Functional analysis of CYP6AE68, a cytochrome P450 gene associated with indoxacarb resistance in Spodoptera litura (Lepidoptera: Noctuidae)

Tetraniliprole risk assessment: Unveiling a hidden threat for managing a generalist herbivore

Insecticide resistance poses a significant challenge in managing generalist herbivores such as the tobacco cutworm (TCW), Spodoptera litura. This study investigates the potential risks associated with using the novel diamide insecticide tetraniliprole to control TCW. A tetraniliprole-resistant strain was developed through twelve generations of laboratory selection, indicating an intermediate risk of resistance development. Field monitoring in China revealed a significant incidence of resistance, particularly in the Nanchang (NC) population (>100-fold). Tetraniliprole showed moderate to high cross-resistance to multiple insecticides and was autosomally inherited with incomplete dominance, controlled by multiple genes, some of which belong to the cytochrome P450 family associated with enhanced detoxification. Life table studies indicated transgenerational hormesis, stimulating TCW female fecundity and increasing population net reproduction rates (R0). These findings suggest a potential for pest resurgence under tetraniliprole use. The integrated risk assessment provides a basis for the sustainable management of TCW using tetraniliprole.

Self-assembled co-delivery nanoplatform for increasing the broad-spectrum susceptibility of fall armyworm toward insecticides

INTRODUCTION

Unscientific application of insecticides has led to severe resistance of pests to almost all classes of insecticides. Enhanced detoxification is the most common mechanism for this kind of resistance.

OBJECT

Fall armyworm (FAW) has developed insecticide resistance, which is often linked to the overexpression of detoxification genes. Herein, a multicomponent nano-pesticide is designed to increase its broad-spectrum susceptibility toward insecticides.

METHOD

Regulatory function of nuclear factor erythroid 2-related factor 2 (Nrf2) in detoxification was confirmed using transcriptome sequencing, quantitative real-time PCR and enzyme activity measurement. A star polycation (SPc) was adopted to construct the pesticide/SPc/complex, whose self-assembly mechanism and characterization were examined using isothermal titration calorimetry, dynamic light scattering and transmission electron microscope. The delivery efficiency of SPc-loaded dsRNA was examined in vitro and in vivo using fluorescent tracer technique. A multicomponent nano-pesticide was created through the integration of bacterial expression system and nano-delivery system, and its bioactivity was tested in laboratory and field.

RESULTS

We confirmed the crucial role of Nrf2 in regulating the detoxification in FAW, and silencing Nrf2 could decrease detoxification gene expression and increase insecticide susceptibility. We then applied the SPc to self-assemble a nanoplatform for delivering Nrf2 double-stranded RNA (dsRNA) and pesticide simultaneously. Nano-sized pesticide/SPc/dsRNA complex exhibited high delivery efficiency in vitro and in vivo. Excitingly, the insecticidal activities of pesticide/SPc/dsNrf2 complexes were remarkably improved with the normalized synergistic ratios of 5.43-6.25 for chlorantraniliprole, 4.45-15.00 for emamectin benzoate, and 6.75-15.00 for spinetoram. Finally, we developed a multicomponent nano-pesticide (pesticide/SPc/dsNrf2 complex) using a bacterial expression system and nano-delivery system. This approach exhibited excellent leaf protection and pest control efficacy.

CONCLUSION

The integration between the pesticide nanometerization and insecticide susceptibility improvement offers a promising strategy to increase insecticidal activity. Our study provides a revolutionary and universal strategy to increase insecticidal activity and decease application doses.

