Insect Pest Of Rice Research Articles

ChiloDB: a genomic and transcriptome database for an important rice insect pest Chilo suppressalis

ChiloDB is an integrated resource that will be of use to the rice stem borer research community. The rice striped stem borer (SSB), Chilo suppressalis Walker, is a major rice pest that causes severe yield losses in most rice-producing countries. A draft genome of this insect is available. The aims of ChiloDB are (i) to store recently acquired genomic sequence and transcriptome data and integrate them with protein-coding genes, microRNAs, piwi-interacting RNAs (piRNAs) and RNA sequencing (RNA-Seq) data and (ii) to provide comprehensive search tools and downloadable data sets for comparative genomics and gene annotation of this important rice pest. ChiloDB contains the first version of the official SSB gene set, comprising 80 479 scaffolds and 10 221 annotated protein-coding genes. Additionally, 262 SSB microRNA genes predicted from a small RNA library, 82 639 piRNAs identified using the piRNApredictor software, 37 040 transcripts from a midgut transcriptome and 69 977 transcripts from a mixed sample have all been integrated into ChiloDB. ChiloDB was constructed using a data structure that is compatible with data resources, which will be incorporated into the database in the future. This resource will serve as a long-term and open-access database for research on the biology, evolution and pest control of SSB. To the best of our knowledge, ChiloDB is one of the first genomic and transcriptome database for rice insect pests.Database URL: http://ento.njau.edu.cn/ChiloDB.

Seasonal migration of Cnaphalocrocis medinalis (Lepidoptera: Crambidae) over the Bohai Sea in northern China.

The rice leaf roller, Cnaphalocrocis medinalis (Guenée), is a serious insect pest of rice with a strong migratory ability. Previous studies on the migration of C. medinalis were mostly carried out in tropical or subtropical regions, however, and what the pattern of seasonal movements this species exhibits in temperate regions (i.e. Northern China, where they cannot overwinter) remains unknown. Here we present data from an 11-year study of this species made by searchlight trapping on Beihuang Island (BH, 38°24'N; 120°55'E) in the centre of the Bohai Strait, which provides direct evidence that C. medinalis regularly migrates across this sea into northeastern agricultural region of China, and to take advantage of the abundant food resources there during the summer season. There was considerable seasonal variation in number of C. medinalis trapped on BH, and the migration period during 2003-2013 ranged from 72 to 122 days. Some females trapped in June and July showed a relatively higher proportion of mated and a degree of ovarian development suggesting that the migration of this species is not completely bound by the 'oogenesis-flight syndrome'. These findings revealed a new route for C. medinalis movements to and from Northeastern China, which will help us develop more effective management strategies against this pest.

Effect of synergists on susceptibility to chlorantraniliprole in field populations of Chilo suppressalis (Lepidoptera: Pyralidae).

The Asiatice stem borer, Chilo suppressalis (Walker), an important rice insect pest in China, has developed resistances to several classes of insecticides. To control C. suppressalis, chlorantraniliprole has been introduced as a novel insecticide in rice field since 2008. It is an anthranilic diamide insecticide that binds and activates ryanodine receptors (RyR). The susceptibility of field populations of C. suppressalis to chlorantraniliprole was determined in this study. The hypotheses of equality and parallelism showed that regression lines in the tested five populations were neither equal nor parallel. The Ruian, Cangnan, and Liangyungang populations (RA12, CN12, and LYG12) collected in 2012 had lower LD50 values, whereas the Zhuji populations (ZJ12 and ZJ13) collected in 2012 and 2013 were approximately 15 times more tolerant than the RA12 population. To determine the potential mechanisms involved in this tolerance variation, synergism bioassays were performed. Significant differences in susceptibility were found between without synergist and with synergist for the three populations (RA12, LYG12, and ZJ13), based on the tests for the hypotheses of equality. In RA12 and LYG12 populations with chlorantraniliprole, the addition of piperonyl butoxide (PBO) significantly synergized the activity, with synergism ratios of 2.68- and 2.33-fold, respectively, whereas addition of S,S,S-tributyl phosphorotrithioate (DEF) and diethyl maleate (DEM) had no synergist effect. In ZJ13 population with chlorantraniliprole, the addition of PBO and DEF increased synergism ratios by 12.43- and 6.31-fold, respectively, whereas addition of DEM had no significant effect on the toxicity against ZJ13 larvae. These susceptibility and synergism data suggested that detoxification enzymes might be involved in the tolerance variation to chlorantraniliprole in field populations of C. suppressalis.

