Chilo Suppressalis Walker Research Articles

Behavioral and Physiological Adaptation to Soil Moisture in the Overwintering Larvae of the Rice Stem Borer in the Subtropics

Diapausing larvae of the rice stem borer, Chilo suppressalis Walker, overwinter in rice stubble. During overwintering, the larvae may move to sites with suitable moisture and undergo physiological changes to prepare for the declining temperature. This study measured the behavioral and physiological adaptation to soil moisture (25%, 50%, and 75% of saturated soil water content) in the diapausing larvae at 30, 60, and 90 days of treatment. The results showed that the diapausing C. suppressalis larvae behaviorally exhibited hygrotaxis and distributed mainly (65%) in the lower part (0–10 cm above the soil level) of the rice stem where the moisture was higher. Physiologically, the insects showed significantly decreased glycogen content and weight whereas increased trehalose content with decreasing soil moisture. In the subtropics where this study was conducted, the supercooling points of the insects were lower than the lowest ambient temperature, and the soil moisture had no significant effects on the cold hardiness (supercooling point) and survival of the diapausing C. suppressalis larvae. The decreased larval weight at low soil moisture may reduce the post-diapause reproductive potential of the larvae, which may open the potential of developing agronomic measures-based management of the overwintering C. suppressalis population.

Herbivory by Striped Stem Borer Triggers Polyamine Accumulation in Host Rice Plants to Promote Its Larval Growth.

Polyamines (PAs) are ubiquitous low-molecular-weight aliphatic polycations in all living organisms, which are crucial for plant response to abiotic and biotic stresses. The role of PAs in plant disease resistance has been well documented. However, their involvement in plant-pest interactions remains unclear. Here, the role of PAs in rice against striped stem borer (SSB, Chilo suppressalis Walker), a destructive pest in rice production worldwide, was investigated. SSB larval infestation led to a substantial accumulation of free putrescine (Put) in rice seedlings, which was in parallel with an elevated expression of host PA biosynthesis genes Arginine Decarboxylase1 (ADC1) and ADC2. Moreover, SSB larval oral secretion application with wounding further raised the transcripts of ADC1 and ADC2 in rice compared with wounding treatment alone. The larval growth on both rice plants and artificial diet was promoted by the exogenous application of PA and inhibited by a PA biosynthesis inhibitor. On the other hand, the rice defense responses, including polyphenol oxidase (PPO) and peroxidase (POD) activities, as well as protease inhibitor level, were enhanced by a Put supplement and reduced by an ADC inhibitor. Our results indicate that SSB herbivory triggers polyamine accumulation in host rice plants, which is beneficial to SSB in rice-SSB interaction.

Insecticidal potential of Ajwain essential oil and its major components against Chilo suppressalis Walker

Insecticidal potential of Ajwain essential oil and its major components against Chilo suppressalis Walker

Insecticide resistance monitoring in field populations of Chilo suppressalis Walker (Lepidoptera: Crambidae) from central China.

Chilo suppressalis Walker (Lepidoptera: Crambidae) is a devastating rice crop pest in China. Chemical insecticides have been used to effectively managing C. suppressalis field populations in most of China's agricultural regions. However, due to the intensive and extensive application of these insecticides, C. suppressalis has developed widespread resistance to many active ingredients. Thus, insecticide resistance development is a genuine concern for all crop specialists and growers. In this study, using the topical application method, we assessed the susceptibility of forty-six field populations of C. suppressalis to three insecticides in three Central Chinese provinces from 2010 to 2021. Our findings revealed that field populations of C. suppressalis built moderate to high levels of resistance to triazophos (Resistance Ratio (RR) = 41.9-250.0 folds), low to moderate levels of resistance to chlorpyrifos (RR = 9.5-95.2 folds), with the exception of the Zhijiang population in 2013 and the Xinyang population in 2015 at 4.8 folds and 3.4 folds resistance rates, respectively, despite showing susceptibility, and low and moderate levels of resistance to abamectin (RR = 4.1-53.5 folds). There were significant correlations between the activity of the detoxification enzymes (CarE) and the log LD50 values of triazophos. These results should help effective insecticide resistance management strategies reduce the risk of rapid build-ups of resistance to insecticides and slow down the process of selection for insecticide resistance.

