Chilo Suppressalis Research Articles

Genome-wide identification and functional analysis of long non-coding RNAs in Chilo suppressalis reveal their potential roles in chlorantraniliprole resistance.

Long non-coding RNAs, referred to as lncRNAs, perform essential functions in some biological processes, including reproduction, metamorphosis, and other critical life functions. Yet, lncRNAs are poorly understood in pesticide resistance, and no reports to date have characterized which lncRNAs are associated with chlorantraniliprole resistance in Chilo suppressalis. Here, RNA-seq was performed on two strains of C. suppressalis exposed to chlorantraniliprole: one is a susceptible strain (S), and the other is a resistant strain (R). In total, 3,470 lncRNAs were identified from 40,573 merged transcripts in six libraries, including 1,879 lincRNAs, 245 intronic lncRNAs, 853 sense lncRNAs, and 493 antisense lncRNAs. Moreover, differential expression analysis revealed 297 and 335 lncRNAs upregulated in S and R strains, respectively. Differentially expressed (DE) lncRNAs are usually assumed to be involved in the chlorantraniliprole resistance in C. suppressalis. As potential targets, adjacent protein-coding genes (within <1000kb range upstream or downstream of DE lncRNAs), especially detoxification enzyme genes (cytochrome P450s, carboxyl/cholinesterases/esterases, and ATP-binding cassette transporter), were analyzed. Furthermore, the strand-specific RT-PCR was conducted to confirm the transcript orientation of randomly selected 20 DE lincRNAs, and qRT-PCR was carried out to verify the expression status of 8 out of them. MSTRG.25315.3, MSTRG.25315.6, and MSTRG.7482.1 were upregulated in the R strain. Lastly, RNA interference and bioassay analyses indicated overexpressed lincRNA MSTRG.7482.1 was involved in chlorantraniliprole resistance. In conclusion, we represent, for the first time, the genome-wide identification of chlorantraniliprole-resistance-related lncRNAs in C. suppressalis. It elaborates the views underlying the mechanism conferring chlorantraniliprole resistance in lncRNAs.

Factors affecting rice wastage in Mazandaran Province, Iran

This study investigated factors influencing rice wastage in Mazandaran Province, Iran. The wastage was estimated by a combination of the Delphi technique and interviews. Nineteen experts were sampled by snowball sampling for the Delphi technique. In addition, a sample of 258 farmers was sampled using Cochran's formula. Ordinal logistic regression using STATA Software was employed for data analysis. According to the results, 12 local factors influencing rice wastage were derived among which 'pests (Chilo suppressalis, Ephydra afghanica Dahl, etc.)', accounting for 5% of the wastage, was found to be the most important cause of wastage in the region. The findings also showed six factors - including age, educational level, farm area, mean crop yield, number of machines owned, and waste management knowledge - had significant and positive impact on increasing the wastage and discriminated the paddy growers in four groups, i.e., farmers with low, relatively low, relatively high and high wastage.

Molecular and functional analysis of chitin synthase genes in Chilo suppressalis (Lepidoptera: Crambidae).

The rice stem borer, Chilo suppressalis, has developed a high level of resistance to many of the compounds currently used for control. There is therefore an urgent need to develop novel control methods for C.suppressalis. Insect chitin synthases (CHS) have attracted interest as a potential target for insect pest management. However, to date, CHS have not been characterized in C.suppressalis. Two CHS genes (CsCHS1 and CsCHS2) were identified and cloned from C.suppressalis. Two transcript variants were identified for CsCHS1, CsCHS1a and CsCHS1b. Spatiotemporal expression profiling showed that both transcripts of CsCHS1 are most highly expressed on the last day of each larval instar stage and show the highest expression levels in the integument. In contrast, CsCHS2 is predominantly expressed during the larval feeding stages and shows the highest expression levels in the midgut. Knockdown of CsCHS1 by RNA interference significantly inhibited the molting and pupation of C.suppressalis, and knockdown of CsCHS2 significantly affected growth during the larval stage, but had no significant effect on the pupation. Moreover, knockout of CsCHS1 by CRISPR/Cas9 genome editing severely lowered the hatching rate, larval survivorship, pupation rate, and eclosion rate, but only larval survivorship at the G0 generation was lowered after the knockout of CsCHS2. These results demonstrate that CsCHS1 and CsCHS2 play vital roles in the growth and development of C.suppressalis, and so have potential as insecticidal targets for the control of this highly damaging pest.