Transcriptome Analysis of Fat Bodies from Two Brown Planthopper (Nilaparvata lugens) Populations with Different Virulence Levels in Rice

BackgroundThe brown planthopper (BPH), Nilaparvata lugens (Stål), one of the most serious rice insect pests in Asia, can quickly overcome rice resistance by evolving new virulent populations. The insect fat body plays essential roles in the life cycles of insects and in plant-insect interactions. However, whether differences in fat body transcriptomes exist between insect populations with different virulence levels and whether the transcriptomic differences are related to insect virulence remain largely unknown.Methodology/Principal FindingsIn this study, we performed transcriptome-wide analyses on the fat bodies of two BPH populations with different virulence levels in rice. The populations were derived from rice variety TN1 (TN1 population) and Mudgo (M population). In total, 33,776 and 32,332 unigenes from the fat bodies of TN1 and M populations, respectively, were generated using Illumina technology. Gene ontology annotations and Kyoto Encyclopedia of Genes and Genomes (KEGG) orthology classifications indicated that genes related to metabolism and immunity were significantly active in the fat bodies. In addition, a total of 339 unigenes showed homology to genes of yeast-like symbionts (YLSs) from 12 genera and endosymbiotic bacteria Wolbachia. A comparative analysis of the two transcriptomes generated 7,860 differentially expressed genes. GO annotations and enrichment analysis of KEGG pathways indicated these differentially expressed transcripts might be involved in metabolism and immunity. Finally, 105 differentially expressed genes from YLSs and Wolbachia were identified, genes which might be associated with the formation of different virulent populations.Conclusions/SignificanceThis study was the first to compare the fat-body transcriptomes of two BPH populations having different virulence traits and to find genes that may be related to this difference. Our findings provide a molecular resource for future investigations of fat bodies and will be useful in examining the interactions between the fat body and virulence variation in the BPH.

Fine mapping of brown planthopper (Nilaparvata lugens Stål) resistance gene Bph28(t) in rice (Oryza sativa L.)

The brown planthopper (BPH; Nilaparvata lugens Stal) is one of the most destructive insect pests of rice (Oryza sativa L.) throughout the Asian rice-growing countries. DV85 is a BPH-resistant indica variety. A single dominance gene conferring resistance in DV85 was previously mapped on the long arm of chromosome 11. The objectives of this study were to investigate feeding behaviors of BPH on DV85 plants and fine-map the BPH resistance gene, here designated Bph28(t). A seedling bulk test was conducted to identify resistant plant reactionsvg to BPH feeding. The results showed that the resistance of DV85 functions by means of tolerance during BPH attack, rather than non-preference and antibiosis. For fine mapping, two F2 populations were developed by crossing DV85 with the susceptible japonica variety Kinmaze and indica 9311. A high-resolution genetic map harboring Bph28(t) was constructed and Bph28(t) was finally physically defined to an interval of 64.8 kb between markers Indel55 and Indel66. The fine-mapped Bph28(t) gene will facilitate marker-assisted gene pyramiding for BPH resistance.

