to 66.67%. This indicates that TcCYP6BQ8 may be involved in T. castaneum's metabolism of terpinen-4-ol. Correlation investigation between the CYP6BQ8 gene and terpinen-4-ol resistance in T. castaneum revealed that the TcCYP6BQ8 gene was one of the factors behind T. castaneum's resistance to terpinen-4-ol. This discovery may provide a new theoretical foundation for future regulation of T. castaneum.

Spinosad-associated modulation of select cytochrome P450s and glutathione S-transferases in the Colorado potato beetle, Leptinotarsa decemlineata

The Colorado potato beetle (Leptinotarsa decemlineata (Say)) is an insect pest that threatens potato crops. Multiple options exist to limit the impact of this pest even though insecticides remain a primary option for its control. Insecticide resistance has been reported in Colorado potato beetles and a better understanding of the molecular players underlying such process is of utmost importance to optimize the tools used to mitigate the impact of this insect. Resistance against the insecticide spinosad has been reported in this insect and this work thus aims at exploring the expression of targets previously associated with insecticide response in Colorado potato beetles exposed to this compound. Amplification and quantification of transcripts coding for cytochrome P450s and glutathione S-transferases were conducted via qRT-PCR in insects treated with varying doses of spinosad and for different time duration. This approach notably revealed differential expression of CYP6a23 and CYP12a5 in insects exposed to low doses of spinosad for 4 h as well as modulation of CYP6a13, CYP6d4, GST, GST1, and GST1-Like in insects treated with high doses of spinosad for the same duration. RNAi-based targeting of CYP4g15 and CYP6a23 was associated with marked reduction of transcript expression 7 days following dsRNA injection and reduction of the former had a marked impact on insect viability. In general, results presented here provide novel information regarding the expression of transcripts relevant to spinosad response in Colorado potato beetles and reveal a novel target to consider in the development of RNAi-based strategies aimed at this potato pest.

The role of structural variants in pest adaptation and genome evolution of the Colorado potato beetle, Leptinotarsa decemlineata (Say)

Structural variation has been associated with genetic diversity and adaptation. Despite these observations, it is not clear what their relative importance is for evolution, especially in rapidly adapting species. Here, we examine the significance of structural polymorphisms in pesticide resistance evolution of the agricultural super-pest, the Colorado potato beetle, Leptinotarsa decemlineata. By employing a parent offspring trio sequencing procedure, we develop highly contiguous reference genomes to characterize structural variation. These updated assemblies represent >100-fold improvement of contiguity and include derived pest and ancestral nonpest individuals. We identify >200,000 structural variations, which appear to be nonrandomly distributed across the genome as they co-occur with transposable elements and genes. Structural variations intersect with exons in a large proportion of gene annotations (~20%) that are associated with insecticide resistance (including cytochrome P450s), development, and transcription. To understand the role structural variations play in adaptation, we measure their allele frequencies among an additional 57 individuals using whole genome resequencing data, which represents pest and nonpest populations of North America. Incorporating multiple independent tests to detect the signature of natural selection using SNP data, we identify 14 genes that are probably under positive selection, include structural variations, and SNPs of elevated frequency within the pest lineages. Among these, three are associated with insecticide resistance based on previous research. One of these genes, CYP4g15, is coinduced during insecticide exposure with glycosyltransferase-13, which is a duplicated gene enclosed within a structural variant adjacent to the CYP4g15 genic region. These results demonstrate the significance of structural variations as a genomic feature to describe species history, genetic diversity, and adaptation.

Contribution of UDP-glycosyltransferases to chlorpyrifos resistance in Nilaparvata lugens

As a multigene superfamily of Phase II detoxification enzymes, uridine diphosphate (UDP)-glycosyltransferases (UGTs) play important roles in the metabolism of xenobiotics including insecticides. In this study, 5-nitrouracil, an inhibitor of UGT enzyme activity, effectively increased the toxicity of chlorpyrifos to the chlorpyrifos-resistant strain of Nilaparvata lugens, one of the most resistant rice pests. The enzyme content of UGT in the resistant strain was significantly higher than that in the susceptible strain. Among 20 identified UGT genes, UGT386H2, UGT386J2, UGT386N2 and UGT386P1 were found significantly overexpressed in the resistant strain and can be effectively induced by chlorpyrifos. These four UGT genes were most highly expressed in the midgut and/or fat body, two main insect detoxification tissues. Amino acid sequence alignments revealed that these four UGTs contained a variable N-terminal substrate-binding domain and a conserved C-terminal sugar donor-binding domain. Furthermore, homology modeling and molecular docking analyses showed that these UGTs could stably bind to chlorpyrifos and chlorpyrifos oxon, with the binding free energies from -19.4 to -110.62 kcal mol^-1. Knockdown of UGT386H2 or UGT386P1 by RNA interference dramatically increased the susceptibility of the resistant strain to chlorpyrifos. These findings suggest that overexpression of these two UGT genes contributes to chlorpyrifos resistance in N. lugens.

Biochemical and Molecular Analysis of Field Resistance to Spirodiclofen in Panonychus citri (McGregor)

Spirodiclofen is one of the most widely used acaricides in China. The citrus red mite, Panonychus citri (McGregor) (Acari: Tetranychidae), is one of the most destructive citrus pests worldwide and has developed a high resistance to spirodiclofen. However, the molecular mechanism of spirodiclofen resistance in P. citri is still unknown. In this study, we identified a field spirodiclofen-resistant strain (DL-SC) that showed 712-fold resistance to spirodiclofen by egg bioassay compared to the susceptible strain. Target-site resistance was not detected as non-synonymous mutations were not found by amplification and sequencing of the ACCase gene of resistant and susceptible strains; in addition, the mRNA expression levels of ACCase were similar in both resistant and susceptible strains. The activity of detoxifying enzymes P450s and CCEs in the resistant strain was significantly higher than in the susceptible strain. The transcriptome expression data showed 19 xenobiotic metabolisms genes that were upregulated. Stage-specific expression profiling revealed that the most prominent upregulated gene, CYP385C10, in transcriptome data was significantly higher in resistant strains in all stages. Furthermore, functional analysis by RNAi indicated that the mortality caused by spirodiclofen was significantly increased by silencing the P450 gene CYP385C10. The current results suggest that overexpression of the P450 gene, CYP385C10, may be involved in spirodiclofen resistance in P. citri.