Prospects for Integrating Augmentative and Conservation Biological Control of Leaffolders and Stemborers in Rice

Possibilities to combine augmentative biological control using Trichogramma spp. egg parasitoids and conservation biological control through habitat manipulation, for the management of rice leaffolder and rice stemborer pests have received only cursory mention in the literature. We reviewed information on the use of Trichogramma releases and on habitat manipulation to manage leaffolders and stemborers in rice. Stemborers have become a priority for biological control since the 1990s with research focusing mainly on Chilo suppressalis in China and Iran, Scirpophaga incertulas in South and Southeast Asia, and Chilo agamemnon in Egypt. In most cases, 100 K wasps (T. japonicum or T. chilonis) released over 30–100 release points ha−1 at least once during early crop stages, resulted in good control (&gt;50% reduction in damage). Despite positive results accumulated over decades, larger scale releases in rice have only been conducted very recently. Research on conservation biological control of stemborers has focused on manipulating rice field habitat, particularly along rice bunds (levees). Several studies reported higher Trichogramma densities or greater egg parasitism in rice fields with flowering plants on bunds compared to control fields (without bund vegetation and usually with insecticides). These trends have mainly been attributed to nectar as a supplementary food for the adult wasps, although evidence for this mechanism is weak. Trap plants, such as vetiver grass (Chrysopogon zizanioides) attract ovipositing stemborers, but suppress larval development. Repellent and banker plants have not yet been identified for rice stemborers or leaffolders. We outline the opportunities and challenges for combining augmentative and conservation biological control of leaffolders and stemborers in rice.

Stemborer-induced rice plant volatiles boost direct and indirect resistance in neighboring plants.

Herbivore-induced plant volatiles (HIPVs) are known to be perceived by neighboring plants, resulting in induction or priming of chemical defenses. There is little information on the defense responses that are triggered by these plant-plant interactions, and the phenomenon has rarely been studied in rice. Using chemical and molecular analyses in combination with insect behavioral and performance experiments, we studied how volatiles emitted by rice plants infested by the striped stemborer (SSB) Chilo suppressalis affect defenses against this pest in conspecific plants. Compared with rice plants exposed to the volatiles from uninfested plants, plants exposed to SSB-induced volatiles showed enhanced direct and indirect resistance to SSB. When subjected to caterpillar damage, the HIPV-exposed plants showed increased expression of jasmonic acid (JA) signaling genes, resulting in JA accumulation and higher levels of defensive proteinase inhibitors. Moreover, plants exposed to SSB-induced volatiles emitted larger amounts of inducible volatiles and were more attractive to the parasitoid Cotesia chilonis. By unraveling the factors involved in HIPV-mediated defense priming in rice, we reveal a key defensive role for proteinase inhibitors. These findings pave the way for novel rice management strategies to enhance the plant's resistance to one of its most devastating pests.

Response of the rice stem borer Chilo suppressalis (Walker) and its parasitoid assemblage to landscape composition

