Brown Planthopper Nilaparvata Lugens Research Articles

Insecticide susceptibilities in populations of two rice planthoppers, Nilaparvata lugens and Sogatella furcifera, immigrating into Japan in the period 2005–2012

The brown planthopper Nilaparvata lugens and the whitebacked planthopper Sogatella furcifera are both important pests on rice throughout Asia. The major cause of recent outbreaks is thought to be the development of insecticide resistance. Thus, the authors monitored insecticide susceptibilities in populations of these two insects immigrating into Japan in the period 2005-2012. Ten insecticides were tested, including members of the organophosphate, carbamate, pyrethroid, neonicotinoid and phenylpyrazole groups. The LD50 values of N. lugens against imidacloprid increased from 2005 (0.7 µg g(-1)) to 2012 (98.5 µg g(-1)). The resistance ratio (LD50 value in 2012/baseline LD50 value in 1992) was 615.5. In contrast, LD50 values of N. lugens against fipronil were <1.0 µg g(-1) up to 2012, suggesting that N. lugens had developed no insecticide resistance to this insecticide. However, S. furcifera exhibited resistance against fipronil up to 2012. Except for the case of malathion, the resistances of N. lugens against members of the organophosphate and carbamate groups were closely similar in the period 2005-2012 to earlier determinations in 1984 and 1985. Species-specific insecticide resistance (imidacloprid resistance in N. lugens and fipronil resistance in S. furcifera) is ongoing in populations of the two planthoppers immigrating into Japan.

Ovarian development status and population characteristics of Sogatella furcifera (Horváth) and Nilaparvata lugens (Stål): implications for pest forecasting

AbstractMigratory behaviour in insects correlates with reproductive development in females, and migration often occurs during the pre‐reproductive stage of adults. The relationship between ovarian development and population status of the white‐backed planthopper Sogatella furcifera (Horváth) and the brown planthopper Nilaparvata lugens (Stål) was evaluated. Females of both species were captured in rice fields and light traps and then dissected in double‐season rice‐farming regions of southern China. The ovarian development of S. furcifera and N. lugens was divided into five levels, following previous studies. The population statuses of both species were examined based on the ovarian development of female adults caught in rice paddies. The ovarian development in N. lugens females caught in light traps mostly ranged from level I to level II, whereas that in S. furcifera females caught in light traps mostly ranged from level I to level III. During peak immigration, ovarian development in N. lugens females was mainly at level II, whereas that in S. furcifera females was mainly at level II and sporadically at level III. During peak emigration, both S. furcifera and N. lugens showed level I ovarian development. The temporal dynamics of ovarian development in light trap catches revealed that (i) significant emigration and partial immigration periods occur in S. furcifera, with ovarian development mainly at level I and sporadically from level II to level III and (ii) numerous immigrants of N. lugens were detected during sedentary and local breeding periods. The temporal dynamics of ovarian development provides more information than does the paddy population. Thus, this study proposes another method for pest forecasting, which is more precise and efficient than conventional forecasting methods such as light trap catching and monitoring population dynamics in rice fields.

The genome- and transcriptome-wide analysis of innate immunity in the brown planthopper, Nilaparvata lugens

BackgroundThe brown planthopper (Nilaparvata lugens) is one of the most serious rice plant pests in Asia. N. lugens causes extensive rice damage by sucking rice phloem sap, which results in stunted plant growth and the transmission of plant viruses. Despite the importance of this insect pest, little is known about the immunological mechanisms occurring in this hemimetabolous insect species.ResultsIn this study, we performed a genome- and transcriptome-wide analysis aiming at the immune-related genes. The transcriptome datasets include the N. lugens intestine, the developmental stage, wing formation, and sex-specific expression information that provided useful gene expression sequence data for the genome-wide analysis. As a result, we identified a large number of genes encoding N. lugens pattern recognition proteins, modulation proteins in the prophenoloxidase (proPO) activating cascade, immune effectors, and the signal transduction molecules involved in the immune pathways, including the Toll, Immune deficiency (Imd) and Janus kinase signal transducers and activators of transcription (JAK-STAT) pathways. The genome scale analysis revealed detailed information of the gene structure, distribution and transcription orientations in scaffolds. A comparison of the genome-available hemimetabolous and metabolous insect species indicate the differences in the immune-related gene constitution. We investigated the gene expression profiles with regards to how they responded to bacterial infections and tissue, as well as development and sex expression specificity.ConclusionsThe genome- and transcriptome-wide analysis of immune-related genes including pattern recognition and modulation molecules, immune effectors, and the signal transduction molecules involved in the immune pathways is an important step in determining the overall architecture and functional network of the immune components in N. lugens. Our findings provide the comprehensive gene sequence resource and expression profiles of the immune-related genes of N. lugens, which could facilitate the understanding of the innate immune mechanisms in the hemimetabolous insect species. These data give insight into clarifying the potential functional roles of the immune-related genes involved in the biological processes of development, reproduction, and virus transmission in N. lugens.