Genome-wide and expression-profiling analyses of the cytochrome P450 genes in Tenebrionidea

Cytochrome P450 monooxygenases (CYPs) are present in almost all areas of the tree of life. As one of the largest and most diverse superfamilies of multifunctional enzymes, they play important roles in the metabolism of xenobiotics and biosynthesis of endogenous compounds, shaping the success of insects. In this study, the CYPome (an omics term for all the CYP genes in a genome) diversification was examined in the four Tenebrionidea species through genome-wide analysis. A total of 483 CYP genes were identified, of which 103, 157, 122, and 101 were respectively deciphered from the genomes of Tebebrio molitor, Asbolus verucosus, Hycleus cichorii and Hycleus phaleratus. These CYPs were classified into four major clans (mitochondrial, CYP2, CYP3, and CYP4), and clans CYP3 and CYP4 are most diverse. Phylogenetic analysis showed that most CYPs of these Tenebrionidea beetles from each clan had a very close 1:1 orthology to each other, suggesting that they originate closely and have evolutionally conserved function. Expression analysis at different developmental stages and in various tissues showed the life stage-, gut-, salivary gland-, fat body-, Malpighian tubule-, antennae-, ovary- and testis-specific expression patterns of T. molitor CYP genes, implying their various potential roles in development, detoxification, immune response, digestion, olfaction, and reproduction. Our studies provide a platform to understand the evolution of Tenebrionidea CYP gene superfamily, and a basis for further functional investigation of the T. molitor CYPs involved in various biological processes.

Silencing of Cytochrome P450 Gene AgoCYP6CY19 Reduces the Tolerance to Host Plant in Cotton- and Cucumber-Specialized Aphids, Aphis gossypii

Cytochrome P450 monooxygenases play important roles in insect metabolism and detoxification of toxic plant substances. However, the function of CYP6 family genes in degrading plant toxicants in Aphis gossypii has yet to be elucidated. In this study, AgoCYP6CY19, an A. gossypii CYP gene that differentially expresses in cotton- and cucumber-specialized aphids, was characterized. Spatiotemporal expression profiling revealed that AgoCYP6CY19 expression was higher in second instar nymph and 7 day old adults than in other developmental stages. Although the expression of AgoCYP6CY19 was significantly higher in cotton-specialized aphids, AgoCYP6CY19 silencing significantly increased larval and adult mortality and reduced total fecundity in both cotton- and cucumber-specialized aphids. What is more, the expression of AgoCYP6CY19 was significantly induced after the cotton-specialized and cucumber-specialized aphids fed on epigallocatechin gallate (EGCG) and cucurbitacin B (CucB), respectively. These findings demonstrate that AgoCYP6CY19 plays a pivotal role in toxic plant substance detoxification and metabolism. Functional knowledge about plant toxicity tolerance genes in this major pest can provide new insights into insect detoxification of toxic plant substances and insecticides and offer new targets for agricultural pest control strategies.

Repeated exposure of fluazinam fungicides affects gene expression profiles yet carries no costs on a nontarget pest

Fungicides are used to control pathogenic fungi of crop species, but they have also been shown to alter behavioral, life history and fitness related traits of nontarget insects. Here, we tested the fungicide effects on feeding behavior, survival and physiology of the nontarget pest insect, the Colorado potato beetle (CPB) (Leptinotarsa decemlineata). Feeding behavior was studied by a choice test of adult beetles, which were allowed to choose between a control and a fungicide (fluazinam) treated potato leaf. Larval survival was recorded after 24 and 72 h exposure to control and fungicide-treated leaves with 2 different concentrations. The adults did not show fungicide avoidance behavior. Similarly, survival of the larvae was not affected by the exposure to fungicides. Finally, to understand the effects of fungicides at the physiological level (gene expression), we tested whether the larval exposure to fungicide alter the expression of 5 metabolic pathway and stress associated genes. Highest concentration and 72-h exposure caused upregulation of 1 cytochrome P450 (CYP9Z14v2) and 1 insecticide resistance gene (Ldace1), whereas metabolic detoxification gene (Ugt1) was downregulated. At 24-h exposure, highest concentration caused downregulation of another common detoxification gene (Gs), while both exposure times to lowest concentration caused upregulation of the Hsp70 stress tolerance gene. Despite these overall effects, there was a considerable amount of variation among different families in the gene expression levels. Even though the behavioral effects of the fungicide treatments were minor, the expression level differences of the studied genes indicate changes on the metabolic detoxifications and stress-related pathways.

Activation of the ROS/CncC Signaling Pathway Regulates Cytochrome P450 CYP4BQ1 Responsible for (+)-α-Pinene Tolerance in Dendroctonus armandi

Bark beetles mainly rely on detoxification enzymes to resist the host tree's defense against oleoresin terpenes. Cytochrome P450 enzymes (CYPs) play an important role in the detoxification of plant allelochemicals and pesticides in insect. One P450 gene (DaCYP4BQ1) is associated with the response of (+)-α-pinene in Dendroctonus armandi. However, the regulatory mechanism of this P450 gene response to (+)-α-pinene is still unknown. In this study, spatiotemporal expression profiling indicated that CYP4BQ1 was highly expressed in adult and larval stages of D. armandi, and it was predominantly expressed in fat body, midgut, and Malpighian tubules of adults. Moreover, the expression of CYP4BQ1 significantly increased after exposure to (+)-α-pinene, and depletion of it decreased the tolerance of adults to (+)-α-pinene. In addition, (+)-α-pinene treatment induced the expression of the transcription factors cap 'n' collar isoform C (CncC) and its binding factor muscle aponeurosis fibromatosis (Maf), elevated the level of hydrogen peroxide (H₂O₂), and increased the activities of antioxidant enzymes. Silencing CncC suppressed CYP4BQ1 expression and enhanced the susceptibility of beetles to (+)-α-pinene. Similarly, application of the reactive oxygen species (ROS) scavenger N-acetylcysteine reduced the production and accumulation of H₂O₂, suppressed the expression of CncC, Maf, and CYP4BQ1 and led to decreased tolerance of adults to (+)-α-pinene. In contrast, ingestion of the CncC agonist curcumin elevated CYP4BQ1 expression and enhanced (+)-α-pinene tolerance. The results demonstrate that, in D. armandi, (+)-α-pinene induces CYP4BQ1 via activation of the ROS/CncC signaling pathway.