The rice stem borer (RSB), Chilo suppressalis (Walker), is an economically important pest of rice in subtropical Asia. Up till present, it remains unknown how pest abundance and parasitoid-mediated biological control are modulated by landscape composition. In this study, 20 rice fields with varying proportion of non-crop habitat in (2000 m radius) landscape sectors were selected in China’s Jiangxi province. RSB infestation levels were highest in agriculture-dominated landscapes. Meanwhile, parasitism rate increased with pest pressure but was not related to landscape-level non-crop habitat cover. Landscape-level responses of parasitoids were species-specific and likely modulated by functional traits. The specialist parasitoid Cotesia chilonis (Munakata) responded negatively to non-crop habitat, while positive responses were recorded for the generalists Eriborus sinicus (Holmgren) and Microgaster russata (Haliday). Our work unveils the occurrence of a bottom-up cascade in which spatiotemporal rice cropping patterns shape pest pressure and parasitism dynamics, with more diverse landscapes experiencing lower RSB infestation levels. Non-crop habitats within the landscape matrix equally retained parasitoid species with varying feeding modes and attack strategies. Hence, despite its (globally) inconsistent impacts on biological control, agricultural landscape diversification can directly benefit pest suppression and thus remains a valuable component of the ecological intensification toolbox.

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.

Morphology and ultrastructure of antennal sensilla of the parasitic wasp Baryscapus dioryctriae (Hymenoptera: Eulophidae).

Baryscapus dioryctriae is an endoparasitic wasp in the pupae of many Pyralidae pests, such as Dioryctria mendacella, Ostrinia furnacalis, and Chilo suppressalis. To provide requisite background for our ongoing research on the mechanisms of host location in B. dioryctriae, the morphology, abundance, distribution, and ultrastructure of the antennal sensilla were investigated using scanning and transmission electron microscopy. The geniculate antennae of B. dioryctriae are composed of scape, pedicel, and flagellum. Eight types of sensilla including Böhm sensilla, chaetica, trichodea, basiconic capitate peg, campaniformia, placodea, coeloconica, and sensilla styloconicum with a long hair were identified on both sexes. Sexual dimorphism exists in the antennae of B. dioryctriae. The number of flagellomere in males is over females, and the subtypes and abundance of sensilla are also different between the sexes. Additionally, the possible functions of distinct sensilla were discussed, which varies from olfaction, contact chemoreceptive, mechanoreception to hygro-/thermoreception, especially, the sensilla trichodea and placodea might be involved in olfactory perception in B. dioryctriae. These results provide an essential basis for further study on chemical communication between B. dioryctriae and their hosts, and contribute to the development of B. dioryctriae becoming an effective biocontrol agent against the pests of agriculture and forestry.

Chilo suppressalis heat shock proteins are regulated by heat shock factor 1 during heat stress.

Heat shock factor 1 (HSF1) functions to maintain cellular and organismal homeostasis by regulating the expression of target genes, including those encoding heat shock proteins (HSPs). In the present study, the gene encoding HSF1 was cloned from the rice pest Chilo suppressalis, and designated Cshsf1. The deduced protein product, CsHSF1, contained conserved domains typical of the HSF1 family, including a DNA-binding domain, two hydrophobic heptad repeat domains, and a C-terminal transactivation domain. Real-time quantitative PCR showed that Cshsf1 was highly expressed in hemocytes. Expression analysis in different developmental stages of C. suppressalis revealed that Cshsf1 was most highly expressed in male adults. RNAi-mediated silencing of Cshsf1 expression reduced C. suppressalis survival at high temperatures. To investigate the regulatory interactions between Cshsf1 and Cshsps, the promoters and expression patterns of 18 identified Cshsps in C. suppressalis were analysed; four types of heat shock elements (HSEs) were identified in promoter regions including canonical, tail-tail, head-head, and step/gap. The expression of Cshsp19.0, Cshsp21.7B, Cshsp60, Cshsp70 and Cshsp90 was positively regulated by Cshsf1; however, Cshsp22.8, Cshsp702, Cshsp705 and Cshsp706 gene expression was not altered. This study provides a foundation for future studies of HSF1 in insects during thermal stress.

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.

Time-Series Transcriptomic Analysis Reveals the Molecular Profiles of Diapause Termination Induced by Long Photoperiods and High Temperature in Chilo suppressalis.