Characterization of cysteine protease-like genes in the striped rice stem borer, Chilo suppressalis

The striped rice stem borer, Chilo suppressalis (Walker), is a major pest for rice production in China and the rest of Southeast Asia. Chemical control is the main means to alleviate losses due to this pest, which causes serious environmental pollution. An effective and environmentally friendly approach is needed for the management of the striped rice stem borer. Cysteine proteases in insects could be useful targets for pest management either through engineering plant protease inhibitors, targeting insect digestive cysteine proteases, or through RNA interference-based silencing of cysteine proteases, disrupting developmental regulation of insects. In this study, eight cysteine protease-like genes were identified and partially characterized. The genes CCO2 and CCL4 were exclusively expressed in the larval gut, and their expression was affected by the state of nutrition in the insect. The expression of CCL2, CCL3, and CCO1 was significantly affected by the type of host plant, suggesting a role in host plant - insect interactions. Our initial characterization of the striped rice stem borer cysteine protease-like genes provides a foundation for further research on this important group of genes in this major insect pest of rice.

Biological Control of African Rice Gall Midge (Orseolia oryzivora, Harris and Gagné) in Nigeria: A Review

African rice gall midge (AfRGM),Orseolia oryzivoraHarris and GagnE(Diptera: Ceccidomyiidae) is a serious insect pest of lowland rice in Africa ,and is capable of causing total crop failure in endemic areas. Of all the control measu

Cell culture of the rice brown planthopper, Nilaparvata lugens Stål (Hemiptera: Delphacidae)

The rice brown planthopper (BPH), Nilaparvata lugens (Stål), is one of the most destructive insect pests of rice in Asia. Although resistant rice varieties can be effective in managing planthopper populations, BPH has repeatedly been able to overcome resistant rice varieties. It is possible that BPH adaptation to resistant rice varieties may be related to its endosymbionts. We investigated methods for culturing BPH cells in order to study in-depth interactions between rice, BPH, and its endosymbionts. In this study, we tested EX-CELL™ 405, EX-CELL™ 420, Mitsuhashi and Maramorosch's medium, and Kimura's medium, for in vitro culture of BPH cells. Only Kimura's medium was found to be suitable for BPH cell culture, and BPH embryos around blastokinetic stage were the best source for BPH cell culture. Cells from BPH embryonic tissues adhered to the plate substrate, and the migration of cells was observed within 24h in primary culture. After 3mo of subculture, various types of BPH cells were successfully maintained in the Kimura's medium.

Effect of cultivars and botanicals on the incidence of major insect pests in lowland rice

A field experiment was conducted during the wet season of 2011 at the experimental farm of ICAR Complex for North East hill region, Jharnapani, Medziphema, Nagaland using Split Plot Design to study on the effect of cultivars and botanicals on the incidence of major insect pests in lowland rice. A rice variety, Ranjit and two rice cultivars, Miracle rice and Jalukie special were selected and three major pests were taken into account for the study. Peak incidence of rice stem borer and leaf folder in all the three varieties were observed at 105 days after transplanting of the crop. Jalukie special harboured the maximum number of borer population (26.67%) followed by ranjit (26.30%) and miracle rice (23.00%). Leaf folder incidence was maximum in ranjit (29.47%) followed by miracle rice (27.83%) and lowest incidence was in jalukie special (27.33%). The incidence of ear head bug was observed from 60 days after transplanting till harvest. Peak incidence was observed at 120 days after transplanting. Incidence was highest in ranjit (4.43 bugs 5 sweeps−1) followed by Miracle ice (3.57 bugs 5 sweeps−1) and Jalukie special (3.13 bugs 5 sweeps−1). Among the botanical treatments, Litsea citrata seed extract was found to give effective control against the three pests almost at par with Monocrotophos. Crude stem extract of Costus speciosus and seed extract of Chenopodium ambrosioides were also found to be effective in reducing the pests.

