Synergism of Cry1Ca toxicity by gut resident Enterococcus spp. in the rice stem borer, Chilo suppressalis.

The bacterium Bacillus thuringiensis (Bt) is the most economically successful biopesticide to date, and Bt insecticidal proteins are produced in transgenic crops for pest control. However, relevant details in the Bt-mediated killing process remain undefined. In our previous research, we observed reduced larval susceptibility to Bt Cry1Ca in Chilo suppressalis, a major rice pest in China, after gut microbiota elimination. Here, we tested the hypothesis that gut microbiota, particularly abundant Enterococcus spp., influences C. suppressalis susceptibility to Cry1Ca. We isolated and identified four Enterococcus spp. from C. suppressalis gut microbiota and evaluated their impact on Cry1Ca toxicity. Among the four Enterococcus spp. identified, three of them (E. casseliflavus, E. faecalis, and E. mundtii) dramatically increased larval mortality when introduced in axenic C. suppressalis challenged with Cry1Ca. Gut epithelial damage by Cry1Ca promoted the translocation of Enterococcus spp. from the gut lumen into the hemocoel, where they proliferated and induced larval melanization and hemocyte apoptosis. Our combined findings demonstrate that the presence of specific gut microbiota can greatly affect susceptibility to Cry1Ca through melanization and apoptosis of hemocytes. Better understanding of the Bt intoxication process guides the development of bio-enhancers for Bt-based microbial biopesticides and potential improvement of transgenic crops.

Neutral Dietary Effects of Two MicroRNAs, Csu-Novel-260 and Csu-Mir-14, on the Non-Target Arthropod Folsomia candida.

RNA interference (RNAi) that is triggered by small or short RNAs has shown enormous potential in the development of pest control strategies. Two microRNAs (miRNAs), Csu-novel-260 and Csu-miR-14, were used in insect-resistant genetically engineered (IRGE) rice lines to confer resistance to Chilo suppressalis. However, a risk assessment of RNAi-based products is essential to determine the safety of a biopesticide or IRGE crop for commercialization. The non-target organism Folsomia candida, which plays an important ecological role as a soil decomposer in agricultural ecosystems, was used to assess the risk of miRNAs Csu-novel-260 and Csu-miR-14. In this study, a dietary miRNA toxicity assay system was established in F. candida. The expression levels of target genes, survival rate, fecundity and body size were investigated to evaluate the effects of the miRNAs on F. candida under the worst-case scenario. The results showed that the dietary miRNA toxicity assay system could be used for risk assessment of miRNA in F. candida. The target genes of miRNAs were influenced by miRNA at some time points. However, no significant differences were observed in the life-table parameters in F. candida fed with a diet containing miRNAs. The dietary effects of two miRNAs on F. candida are neutral.

Downregulation of the CsABCC2 gene is associated with Cry1C resistance in the striped stem borer Chilo suppressalis.

Chilo suppressalis is a major target pest of transgenic rice expressing the Bacillus thuringiensis (Bt) Cry1C toxin in China. The evolution of resistance of this pest is a major threat to Bt rice. Since Bt functions by binding to receptors in the midgut (MG) of target insects, identification of Bt functional receptors in C. suppressalis is crucial for evaluating potential resistance mechanisms and developing effective management strategies. ATP-binding cassette (ABC) transporters have been vastly reported to interact with Cry1A toxins, as receptors and their mutations cause insect Bt resistance. However, the role of ABC transporters in Cry1C resistance to C. suppressalis remains unknown. Here, we measured CsABCC2 expression in C. suppressalis Cry1C-resistant (Cry1C-R) and Cry1C-susceptible strains (selected in the laboratory) via quantitative real-time PCR (qRT-PCR); the transcript level of CsABCC2 in the Cry1C-R strain was significantly lower than that in the Cry1C-susceptible strain. Furthermore, silencing CsABCC2 in C. suppressalis via RNA interference (RNAi) significantly decreased Cry1C susceptibility. Overall, CsABCC2 participates in Cry1C mode of action, and reduced expression of CsABCC2 is functionally associated with Cry1C resistance in C. suppressalis.