Frequency and diversity of indoxacarb resistance in Australian Helicoverpa armigera (Lepidoptera: Noctuidae)

Annual indoxacarb resistance in Helicoverpa armigera (Hübner) populations collected from various crops in Australia was monitored between 2013 and 2023. Resistance frequency determined by F2 screening using a predetermined discriminating dose of indoxacarb, was lowest in the 2013-2014 and 2015-2016 seasons at 0.0164 and 0.0246, respectively. Resistance then increased significantly to a ten-year high of 0.0869 in 2018-2019 but declined to 0.0557 in 2019-2020 during a severe drought, remaining relatively stable thereafter to 2023. Indoxacarb resistance was first detected in H. armigera collected from maize in the Gwydir valley, New South Wales, in 2013 (strain GY7-39). In 2017, a second indoxacarb resistant H. armigera strain (UN1U3-10) was isolated from a population collected in chickpeas in the Liverpool Plains, New South Wales. Indoxacarb resistance of this strain was characterized to evaluate its potential to compromise the ongoing effectiveness of insecticide resistance management strategies in Australian farming systems. Survival at the discriminating dose of indoxacarb in UN1U3-10 was 28.9, 52.6, 86.7, and 92.9% in the F2, F3, F4, and F5, respectively. Following introgression with a susceptible strain and reselection with the discriminating dose of indoxacarb, the resistance ratio of UN1U3-10 was approximately 800-fold. Resistance was autosomal, incompletely dominant and conferred by more than 1 locus. While indoxacarb resistance in UN1U3-10 did not confer to emamectin benzoate or spinetoram and there was no evidence of major cross-resistance to the Bt toxins Cry1A, Cry2A or Vip3A, there was 5-fold reduced sensitivity to chlorantraniliprole. Indoxacarb resistance was suppressed by approximately 10-fold by PBO with no synergism by TPP or DEM, suggesting the involvement of cytochrome P450 enzymes. A stability analysis indicated a fitness cost may be associated with the genes that confer resistance in the UN1U3-10 strain. The potential risk for diverse indoxacarb resistance in the Australian H. armigera population is discussed.

DIMBOA-induced gene expression, activity profiles of detoxification enzymes, multi-resistance mechanisms, and increased resistance to indoxacarb in tobacco cutworm, Spodoptera litura (Fabricius)

Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) is one of the most destructive insect pests owned strong resistance to different insecticides. Indoxacarb as a novel oxadiazine insecticide becomes the main pesticide against S. litura. DIMBOA [2,4-dihydroxy-7-methoxy-2 H-1,4-benz-oxazin-3(4 H)-one] is involved in important chemical defense processes in corn plants. However, the insects' adaptation mechanism to insecticides when exposed to defensive allelochemicals in their host plants remains unclear. Here, we assessed multi-resistance, and resistance mechanisms based on S. litura life history traits. After 18 generations of selection, indoxacarb resistance was increased by 61.95-fold (Ind-Sel) and 86.06-fold (Dim-Sel) as compared to the Lab-Sus. Also, DIMBOA-pretreated larvae developed high resistance to beta-cypermethrin, chlorpyrifos, phoxim, chlorantraniliprole, and emamectin benzoate. Meanwhile, indoxacarb (LC50) was applied to detect its impact on thirty-eight detoxification-related genes expression. The transcripts of SlituCOE073, SlituCOE009, SlituCOE074, and SlituCOE111 as well as SlGSTs5, SlGSTu1, and SlGSTe13 were considerably raised in the Ind-Sel strain. Among the twenty-three P450s, CYP6AE68, CYP321B1, CYP6B50, CYP9A39, CYP4L10, and CYP4S9v1 transcripts denoted significantly higher levels in the Ind-Sel strain, suggesting that CarEs, GSTs and P450s genes may be engaged in indoxacarb resistance. These outcomes further highlighted the importance of detoxification enzymes for S. litura gene expression and their role in responses to insecticides and pest management approaches.

Indoxacarb resistance in Iranian populations of Tuta absoluta (Lepidoptera: Gelechiidae): Cross-resistance, biochemical and molecular mechanisms