Seasonal changes in temperature and rainfall and its relationship with the incidence of weeds and insect pests in rice (Oryza sativaL) cultivation in Sri Lanka

Weeds and insect pests are the key yield determinants of rice (Oryza sativa L.) that can be influenced by climatic parameters. The changes of ambient temperature and rainfall regime from 1982 to 2012 during two major growing seasons, Yala (March to August) and Maha (September to February) and their relationship with incidence of weeds and insect pests of rice were studied in three major rice growing districts of Sri Lanka, namely Anuradhapura, Polonnaruwa and Kurunegala. These districts were selected based on the availability of long term meteorological data and crop statistics. Occurrence of extreme climatic events during the study period was identified in relation to the base period (1961–1990) and their relationship with El Niño and La Niña events (ENSO) was examined. Costs of weed control and insect pest control published by the Department of Agriculture were used as proxies to the changes of weed and insect pest incidence, respectively. The difference in day and night ambient temperatures has significantly increased in Polonnaruwa (Yala: 0.066°C year−1, Maha: 0.0465°C year−1) and Kurunegala (Yala: 0.034°C year−1; Maha: 0.024°C year−1) districts. Cost for weed control has significantly decreased in Polonnaruwa district during Yala and Maha seasons at a rate of 0.81 and 0.42 US$ ha−1 season−1, respectively, in spite of increasing temperature regime. All extreme rainfalls events were recorded in ENSO years at Anuradhapura, Polonnaruwa and Kurunegala districts during the Yala season. The highest weed control costs have recorded during ENSO years in Anuradhapura and Polonnaruwa districts and that of insect pest control was recorded during ENSO years in Kurunegala district. There was no distinct linear correlation between climatic variables and, weed and insect pest incidences. However, an apparent relationship was evident between occurrence of extreme rainfall events and ENSO events. Moreover, it is likely that weed and insect pest incidences would be relatively higher during ENSO years.

Comparing Efficacy of Biopesticides for the Management of Insect Pests in Aromatic Rice under Organic Farming System

Field experiments were conducted in farmer's rice fields at village Saholi, Punjab, India during 2012 and 2013 to test the efficacy of different plant based biopesticides and microbials against insect pests of aromatic rice ( Pusa 1121 and Basmati 386) grown under organic farming system. In all, five biopesticide formulations (2 plant based; 3 microbials) were tested for their efficacy. Neem azal 1% @ 1250 ml/ha showed its supermacy in reducing the incidence of leaf folder (0.97-5.66% DL), dead hearts (0.98-1.67% DH), white ear heads (1.07-2.05%), plant hopper(s) population (0.11-0.40/plant) and resulted in higher grain yields (25.54-36.47 q/ha) compared with ohter treatments. Similarly, the application of Neem azal 1% @ 1000, Dipel WP @ 2.0 kg/ha, Karanja oil 2.0% and Myco-Jaal 10% SC @ 2.0 litre per ha significantly reduced the incidence of leaf folder, dead hearts and white earheads increased grain yields in comparison to untreated control. Microbials, by large, were ineffective to control plant hoppers' infestation except Myco-Jaal 10% SC @ 2.0 litre per ha, which managed to control plant hopper(s) population and was on a par with plant based biopesticides.

Effect of nitrogen levels and varieties on the incidence of leaf folder and stem borer of basmati rice in Punjab, India

Effect of different varieties and nitrogen levels on the incidence of insect-pests of rice was studied at Panjab Agricultural Univesity, Gurdaspur. The highest incidence of rice leaf folder, Cnaphalocrocis medinalis (Guenee) and stem borer Scripophaga incertulas (Walker) was recorded from the basmati variety Punjab Bas-2. The incidence of leaf folder and stem borer increased with increase in nitrogen level.

The insect ecdysone receptor is a good potential target for RNAi-based pest control.