Proteome Analysis of Rice (Oryza sativa L.) Mutants Reveals Differentially Induced Proteins during Brown Planthopper (Nilaparvata lugens) Infestation

Although rice resistance plays an important role in controlling the brown planthopper (BPH), Nilaparvata lugens, not all varieties have the same level of protection against BPH infestation. Understanding the molecular interactions in rice defense response is an important tool to help to reveal unexplained processes that underlie rice resistance to BPH. A proteomics approach was used to explore how wild type IR64 and near-isogenic rice mutants with gain and loss of resistance to BPH respond during infestation. A total of 65 proteins were found markedly altered in wild type IR64 during BPH infestation. Fifty-two proteins associated with 11 functional categories were identified using mass spectrometry. Protein abundance was less altered at 2 and 14 days after infestation (DAI) (T1, T2, respectively), whereas higher protein levels were observed at 28 DAI (T3). This trend diminished at 34 DAI (T4). Comparative analysis of IR64 with mutants showed 22 proteins that may be potentially associated with rice resistance to the brown planthopper (BPH). Ten proteins were altered in susceptible mutant (D1131) whereas abundance of 12 proteins including S-like RNase, Glyoxalase I, EFTu1 and Salt stress root protein “RS1” was differentially changed in resistant mutant (D518). S-like RNase was found in greater quantities in D518 after BPH infestation but remained unchanged in IR64 and decreased in D1131. Taken together, this study shows a noticeable level of protein abundance in the resistant mutant D518 compared to the susceptible mutant D1131 that may be involved in rendering enhanced level of resistance against BPH.

OsMPK3 positively regulates the JA signaling pathway and plant resistance to a chewing herbivore in rice

KEY MESSAGE : Silencing OsMPK3 decreased elicited JA levels, which subsequently reduced levels of herbivore-induced trypsin protease inhibitors (TrypPIs) and improved the performance of SSB larvae, but did not influence BPH. Mitogen-activated protein kinases (MPKs) are known to play an important role in plant defense by transferring biotic and abiotic signals into programmed cellular responses. However, their functions in the herbivore-induced defense response in rice remain largely unknown. Here, we identified a MPK3 gene from rice, OsMPK3, and found that its expression levels were up-regulated in response to infestation by the larvae of the striped stem borer (SSB) (Chilo suppressalis), to mechanical wounding and to treatment with jasmonic acid (JA), but not to infestation by the brown planthopper (BPH) Nilaparvata lugens or to treatment with salicylic acid. Moreover, mechanical wounding and SSB infestation induced the expression of OsMPK3 strongly and quickly, whereas JA treatment induced the gene more weakly and slowly. Silencing OsMPK3 (ir-mpk3) reduced the expression of the gene by 50-70%, decreased elicited levels of JA and diminished the expression of a lipoxygenase gene OsHI-LOX and an allene oxide synthase gene OsAOS1. The reduced JA signaling in ir-mpk3 plants decreased the levels of herbivore-induced trypsin protease inhibitors (TrypPIs) and improved the performance of SSB larvae, but did not influence BPH. Our findings suggest that the gene OsMPK3 responds early in herbivore-induced defense and can be regulated by rice plants to activate a specific and appropriate defense response to different herbivores.