Survival and adaptation to seasonal changes are challenging for insects. Many temperate insects such as the rice stem borer (Chilo suppressalis) overcome the adverse situation by entering diapause, wherein development changes dynamically occur and metabolic activity is suppressed. The photoperiod and temperature act as major environmental stimuli of diapause. However, the physiological and molecular mechanisms that interpret the ecologically relevant environmental cues in ontogenetic development during diapause termination are poorly understood. Here, we used genome-wide high-throughput RNA-sequencing to examine the patterns of gene expression during diapause termination in C. suppressalis. Major shifts in biological processes and pathways including metabolism, environmental information transmission, and endocrine signalling were observed across diapause termination based on over-representation analysis, short time-series expression miner, and gene set enrichment analysis. Many new pathways were identified in diapause termination including circadian rhythm, MAPK signalling, Wnt signalling, and Ras signalling, together with previously reported pathways including ecdysteroid, juvenile hormone, and insulin/insulin-like signalling. Our results show that convergent biological processes and molecular pathways of diapause termination were shared across different insect species and provided a comprehensive roadmap to better understand diapause termination in C. suppressalis.

Lethal and Sublethal Effects of Fluxametamide on Rice-Boring Pest, Rice Stem Borer Chilo suppressalis

(1) Background: Fluxametamide is a novel isoxazoline insecticide. Rice stem borer Chilo suppressalis (Walker) is a destructive Lepidoptera pest of rice in China, and novel effective insecticides are required to be developed for controlling it due to its increasing resistance levels. (2) Results: In the lethal assay, the insecticidal activity of fluxametamide with median lethal dose (LD50) value of 1.308 mg/kg to the fourth-instar larvae of C. suppressalis was higher than that of chlorantraniliprole (LD50, 3.112 mg/kg) and lower than that of emamectin benzoate (LD50, 0.006 mg/kg). In the sublethal (LD10 and LD30) assay, the duration of third to sixth-instar larvae, the pupal duration, pupation rate, and life cycle rate were significantly increased in F0 generation. Both the length and weight of the ovarian tube were decreased with the dose increase of fluxametamide, and were significantly smaller in the LD30 treatment than those of the control group. In F1 generation, only the duration of eggs was significantly increased with LD30 treatment of fluxametamide, whereas other developmental parameters had no significant change. (3) Conclusion: Fluxametamide had relatively strong lethal and sublethal effects on C. suppressalis and probably was able to affect the population growth and progeny of C. suppressalis.

RNA interference knockdown of insulin receptor inhibits ovarian development in Chilo suppressalis.

The nutritional signaling pathway regulates an insect's size, development, and lifespan, as well as playing a vital role in reproduction. The insulin/insulin-like growth factor signaling (IIS) pathway plays a key role in the nutrition signaling pathway. As an integral component of the IIS pathway, insulin receptor (InR), a receptor tyrosine kinase, plays a role in the insulin pathway by controlling reproduction in many insect species. However, the precise molecular function of InR in non-model insect reproduction is poorly understood. In our study, Chilo suppressalis, a well-known rice pest, was used as a molecular system to determine the role of InR in insect reproduction. Sequencing the InR gene of C. suppressalis, comparing the amino acid sequence-specific structure, and constructing a phylogenetic tree revealed that this gene has four main domains: ligand binding L domain, Furin-like region, fibronectin type III domains, and Tyrosine kinase catalytic domain, which were all highly conserved in insects. By characterizing the spatiotemporal expression profile of InR in different developmental stages and tissues, we found that InR gene expression was highest on the 3-day old in female pupae, 6th instar larvae, and fat body on the 6-day old in female pupae. InR gene expression may promote the molting and pupation of larvae and play a role in reproduction in the fat body. Furthermore, the RNA interference knockdown of InR dramatically reduced yolk deposition and blocked oocyte maturation. After suppression of InR, the expression of several other genes fluctuated to varying degrees. In conclusion, InR is vital to reproduction and is expected to become a new target for pest management.