RNA interference (RNAi) has great potential for use in insect pest control. However, some significant challenges must be overcome before RNAi-based pest control can become a reality. One challenge is the proper selection of a good target gene for RNAi. Here, we report that the insect ecdysone receptor (EcR) is a good potential target for RNAi-based pest control in the brown planthopper Nilaparvata lugens, a serious insect pest of rice plants. We demonstrated that the use of a 360 bp fragment (NlEcR-c) that is common between NlEcR-A and NlEcR-B for feeding RNAi experiments significantly decreased the relative mRNA expression levels of NlEcR compared with those in the dsGFP control. Feeding RNAi also resulted in a significant reduction in the number of offspring per pair of N. lugens. Consequently, a transgenic rice line expressing NlEcR dsRNA was constructed by Agrobacterium- mediated transformation. The results of qRT-PCR showed that the total copy number of the target gene in all transgenic rice lines was 2. Northern blot analysis showed that the small RNA of the hairpin dsNlEcR-c was successfully expressed in the transgenic rice lines. After newly hatched nymphs of N. lugens fed on the transgenic rice lines, effective RNAi was observed. The NlEcR expression levels in all lines examined were decreased significantly compared with the control. In all lines, the survival rate of the nymphs was nearly 90%, and the average number of offspring per pair in the treated groups was significantly less than that observed in the control, with a decrease of 44.18-66.27%. These findings support an RNAi-based pest control strategy and are also important for the management of rice insect pests.

A novel synthetic Cry1Ab gene resists rice insect pests.

A few insect control genes of Bacillus thuringiensis have been modified successfully to increase the expression in plants by replacing rare codons, increasing GC content, and avoiding the DNA elements that could cause premature transcription termination, mRNA instability, and potential methylation. However, the modification process was intricate and often confused researchers. In this study, we adopted a simple method to modify Cry1Ab only by individually replacing its amino acid sequence with corresponding rice-preferred codons based on analysis of 92,188 coding DNA sequences. Unexpectedly, all elements of A+T richness, which terminate or destabilize transcription in plants, were avoided in the newly designed mCry1Ab. However, mCry1Ab had 2 notable features: less synonymous codons and high GC content. mCry1Ab only employed 22 of the 61 codons to encode protein and had an enhanced GC content of 65%. The increase in GC content caused abundant potential methylation signals to emerge in mCry1Ab. To test whether mCry1Ab could be expressed in rice, we transferred it into Oryza japonica variety Wanjing97. Insect bioassays revealed that transgenic plants harboring this gene driven by 2 promoters, CaMV35S and OsTSP I, were highly resistant to rice leaffolder (Cnaphalocrocis medinalis). Analysis of R0 to R2 generation plants indicated that the mCry1Ab was inherited stably by the progeny. Our study provided a simple modified method for expressing exogenous genes in rice and confirmed that less synonymous codons and high GC content do not affect transgene expression in rice.

Keragaman Jenis dan Kelimpahan Populasi Penggerek Batang Padi dan Serangga Lain Berpotensi Hama Pada Ekosistem Sawah Organik

Rice stem borer is a main pest of paddy rice in Central Java. The main rice stem borer are yellow rice borer, Scirpophaga incertulas Walker, and white rice borer, S. innonata Walker. Other species are pink borer Sesamia inferens Walker, striped rice borer Chilo suppressalis Walker, dark-headed rice borer, C. polychrysus Meyrick, and glossy rice borer, C. auricilius Dudgeon. Besides rice stem borer, there are many other insect which are potential as rice pest, i.e., grasshopper, rice ear bug, brown planthopper, etc. Organic agriculture in Central Java have not been applied yet, hence there is still lack of information, including species diversity information and abundance of rice stem borer population and other potential insect pest on rice. Species diversity and population abundance of rice stem borer and other potential insect in organic rice ecosystem differ with the inorganic one. The objective of this research is to study species diversity and abundance of rice stem borer population and other potential pest in organic rice ecosystem. The study was conducted in organic rice of Bakalrejo Village, Susukan Sub district, District of Semarang. Species diversity and population abundance was analyzed using Shanon-Wiener’s species diversity index (H’), population abundance index (Di), and population evenness index (e). Pattern of species diversity, population abundance, population evenness were temporally analyzed using population dynamic curve. Sampling of species diversity and population abundance was performed during a crop planting season with twice of sampling frequency. The result shows that rice stem borer found were yellow rice borer with its population fluctuated temporally and pink rice borer with its population were few and scarce. The highest diversity found during rice generative phase until ripen and decline in line with the age of rice. Species diversity index in vegetative phase was below 2, while during generative phase until ripen increased above 2. Insect population abundance declined in the end vegetative phase and increased in the beginning of reproductive phase until ripen phase. Population evenness index in all growth phase of rice were relatively high and similar. Keywords : organic rice, rice stem borer, insect pest of rice.