Cover Caption

RNA interference (RNAi) has been considered as a potential strategy for insect pest control especially for sucking insects, for example, planthoppers, aphids and psyllids. Metamorphosis is a unique developmental model of insects. Therefore, using RNAi technology, regulating the key genes during insect growth and development will not affect other organisms. This strategy probably realizes biological and ecological safety of insect pest control. Photo in cover shows a brown planthopper Nilaparvata lugens molting. Photo provided by Prof. Xue‐Xia Miao.

Genome‐wide analysis of Nilaparvata lugens nymphal responses to high‐density and low‐quality rice hosts

The brown planthopper (BPH) Nilaparvata lugens is an economically important pest on rice plants. In this study, the higher population density and yellow-ripe stage of rice plants were used to construct adverse survival conditions (ASC) against BPH nymphs. Simultaneously, the low population density and tillering stage of rice plants were used to establish a suitable survival condition (SSC) as a control. Solexa/Illumina sequencing was used to identify genes of BPH nymphs responding to ASC. Significantly longer duration development of BPH nymphs and significantly lower brachypterous ratio of BPH adults were observed by ASC compared with SSC. A total of 2 544 differentially expressed genes (DEGs) were obtained and analyzed by BLASTx, Gene Ontology and KEGG Orthology. Gene ontology analysis revealed that the DEGs were mainly involved in categories of cell, cell part, cellular process, binding, catalytic, organelle and metabolic processes. 1 138 DEGs having enzyme commission numbers were assigned to different metabolic pathways. The largest clusters were neurodegenerative diseases (137, 12.0%), followed by carbohydrate metabolism (113, 9.9%), amino acid metabolism (94, 8.3%), nucleotide metabolism (76, 6.7%), energy metabolism (64, 5.6%), translation (60, 5.3%), lipid metabolism (58, 5.1%), and folding, sorting and degradation (52, 4.6%). Expressing profile of 11 DEGs during eight nymphal developmental stages of BPH were analyzed by quantitative real-time polymerase chain reaction. The 11 genes exhibited differential expression between ASC and SSC during at least one developmental stage. The DEGs identified in this study provide molecular proof of how BPH reconfigures its gene expression profile to adapt to overcrowding and low-quality hosts.

Southern rice black-streaked dwarf virus: a white-backed planthopper-transmitted fijivirus threatening rice production in Asia

Southern rice black-streaked dwarf virus (SRBSDV), a non-enveloped icosahedral virus with a genome of 10 double-stranded RNA segments, is a novel species in the genus Fijivirus (family Reoviridae) first recognized in 2008. Rice plants infected with this virus exhibit symptoms similar to those caused by Rice black-streaked dwarf virus. Since 2009, the virus has rapidly spread and caused serious rice losses in East and Southeast Asia. Significant progress has been made in recent years in understanding this disease, especially about the functions of the viral genes, rice–virus–insect interactions, and epidemiology and control measures. The virus can be efficiently transmitted by the white-backed planthopper (WBPH, Sogatella furcifera) in a persistent circulative propagative manner but cannot be transmitted by the brown planthopper (Nilaparvata lugens) and small brown planthopper (Laodelphax striatellus). Rice, maize, Chinese sorghum (Coix lacryma-jobi) and other grass weeds can be infected via WBPH. However, only rice plays a major role in the virus infection cycle because of the vector’s preference. In Southeast Asia, WBPH is a long-distance migratory rice pest. The disease cycle can be described as follows: SRBSDV and its WBPH vector overwinter in warm tropical or sub-tropical areas; viruliferous WBPH adults carry the virus from south to north via long-distance migration in early spring, transmit the virus to rice seedlings in the newly colonized areas, and lay eggs on the infected seedlings; the next generation of WBPHs propagate on infected seedlings, become viruliferous, disperse, and cause new disease outbreaks. Several molecular and serological methods have been developed to detect SRBSDV in plant tissues and individual insects. Control measures based on protection from WBPH, including seedbed coverage, chemical seed treatments, and chemical spraying of seedlings, have proven effective in China.