Development and Temperature-induced Expression of a HSP90 Gene Lacking Introns in Cotesia chilonis (Hymenoptera: Braconidae)

Abstract Cotesia chilonis (Munakata) is the predominant parasitic wasp of Chilo suppressalis Walker (Lepidoptera: Pyralidea), a major rice pest in China. As climate change continues to intensify, C. chilonis and C. suppressalis must adapt to the increased frequency of adverse temperatures. In this study, the novel Cchsp90-2 was isolated and characterized from C. chilonis. The full-length Cchsp90-2 cDNA was 2689 bp and encoded 728 amino acids with an isoelectric point of 4.93. Cchsp90-2 encodes three heat shock protein 90 (HSP90) family signatures, and the alignment of genomic and cDNA sequences revealed that Cchsp90-2 does not contain introns. Real-time quantitative PCR revealed that Cchsp90-2 was induced in eggs and adults; however, larvae and pupae showed no significant differences in Cchsp90-2 expression levels. Cchsp90-2 was induced at both high and low temperatures, with very high expression levels after a 2-h exposure to 33°C or −13°C. This study provides insight into the mechanistic basis of thermal tolerance in C. chilonis and has implications for deploying this wasp to control C. suppressalis.

Differences in susceptibility to chlorantraniliprole between Chilo suppressalis (Lepidoptera: Crambidae) and two dominant parasitic wasps collected from Sichuan Province, China

Chilo suppressalis Walker (Lepidoptera: Crambidae) is one of the most destructive pests occurring in the rice-growing regions of Asia. Parasitoids, mainly egg parasitoids, have been of interest for several years even with practical used cases. Therefore, the potential impact of insecticides on natural enemies needs great attention. In this study, chlorantraniliprole was evaluated for its impact on C. suppressalis and two dominant parasitic wasps. Bioassays showed that chlorantraniliprole had negligible toxicity to Eriborus terebrans but was significantly toxic to Chelonus munakatae; the mortality exceeded 50% when the concentration reached 46.83 ng/cm2. Enzyme assays suggested that the significantly different carboxylesterase activity may be involved in the high-level detoxification metabolism of E. terebrans. According to the results of enzyme gene correlation analysis, P450s may be the dominant factor in the detoxification metabolism of C. munakatae. In addition, the ryanodine receptor C-terminus of C. suppressalis (CsRyR), C. munakatae (CmRyR) and E. terebrans (EtRyR) were successfully cloned. Different amino acids at resistance mutation I4758 M between susceptible C. suppressalis (I) and parasitic wasps (M) may be related to susceptibility differences. Simulated docking showed that CsRyR and CmRyR can interact with chlorantraniliprole but not EtRyR. More interaction forces were formed between CsRyR and chlorantraniliprole than CmRyR. Furthermore, a Pi-Pi T-shape formed between 73PHE in CsRyR and the benzene ring in chlorantraniliprole. These results indicated that both detoxification metabolism and the target site could mediate the susceptibility difference between C. suppressalis and its parasitic wasps.

Insecticidal Potential of Ajwain Essential Oil and its Major Components Against Chilo Suppressalis Walker

Insecticidal Potential of Ajwain Essential Oil and its Major Components Against Chilo Suppressalis Walker

Transgenic double-stranded RNA rice, a potential strategy for controlling striped stem borer (Chilo suppressalis).

Although the striped stem borer (SSB, Chilo suppressalis Walker) is a devastating pest of rice that causes significant economic losses, management options are currently limited. Plant-mediated RNA interference (RNAi) is an emerging crop protection technique in which transgenic plants are modified to express insect-specific double-stranded RNAs (dsRNAs) that trigger RNAi silencing in target pests. In this study, an RNAi-based screen of 35 candidate SSB genes identified a small heat shock protein gene (CssHsp) as a potential plant-based RNAi target. To assess its utility in planta, a total of 39 transgenic rice plants were generated, with 11 independent transformants found to contain a single copy of the dsCssHsp expression cassette. In life-time feeding bioassays, three transgenic lines (DS10, DS35, DS36) were found to have significant negative impacts on SSB populations. After feeding for 8 days, mortality in the three transgenic lines exceeded 60%. By pupation, mortality further increased to 90% and few SSB survived to eclosion. Gene expression analyses confirmed that CssHsp transcript levels were significantly reduced after feeding on the transgenic dsCssHsp rice. These results demonstrate the potential for developing a plant-mediated RNAi strategy targeting CssHsp as a more biorational field-based approach for SSB control. © 2021 Society of Chemical Industry.