Tuta absoluta (Meyrick) is an invasive tomato pest that occurs worldwide, including Iran. This study investigates the occurrence of resistance to indoxacarb, an oxadiazine insecticide, and the underlying mechanisms in Iranian populations of T. absoluta. Bioassays were performed on second-instar larvae using indoxacarb alone and in combination with three synergists: Piperonyl butoxide (PBO), diethyl maleate (DEM), and triphenyl phosphate (TPP). The activities of the main detoxification enzymes, including glutathione S-transferases (GST), general carboxylesterases (CarEs), and P450 monooxygenases (P450s), were evaluated. In addition, the presence of known amino acid substitutions in the IV segment 6 domain of the T. absoluta sodium channel was investigated. The results showed that resistance rates to indoxacarb in Iranian populations ranged from 2.37- to 14.45-fold. However, pretreatment with synergists did not significantly increase the toxicity of indoxacarb. Enzyme assays showed that Ardabil (Ar) and Kerman (Kr) populations had the highest CarEs activity, while Ar population showed the highest P450 activity. However, the observed increases in enzyme activities were <2-fold. Two indoxacarb resistance mutations, F1845Y and V1848I, were detected. Apart from a significant and positive correlation between LC50 values of indoxacarb and thiocyclam hydrogen oxalate, no cross-resistance between indoxacarb and other insecticides was detected. Overall, these results suggest that populations of T. absoluta in Iran have developed resistance to indoxacarb, primarily through changes at the target site.

Inducible Cytochrome P450s in the Fat Body and Malpighian Tubules of the Polyphagous Pests of Spodoptera litura Confer Xenobiotic Tolerance

Cytochrome P450 plays vital roles in detoxifying xenobiotics. In this study, SlCYP340A and SlCYP340L expression in the Spodoptera litura fat body and SlCYP332A1, SlCYP6AB12, SlCYP6AB58, SlCYP6AB59, and SlCYP6AN4 expression in the Malpighian tubules were significantly upregulated after cyantraniliprole exposure, and SlCYP6AB58 and SlCYP6AB59 expression levels were simultaneously increased in the Malpighian tubules after gossypol treatment. Drosophila ectopically expressing candidate P450 genes showed that SlCYP332A1, SlCYP6AB12, SlCYP6AB59, SlCYP6AN4, and SlCYP340A conferred cyantraniliprole tolerance. The overexpression of SlCYP6AB58 and SlCYP6AB59 in Drosophila increased the number of eggs laid under the gossypol treatment. Moreover, the knockdown of SlCYP332A1, SlCYP6AB12, SlCYP6AB59, SlCYP6AN4, and SlCYP340A increased S. litura mortality under the cyantraniliprole treatment. Homology modeling and molecular docking results suggested that candidate P450 has the potential to bind with cyantraniliprole. These results indicate that the CYP3 and CYP4 genes participate in cyantraniliprole detoxification and that SlCYP6AB59 may be simultaneously involved in the gossypol tolerance of S. litura.

Phenolic secondary metabolites from Acorus calamus (Acorales: Acoraceae) rhizomes: the feeding deterrents for Spodoptera litura (Lepidoptera: Noctuidae)

Spodoptera litura Fabricius (Lepidoptera: Noctuidae) is one of the most destructive pests of various crops cultivated in Thailand. Spodoptera litura larvae, at early stages, attack the leaves and feed on every part of infested crops in later stages. Acorus calamus essential oil contains toxic asarones, which are generalistic cytotoxic compounds. However, the present study is the first attempt to look at safer metabolites from the rhizomes that could deter insect feeding. The objective was to use such compounds as safer residues on crops that would prevent the feeding of herbivorous lepidopterans. Accordingly, phenolic metabolites were isolated and evaluated to establish the feeding deterrence against polyphagous S. litura larvae. Methanol extract of A. calamus, chrysin, and 4-hydroxy acetophenone compounds were the most effective feeding deterrents with FD50 of 87.18, 10.33, and 70.77 µg/cm2, respectively, after 4 h of feeding on treated kale leaves in a no-choice leaf disc assay. Chrysin also reduced carboxylesterase activities (1.37-fold), whereas A. calamus methanol extract reduced glutathione-S-transferase activities (1.44-fold). Some larvae were also seen dead if they consumed the treated kale leaves. Feeding deterrent activity in the methanol extract of A. calamus was due to chrysin and 4-hydroxy acetophenone. The large-scale utilization of such compounds could help develop feeding deterrent strategies in the integrated pest management of lepidopterans.

