Genome-wide patterns of copy number variations in Spodoptera litura

Azadirachtin exposure inhibit ovary development of Spodoptera litura (Lepidoptera: Noctuidae) by altering lipids metabolism event and inhibiting insulin signaling pathways

Lipids are main energy source for insects reproduction, which are becoming emerging target for pest management. Azadirachtin (AZA) is a multi-targeted and promising botanical insecticide, but its reproduction toxicity mechanism related to lipids metabolism is poorly understood. Here, we applied lipidomic and transcriptomic to provide a comprehensive resource for describing the effect of AZA on lipids remodeling in ovary of Spodoptera litura. The results showed that AZA exposure obviously altered the contents of 130 lipids subclasses (76 upregulated and 54 downregulated). In detail, AZA exposure changed the length and saturation degrees of fatty acyl chain of most glycerolipid, phospholipid and sphingolipid as well as the expression of genes related to biosynthesis of unsaturated fatty acids and fatty acids elongation. Besides, following the abnormal lipids metabolism, western blot analysis suggested that AZA induce insulin resistance-like phenotypes by inhibiting insulin receptor substrates (IRS) /PI3K/AKT pathway, which might be responsible for the ovary abnormalities of S. litura. Collectively, our study provided insights into the lipids metabolism event in S. litura underlying AZA exposure, these key metabolites and genes identified in this study would also provide important reference for pest control in future.

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.

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.

Proteomic profiling for ovarian development and azadirachtin exposure in Spodoptera litura during metamorphosis from pupae to adults

Azadirachtin is one of the most successful botanical pesticides in agricultural pest control. To build a repertoire of proteins and pathways in response to azadirachtin exposure during ovarian development, iTRAQ-based comparative proteomic was conducted. 1423 and 1686 proteins were identified as differentially accumulated proteins (DAPs) by comparing the protein abundance in adult ovary with that in pupal ovary under normal and azadirachtin exposure condition, respectively. Bioinformatics analysis indicated that pupae-to-adult transition requires proteins related to proteasome and branched chain amino acids (BCAAs) degradation for ovary development. Azadirachtin exposure strongly affected glycosylation-related pathway. And proteins related to vitamin B6 synthesis were necessary for ovary development under normal and AZA-exposure condition. RNAi assays confirmed the essential roles of DAPs related to glycosylation and vitamin B6 synthesis in moth growth and ovary development. The results enhance our understanding of the molecular regulatory network for ovary development and provide valuable resources for using AZA-responsive proteins to develop novel bio-rational insecticides.

Transcriptomics and metagenomics of common cutworm (Spodoptera litura) and fall armyworm (Spodoptera frugiperda) demonstrate differences in detoxification and development

BACKGROUND

Spodoptera litura is an important polyphagous pest that causes significant damage to the agricultural sector. We performed RNA-seq of 15 S. litura individuals from larval (fifth and sixth instar larvae), chrysalis, and adult developmental stages. We also compared the S. litura transcriptome data with Spodoptera frugiperda across the same developmental stages, which was sequenced in our previous study.

RESULTS

A total of 101,885 differentially expressed transcripts (DETs) were identified in S. litura. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses indicated that S. litura may undergo active xenobiotic and detoxifying metabolism during its larval and adult stages, which may explain difficulties with current population control measures. We also found that DETs of single-copy orthologous genes between S. litura and S. frugiperda were involved in basic metabolism and development. However, energy and metabolic processes genes had a higher expression in S. litura, whereas nervous and olfactory function genes had a higher expression in S. frugiperda. Metagenomics analysis in larval S. litura and S. frugiperda revealed that microbiota participate in the detoxification and metabolism processes, but the relative abundance of detoxification-related microbiota was more abundant in S. frugiperda. Transcriptome results also confirmed the detoxification-related pathway of S. frugiperda was more abundant than in S. litura.

CONCLUSIONS

Significant changes at transcriptional level were identified during the different development stages of S. litura. Importantly, we also identified detoxification associated genes and gut microbiota between S. litura and S. frugiperda at different developmental stages, which will be valuable in revealing possible mechanisms of detoxification and development in these two lepidopterans.

Screening of Helicoverpa armigera Mobilome Revealed Transposable Element Insertions in Insecticide Resistance Genes

Simple Summary

Transposable elements (TEs) are mobile DNA sequences that can copy themselves within a host genome. TE-mediated changes in regulation can lead to massive and rapid changes in expression, responses that are potentially highly adaptive when an organism is faced with a mortality agent in the environment, such as an insecticide. Helicoverpa armigera shows a hight number of reported cases of insecticide resistance worldwide, having evolved resistance against pyrethroids, organophosphates, carbamates, organochlorines, and recently to macrocyclic lactone spinosad and several Bacillus thuringiensis toxins. In the present study, we conducted a TE annotation using combined approaches, and the results revealed a total of 8521 TEs, representing 236,132 copies, covering 12.86% of the H. armigera genome. In addition, we underlined TE insertions in defensome genes and we successfully identified nine TE insertions belonging to the RTE, R2, CACTA, Mariner and hAT superfamilies.