Trans-kingdom expression of an insect endogenous microRNA in rice enhances resistance to striped stem borer Chilo suppressalis.

The striped stem borer (SSB), Chilo suppressalis Walker, is a major pest of rice worldwide. Breeding of transgenic rice expressing Bacillus thuringiensis (Bt) toxins is a powerful strategy to control SSB. However, pests may evolve certain resistance to Bt toxins in transgenic plants. Hence, new controlling strategies must be continuously developed. We successfully generated SSB-resistant rice (csu-53) expressing the artificial microRNA (amiRNA) of SSB endogenous miRNA (csu-novel-miR53) through the RNAi-based technology. Feeding assays demonstrated that csu-53 rice inhibited larval growth, delayed pupation time, and reduced pupal weight and eclosion rate of SSB larva. In a 10-day feeding experiment, the miRNA mimic of csu-novel-miR53 also suppressed larval growth and more importantly increased larval mortality. Transcriptome analysis identified 28 differentially expressed unigenes (DEGs) in the midgut between SSB larvae fed on csu-53 rice and the wild type. One DEG (DN90065_c0_g12) validated by qRT-PCR had a predicted target site of csu-novel-miR53. In addition, in vitro double-stranded RNA synthesis and further feeding assay proved that DN90065_c0_g12 is most likely the target of csu-novel-miR53. amiRNA-mediated strategy can be applied to the development of insect-resistant crops, and the novel amiRNA csu-novel-miR53 of SSB has important application potential in developing SSB resistant rice. © 2021 Society of Chemical Industry.

Transcriptomic analysis of pre-diapause larvae of Chilo suppressalis (Walker) (Lepidoptera: Pyralidae) in natural populations

Chilo suppressalis Walker is a devastating pest of rice in Asia and exhibits facultative diapause in the larval stage. Most prior experiments on diapausing and non-diapausing C. suppressalis were conducted in the laboratory. In this study, transcriptome analyses were performed on pre-diapausing larvae collected from field populations of C. suppressalis and compared to laboratory populations. Among 2674 differentially expressed genes (DEGs), 32 DEGs related to pre-diapause and 239 universally expressed genes were screened; these were primarily enriched in “neuroactive ligand-receptor interaction”, “lysosome” and “glycerolipid metabolism” in KEGG pathway analysis. With respect to clusters of orthologous genes (COG), DEGs were assigned to “posttranslational modification, protein turnover, chaperones”, “carbohydrate transport and metabolism”, and “secondary metabolite biosynthesis, transport and catabolism” categories. Further analysis also revealed that a key “circadian clock-controlled protein” gene is sensitive to photoperiod and significantly decreased during the pre-diapause phase. Genes encoding two small heat shock proteins, hsp21.4 and hsp27.2, were significantly expressed on August 15 as compared to three other sampling times in August 2018. Eight DEGs were randomly chosen and evaluated by real-time quantitative PCR (RT-qPCR) to validate the accuracy of the transcriptome data. The expression of six DEGs (gene-evm_000752, gene-evm_006486, gene-evm_008626, gene-evm_002485, gene-evm_011981 and Chilo_suppressalis_newGene_18103) showed significant same patterns of differential expression in both the RT-qPCR and RNA-Seq analyses. This study increases our understanding of the complex physiological and molecular mechanisms involved in C. suppressalis at the pre-diapause phase.