Low concentration of indoxacarb interferes with the growth and development of silkworm by damaging the structure of midgut cells

As an important economic insect, Bombyx mori plays an essential role in the development of the agricultural economy. Indoxacarb, a novel sodium channel blocker insecticide, has been widely used for the control of various pests in agriculture and forestry, and its environmental pollution caused by flight control operations has seriously affected the safe production of sericulture in recent years. However, the lethal toxicity and adverse effects of indoxacarb on silkworm remain largely unknown. In this study, the toxicity of indoxacarb on the 5th instar larvae of silkworm was determined, with an LC50 (72 h) of 2.07 mg/L. Short-term exposure (24 h) to a low concentration of indoxacarb (1/2 LC50) showed significantly reduced body weight and survival rate of silkworm larvae. In addition, indoxacarb also led to decreased cocoon weight and cocoon shell weight, but had no significant effects on pupation, adult eclosion, and oviposition. Histopathological and ultrastructural analysis indicated that indoxacarb could severely damage the structure of the midgut epithelial cells, and lead to physiological impairment of the midgut. A total of 3883 differentially expressed genes (DEGs) were identified by midgut transcriptome sequencing and functionally annotated using GO and KEGG. Furthermore, the transcription level and enzyme activity of the detoxification related genes were determined, and our results suggested that esterases (ESTs) might play a major role in metabolism of indoxacarb in the midgut of B. mori. Future studies to examine the detoxification or biotransformation function of candidate genes will greatly enhance our understanding of indoxacarb metabolism in B. mori. The results of this study provide a theoretical basis for elucidating the mechanism of toxic effects of indoxacarb on silkworm by interfering with the normal physiological functions of the midgut.

Synthesis, and biological evaluation of pyrazole matrine derivatives as an insecticide against Spodoptera frugiperda

As one of the major threats to global food security, Spodoptera frugiperda (S. frugiperda) is highly gaining consideration due to its severe damage. Matrine is a widely and effectively used botanical insecticide in controlling S.frugiperda but lacks a rapidly available effect. To further improved the insecticidal activity of matrine based on combination principles, this work synthesized five new pyrazole matrine derivatives (PMDs) using Michael addition and investigated insecticidal activity against 2nd instar larvae of S. frugiperda(in vivo) and its isolated cell(in vitro). Our result demonstrated that PMDs show higher pesticidal activity than that matrine in both in vitro and in vivo assays. The most toxic derivatives in vitro and in vivo are PMD-3 and PMD-1, with IC50 of 2.49 mM and LC50 of 22.76 mg/L respectively. This research also investigates the anti-proliferation mechanism of PMDs based on isolated cells. PMDs decrease mitochondria membrane potential, arrested cell cycle at the G2/M phase, and upregulated Caspase 3, Caspase 9, and Apaf-1 to induce Caspase-dependent apoptosis. For Caspase-independent apoptosis, AIF and Endo G were found to be upregulated. Besides, pro-apoptotic factors like p53, IBM-1, and anti-apoptotic factors like IAP were upregulated. Moreover, we supposed that there was a linkage between lysosomes and PMD-induced apoptosis according to increased apoptosis rate, activated lysosomes, and upregulated Cathepsin B. This research provides new ideas for the synthesis of matrine derivatives and further demonstrated the anti-proliferation mechanism of PMDs.

Functional roles of two novel P450 genes in the adaptability of Conogethes punctiferalis to three commonly used pesticides