Characterization of the Distal-less gene homologue, NlDll, in the brown planthopper, Nilaparvata lugens (Stål)

The brown planthopper, Nilaparvata lugens (Stål), is a globally devastating insect pest of rice, particularly in eastern Asia. Distal-less or Dll is a highly conserved and well studied transcription factor required for limb formation in invertebrates and vertebrates. We have identified a homologue of this gene, NlDll, and demonstrated that it is expressed in all life stages of N. lugens, particularly in adult brachypterous females. When we compared between specific adult tissues it was expressed most strongly in wings. Using RNAi techniques we demonstrated that downregulation of NlDll in the 3rd instar larvae led to the disrupted development of the leg, while downregulation of NlDll in the 5th instar larvae led to abnormal wing formation. Ectopic over-expression of NlDll in Drosophila melanogaster using the GAL4–UAS system led to fatal or visible phenotypic changes such as the loss of normal wing structure and disrupted haltere structure. Our work suggests that NlDll is a conserved homologue of Distal-less and is required for both leg development and wing structure. Since researches have shown that Dll is required for wing morphogenesis, understanding the role of NlDll during the wing development will further provide a basis for revealing the molecular mechanism of the wing dimorphism in brown planthopper. In the future, NlDll could be used as a target gene for brown planthopper pest management in the field.

Effect of the insecticide Lambda-cyhalothrin on rice spider populations in southern Brazil

The adverse effect that insecticides have on spider populations is of major concern since these predators are a component in the biological control of rice insect pest populations. This study was designed to determine the effect of the pyrethroid insecticide, Lambda-cyhalothrin, on spider populations in rice fields. Treatments consisted of plots treated once with the insecticide and untreated plots (control). Spiders were sampled four times per crop year over a two year period in each of three sites in the state of Rio Grande dol Sul, Brazil. Treatments were replicated four times. Sweep net sampling was conducted to sample the araneofauna. Overall 1,961 spiders were collected, with a predominance of juveniles over adults. Between treatments, there were significantly larger numbers of spiders and species richness in areas without insecticide. There were also significant differences among areas (sites) and among days after the insecticide application. Of the 12 recorded families, Araneidae and Tetragnathidae dominated, and were both strongly affected by insecticide application, decreasing more than 50% in those locations. Overall, 37 species were recorded (insecticide: 29; without: 26), eleven species were exclusive for rice without insecticide and eight for rice with insecticide. Alpaida veniliae (Keyserling, 1865) (n = 236) and Tetragnathaaff.jaculator (108) were the most abundant in both treatments, but with large decreases in abundance in rice with insecticide. Among guilds, the predominance was for orb weavers (67.3%) in all locations, but with much lower values for those spiders in rice with insecticide application. This study illustrates that the spider fauna in rice fields are adversely affected by the application of the insecticide Lambda-cyhalothrin.

Inducible expression of a fusion gene encoding two proteinase inhibitors leads to insect and pathogen resistance in transgenic rice