Cultivated rice enhances an insect herbivore-parasitoid interaction compared with a wild grass due to its thinner stems

Crops are more susceptible to insect herbivores than wild plants. It is generally considered that crops combining with farm practices tend to disrupt insect herbivore-enemy interactions. In this study, we compared the parasitism rate of the rice stem borer Chilo suppressalis Walker by its specialized endoparasitoid wasp Cotesia chilonis Matsumura in cultivated rice Oryza sativa L. with that in the wild water-oat Zizania latifolia Griseb. The wild water-oat was never sprayed or fertilized. The parasitism rate was >10-fold higher in cultivated rice than in the wild water-oat. The difference was subsequently confirmed in a common garden experiment which the two host plants were interplanted in the same field. Laboratory assays indicated that female adults of C. chilonis did not discriminate the odors of cultivated rice and the wild water-oat. Larvae of C. chilonis did not develop differently within the haemocoele of the rice feeders and the wild water-oat feeders of the rice stem borer. However, the attack efficiency of C. chilonis significantly negatively correlated the thickness of stems in which the rice stem borers were dwelling. We conclude that cultivated rice has thinner stems than the wild water-oat, which is an important reason why the parasitism rate in cultivated rice is significantly higher than that in the wild water-oat. This finding may be just an exceptional case of the theory of the herbivore-enemy interactions in agroecosystems, but it implies that it is possible to enhance the control efficiencies in agroecosystems by designing appropriate crop phenotypes to promote the search and attack of natural enemies.

Ontogenetic description of Proctolaelaps bickleyi (Bram) (Acari: Melicharidae), newly recorded from lepidopteran insect cultures in Japan

Proctolaelaps bickleyi (Bram) (Acari: Melicharidae) is an edaphic predatory mite commonly associates with insects. Although P. bickleyi has been reported from many countries worldwide, it is reported herein for the first time in Japan from laboratory cultures of Chilo suppressalis (Walker) and Cossus insularis (Staudinger) (Lepidoptera: Crambidae, Cossidae). Proctolaelaps bickleyi is redescribed and illustrated from females, males, deutonymphs, protonymphs and larvae. The morphological ontogeny of idiosomal and leg chaetotaxy is discussed and a key to the Japanese species of Proctolaelaps is provided.

Gut microbial communities associated with phenotypically divergent populations of the striped stem borer Chilo suppressalis (Walker, 1863)

Chilo suppressalis (Walker, 1863) is a serious stem borer of rice and water-oat plants, and has phenotypically diverged into rice and water-oat populations. Insect gut microbiota plays an important role in the host life and understanding the dynamics of this complicated ecosystem may improve its biological control. The effect of diet and gut compartments on the gut microflora of divergent populations of C. suppressalis is not fully clear. Herein, we characterized the gut microbiota of C. suppressalis populations fed on two hosts (i.e., water-oats fruit pulps and rice seedlings), by sequencing the V3–V4 hypervariable region of the 16S rRNA gene using the Illumina MiSeq platform. Gut bacterial communities showed variation in relative abundance among C. suppressalis populations fed on water-oats fruit pulps or rice seedlings. Proteobacteria and Firmicutes became the predominant phyla, and Enterobacteriaceae, Enterococcaceae and Halomonadaceae were the predominant family in all C. suppressalis populations. The highest bacteria diversity was found in the midgut of the rice population fed on water-oat fruit pulps. Bacterial communities in the midgut were more diverse than those in the hindgut. The bacterial genera distribution showed great differences due to diet types and gut compartments among populations. Our results demonstrated that the host plants tested had a considerable impact on gut bacterial composition of C. suppressalis populations. Additionly, the unique gut morphology and physiological conditions (viz., oxygen content, enzymes) also contributed to variation in microbiomes. In conclusion, our study provided an important insight into investigation of insect-bacteria symbioses, and biocontrol of this species and other related lepidopterans.

Immunological interactions of Chilo suppressalis Walker (Lepidoptera: Crambidae) with the native entomopathogenic fungi

Entomopathogenic fungi can attack many insect hosts and have been applied as the eco-friendly alternatives to synthetic chemicals for the control of pests. Insects have developed different defense systems encountering entomopathogens including humoral and cellular immune responses. In the present study, injection of some native entomopathogenic fungi to the Chilo suppressalis Walker larvae resulted in an enhancement of the cellular and antimicrobial defenses. The numbers of total and differential hemocytes increased rapidly in the first 3 and 6 h but those gradually reduced 12 and 24 h post-injections. The nodule formation and phenoloxidase activity increased at the time intervals after fungal infection. A similar trend was found in the transcription of antimicrobial peptides including attacin1 and 2, cecropin1 and 2, gallerimycin, defensin, lysozyme, and prophenoloxidase-activating proteinase-3 during infection fungi. In all cases, the target gene transcription was upper in the larvae injected by the fungi than that of control larvae. These results may elucidate better knowledge on the interaction of the fungi present in agroecosystems with the target insect pest.