Introduction: Insect cytochrome P450 (CYP450) genes play important roles in the detoxification and metabolism of xenobiotics, such as plant allelochemicals, mycotoxins and pesticides. The polyphagous Conogethes punctiferalis is a serious economic pest of fruit trees and agricultural crops, and it shows high adaptability to different living environments. Methods: The two novel P450 genes CYP6CV1 and CYP6AB51 were identified and characterized. Quantitative real-time PCR (qRT-PCR) technology was used to study the expression patterns of the two target genes in different larval developmental stages and tissues of C. punctiferalis. Furthermore, RNA interference (RNAi) technology was used to study the potential functions of the two P450 genes by treating RNAi-silenced larvae with three commonly used pesticides. Results: The CYP6CV1 and CYP6AB51 genes were expressed throughout various C. punctiferalis larval stages and in different tissues. Their expression levels increased along with larval development, and expression levels of the two target genes in the midgut were significantly higher than in other tissues. The toxicity bioassay results showed that the LC₅₀ values of chlorantraniliprole, emamectin benzoate and lambda-cyhalothrin on C. punctiferalis larvae were 0.2028 μg/g, 0.0683 μg/g and 0.6110 mg/L, respectively. After treating with different concentrations of chlorantraniliprole, emamectin benzoate and lambda-cyhalothrin (LC₁₀, LC₃₀, LC₅₀), independently, the relative expressions of the two genes CYP6CV1 and CYP6AB51 were significantly induced. After the dsRNA injection, the expression profiles of the two CYP genes were reduced 72.91% and 70.94%, respectively, and the mortality rates of the larvae significantly increased when treated with the three insecticides independently at LC₁₀ values. Discussion: In the summary, after interfering with the CYP6CV1 and CYP6AB51 in C. punctiferalis, respectively, the sensitivity of C. punctiferalis to chlorantraniliprole, emamectin benzoate and lambda-cyhalothrin was significantly increased, indicating that the two CYP6 genes were responsible for the adaptability of C. punctiferalis to the three chemical insecticides in C. punctiferalis. The results from this study demonstrated that CYP6CV1 and CYP6AB51 in C. punctiferalis play crucial roles in the detoxification of chlorantraniliprole, emamectin benzoate and lambda-cyhalothrin.

Activation of the CncC pathway is involved in the regulation of P450 genes responsible for clothianidin resistance in Bradysia odoriphaga

BACKGROUND

Insect cytochrome P450 monooxygenases (P450s) play a key role in the detoxification metabolism of insecticides and their overexpression is often associated with insecticide resistance. Our previous research showed that the overexpression of four P450 genes is responsible for clothianidin resistance in B. odoriphaga. In this study, we characterized another P450 gene, CYP6FV21, associated with clothianidin resistance. However, the molecular basis for the overexpression of P450 genes in clothianidin-resistant strain remains obscure in B. odoriphaga.

RESULTS

In this study, the CYP6FV21 gene was significantly overexpressed in the clothianidin-resistant (CL-R) strain. Clothianidin exposure significantly increased the expression level of CYP6FV21. Knockdown of CYP6FV21 significantly increased the susceptibility of B. odoriphaga larvae to clothianidin. The transcription factor Cap 'n' Collar isoform-C (CncC) was highly expressed in the midgut of larvae in B. odoriphaga. The expression level of CncC was higher in the CL-R strain compared with the susceptible (SS) strain. Clothianidin exposure caused reactive oxygen species (ROS) accumulation and significantly increased the expression level of CncC. Knockdown of CncC caused a significant decrease in the expression of CYP3828A1 and CYP6FV21, and P450 enzyme activity, and led to a significant increase in mortality after exposure to lethal concentration at 30% (LC₃₀ ) of clothianidin. After treatment with CncC agonist curcumin, the P450 activity and the expression levels of CYP3828A1 and CYP6FV21 significantly increased, and larval sensitivity to clothianidin decreased. The ROS scavenger N-acetylcysteine (NAC) treatment significantly inhibited the expression levels of CncC, CYP3828A1 and CYP6FV21 in response to clothianidin exposure and increased larval sensitivity to clothianidin.

CONCLUSION

Taken together, these results indicate that activation of the CncC pathway by the ROS burst plays a critical role in clothianidin resistance by regulating the expression of CYP3828A1 and CYP6FV21 genes in B. odoriphaga. This study provides more insight into the mechanisms underlying B. odoriphaga larval resistance to clothianidin. © 2023 Society of Chemical Industry.