Plant proteinase inhibitors (PIs) are considered as candidates for increased insect resistance in transgenic plants. Insect adaptation to PI ingestion might, however, compromise the benefits received by transgenic expression of PIs. In this study, the maize proteinase inhibitor (MPI), an inhibitor of insect serine proteinases, and the potato carboxypeptidase inhibitor (PCI) were fused into a single open reading frame and introduced into rice plants. The two PIs were linked using either the processing site of the Bacillus thuringiensis Cry1B precursor protein or the 2A sequence from the foot-and-mouth disease virus (FMDV). Expression of each fusion gene was driven by the wound- and pathogen-inducible mpi promoter. The mpi-pci fusion gene was stably inherited for at least three generations with no penalty on plant phenotype. An important reduction in larval weight of Chilo suppressalis fed on mpi-pci rice, compared with larvae fed on wild-type plants, was observed. Expression of the mpi-pci fusion gene confers resistance to C.suppressalis (striped stem borer), one of the most important insect pest of rice. The mpi-pci expression systems described may represent a suitable strategy for insect pest control, better than strategies based on the use of single PI genes, by preventing insect adaptive responses. The rice plants expressing the mpi-pci fusion gene also showed enhanced resistance to infection by the fungus Magnaporthe oryzae, the causal agent of the rice blast disease. Our results illustrate the usefulness of the inducible expression of the mpi-pci fusion gene for dual resistance against insects and pathogens in rice plants.

Evaluation of neonicotinoids as pyrethroid alternatives for rice water weevil management in water-seeded rice

The rice water weevil (RWW), Lissorhoptrus oryzophilus (Kuschel) (Coleoptera: Curculionidae), is the most destructive insect pest of rice in the United States. Water-seeded rice, which is flooded at an earlier stage of crop development than drill-seeded rice, is at heightened risk of loss from root-feeding RWW larvae. Pyrethroids, the most widely used group of foliar insecticides for RWW control, have inherent limitations such as limited residual activity, narrow window of activity and extreme toxicity to non-target aquatic organisms. An array of field, lab and greenhouse experiments was conducted to compare the activity of two neonicotinoids with that of λ-cyhalothrin, a widely used pyrethroid, against the RWW. Small-plot efficacy trials were conducted during 2009, 2010 and 2011. Foliar clothianidin (Belay 2.13 SC) and a granular formulation (3%) of dinotefuran applied to plots were as effective as, and showed greater residual activity than, foliar applications of λ-cyhalothrin. Topical bioassays on adult weevils revealed that clothianidin possessed lower contact toxicity than λ-cyhalothrin. Residual assays using weevils placed on foliage of sprayed plots revealed that the toxic and sublethal behavioral effects of clothianidian on adult weevils were more persistent for clothianidin than for λ-cyhalothrin. Granular dinotefuran applied to greenhouse-grown plants previously infested with weevil larvae showed excellent larvicidal activity. Overall, these studies showed that neonicotinoids have potential as pyrethroid replacements against the RWW in water-seeded rice culture.

Geographic susceptibility of Chilo suppressalis Walker (Lepidoptera: Crambidae), to chlorantraniliprole in China

Chilo suppressalis Walker, the rice striped stem borer (RSSB) is one of the most serious lepidopteron insect pests of rice in Asia. The registration of chlorantraniliprole added an option for the chemical control of RSSBs. In this study, the geographic variability of susceptibility of field-collected RSSBs to chlorantraniliprole was assessed to establish a baseline for future comparisons of field population responses to the increased use of chlorantraniliprole products. Thirty-one RSSB colonies were established from 22 geographic areas in seven provinces of China, and were evaluated for chlorantraniliprole susceptibility. The range of mean lethal concentration (LC50 ) values in response to this chemical was between 0.821 and 17.720 mg (AI)/L across the populations. Susceptibility was significantly different (21.7-fold for LC50 and 55.6-fold for LC90 ) across the various geographic populations. No significant correlations were detected between the LC50 values of chlorantraniliprole and four conventional insecticides (monosultap, triazophos, chlorpyrifos and abamectin). These results revealed great geographical variations in chlorantraniliprole susceptibilities among different geographic populations of RSSBs, which might indicate the potential for RSSBs to develop resistance to chlorantraniliprole. The effective execution of insecticide resistance monitoring programs and management strategies is urgently needed in China to sustain RSSB susceptibility to chlorantraniliprole.