Insights into the Use of Eco-Friendly Synergists in Resistance Management of Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)

The Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say), is the most notorious insect pest of potato globally. Injudicious use of insecticides for management of this pest has resulted in resistance to all major groups of insecticides along with many human, animal health, and environmental concerns. Additionally, the input cost of insecticide development/discovery is markedly increasing because each year thousands of chemicals are produced and tested for their insecticidal properties, requiring billions of dollars. For the management of resistance in insect pests, synergists can play a pivotal role by reducing the application dose of most insecticides. These eco-friendly synergists can be classified into two types: plant-based synergists and RNAi-based synergists. The use of plant-based and RNAi-based synergists in resistance management of insect pests can give promising results with lesser environmental side effects. This review summarizes the resistance status of CPB and discusses the potential advantage of plant-based and RNAi-based synergists for CPB resistance management. It will motivate researchers to further investigate the techniques of using plant- and RNAi-based synergists in combination with insecticides.

Three cytochrome P450 CYP4 family genes regulated by the CncC signaling pathway mediate phytochemical susceptibility in the red flour beetle, Tribolium castaneum

BACKGROUND

Insect cytochrome P450 monooxygenases (P450s) play a crucial role in phytochemical metabolism and tolerance. Three P450 genes (TcCYP4Q3, TcCYP4Q5, and TcCYP4Q7) are associated with the response of eugenol in Tribolium castaneum. However, the responding mechanisms of these P450 genes to eugenol remain unknown.

RESULTS

Here, spatiotemporal expression profiling revealed that TcCYP4Q3 and TcCYP4Q5 were most highly expressed in late adult, while TcCYP4Q7 was predominantly expressed in late larva; and all of these three P450 genes were mainly expressed in the fat body of larvae. Furthermore, the expressions of these three P450 genes were significantly up-regulated after exposure to eugenol, and depletion of them enhanced the susceptibility of beetles to eugenol. Interestingly, RNA interference (RNAi) against the CncC gene, a transcription factor of CncC signaling pathway associated with regulation of insect P450s in response to phytochemicals, reduced the transcripts of these three P450 genes following exposure to eugenol. Investigation of CncC signaling pathway showed that this pathway could be activated by eugenol.

CONCLUSION

Altogether, the results indicate that these three P450 genes are regulated by CncC signaling pathway to participate in the susceptibility of Tribolium castaneum to phytochemicals. These findings will aid implications for the development of novel therapeutics to control pest. © 2022 Society of Chemical Industry.

Functional investigation of lncRNAs and target cytochrome P450 genes related to spirotetramat resistance in Aphis gossypii Glover

BACKGROUND

Spirotetramat is a tetramic acid derivative insecticide with novel modes of action for controlling Aphis gossypii Glover in the field. Previous studies have shown that long noncoding RNAs (lncRNAs) and cytochrome P450 monooxygenases (P450s) are involved in the detoxification process. However, the functions of lncRNAs in regulating P450 gene expression in spirotetramat resistance in A. gossypii are unknown.

RESULTS

In this study, we found CYP4CJ1, CYP6CY7 and CYP6CY21 expression levels to be significantly upregulated in a spirotetramat-resistant (SR) strain compared with a susceptible (SS) strain. Furthermore, knockdown of CYP4CJ1, CYP6CY7 and CYP6CY21 increased nymph and adult mortality in the SR strain following exposure to spirotetramat. Drosophila ectopically expressing CYP380C6, CYP4CJ1, CYP6DA2, CYP6CY7 and CYP6CY21 showed significantly decreased mortality after spirotetramat exposure, and CYP380C6, CYP4CJ1 and CYP6CY21 are putative targets of six lncRNAs. Silencing of lncRNAs MSTRG.36649.2/5 and MSTRG.71880.1 changed CYP6CY21 and CYP380C6 expression, altering the sensitivity of the SR strain to spirotetramat. Moreover, MSTRG.36649.2/5 did not compete for microRNA (miRNA) binding to regulate CYP6CY21 expression.

CONCLUSION

Our results confirm that CYP380C6, CYP4CJ1, CYP6DA2, CYP6CY7 and CYP6CY21 are potentially involved in the development of spirotetramat resistance in A. gossypii, and MSTRG.36649.2/5 and MSTRG.71880.1 probably regulate CYP6CY21 and CYP380C6 expression other than through the "sponge effect" of competing for miRNA binding. Our results provide a favorable molecular basis for studying cotton aphid P450 genes and lncRNA functions in spirotetramat resistance development.

Identification and Characterization of UDP-Glycosyltransferase Genes in a Cerambycid Beetle, Pharsalia antennata Gahan, 1894 (Coleoptera: Cerambycidae)

The cerambycid beetle, Pharsalia antennata Gahan, 1894 (Coleoptera: Cerambycidae), is a wood-boring pest that spends most of its life cycle in the trunks or under the bark of trees. These distinctive biological characteristics make it likely that this beetle will encounter a number of plant defensive compounds, coupled with a broad range of host plants, possibly resulting in the overexpression or expansion of uridine diphosphate (UDP)-glycosyltransferase (UGT) genes. Here, we identified and characterized the UGT gene family in P. antennata through transcriptome data, sequence and phylogenetic analyses, and PCR and homology modeling approaches. In total, 59 transcripts encoding UGTs were identified, 34 of which harbored full-length sequences and shared high conservation with the UGTs of Anoplophora glabripennis. Of the 34 PantUGTs, only 31.78% amino acid identity was observed on average, but catalytic and sugar binding residues were highly conserved. Phylogenetic analyses revealed four Cerambycidae-specific clades, including 30 members from P. antennata. Combining the transcriptome and PCR data showed that PantUGTs had a wide tissue expression, and the majority of the genes were presented mainly in antennae or abdomens, suggesting their putative roles in olfaction and detoxification. This study provides, for the first time, information on the molecular and genetic basis of P. antennata, greatly enhancing our knowledge of the detoxification-related UGT gene family.

Plastid Transformation of Micro-Tom Tomato with a Hemipteran Double-Stranded RNA Results in RNA Interference in Multiple Insect Species

Plant-mediated RNA interference (RNAi) holds great promise for insect pest control, as plants can be transformed to produce double-stranded RNA (dsRNA) to selectively down-regulate insect genes essential for survival. For optimum potency, dsRNA can be produced in plant plastids, enabling the accumulation of unprocessed dsRNAs. However, the relative effectiveness of this strategy in inducing an RNAi response in insects using different feeding mechanisms is understudied. To investigate this, we first tested an in vitro-synthesized 189 bp dsRNA matching a highly conserved region of the v-ATPaseA gene from cotton mealybug (Phenacoccus solenopsis) on three insect species from two different orders that use leaf-chewing, lacerate-and-flush, or sap-sucking mechanisms to feed, and showed that the dsRNA significantly down-regulated the target gene. We then developed transplastomic Micro-tom tomato plants to produce the dsRNA in plant plastids and showed that the dsRNA is produced in leaf, flower, green fruit, red fruit, and roots, with the highest dsRNA levels found in the leaf. The plastid-produced dsRNA induced a significant gene down-regulation in insects using leaf-chewing and lacerate-and-flush feeding mechanisms, while sap-sucking insects were unaffected. Our results suggest that plastid-produced dsRNA can be used to control leaf-chewing and lacerate-and-flush feeding insects, but may not be useful for sap-sucking insects.