RNA interference in cytochrome P450 monooxygenase (CYP) gene results in reduced insecticide resistance in Megalurothrips usitatus Bagnall

Genes of the cytochrome P450 (CYP450) superfamily are known to be involved in the evolution of insecticide resistance. In this study, the transcriptomes of two Megalurothrips usitatus Bagnall (Thysanoptera: Thripidae) strains (resistant and susceptible) were screened for detoxification genes. MusiDN2722 encodes a protein composed of 504 amino acid residues with a relative molecular mass of 57.3 kDa. Multiple sequence alignment and phylogenetic analysis showed that MusiDN2722 is a member of the CYP450 family and has characteristics of the conserved CYP6 domain shared by typical CYP450 family members. RT-qPCR (real-time quantitative polymerase chain reaction) analysis showed that MusiDN2722 was upregulated in the acetamiprid-resistant strain compared with the susceptible strain (p &lt; 0.05), and the relative expression level was significantly higher at 48 h after exposure than at 24 h after exposure. The interference efficiency of the injection method was higher than that of the membrane-feeding method. Silencing of MusiDN2722 through RNA interference significantly increased the sensitivity of M. usitatus to acetamiprid. Overall, this study revealed that MusiDN2722 plays a crucial role in the resistance of M. usitatus to acetamiprid. The findings will not only advance our understanding of the role of P450s in insecticide resistance but also provide a potential target for the sustainable control of destructive pests such as thrips.

Baseline Susceptibility, Cross-Resistance, and Sublethal Effects of Broflanilide, a Novel Meta-Diamide Pesticide, in Spodoptera litura

Spodoptera litura is a damaging and notorious insect pest of agricultural crops that has developed resistance to various insecticides. Broflanilide is a novel pesticide with a unique mode of action that displays high efficiency against lepidopterous larvae. We here determined the baseline susceptibility of a laboratory strain of S. litura to broflanilide and 10 other popular insecticides. Furthermore, we measured susceptibility and cross-resistance using three common insecticides in 11 field-collected S. litura populations. Broflanilide caused the highest toxicity among all tested insecticides, with the laboratory strain and all field-collected populations showing high susceptibility. Moreover, no cross-resistance was detected between broflanilide and the other tested insecticides. We subsequently evaluated the sublethal effects of broflanilide and found that treatment with the 25% lethal concentration (LC25) prolonged the development duration in the larvae, reduced the pupation rate and pupae weight, and decreased egg hatchability. Finally, the activities of three detoxifying enzymes were measured in S. litura after treatment with the LC25 dose. The results suggested that enhanced cytochrome P450 monooxygenase (P450) activity could be involved in broflanilide detoxification. Overall, these findings demonstrate the strong toxicity and significant sublethal effects of broflanilide in S. litura and suggest that increased P450 activity may be associated with broflanilide detoxification.

Two P450 genes, CYP6SN3 and CYP306A1, involved in the growth and development of Chilo suppressalis and the lethal effect caused by vetiver grass

Chilo suppressalis is a widely distributed pest occurring in nearly all paddy fields, which has developed high level resistance to different classes of insecticides. Vetiver grass has been identified as a dead-end trap plant for the alternative control of C. suppressalis. In this study, two cytochrome P450 monooxygenase (P450) genes, CsCYP6SN3 and CsCYP306A1, were identified and characterized, which are expressed at all developmental stages, with the highest expression in the midguts and fat bodies of 3rd instar larvae. Vetiver significantly inhibited the expression levels of CsCYP6SN3 and CsCYP306A1 in 3rd larvae after feeding. RNA interference showed that silencing CsCYP6SN3 and CsCYP306A1 genes dramatically reduced the pupation rate and pupa weight. Feeding on vetiver after silencing CsCYP6SN3 and CsCYP306A1 led to higher mortality compared with feeding on rice. In conclusion, these findings indicated that the expression levels of CsCYP6SN3 and CsCYP306A1 were associated with the lethal effect of vetiver against C. suppressalis larvae and functional knowledge about these two detoxification genes could provide new targets for agricultural pest control.