Screening and Virulence of the Entomopathogenic Fungi Associated with Chilo suppressalis Walker.

The current study aimed to explore the entomopathogenic fungi associated with the larvae of Chilo suppressalis Walker, a serious pest of rice, in northern Iran. The collected specimens were cultured and identified through morphological and molecular methods. The 38 specimens were identified by microscopic examination and genetic sequencing of the ITS region as follows: twenty-one isolates of Beauveria bassiana, five isolates of Akanthomyces lecanii, four isolates of Akanthomyces muscarious, three isolates of Metarhizium anisopliae, two isolates of Hirsutella subulata, two isolates of Trichoderma sp. and one isolate of Aspergillus sp. All the identified isolates were treated on the larvae through bioassay, evaluating the amount of hydrophobin and the activities of proteases, chitinases and lipase to find their virulence. Moreover, the percentage of thermotolerant and cold activity of the isolates were tested to determine their environmental persistence. The overall results revealed the isolates of B. bassiana, including BBRR1, BBAL1 and BBLN1 as the most virulent and environmental adaptive isolates among the fungi associated with C. suppressalis.

Incidence of Wohlbachia, cardinium, spiroplasma and Phage Wo in Different Geographical Populations of Chilo suppressalis (Lepidoptera: Pyralidae) from China

Using specific primers, we measured the infection status of Wolbachia, WO, Cardinium, and Spiroplasma in Chilo suppressalis (Walker) (Lepidoptera: Crambidae) collected from 14 locations in China, and conducted phylogenetic analysis of the three endosymbionts. The results showed that eight geographical populations of C. suppressalis were infected by Wolbachia. The infection rates of Wolbachia in four geographical populations had no significant difference between 2011 and 2012 (P>0.05). There were five geographical populations infected with Cardinium and seven geographical populations infected with Spiroplasma. Seven populations of C. suppressalis carrying Wolbachia were also infected with WO. The maximum parsimony tree shows that Wolbachia from C. suppressalis, Pieris rapae, Coliaserate poliographus and Tetranychus urticae fall into the same clade. Cardinium from C. suppressalis joins together with Cardinium from Oppiella nova. Spiroplasma in C. suppressalis has a close relationship with that of Fannia manicata. In conclusion, infections of three endosymbionts showed regional differences, and there were eight geographical populations infected with more than one endosymbiont. Our study found, for the first time, double infection with Wolbachia and Spiroplasma in one sample from Xinzhou. Phylogenetic analysis of the three endosymbionts proved that the endosymbionts can transfer horizontally between different individuals of the same or different hosts.

Mechanisms for multiple resistances in field populations of rice stem borer, Chilo suppressalis (Lepidoptera: Crambidae) from Sichuan Province, China

Chilo suppressalis Walker (Lepidoptera: Crambidae) is a widely destructive pest occurring in rice, particularly in the rice-growing regions of Asia. In recent years, C. suppressalis has developed resistance to several insecticides because of the extensive use of insecticides. The resistance levels to four insecticides were determined among populations from different regions of Sichuan Province, China, using a drop-method bioassay. Based on LC50 values of a laboratory susceptible strain, all field populations showed moderate level of resistance to triazophos (23.9- to 83.5-fold) and were either susceptible or had a low level of resistance to abamectin (2.1- to 5.8-fold). All field-collected populations had a low or moderate level of resistance to chlorpyrifos (1.7- to 47.1-fold) and monosultap (2.7- to 13.5-fold). The synergism experiment indicated that the resistance of the XW19 to triazophos may be associated with cytochrome P450 monooxygenases (P450s), with the highest synergistic ratio (SR) of 3.05-fold and increased ratio (IR) of 2.28-fold for piperonylbutoxide (PBO). The P450 activity of the TJ19 population was the greatest among the six field populations. Moreover, the relative expression levels of four resistance-related P450 genes were detected with qRT-PCR, and the results indicated that CYP324A12, CYP321F3 and CYP9A68 were overexpressed in the resistant population, especially in the XW19 population (by 1.2-, 3.4 -, and 18.0-fold, respectively). In addition, the relative expression levels of CYP9A68 among the CZ19 and TJ19 populations were also enhanced 10.5- and 24.9-fold, respectively. These results suggested that CYP324A12, CYP321F3 and CYP9A68 may be related to the resistance development of C. suppressalis to triazophos.