The Genome of Rhyzopertha dominica (Fab.) (Coleoptera: Bostrichidae): Adaptation for Success

The lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae), is a major global pest of cereal grains. Infestations are difficult to control as larvae feed inside grain kernels, and many populations are resistant to both contact insecticides and fumigants. We sequenced the genome of R. dominica to identify genes responsible for important biological functions and develop more targeted and efficacious management strategies. The genome was assembled from long read sequencing and long-range scaffolding technologies. The genome assembly is 479.1 Mb, close to the predicted genome size of 480.4 Mb by flow cytometry. This assembly is among the most contiguous beetle assemblies published to date, with 139 scaffolds, an N₅₀ of 53.6 Mb, and L₅₀ of 4, indicating chromosome-scale scaffolds. Predicted genes from biologically relevant groups were manually annotated using transcriptome data from adults and different larval tissues to guide annotation. The expansion of carbohydrase and serine peptidase genes suggest that they combine to enable efficient digestion of cereal proteins. A reduction in the copy number of several detoxification gene families relative to other coleopterans may reflect the low selective pressure on these genes in an insect that spends most of its life feeding internally. Chemoreceptor genes contain elevated numbers of pseudogenes for odorant receptors that also may be related to the recent ontogenetic shift of R. dominica to a diet consisting primarily of stored grains. Analysis of repetitive sequences will further define the evolution of bostrichid beetles compared to other species. The data overall contribute significantly to coleopteran genetic research.

Functionally characterized arthropod pest and pollinator cytochrome P450s associated with xenobiotic metabolism

The cytochrome P450 family (P450s) of arthropods includes diverse enzymes involved in endogenous essential physiological functions and in the oxidative metabolism of xenobiotics, insecticides and plant allelochemicals. P450s can also establish insecticide selectivity in bees and pollinators. Several arthropod P450s, distributed in different phylogenetic groups, have been associated with xenobiotic metabolism, and some of them have been functionally characterized, using different in vitro and in vivo systems. The purpose of this review is to summarize scientific publications on arthropod P450s from major insect and mite agricultural pests, pollinators and Papilio sp, which have been functionally characterized and shown to metabolize xenobiotics and/or their role (direct or indirect) in pesticide toxicity or resistance has been functionally validated. The phylogenetic relationships among these P450s, the functional systems employed for their characterization and their xenobiotic catalytic properties are presented, in a systematic approach, including critical aspects and limitations. The potential of the primary P450-based metabolic pathway of target and non-target organisms for the development of highly selective insecticides and resistance-breaking formulations may help to improve the efficiency and sustainability of pest control.

Transcriptional analysis of Bemisia tabaci MEAM1 cryptic species under the selection pressure of neonicotinoids imidacloprid, acetamiprid and thiamethoxam

BACKGROUND

Neonicotinoids are widely applied in the control of the destructive agricultural pest Bemisia tabaci, and resistance against these chemicals has become a common, severe problem in the control of whiteflies. To investigate the molecular mechanism underlying resistance against nenonicotinoids in whiteflies, RNA-seq technology was applied, and the variation in the transcriptomic profiles of susceptible whiteflies and whiteflies selected by imidacloprid, acetamiprid and thiamethoxam treatment was characterized.

RESULTS

A total of 90.86 GB of clean sequence data were obtained from the 4 transcriptomes. Among the 16,069 assembled genes, 584, 110 and 147 genes were upregulated in the imidacloprid-selected strain (IMI), acetamiprid-selected strain (ACE), and thiamethoxam (THI)-selected strain, respectively, relative to the susceptible strain. Detoxification-related genes including P450s, cuticle protein genes, GSTs, UGTs and molecular chaperone HSP70s were overexpressed in the selected resistant strains, especially in the IMI strain. Five genes were downregulated in all three selected resistant strains, including 2 UDP-glucuronosyltransferase 2B18-like genes (LOC 109030370 and LOC 109032577).

CONCLUSIONS

Ten generations of selection with the three neonicotinoids induced different resistance levels and gene expression profiles, mainly involving cuticle protein and P450 genes, in the three selected resistant whitefly strains. The results provide a reference for research on resistance and cross-resistance against neonicotinoids in B. tabaci.

Exposure to Temperature and Insecticides Modulates the Expression of Small Noncoding RNA-Associated Transcripts in the Colorado Potato Beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)

The Colorado potato beetle (Leptinotarsa decemlineata (Say)) is an insect that can adapt to various challenges, including temperature fluctuations or select insecticide treatments. This pest is also an ongoing threat to the potato industry. Small noncoding RNAs such as miRNAs, which can control posttranscriptionally the expression of various genes, and piRNAs, which can notably impact mRNA turnover, are modulated in insects under different conditions. Unfortunately, information regarding the expression status of key players involved in their synthesis and function is for the most part lacking. The current study thus aims at assessing the levels of such targets in L. decemlineata exposed to hot and cold temperatures as well as treated to the insecticides chlorantraniliprole, clothianidin, imidacloprid, and spinosad. Transcript expression levels of Ago1, Ago2, Ago3, Dcr2a, Dcr2b, Expo-5, Siwi-1, and Siwi-2, components of pathways associated with small noncoding RNA production or function, were measured by qRT-PCR and revealed modulation of select transcripts in response to temperature challenges and to select insecticides. RNAi-mediated reduction of Ago2 transcript levels in L. decemlineata injected with Ago2-targeting dsRNA and exposed to cold and warm temperatures was also conducted. Changes in survival rates were observed for the latter condition in dsRNA- versus saline-injected insects. These results showcase the differential expression of select targets involved in small noncoding RNA homeostasis and provide leads for the subsequent assessment of their involvement during stress response in L. decemlineata using RNAi-based approaches.