Disruption of CYP6DF1 and CYP6DJ2 increases the susceptibility of Dendroctonus armandi to (+)-α-pinene

Bark beetles rely on detoxifying enzymes to resist the defensive oleoresin terpenes of the host tree. Insect cytochrome P450 (CYPs) plays a key role in the detoxification of plant allelochemicals and pesticides. CYP6 family is unique to Insecta, and its biochemical function is basically related to catabolize heterologous substances. In this study, two Dendroctonus armandi CYP6 genes, CYP6DF1 and CYP6DJ2, were characterized. Spatiotemporal expression profiling revealed that CYP6DF1 and CYP6DJ2 expressions were higher in larvae and adult stages of D. armandi than in egg and pupae stages, and that two genes predominantly expressed in brain, midgut, fat body, or Malpighian tubules. Moreover, CYP6DF1 and CYP6DJ2 expressions were significantly induced after exposure to (+)-α-pinene. Importantly, silencing CYP6DF1 and CYP6DJ2 significantly inhibited the CYP activity and increased the mortality in the adults fumigated with (+)-α-pinene. Additionally, piperonyl butoxide exposure to adults also increase the sensitivity after treatment with (+)-α-pinene, which led to a significant reduction of the CYP activity, resulting a significant increase in adult mortality. These results suggest that the CYP6 family plays a key role in determining the susceptibility of D. armandi to (+)-α-pinene, which may have implications for the development of novel therapeutics to control this important pest.

Herbivore-induced tomato plant volatiles lead to the reduction of insecticides susceptibility in Spodoptera litura

Herbivore-induced plant volatiles (HIPVs) have been associated with plant-plant-herbivorous-natural enemies communication and an enhanced response to the subsequent attack. Spodoptera litura is a serious cosmopolitan pest that has developed a high level of resistance to many insecticides. However, the underlying molecular and biochemical mechanism by which HIPV priming reduces S. litura larval sensitivity to insecticides remains largely unknown. This study was conducted to explore the potential of volatile from undamaged, or artificially damaged, or S. litura-damaged tomato plants on the susceptibility of S. litura to the insecticides beta-cypermethrin indoxacarb and chlorpyrifos. We found that larvae exposed to volatile from S. litura-damaged or artificially damaged tomato plants were significantly less susceptible to the three insecticides than those exposed to volatile from undamaged tomato plants. Elevated activities of detoxifying enzymes [cytochrome P450 monooxygenases (P450s), glutathione S-transferases (GSTs), and esterases (ESTs)], were expressed in S. litura larvae exposed to volatile from S. litura-damaged tomato plants than those exposed to volatile from undamaged tomato plants. Similarly, seven detoxification-related genes [GSTs (SlGSTe1, SlGSTo1, and SlGSTe3) and P450s (CYP6B48, CYP9A40, CYP321A7, and CYP321B1)] in the midgut and fat body of larvae were up-regulated under exposure to volatile from S. litura-damaged tomato plants. Increased volatile organic compounds emissions were detected in the headspace of tomato plants damaged by S. litura compared to the undamaged plants. Collectively, these findings suggest that HIPVs can considerably reduce caterpillar susceptibility to insecticides, possibly through induction-enhanced detoxification mechanisms, and provide valuable information for implementing an effective integrated pest management strategy.

CRISPR/Cas9-Mediated Knockout Reveals the Involvement of CYP304F1 in β-Cypermethrin and Chlorpyrifos Resistance in Spodoptera litura

Functions of insect CYP2 clan P450s in insecticide resistance are relatively less reported. In Spodoptera litura, a gene from the CYP2 clan (CYP304F1) was validated to be up-regulated significantly in a pyrethroid- and organophosphate-resistant population (QJ) than a susceptible population by RNA-Seq and qRT-PCR. Spatial-temporal expression indicated the high expression of CYP304F1 in the fourth, fifth, and sixth instar larvae and the metabolism-related tissue fat body and malpighian tubules. CYP304F1 was knocked out by CRISPR/Cas9, and a homozygous population (QJ-CYP304F1) with a G-base deletion at exon 2 was obtained after selection. Bioassay results showed that the LD₅₀ values to β-cypermethrin and chlorpyrifos in the QJ-CYP304F1 population decreased significantly, and the resistance ratio was both 1.81-fold in the QJ population compared with that in the QJ-CYP304F1 population. The toxicity of fenvalerate, cyhalothrin, or phoxim showed no significant change. These results suggested that CYP304F1 is involved in β-cypermethrin and chlorpyrifos resistance in S. litura.