Genetic structure of rice striped stem borer, Chilo suppressalis (Lepidoptera:Crambidae) in North of Iran

Information on the genetic structure of rice striped stem borer, Chilo suppressalis (Walker), is essential for an effective pest management program and can corporate with control program and prompt the modification of current control methods. In this study, the genetic structure of COI gene has been investigated for 18 populations of this pest in north of Iran. Chilo suppressalis specimens were collected from rice fields on rice and weeds in Guilan and Mazanderan provinces, at Caspian Sea coast at both seasonal activity (spring) and overwintering stage from May through October 2018 and identified using morphological characters. Genetic structure of 18 populations of the species was evaluated using polymerase chain reaction (PCR)-direct-sequencing of a fragment (869 bp) of mtDNA-COI gene. Results revealed that almost all specimens from different generations, hosts, and locations belong to a single haplotype very close to a South Korean haplotype. To the best our knowledge, it is the first comprehensive molecular typing of striped stem borer in both Northern provinces of the country and suggests a high gene flow among different populations of this pest in the region.

The response to flooding of two overwintering rice stem borers likely accounts for their changing impacts

The rice striped stem borer (SSB), Chilo suppressalis Walker, and the rice yellow stem borer (YSB), Scirpophaga incertulas Walker, are two of the most damaging pests of rice plant, whose relative crop damage has changed in recent years. Here, we carried out experiments and surveys to understand the potential impact of field flooding on populations of these species. YSB had a consistently higher mortality rate than SSB in overwintering populations. We show that SSB survived under submersion better than YSB, crawled more strongly than YSB, and escaped more effectively from a waterlogged environment than YSB. These differences may relate partly to the longer abdominal prolegs and thoracic legs of SSB than YSB. These factors likely explain why YSB has a higher mortality rate than SSB in overwintering populations and why the relative importance of YSB is declining in some areas. In addition, the flooding method provides an effective cultural practice for some crops. Our results uncover the reasons why flooding practice is more effective for YSB than SSB. The results also point to an effective control measure for YSB.

Cloning and functional identification of a Chilo suppressalis-inducible promoter of rice gene, OsHPL2.

Promoters play a key role in driving insect-resistant genes during breeding of transgenic plants. In current transgenic procedures for breeding rice resistance to striped stem borer (Chilo suppressalis Walker, SSB), the constitutive promoter is used to drive the insect-resistant gene. To reduce the burden of constitutive promoters on plant growth, isolation and identification of insect-inducible promoters are particularly important. However, few promoters are induced specifically by insect feeding. We found rice hydroperoxide lyase gene (OsHPL2) (LOC_Os02g12680) was upregulated after feeding by SSB. We subsequently cloned the promoter of OsHPL2 and analysed its expression pattern using the β-glucuronidase (GUS) reporter gene. Histochemical assays and quantitative analyses of GUS activity confirmed that P HPL2 :GUS was activated by SSB, but did not respond to brown planthopper (Nilaparvata lugens Stål, BPH) infestation, mechanical wounding or phytohormone treatments. A series of 5' truncated assays were conducted and three positive regulatory regions (-1452 to -1213, -903 to -624, and -376 to -176) induced by SSB infestation were identified. P2R123-min 35S and P2TR2-min 35S promoters linked with cry1C of transgenic plants showed the highest levels of Cry1C protein expression and SSB larval mortality. We identified an SSB-inducible promoter and three positive internal regions. Transgenic rice plants with the OsHPL2 promoter and its positive regions driving cry1C exhibited the expected larvicidal effect on SSB. Our study is the first report of an SSB-inducible promoter that could be used as a potential resource for breeding insect-resistant transgenic crops. © 2020 Society of Chemical Industry.