Landscape composition affects parasitoid body size in species-specific manner: A case study in Asian rice systems

The top-down effect of natural enemies on pests is a crucial ecosystem service supporting integrated pest management. However, the variation in morphological traits of parasitoids in different landscape contexts and the differences in parasitoid emergence rate caused by this variation are still poorly known. We measured the inter-tegular distance (ITD) and body mass of three parasitoids– Cotesia chilonis (Munakata), Eriborus sinicus (Holmgren), and Microgaster russata Haliday – on overwintering larvae of Chilo suppressalis (Walker), the rice stem borer (RSB), collected from 20 rice paddies along a landscape heterogeneity gradient. Our objectives were to assess how landscape composition and landscape diversity affect functional traits (ITD and body mass) of species-specific parasitoid, and individual body size for its impact on biological control. From a total of 5002 sampled individuals of the three parasitoids, regression analysis revealed that (1) the presence of water bodies within the landscape respectively positive affected the ITD of E. sinicus and M. russata at 2000 m scales, landscape factors had yet no discernible effects on either the body size (ITD or body mass) of C. chilonis, (2) habitats with high landscape diversity had a negative effect on body size (ITD and body mass) of the solitary parasitoids E. sinicus at 200 m scales, and (3) a significantly negative correlation was found between the parasitoid emergence rate and ITD of E. sinicus. Our findings suggest that parasitoids’ body sizes may respond differently among species to landscape features. Solitary parasitoids in our study were more sensitive to variation in habitat resource-availability than was the gregarious parasitoid. We conclude that landscape habitat changes can affect the body size and parasitism of parasitoids, modifying their biocontrol services against pests.

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.

COI-gene Based Molecular Identification of Chilo partellus Swinhoe (Lepidoptera: Pyralidae) Infesting Maize in Lahore, Pakistan

The significance of maize (Zea mays L.) is well-known across the globe. Chilo partellus Swinhoe (Lepidoptera: Pyralidae) is one of the severe biotic constraints of maize production in Afro-Asian countries like Pakistan. Mitochondrial cytochrome oxidase I (COI) is considered as a universally accurate and authentic barcoding region to identify any insect species on the molecular level. In this study, the COI gene was selected for molecular identification of C. partellus. The insect larvae were collected from maize fields in Lahore, Pakistan. The sequence results revealed an amplicon size of 717 bp, which showed 100% homology to C. partellus species present in Karnataka, India upon BLAST. Maximum likelihood-based phylogenetic analysis with Chilo suppressalis and C. infuscatelus was studied and performed using MEGA 6. Multiple sequence alignment analysis showed the similarities and differences among intra- and inter-species levels. This is one of the primary or initial reports of molecular identification of lepidopterans in Pakistan. The study recommends utilization of molecular advancement for accurate species identification.

Review on bionomics and management of rice stem borer

Rice (Oryza sativa L.) is used as staple food for the overwhelming majority of the world’s population. Rice production hampered mostly by stem borers like, yellow stem borer (Scirpophaga incertulas) pink stem borer (Sesamia inference), dark headed stem borer (Chilo polychrysus), stripped stem borer (Chilo suppressalis). For minimize the infestation farmers use different resistant rice cultivars like, TKM 6, PTB 10, Su Yai 20, Mudgo, DV 139, Taitung 16, Gontra Bidhan 3, MTU-2020, IR 50, NDR-97, etc. against stem borer population. For controlling deleterious pest population farmers mostly use insecticide which exhibit good results than any botanicals against rice pests. Other techniques including using microbial pesticides, other biocontrol agents, use of pheromones or allomones, staggered planting, synchronized planting, removal of infected leaves, steams with pruning shears, using of trap crop, etc. are effective for control rice pests. But indiscriminate use of chemical insecticides results in great economic loss with destabilizing of biodiversity and resulting cross resistance against insecticides. So, pest population ecology based sustainable management strategies of such pest species is very essential for climate smart pest management (CSPM) as well as climate smart agriculture (CSA) of rice and other crops in the near future.

FAR knockout significantly inhibits Chilo suppressalis survival and transgene expression of double-stranded FAR in rice exhibits strong pest resistance.