Overexpression of Multiple Cytochrome P450 Genes Conferring Clothianidin Resistance in Bradysia odoriphaga

Cytochrome P450 monooxygenases (P450s) play important roles in the detoxification metabolism of xenobiotics and are involved in the resistance of insects to many insecticides. In this study, piperonyl butoxide (PBO), an inhibitor of P450 enzyme activity, significantly increased the toxicity of clothianidin in the clothianidin-resistant (CL-R) population of Bradysia odoriphaga. The enzyme activity of P450 in the CL-R population was significantly higher than that in the SS population. Furthermore, four P450 genes were found to be significantly overexpressed in the CL-R population. Tissue-specific expression analysis indicates that CYP9J57, CYP3828A1, CYP6SX1, and CYP6QE1 were most highly expressed in the midgut and/or Malpighian tubules. After exposure to LC₃₀ of clothianidin, the expression levels of the four P450 genes were significantly upregulated. The RNAi-mediated knockdown of CYP9J57, CYP3828A1, and CYP6QE1 significantly increased the susceptibility of B. odoriphaga to clothianidin. These results suggest that P450 genes are involved in clothianidin resistance in B. odoriphaga. This provides a better understanding of P450-mediated clothianidin resistance in B. odoriphaga and will contribute to the management of insect resistance to insecticides.

MicroRNA-190-5p confers chlorantraniliprole resistance by regulating CYP6K2 in Spodoptera frugiperda (Smith)

The fall armyworm Spodoptera frugiperda (Smith) (FAA) is responsible for considerable losses in grain production, and chemical control is the most effective strategy. However, frequent insecticide application can lead to the development of resistance. In insects, cytochrome P450 plays a crucial role in insecticide metabolism. CYP6K2 is related to FAA resistance to chlorantraniliprole. However, the regulatory mechanism of CYP6K2 expression is poorly understood. In this study, a conserved target of isolated miRNA-190-5p was located in the 3' UTR of CYP6K2 in FAA. A luciferase reporter analysis showed that in FAA, miRNA-190-5p can combine with the 3'UTR of CYP6K2 to suppress its expression. Injected miRNA-190-5p agomir significantly reduced CYP6K2 abundance by 54.6% and reduced tolerance to chlorantraniliprole in FAA larvae, whereas injected miRNA-190-5p antagomir significantly increased CYP6K2 abundance by 1.77-fold and thus improved chlorantraniliprole tolerance in FAA larvae. These results provide a basis for further research on the posttranscriptional regulatory mechanism of CYP6K2 and will facilitate further study on the function of miRNAs in regulating tolerance to chlorantraniliprole in FAA.

Indoxacarb resistance-associated mutation of Liriomyza trifolii in Hainan, China

Liriomyza trifolii, which has been recently prevalent in China, harms more than 300 plant species, especially cowpea in Hainan. This pest also affects the quality and production of vegetables in winter. Indoxacarb is the first commercial oxadiazine pesticide, which is a new efficient insecticide used to control pests of Diptera, including L. trifolii. The unique mechanism of indoxacarb is that indenyl is transformed into N-demethoxycarbonyl metabolite (DCJW) in insects and acts on inactivated sodium channel; DCJW could then destroy the conduction of nerve impulses, which leads to movement disorders, feeding stoppage, paralysis, and eventually the death of pests. The field population of L. trifolii developed resistance by 769 times higher than the sensitive population in Sanya, Hainan. Results revealed the existence of a mutation (i.e., V1848I) in the sixth transmembrane segment of Domain IV of the sodium channel in the field population. The homozygous resistant genotype frequency for the V1848I mutation was 10-15% among the three field-collected populations. This paper reports for the first time the presence of the kdr mutation V1848I in resistant populations of L. trifolii to indoxacarb. The present study will contribute to the understanding of the evolution of indoxacarb resistance and contribute to the development of resistance management practices for winter vegetables in Hainan.