褐飞虱致害性研究进展

褐飞虱(Nilaparvata lugens Stal，Homoptera: Delphacidae)是一种重要的水稻害虫，可以直接取食或将病菌和病毒传给水稻，从而给粮食生产带来巨大损失。目前，由于能克服寄主抗性的新褐飞虱致害性种群出现，导致其危害越来越严重。研究褐飞虱致害性遗传变异规律对于抗性品种的选育与应用具有很重要的意义。本文就褐飞虱致害性种群的田间发生情况，鉴定方法，遗传分析，分子生物学和内共生菌等方面进行了阐述。 Brown planthopper (Nilaparvata lugens Stal) (Homoptera: Delphacidae) is economically impor- tant pest on rice that feed directly or serve as vectors of pathogenic microorganisms and viruses to crops, re- sulting in significant damage and yield losses for farmers. In recent decades, brown planthopper has become notorious due to the emergence of new, virulent populations that can overcome host resistance. Thus, it is important to study virulent variation of the brown planthopper for the breeding and applying of resistant rice varieties. In this study, I review that the virulent population of brown planthopper distributed in rice fields and that the other content included the method of identification, the analysis of genetic basis, molecular boil- ogy and the relation of virulence with symbionts.

Snowdrop lectin (Galanthus nivalis agglutinin: GNA) 유전자 도입에 의한 벼멸구 저항성 형질전환 벼 개발

Transgenic rice plants with increased resistance to rice brown planthopper (Nilaparvata lugens Stal) were generated by particle bombardment-mediated transformation of plants with a gene encoding snowdrop lectin (Galanthus nivalis agglutinin; GNA) under control of the rice Rubisco small subunit (rbcS) promoter.. A large number of transgenic rice plants containing the GNA gene were generated. The integration, expression, and inheritance of this gene in the R1 and R2 generations were demonstrated by Southern and western blot analyses. The plants contained one to five copies of the transgene. The GNA protein comprised approximately 0.01-2.0% of total soluble protein in the R1 and R2 transgenic plants. Insect bioassays and feeding studies showed that the GNA protein expressed in the R2 transgenic rice plants reduced the survival of brown planthoppers. The introduction of GNA into rice plants therefore can help to control insect pests.

Rice Resistance to Planthoppers and Leafhoppers

For over 50 years, host-plant resistance has been regarded as an efficient method to reduce yield losses to rice caused by delphacid and cicadelid hoppers. Already a number of resistant rice varieties have been developed and deployed throughout Asia. To date, over 70 hopper resistance genes have been identified in rice; however, less than 10 genes have been deliberately introduced to commercial rice varieties. Currently, due to recent brown planthopper (Nilaparvata lugens [Stål]) and whitebacked planthopper (Sogatella furcifera [Horvath]) outbreaks occurring at an unprecedented scale, researchers are working toward a second generation of resistant varieties using newly identified gene loci and applying new molecular breeding methods. This paper reviews advances in the identification of resistance genes and QTLs against hoppers in rice. It collates all published information on resistance loci and QTLs against the major rice planthoppers and leafhoppers and presents information on gene locations, genetic markers, differential varieties, and wild rice species as sources of resistance. The review indicates that, whereas progress in the identification of genes has been rapid, considerable tidying of the information is required, especially regarding gene nomenclature and resistance spectra. Furthermore, sound information on gene functioning is almost completely lacking. However, hopper responses to resistance mechanisms are likely to be similar because a single phenotyping technique has been applied by most national and international breeding programs during germplasm screening. The review classifies genes occurring at two chromosome regions associated with several identified resistance loci and highlights these (Chr4S: BphR-R and Chr12L: BphR-R) as general stress response regions. The review calls for a greater diversity of phenotyping methods to enhance the durability of resistant varieties developed using marker-aided selection and emphasizes a need to anticipate the development of virulent hopper populations in response to the field deployment of genes.