Knockdown of Uridine Diphosphate Glucosyltransferase 86Dg Enhances Susceptibility of Tribolium castaneum (Coleoptera: Tenebrionidae) to Artemisia vulgaris (Asterales: Asteraceae) Essential Oil

Uridine diphosphate glucosyltransferases (UGTs), which are phase II detoxification enzymes, are found in various organisms. These enzymes play an important role in the detoxification mechanisms of plant allelopathy and in insects. Artemisia vulgaris L. (Asterales: Asteraceae: Artemisia) essential oil has strong contact toxicity to Tribolium castaneum Herbst (Coleoptera: Tenebrionidae) larvae. However, the effect of A. vulgaris essential oil on UGTs is unclear. In this study, A. vulgaris essential oil was shown to significantly induce the expression of the TcUgt86Dg transcript. Furthermore, treatment of TcUgt86Dg-silenced individuals with A. vulgaris essential oil resulted in higher mortality than for the control individuals, indicating that TcUgt86Dg is involved in detoxification of A. vulgaris essential oil in T. castaneum. The developmental expression profile showed that the expression of TcUgt86Dg in late adults was higher than in other developmental stages. Furthermore, the expression profile in adult tissues revealed higher expression of TcUgt86Dg in the head, antenna, fat body, and accessory gland than in other tissues. These data show that TcUgt86Dg may be involved in the metabolism of exogenous toxins by T. castaneum; thus, our results have elucidated one possible mechanism of resistance to A. vulgaris essential oil and provide a theoretical basis for a control scheme for T. castaneum.

Generational sensitivity alteration in Chironomus yoshimatsui to carbamate and pharmaceutical chemicals and the effect on Catalase, CYP450, and hemoglobin gene transcription

To ascertain the tolerance mechanisms of aquatic organisms to artificial chemicals, intergenerational sensitivity changes of Chironomus yoshimatsui to a carbamate pesticide (pirimicarb) and pharmaceutical chemical (diazepam) were investigated. The larvae (<48-h-old) in each generation were exposed to both chemicals for 48 h and then the surviving chironomids were cultured until the fifth generation (F0-F4) without chemical addition. The 48-h 50% effective concentration (EC₅₀) value of chironomids was determined for each generation. In the pirimicarb treatment group, the EC₅₀ values significantly increased in F3 and F4, and those in the diazepam treatment group slightly increased. Catalase, Cytochrome P450 and hemoglobin (Hb) mRNA levels were monitored to see whether these were related to the trans-generational sensitivity. Although the generalized linear model results showed that the sensitivity to diazepam was slightly increased in the diazepam treatment, we could not find any mRNA levels related to sensitivity alteration. In contrast, the model approach showed that the chironomids exposed to pirimicarb trans-generationally became tolerant with increasing Hb mRNA levels. Therefore, they might decrease their chemical stress by modifying Hb gene transcription.

Diapause differentially modulates the transcriptomes of fat body and flight muscle in the Colorado potato beetle

Many temperate insects, such as the Colorado potato beetle, enter diapause in winter, during which they arrest their development, suppress their metabolic rate and have high stress tolerance. Diapause phenotypes can be transcriptionally regulated, however many studies to date report only whole animal gene expression rather than tissue-specific processes during diapause. We used RNA-seq to measure gene expression in fat body and flight muscle of diapausing and non-diapausing beetles. We used differential expression and GO enrichment analyses to evaluate longstanding hypotheses about the mechanisms that drive arrested development, changes in energy metabolism, and increased stress tolerance during diapause. We found evidence of G2/M cell cycle arrest, juvenile hormone catabolism, increased antioxidant metabolism, epigenetic modification, transposable element regulation, and cytoskeletal remodeling in both the fat body and flight muscle of diapausing beetles. Beetles differentially modulated the fat body and flight muscle transcriptomes during diapause with fat body playing a larger role in the hypoxia response and immunity, whereas flight muscle had higher abundance of transcripts related to the chaperone response and proteostasis. Our transcriptome provides evidence for distinct roles and responses of fat body and flight muscle during diapause in the Colorado potato beetle, and we provide testable hypotheses for biological processes that appear to drive diapause phenotypes in insects.

Identification of differentially expressed microRNAs under imidacloprid exposure in Sitobion miscanthi

Imidacloprid is a neonicotinoid that targets sucking pests, such as aphids and the green leaf bug and has been widely applied in wheat fields to control wheat aphids in China. To investigate the involvement of miRNAs in imidacloprid resistance, we sequenced small RNA libraries of Sitobion miscanthi Fabricius, across two different treatments using Illumina short-read sequencing technology. As a result, 265 microRNAs (miRNAs), of which 242 were known and 23 were novel, were identified. Quantitative analysis of miRNA levels showed that 23 miRNAs were significantly up-regulated, and 54 miRNAs were significantly down-regulated in the nymphs of S. miscanthi treated with imidacloprid in comparison with those of the control. Modulation of the abundances of differentially expressed miRNAs, smi-miR-316, smi-miR-1000, and smi-miR-iab-4 by the addition of the corresponding antagomir/inhibitor to the artificial diet significantly changed the susceptibility of S. miscanthi to imidacloprid. Subsequently, the post-transcriptional regulatory mechanism was conducted, smi-miR-278 and smi-miR-316 were confirmed to be participated in the post-transcriptional regulation of nAChRα1A and CYP4CJ6, respectively. The results suggested that miRNAs differentially expressed in response to imidacloprid could play a critical regulatory role in the metabolism of S. miscanthi to imidacloprid.

Effect of RNAi targeting CYP6CY3 on the growth, development and insecticide susceptibility of Aphis gossypii by using nanocarrier-based transdermal dsRNA delivery system