Chilo suppressalis is one of the most prevalent and damaging rice pests, causing significant economic losses each year. Chemical control is currently the primary method of controlling C. suppressalis. However, the indiscriminate use of chemical insecticides increases pest resistance, pollutes the environment and poses a significant health threat to humans and livestock, highlighting the need to find safer, more pest-specific and more effective alternatives to pest control. Plant-mediated RNA interference (RNAi) is a promising agricultural pest control method that is highly pest-specific and has less of an impact on the environment. Using multi-sgRNAs/Cas9 technology to delete Fatty acyl-CoA reductase (FAR) of C. suppressalis in the G0 generation, we show that downregulating FAR transcription may significantly increase the mortality rate and darken the epidermis of C. suppressalis compared with the control. Subsequently, we developed dsFAR transgenic rice lines using Agrobacterium-mediated genetic transformation and then screened three strains expressing dsFAR at high levels using transcriptional level analysis. Using transgenic rice stems, a laboratory feeding bioassay indicated that at least one line (L#10) displayed a particularly high level of insect resistance, with an insect mortality rate of more than 80%. In the field trials, dsFAR transgenic rice displayed high levels of resistance to C. suppressalis damage. Collectively, these results suggest the potential of a new environment-friendly, species-specific strategy for rice pest management.

Moth sex pheromones affect interspecific competition among sympatric species and possibly population distribution by modulating pre-mating behavior.

Premating behaviors mediated by pheromones play pivotal roles in animal mating choices. In natural populations of the striped stem borer Chilo suppressalis and the rice leaf roller Cnaphalocrocis medinalis in the rice field habitat, we discovered that Z11-16:Ald, a major component of the C. suppressalis pheromone, modulated the premating behavior of C. medinalis. Z11-16:Ald evoked a strong olfactory response in male antennae and strongly inhibited the sex pheromone trapping of male C. medinalis in the field. The functions of three C. medinalis sex pheromone receptor genes (CmedPR1-3) were verified through heterologous expression in Xenopus oocytes. CmedPR1 responded to Z11-18:OH and Z11-18:Ald, as well as the interspecific pheromone compound Z11-16:Ac of sympatric species; CmedPR2 responded to Z13-18:OH and Z13-18:Ald, as well as the sex pheromone compounds Z11-16:Ald and Z9-16:Ald of sympatric species; and CmedPR3 responded to Z11-18:OH and Z13-18:OH, as well as the interspecific pheromones Z11-16:OH, Z9-16:Ald, Z11-16:Ac, and Z11-16:Ald of sympatric species. Thus, CmedPR2 and CmedPR3 share the ligand Z11-16:Ald, which is not a component of the C. medinalis sex pheromone. Therefore, the sex pheromones of interspecific species affected the input of neural signals by stimulating the sex pheromone receptors on the antennae of male C. medinalis moths, thereby inhibiting the olfactory responses of the male moths to the sex pheromones. Our results demonstrate chemical communication among sympatric species in the rice field habitat, the recognition of intra- and interspecific sex pheromones by olfactory receptors, and how insect premating behaviors are modulated to possibly affect resource partitioning.

A luciferase reporter assay for ecdysone agonists using HEK293T cells.

Ecdysone agonists are a class of insecticides that activate the ecdysone receptor (EcR) heterodimerized with the ultraspiracle (USP). Here, we report a new luciferase reporter assay for ecdysone agonists. The assay employs mammalian HEK293T cells transiently transfected with the EcR and USP genes of Chilo suppressalis, along with the taiman (Tai) gene of Drosophila melanogaster that encodes a steroid receptor coactivator. This assay system gave results consistent with those of radioligand binding assays and showed sensitivity superior to that of the existing in vitro methods. In addition, use of the heterologous host cells precludes perturbation from intrinsic players of the ecdysone signaling, which is a potential drawback of insect cell-based methods. This reporter system is suitable for detailed structure-activity analysis of ecdysone agonists and will serve as a valuable tool for the rational design of novel insect growth regulators.