Effects of the insecticide triazophos on the ultrastructure of the flight muscle of the brown planthopper Nilaparvata lugens Stål (Hemiptera: Delphacidae)

The brown planthopper (BPH), Nilaparvata lugens (Stål) (Hemiptera: Delphacidae), is a long-distance migratory insect pest in temperate eastern Asia and is a classical resurgent rice pest that is induced by insecticides. Knowledge of the effect of insecticides on the flight capacity of insects is needed to understand their migration, which may help to improve the management of insect pests. Our previous study demonstrated that some insecticides enhance the flight capacity of BPH. However, the effect of insecticides on the flight muscle of BPH is not well understood. Thus, the present study examined the effect of triazophos, a classical insecticide that induces the resurgence of BPH, on the ultrastructure of macropterous females using transmission electron microscopy. The results showed that the diameter of myofibrils one and two days after adult female emergence (DAE) following treatment with 40 ppm triazophos was significantly greater than that of the control, increasing by 31.4 and 21.5%, respectively. In addition, the length of the sarcomeres at two and three DAE was significantly greater than that of the control, increasing by 73.8 and 50.8%, respectively. The percentage of mitochondrial volume in the muscle fibres at one and two DAE was 146.2 and 67.7% greater than that of the control, respectively. These findings show that the mechanisms of triazophos-induced enhancement of the flight capacity of BPH involve changes in the ultrastructure of the flight muscle.

Heat Stress Impedes Development and Lowers Fecundity of the Brown Planthopper Nilaparvata lugens (Stål)

This study investigated the effects of sub-lethal high temperatures on the development and reproduction of the brown plant hopper Nilaparvata lugens (Stål). When first instar nymphs were exposed at their ULT50 (41.8°C) mean development time to adult was increased in both males and females, from 15.2±0.3 and 18.2±0.3 days respectively in the control to 18.7±0.2 and 19±0.2 days in the treated insects. These differences in development arising from heat stress experienced in the first instar nymph did not persist into the adult stage (adult longevity of 23.5±1.1 and 24.4±1.1 days for treated males and females compared with 25.7±1.0 and 20.6±1.1 days in the control groups), although untreated males lived longer than untreated females. Total mean longevity was increased from 38.8±0.1 to 43.4±1.0 days in treated females, but male longevity was not affected (40.9±0.9 and 42.2±1.1 days respectively). When male and female first instar nymphs were exposed at their ULT50 of 41.8°C and allowed to mate on reaching adult, mean fecundity was reduced from 403.8±13.7 to 128.0±16.6 eggs per female in the treated insects. Following exposure of adult insects at their equivalent ULT50 (42.5°C), the three mating combinations of treated male x treated female, treated male x untreated female, and untreated male x treated female produced 169.3±14.7, 249.6±21.3 and 233.4±17.2 eggs per female respectively, all significantly lower than the control. Exposure of nymphs and adults at their respective ULT50 temperatures also significantly extended the time required for their progeny to complete egg development for all mating combinations compared with control. Overall, sub-lethal heat stress inhibited nymphal development, lowered fecundity and extended egg development time.

Intermediate herbivory intensity of an aboveground pest promotes soil labile resources and microbial biomass via modifying rice growth

The importance of aboveground herbivores for modifying belowground ecosystems has prompted numerous studies; however, studies can be biased by context dependent conditions which lead to extremely inconsistent results. So far, the impacts of herbivory intensity by important rice pests on rice paddy soil ecosystems are lacking. The aim of this study was to test the hypothesis that intermediate herbivory intensity of the brown planthopper (Nilaparvata lugens Stal) could promote soil labile resources and microbial biomass, while high intensity would show a reverse pattern, by mediating rice plant growth. This study will also help the development of integrative pest management. Four hopper infestation density treatments (0, 4, 8 and 12 nymphs per rice plant) and two infestation duration treatments (9 and 15 days after N. lugens infestation, DAI 9 and DAI 15) were established in a glasshouse experiment. Soil and plant were sampled destructively from four replicates and analysed for soil labile resources availability, soil microbial biomass and plant performance, respectively. The infestation density significantly affected both shoot and root mass of rice (P < 0.05), soil dissolved organic carbon (DOC) and nitrogen (DON), and microbial biomass carbon (MBC) and nitrogen (MBN), and the effects were further enhanced by prolonged infestation duration. Compared to the control (CK) without N. lugens, plant dry mass, DOC, DON, MBC and MBN increased under low (LD) and moderate hopper densities (MD) but decreased under high density (HD) on DAI 9. Moreover, the LD treatment exerted the most promotional effects on DAI 15. Rice root to shoot ratio generally increased in treatments subjected to herbivory. The labile resources and microbial biomass showed close relationships with both shoot and root mass across treatments, in particular with root mass on DAI 15. Such a trend indicated that the shift of photosynthate allocation to belowground contributed to changes of soil resource availability and microbial biomass. Intermediate herbivory intensity showed positive effects on rice seedling performance and, further, promoted soil labile resource availability and microbial biomass. The importance of extrapolating temporal and spatial scale, i.e. from the short-term greenhouse experiment to an entire rice growing season in the field, was highlighted.