RNA interference (RNAi) has been proved to be a viable method for agricultural pest control. Due to the limited uptake of dsRNA in hemiptera insects, this study used nanocarrier SPc (star polycation) transdermal delivery systems to deliver two truncated fragments (P1/P2) dsRNA of the CYP6CY3 for silencing this target gene in Aphis gossypii. After the cotton aphid was sprayed with the SPc + dsP1/P2 mixture, the expression level of target gene in SPc + dsP1 treatment group was not different from that in dsP1 group at 24 h, 48 h, and significantly lower than that in dsP1 group at 60 h, 72 h, respectively; and the expression level of target gene in SPc + dsP2 treatment group was not different from that in dsP2 group at 24 h, and significantly lower than that in dsP2 group from 48 h, 60 h, 72 h, respectively. In addition, the expression level was continuously silenced after spraying the SPc + dsP1/P2 mixture and significant reduced by 79.7% and 84.3% at 48 h compared with the H₂O control group, the mortality rate reached 48.09% and 43.18% at 84 h, respectively. And the cumulative reproduction number of cotton aphids also decreased, but the cumulative death number of newborn nymphs had an increase trend, compared with the control groups. Bioassays after RNAi showed that the silencing of CYP6CY3 increased the susceptibility of the 4^th instar aphid to imidacloprid, and increased mortality by 67.21% and 58.69% at 96 h, respectively. The life table parameters of the offspring from the 4^th instar cotton aphids from the SPc + dsP1/P2 treatment groups showed that the offspring had a longer pre-reproductive period and post-reproductive period. The intrinsic growth rate was 0.231 ± 0.005, 0.210 ± 0.013 and the finite growth rate was 1.260 ± 0.007 and 1.234 ± 0.016 in the SPc + dsP1/P2 treatment group, these two parameters of the two groups were lower than that of the corresponding control，the population doubling time of the two groups was prolonged and the developmental duration was delayed. These results indicate that CYP6CY3 plays a key role in the growth, development, reproduction and detoxification ability in cotton aphids, and may be as a potential RNAi target for controlling aphids, laying the foundation for the development of new environmentally-friendly RNA pesticides in this field.

Knockdown of UGT352A5 decreases the thiamethoxam resistance in Bemisia tabaci (Hemiptera: Gennadius)

Uridine diphosphate (UDP)-glycosyltransferases (UGTs), which are major phase II detoxification enzymes, have been implicated in the glycosylation of lipophilic endobiotics and xenobiotics and thus potentially lead to the evolution of insecticide resistance. In this study, we identified and cloned two putative UGT genes from transcriptome data which are named UGT352A4 and UGT352A5. As demonstrated by qRT-PCR, two UGT genes were over-expressed in the thiamethoxam-resistant (THQR) strain relative to the susceptible (THQS) strain. Moreover, the induction experiment revealed that the expression of the UGT352A5 gene was significantly increased following exposure to thiamethoxam in the THQR strain. Furthermore, the expression of both UGT352A4 and UGT352A5 was downregulated after RNA interference, whereas only the silencing of UGT352A5 resulted in a noticeable increase in the mortality of THQR adults. Our results represent the first line of evidence showing that UGT352A5 might be responsible for conferring thiamethoxam resistance in B. tabaci. The results will be shed new insights for obtaining a better understanding of the role of UGTs in the evolution of insecticide resistance and developing new insect resistance management tactics within the sustainable integrated pest management framework.

Targeted RNA sequencing reveals differential patterns of transcript expression in geographically discrete, insecticide resistant populations of Leptinotarsa decemlineata

BACKGROUND

The Colorado potato beetle (Leptinotarsa decemlineata Say) is a major agricultural pest of commercial potatoes, partially due to its ability to rapidly develop resistance to multiple insecticide modes of action. Patterns of L. decemlineata insecticide resistance in the contiguous United States have been linked to geographic location and regional management practices. Several previous studies have classified enzymes that are overexpressed following L. decemlineata exposure to commercial pesticides, many of which have been linked to xenobiotic metabolism. Studies have further associated geographic disparities in resistance patterns to cross-resistance driven by fungicide exposure in the East Coast and Midwest.

RESULTS

In this study, our objective was to investigate transcript expression of 38 previously classified detoxification enzymes induced by imidacloprid (an insecticide) and chlorothalonil (a fungicide) within five discrete populations of L. decemlineata obtained from areas in the USA representing eastern, midwestern and western production regions. We found unique patterns of transcript expression in different geographic locations, including overexpression of transcripts related to insecticide metabolism within insecticide-resistant populations.

CONCLUSION

The results suggest the genetic response of these populations may be partially linked to geographic location and corresponding management practices. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Optimisation of Cytochrome P450 BM3 Assisted by Consensus-Guided Evolution

Cytochrome P450 enzymes have attracted much interest over the years given their ability to insert oxygen into saturated carbon-hydrogen bonds, a difficult feat to accomplish by traditional chemistry. Much of the activity in this field has centered on the bacterial enzyme CYP102A1, or BM3, from Bacillus megaterium, as it has shown itself capable of hydroxylating/acting upon a wide range of substrates, thereby producing industrially relevant pharmaceuticals, fine chemicals, and hormones. In addition, unlike most cytochromes, BM3 is both soluble and fused to its natural redox partner, thus facilitating its use. The industrial use of BM3 is however stifled by its instability and its requirement for the expensive NADPH cofactor. In this work, we added several mutations to the BM3 mutant R966D/W1046S that enhanced the turnover number achievable with the inexpensive cofactors NADH and NBAH. These new mutations, A769S, S847G, S850R, E852P, and V978L, are localized on the reductase domain of BM3 thus leaving the oxidase domain intact. For NBAH-driven reactions by new mutant NTD5, this led to a 5.24-fold increase in total product output when compared to the BM3 mutant R966D/W1046S. For reactions driven by NADH by new mutant NTD6, this enhanced total product output by as much as 2.3-fold when compared to the BM3 mutant R966D/W1046S. We also demonstrated that reactions driven by NADH with the NTD6 mutant not only surpassed total product output achievable by wild-type BM3 with NADPH but also retained the ability to use this latter cofactor with greater total product output as well.

UDP-Glycosyltransferases from the UGT344 Family Are Involved in Sulfoxaflor Resistance in Aphis gossypii Glover

Simple Summary

The cotton aphid, Aphis gossypii Glover, is a notorious pest in cotton and cucurbit fields. The control of A. gossypii has typically relied on the application of chemical insecticides. Sulfoxaflor is the first commercially available sulfoximine insecticide, which exhibits great efficacy against sap-feeding insect pests and has been applied as an alternative insecticide for controlling of A. gossypii in China. Consequently, A. gossypii quickly developed resistance to this insecticide. Hence, in this study, to clarify the potential detoxifying roles of UGTs (one of the phase II detoxification enzymes) in resistance of A. gossypii against sulfoxaflor, the synergistic effects of two synergists (sulfinpyrazone and 5-nitrouracil) against sulfoxaflor were investigated using the susceptible and laboratory-established sulfoxaflor resistant strain (SulR), and the expression levels of 15 UGT genes were determined by qRT-PCR. Furthermore, the involvement of highly upregulated UGTs in sulfoxaflor-resistant strain was functionally tested by RNA interference (RNAi). Our results suggest that overexpression of UGTs contributes to sulfoxaflor resistance in A. gossypii, which should be useful for understanding sulfoxaflor resistance mechanisms.