Abstract

The cotton bollworm Helicoverpa armigera Hübner (Lepidoptera: Noctuidae) is an important pest of many crops that has developed resistance to almost all groups of insecticides used for its management. Insecticide resistance was often related to Transposable Element (TE) insertions near specific genes. In the present study, we deeply retrieve and annotate TEs in the H. armigera genome using the Pipeline to Retrieve and Annotate Transposable Elements, PiRATE. The results have shown that the TE library consists of 8521 sequences representing 236,132 TE copies, including 3133 Full-Length Copies (FLC), covering 12.86% of the H. armigera genome. These TEs were classified as 46.71% Class I and 53.29% Class II elements. Among Class I elements, Short and Long Interspersed Nuclear Elements (SINEs and LINEs) are the main families, representing 21.13% and 19.49% of the total TEs, respectively. Long Terminal Repeat (LTR) and Dictyostelium transposable element (DIRS) are less represented, with 5.55% and 0.53%, respectively. Class II elements are mainly Miniature Inverted Transposable Elements (MITEs) (49.11%), then Terminal Inverted Repeats (TIRs) (4.09%). Superfamilies of Class II elements, i.e., Transib, P elements, CACTA, Mutator, PIF-harbinger, Helitron, Maverick, Crypton and Merlin, were less represented, accounting for only 1.96% of total TEs. In addition, we highlighted TE insertions in insecticide resistance genes and we successfully identified nine TE insertions belonging to RTE, R2, CACTA, Mariner and hAT superfamilies. These insertions are hosted in genes encoding cytochrome P450 (CyP450), glutathione S-transferase (GST), and ATP-binding cassette (ABC) transporter belonging to the G and C1 family members. These insertions could therefore be involved in insecticide resistance observed in this pest.

Adaptation by copy number variation increases insecticide resistance in the fall armyworm

Understanding the genetic basis of insecticide resistance is a key topic in agricultural ecology. The adaptive evolution of multi-copy detoxification genes has been interpreted as a cause of insecticide resistance, yet the same pattern can also be generated by the adaptation to host-plant defense toxins. In this study, we tested in the fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae), if adaptation by copy number variation caused insecticide resistance in two geographically distinct populations with different levels of resistance and the two host-plant strains. We observed a significant allelic differentiation of genomic copy number variations between the two geographic populations, but not between host-plant strains. A locus with positively selected copy number variation included a CYP gene cluster. Toxicological tests supported a central role for CYP enzymes in deltamethrin resistance. Our results indicate that copy number variation of detoxification genes might be responsible for insecticide resistance in fall armyworm and that evolutionary forces causing insecticide resistance could be independent of host-plant adaptation.

A homoisoflavonoid and a fatty acid in common purslane (Portulaca oleracea L.) synergistically inhibit growth of Spodoptera litura larvae

BACKGROUND

Portulaca oleracea L., common purslane, is an insecticidal plant that has been documented as a 'Chinese indigenous pesticide', and it is seldom visited by insects in the field. However, identification of anti-insect compounds and mechanisms of action are still unclear.

RESULTS

Interplanting purslane with Chinese cabbage demonstrated that purslane may contain secondary compounds that S. litura avoids eating. Four compounds were isolated from P. oleracea by directed anti-insect activity, and their chemical structures were identified by NMR spectra as (9Z,11E,15Z)-13-hydroxyoctadeca-9,11,15-trienoic acid (1), portulacanone A (2), portulacanone D (3), and a new natural product 2,4'-dihydroxy-3',5'-dimethoxychalcone (4). A combination of compound 1 and 2 possessed stronger activity than other combinations (compounds 1 + 3; 1 + 4; 2 + 3; 2 + 4; 3 + 4). Both active compounds were detected in all samples from 23 regions in China, and concentrations in samples collected from 17 regions were generally above 500 μg/kg. Concentrations of compounds 1 and 2 fluctuated greatly from April to November, and reached maximum concentrations of 45 951.44 μg/kg for compound 1 and 3739.09 μg/kg for compound 2 in November. The combination of these compounds (1 + 2) caused mid-gut structural deformation and tissue decay as determined by mid-gut histopathology of S. litura.

CONCLUSION

In general, these active compounds coexisting contributed to partly protect purslane from insects. This research also provides new insights into the use of purslane as important ingredient of botanical pesticide alternatives to traditional chemical pesticides. © 2019 Society of Chemical Industry.