Isolation and characterization of microsatellite markers in brown planthopper (Nilaparvata lugens Stål).

Brown planthopper (Nilaparvata lugens Stål) (Homoptera: Delphacidae) is an economically important pest on rice. In this study, 30 polymorphic microsatellite markers were developed from N. lugens genomic libraries using the method of Fast Isolation by AFLP of Sequence Containing Repeats (FIASCO). Polymorphism of each locus was detected in 48 individuals from two natural populations. These microsatellite loci revealed 2 to 18 alleles, and the expected and observed heterozygosities ranged from 0.042 to 0.937 and from 0.042 to 0.958, respectively. These markers will be useful for the future study of this agricultural pest in population genetics and molecular genetics.

Susceptibility to insecticides of brown planthopper Nilaparvata lugens in the lower Yangtze valley

Adult brown planthopper (BPH), more than 50 females of each population, have been collected from ricefields of Anqing (Anhui Province) and Yangzhou (Jiangsu Province) and multiplied with rice in the laboratory at 25°C, 16 h photoperiod since 1989. Assays were conducted using female adults of F 2 -F 3 within 5 d after emergence by the topical treatment method. Technical grade insecticides were dissolved in analytical grade acetone and five or more diluted concentrations were prepared. For each concentration, 50 macropterous females were treated with 0.05 μL of solution applied by microsyringe on the thoracic dorsum. Monitoring was done 48 h after treatment. Dose-mortality regressions were estimated by probit analysis. LD 50 s were considered to be indicative of resistance and their differences among years were tested by t test.

Specific herbivore‐induced volatiles defend plants and determine insect community composition in the field

In response to insect attack, plants release complex blends of volatile compounds. These volatiles serve as foraging cues for herbivores, predators and parasitoids, leading to plant-mediated interactions within and between trophic levels. Hence, plant volatiles may be important determinants of insect community composition. To test this, we created rice lines that are impaired in the emission of two major signals, S-linalool and (E)-β-caryophyllene. We found that inducible S-linalool attracted predators and parasitoids as well as chewing herbivores, but repelled the rice brown planthopper Nilaparvata lugens, a major pest. The constitutively produced (E)-β-caryophyllene on the other hand attracted both parasitoids and planthoppers, resulting in an increased herbivore load. Thus, silencing either signal resulted in specific insect assemblages in the field, highlighting the importance of plant volatiles in determining insect community structures. Moreover, the results imply that the manipulation of volatile emissions in crops has great potential for the control of pest populations.

Chitin synthase 1 gene and its two alternative splicing variants from two sap-sucking insects, Nilaparvata lugens and Laodelphax striatellus (Hemiptera: Delphacidae)

Chitin synthase (CHS) is an enzyme that is required for chitin formation in insect cuticles and other tissues. In this study, CHS genes from two destructive rice insect pests, the brown planthopper Nilaparvata lugens and the small brown planthopper Laodelphax striatellus, were cloned. Phylogenetic analysis showed that these genes belonged to class CHS1 of the CHS gene family. Most insects possess two CHS genes (CHS1 and CHS2); however, genome and transcriptome searches showed that N. lugens possibly possess only CHS1 in both databases. Two transcript variants (CHS1a and CHS1b) resulting from exclusively alternative splicing (exon 19a or 19b in N. lugens) were identified for each of the two rice planthopper CHS1s. Gene structure comparison using the genomes that are currently sequenced showed that the CHS1 genes in all insects except Acyrthosiphon pisum have two transcript variants. Transcription of NlCHS1a reached its highest level just after molting, whereas NlCHS1b reached its highest expression level 1–2 days before molting. Injection of the N. lugens nymphs with double-strand RNA (dsRNA) of CHS1, CHS1a and CHS1b reduced the corresponding variant transcript levels and exhibited subsequent phenotypes. Silencing of CHS1 and CHS1a resulted in elongated distal wing pads and the “wasp-waisted” or crimpled cuticle phenotypes and eventually died, whereas the phenotypes caused by injection of NlCHS1b dsRNA seem not so obvious although slightly increased mortality was observed. Our results suggest that N. lugens likely lacks CHS2 and CHS1 may be efficient target gene for RNAi-based N. lugens control.