Abstract

UDP-glycosyltransferases (UGTs) are major phase II detoxification enzymes that catalyze the transfer of glycosyl residues from activated nucleotide sugars to acceptor hydrophobic molecules and play very important roles in the biotransformation of various endogenous and exogenous compounds. Our previous studies demonstrated that UGTs participated in the detoxification of insecticides in Aphis gossypii. However, the potential roles of UGTs in A. gossypii resistance to sulfoxaflor are still unclear. In this study, two inhibitors of UGT enzymes, sulfinpyrazone and 5-nitrouracil, significantly increased the toxicity of sulfoxaflor to a resistant strain of A. gossypii, whereas there were no synergistic effects in the susceptible strain. Based on the transcriptome sequencing results, the expression levels of 15 UGTs were analyzed by quantitative real-time PCR, and we found that seven UGT genes were highly over-expressed in a sulfoxaflor-resistant strain compared to the susceptible strain, including UGT344B4, UGT344C5, UGT344A11, UGT344A14, and UGT344L2. Further suppressing the expression of UGT344B4, UGT344C5, and UGT344A11 by RNA interference significantly increased the sensitivity of resistant aphids to sulfoxaflor, indicating that the overexpression of UGT genes is potentially associated with sulfoxaflor resistance. These results could provide valuable information for further understanding the mechanisms of insecticide resistance.

Glycosyltransferases: the multifaceted enzymatic regulator in insects

Glycosyltransferases (GTs) catalyse the reaction of glyco-conjugation of various biomolecules by transferring the saccharide moieties from an activated nucleotide sugar to nucleophilic glycosyl acceptor. In insects, GTs show diverse temporal and site-specific expression patterns and thus play significant roles in forming the complex biomolecular structures that are necessary for insect survival, growth and development. Several insects exhibit GT-mediated detoxification as a key defence strategy against plant allelochemicals and xenobiotic compounds, as well as a mechanism for pesticide cross-resistance. Also, these enzymes act as crucial effectors and modulators in various developmental processes of insects such as eye development, UV shielding, cuticle formation, epithelial development and other specialized functions. Furthermore, many of the known insect GTs have been shown to play a fundamental role in other physiological processes like body pigmentation, cuticular tanning, chemosensation and stress response. This review provides a detailed overview of the multifaceted functionality of insect GTs and summarizes numerous case studies associated with it.

Disruption of the cytochrome P450 CYP6BQ7 gene reduces tolerance to plant toxicants in the red flour beetle, Tribolium castaneum

In insects, the cytochrome P450 CYP6B family plays key roles in the detoxification of toxic plant substances. However, the function of CYP6 family genes in degrading plant toxicants in Tribolium castaneum, an extremely destructive global storage pest, have yet to be elucidated. In this study, a T. castaneum CYP gene, TcCYP6BQ7, was characterized. TcCYP6BQ7 expression was significantly induced after exposure to essential oil of the plant Artemisia vulgaris (EOAV). Spatiotemporal expression profiling revealed that TcCYP6BQ7 expression was higher in larval and adult stages of T. castaneum than in other developmental stages, and that TcCYP6BQ7 was predominantly expressed in the brain and hemolymph from the late larval stage. TcCYP6BQ7 silencing by RNA interference increased larvae mortality in response to EOAV from 49.67% to 71.67%, suggesting that this gene is associated with plant toxicant detoxification. Combined results from this study indicate that the CYP6 family gene TcCYP6BQ7 likely plays a pivotal role in influencing the susceptibility of T. castaneum to plant toxicants. These findings may have implications for the development of novel therapeutics to control this agriculturally important pest.

Proteomic Analyses Detect Higher Expression of C-Type Lectins in Imidacloprid-Resistant Colorado Potato Beetle Leptinotarsa decemlineata Say

Simple Summary

Surveillance and determining the mechanisms of pesticide resistance are key components of resistance management. Mechanisms can be investigated using biochemical, genomic, proteomic and other modern analytical techniques. In the present study, proteomic analyses of Colorado potato beetle (CPB), one of the most adaptable insect pests to both plant toxins and synthetic insecticides, were applied to identify protein differences in insecticide-susceptible and resistant strains. Proteins identified in abdominal and midgut tissues based on separating by 2-dimensional (2-D) gels and mass spectrometry were associated with insect innate immunity. A database search found that the highest match was a C-type lectin (CTL), which is a component in the insect’s innate immune system. The 2-D gel spot identified as a CTL was greater in the insecticide-resistant CPB strain, but the CTL spot size was increased by exposure to imidacloprid in the susceptible strain. This is a novel finding, which suggests that CTLs and insect immunity may respond to certain toxins as well as to pathogens. There may also be a potential application for pest management if insect immunity is targeted.

Abstract

The Colorado potato beetle (CPB) is one of the most adaptable insect pests to both plant toxins and synthetic insecticides. Resistance in CPB is reported for over 50 classes of insecticides, and mechanisms of insecticide-resistance include enhanced detoxification enzymes, ABC transporters and target site mutations. Adaptation to insecticides is also associated with changes in behaviour, energy metabolism and other physiological processes seemingly unrelated to resistance but partially explained through genomic analyses. In the present study, in place of genomics, we applied 2-dimensional (2-D) gel and mass spectrometry to investigate protein differences in abdominal and midgut tissue of insecticide-susceptible (S) and -resistant (R) CPB. The proteomic analyses measured constitutive differences in several proteins, but the highest match was identified as a C-type lectin (CTL), a component of innate immunity in insects. The constitutive expression of the CTL was greater in the multi-resistant (LI) strain, and the same spot was measured in both midgut and abdominal tissue. Exposure to the neonicotinoid insecticide, imidacloprid, increased the CTL spot found in the midgut but not in the abdominal tissue of the laboratory (Lab) strain. No increase in protein levels in the midgut tissue was observed in the LI or a field strain (NB) tolerant to neonicotinoids. With the exception of biopesticides, such as Bacillus thuringiensis (Bt), no previous studies have documented differences in the immune response by CTLs in insects exposed to synthetic insecticides or the fitness costs associated with expression levels of immune-related genes in insecticide-resistant strains. This study demonstrates again how CPB has been successful at adapting to insecticides, plant defenses as well as pathogens.

Association between overexpression of cytochrome P450 genes and deltamethrin resistance in Rhipicephalus microplus

Cytochrome P450 monooxygenases mediated metabolic detoxification has been recognized as one of the mechanisms involved in resistance to pyrethroids, which is a class of pesticides that includes acaricides such as deltamethrin. Several cytochrome P450 (CYP) genes were identified in arthropod pests which are upregulated in response to exposure to pesticides used as acaricides. However, to date, limited information is available with respect to CYP genes and their response to acaricide exposure in ticks. We cloned and sequenced four CYP genes, the CYP41, CYP3006G8, CYP319A1 and CYP4W1 from reference susceptible IVRI-I strain of Rhipicephalus microplus. The expression pattern of the genes was investigated using qPCR in reference susceptible IVRI-I, pyrethroid-resistant IVRI-IV and multi-acaricide resistant IVRI-V strains. The effect of a single exposure of deltamethrin, at a concentration of 2600 μg/mL and 299.7 μg/mL on IVRI-IV and IVRI-V strains, respectively, on the expression of the four CYP genes was evaluated. In IVRI-IV strain, the CYP41 gene was highly overexpressed (FC 8.72) while CYP3006G8 was underexpressed with FC of 0.06. All the four genes were overexpressed in IVRI-V strain. After exposure to deltamethrin, the CYP3006G8 transcript levels were significantly upregulated at all time intervals in both resistant strains with the highest FC of 11.62 at 12 h in IVRI-IV and 13.38 at 3 h in IVRI-V. Our results suggest that the constitutive overexpression of CYP41 and deltamethrin induced upregulation of CYP3006G8 contribute to the development of pyrethroid resistance, specifically deltamethrin, in these two reference strains.

Transcriptomics-Based Approach Identifies Spinosad-Associated Targets in the Colorado Potato Beetle, Leptinotarsa decemlineata

Simple Summary

The Colorado potato beetle Leptinotarsa decemlineata is a potato pest that can cause substantial damages to potato crops worldwide. Multiple approaches have been leveraged to control this pest including the use of a variety of insecticides. Resistance to different insecticides aimed at controlling this insect has been reported and much work has been conducted in recent years to elucidate the underlying molecular changes associated with insecticide resistance in L. decemlineata. However, information is sparse regarding the molecular impact associated with spinosad treatment in this insect pest. The current study thus explores transcriptional changes associated with spinosad response in L. decemlineata exposed to this compound using high-throughput sequencing. Results presented show multiple transcripts of interest that exhibit differential expression in spinosad-treated L. decemlineata and provide a preliminary footprint of transcripts affected by this insecticide in this potato pest. Select targets identified in this signature should be further explored in follow-up studies to better characterize their contribution, if any, in the process of spinosad resistance.

Abstract

The Colorado potato beetle Leptinotarsa decemlineata is an insect pest that threatens potato crops globally. The primary method to control its damage on potato plants is the use of insecticides, including imidacloprid, chlorantraniliprole and spinosad. However, insecticide resistance has been frequently observed in Colorado potato beetles. The molecular targets and the basis of resistance to imidacloprid and chlorantraniliprole have both been previously quantified. This work was undertaken with the overarching goal of better characterizing the molecular changes associated with spinosad exposure in this insect pest. Next-generation sequencing was conducted to identify transcripts that were differentially expressed between Colorado potato beetles exposed to spinosad versus control insects. Results showed several transcripts that exhibit different expression levels between the two conditions, including ones coding for venom carboxylesterase-6, chitinase 10, juvenile hormone esterase and multidrug resistance-associated protein 4. In addition, several microRNAs, such as miR-12-3p and miR-750-3p, were also modulated in the investigated conditions. Overall, this work reveals a molecular footprint underlying spinosad response in Colorado potato beetles and provides novel leads that could be targeted as part of RNAi-based approaches to control this insect pest.

Genome-Wide Identification and Expression Analysis of Udp-Glucuronosyltransferases in the Whitefly Bemisia Tabaci (Gennadius) (HemipterA: Aleyrodidae)

Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is an important agricultural pest worldwide. Uridine diphosphate (UDP)-glucuronosyltransferases (UGTs) are one of the largest and most ubiquitous groups of proteins. Because of their role in detoxification, insect UGTs are attracting increasing attention. In this study, we identified and analyzed UGT genes in B. tabaci MEAM1 to investigate their potential roles in host adaptation and reproductive capacity. Based on phylogenetic and structural analyses, we identified 76 UGT genes in the B. tabaci MEAM1 genome. RNA-seq and real-time quantitative PCR (RT-qPCR) revealed differential expression patterns of these genes at different developmental stages and in association with four host plants (cabbage, cucumber, cotton and tomato). RNA interference results of selected UGTs showed that, when UGT352A1, UGT352B1, and UGT354A1 were respectively silenced by feeding on dsRNA, the fecundity of B. tabaci MEAM1 was reduced, suggesting that the expressions of these three UGT genes in this species may be associated with host-related fecundity. Together, our results provide detailed UGTs data in B.tabaci and help guide future studies on the mechanisms of host adaptation by B.tabaci.

Functional analysis of cytochrome P450 genes linked with acetamiprid resistance in melon aphid, Aphis gossypii

Cytochrome P450 monooxygenases (P450s) are highly conserved multifunctional enzymes that play crucial roles in insecticide resistance development. In this study, the molecular mechanisms of P450s in acetamiprid resistance development to melon aphid, Aphis gossypii was investigated. Acetamiprid resistant (32.64-fold resistance) population (Ace-R) of A. gossypii was established by continuous selection with acetamiprid for 24 generations. Quantitative Real Time PCR was carried out to analyze the expression of P450 genes in both acetamiprid resistant (Ace-R) and susceptible (Ace-S) strains. Result showed that nine genes (CYP6CY14, CYP6DC1, CYP6CZ1, CYP6DD1, CYP6CY5, CYP6CY9, CYP6DA1, CYP6CY18, and CYP6CY16) of CYP3 clade, four genes (CYP302A1, CYP315A1, CYP301A1, and CYP314A1) of CYP2 clade, two genes (CYP4CK1, CYP4G51) of CYP4 clade and three genes (CYP306A1, CYP305E1, CYP307A1) of mitochondrial clade (Mito clad) were significantly up-regulated, in Ace-R compared to Ace-S strain. Whilst CYP4CJ2 gene from (CYP4 clade) was significantly down-regulated in Ace-R strain. Furthermore, RNA interference-mediated knockdown of CYP6CY14, CYP6DC1, and CYP6CZ1 genes significantly increased the sensitivity of Ace-R strain to acetamiprid. Taken together, this study showed that P450 genes especially CYP6CY14, CYP6DC1 and CYP6CZ1 are potentially involved in acetamiprid resistance development in A. gossypii. This study could be useful to understand the molecular basis of acetamiprid resistance mechanism in A. gossypii.