Investigation of the predation potential of different fish species on brown planthopper (Nilaparvata lugens (Stål)) in experimental rice-fish aquariums and tanks

A series of experiments was conducted in rice (Oryza sativa L.)-fish aquariums and concrete tanks at Can Tho University, Vietnam, to investigate the feeding behavior and ability to control brown planthopper (BPH) (Nilaparvata lugens (Stål)) by fish. In the aquarium studies, fish species introduced were: (1) no fish (control), (2) common carp (Cyprinus carpio carpio L.), (3) Nile tilapia (Oreochromis niloticus niloticus L.), (4) climbing perch (Anabas testudineus Bloch), and (5) clown knife (Chitala chitala Hamilton). We found that C. carpio and O. niloticus mostly grazed on filamentous algae as well as periphyton on aquarium walls, bottom and rice tillers in water. They hardly grazed on BPH on the surface. On the contrary, A. testudineus mostly grazed on BPH on rice tillers above the water surface. C. chitala spent a lot of time at the bottom corners of the aquariums without grazing on BPH. A. testudineus spent more time attempting to graze BPH, especially on rice tillers above the water surface as compared to C. carpio and O. niloticus. This resulted in a higher number of BPH eaten by A. testudineus than by C. carpio and O. niloticus. As A. testudineus was the most promising predator of late instar nymphs and adult BPH in the aquarium studies, different sizes of this species were further tested in rice-fish concrete tank conditions at three development stages of the rice crop. All sizes of A. testudineus reduced the number of BPH. The small and medium A. testudineus were more efficient in reducing BPH than the larger ones. The present study suggests that A. testudineus can be incorporated in rice-fish fields as a part of biological control of BPH.

Silencing COI1 in Rice Increases Susceptibility to Chewing Insects and Impairs Inducible Defense

The jasmonic acid (JA) pathway plays a key role in plant defense responses against herbivorous insects. CORONATINE INSENSITIVE1 (COI1) is an F-box protein essential for all jasmonate responses. However, the precise defense function of COI1 in monocotyledonous plants, especially in rice (Oryza sativa L.) is largely unknown. We silenced OsCOI1 in rice plants via RNA interference (RNAi) to determine the role of OsCOI1 in rice defense against rice leaf folder (LF) Cnaphalocrocis medinalis, a chewing insect, and brown planthopper (BPH) Nilaparvata lugens, a phloem-feeding insect. In wild-type rice plants (WT), the transcripts of OsCOI1 were strongly and continuously up-regulated by LF infestation and methyl jasmonate (MeJA) treatment, but not by BPH infestation. The abundance of trypsin protease inhibitor (TrypPI), and the enzymatic activities of polyphenol oxidase (PPO) and peroxidase (POD) were enhanced in response to both LF and BPH infestation, but the activity of lipoxygenase (LOX) was only induced by LF. The RNAi lines with repressed expression of OsCOI1 showed reduced resistance against LF, but no change against BPH. Silencing OsCOI1 did not alter LF-induced LOX activity and JA content, but it led to a reduction in the TrypPI content, POD and PPO activity by 62.3%, 48.5% and 27.2%, respectively. In addition, MeJA-induced TrypPI and POD activity were reduced by 57.2% and 48.2% in OsCOI1 RNAi plants. These results suggest that OsCOI1 is an indispensable signaling component, controlling JA-regulated defense against chewing insect (LF) in rice plants, and COI1 is also required for induction of TrypPI, POD and PPO in rice defense response to LF infestation.