Differential impact of Bt-transgenic rice plantings on bacterial community in three niches over consecutive years.

Transgenic-Bacillus thuringiensis (Bt) crops express insecticidal proteins, which can accumulate in plants and soil where they may influence microbial populations. The impact of Bt crops on bacterial communities has only been assessed under short-term, and results have been contradictory. Here, we analyzed the bacterial communities in three niches, rhizosphere soil (RS), root endosphere (RE) and leaf endosphere (LE), of three Bt rice and their non-Bt parental lines for three consecutive years by high-throughput sequencing. In principal coordinate analysis (PCoA) and PERMANOVA (Adonis) analysis, operational taxonomic units (OTUs) were clustered primarily by niche type and differed significantly in the RE and LE but not in the RS between each of three Bt lines compared with the non-Bt rice line, and not in each respective niche among the three Bt rice lines. The bacterial communities in the RS of different rice lines over the 3 years were clustered mainly by year rather than by lines. The differential bacterial taxa among the lines did not overlap between years, presumably because Cry proteins are rapidly degraded in the soil. A network analysis of RS bacterial communities showed that the network complexity and density for the three Bt rice lines did not decrease compared with those for the non-Bt line. In conclusion, our results demonstrated that bacterial communities differed significantly in RE and LE between Bt and non-Bt rice lines, but the differences were mild and transient, and had no adverse impact on RS over the 3 years. This study provides favorable evidence in support of the commercialization of Bt rice.

The overexpression of insect endogenous microRNA in transgenic rice inhibits the pupation of Chilo suppressalis and Cnaphalocrocis medinalis.

BACKGROUND: Chilo suppressalis and Cnaphalocrocis medinalis are destructive rice pests co-occurring in major rice-growing areas in China. RNA interference (RNAi)-based insect-resistant genetically engineered (IRGE) crops provide a promising approach for pest management by suppressing gene expression or translation. A microRNA (miRNA)-mediated IRGE rice line expressing endogenous Chilo suppressalis miRNA Csu-novel-260, showing significant resistance against Chilo suppressalis, provides an attractive control strategy for Chilo suppressalis by suppressing the expression of the disembodied (dib) gene expression. However, whether this transgenic line also shows the resistance against Cnaphalocrocis medinalis remains unknown. RESULTS: A spatiotemporal expression analysis of Csu-novel-260 in the transgenic rice line was performed by quantitative reverse transcription polymerase chain reaction (qRT-PCR) to determine the paddy field pest exposure dose. In diet feeding assays, a chemically synthesized Csu-novel-260 agomir at 200 fmol g-1 significantly inhibited Chilo suppressalis pupation. However, larval development, survival and pupal weight were not significantly affected. Additionally, the transgenic line significantly affected Cnaphalocrocis medinalis pupation but not larval survival. The qRT-PCR showed that Csdib and Cmdib expression levels were significantly suppressed when the two pests fed on the transgenic line. Additionally, the transgenic line significantly decreased Cry1C-resistant and Cry1C-susceptible Chilo suppressalis larval survival in detached rice tissue feeding assays, indicating that Cry1C-resistant Chilo suppressalis was not cross-resistant to Csu-novel-260 expressed in miRNA-mediated IRGE rice. CONCLUSION: Our study demonstrated that miRNA-mediated IRGE rice significantly inhibited Chilo suppressalis and Cnaphalocrocis medinalis pupation. The results provide a new viewpoint for the application of RNAi-based plants and the inspiration for environmental risk assessment.

Consumption of miRNA-Mediated Insect-Resistant Transgenic Rice Pollen Does Not Harm Apis mellifera Adults.

RNAi-based insect-resistant genetically engineered (IRGE) crops represent a promising approach for pest management by suppressing gene expressions or translation. A developed microRNA-mediated IRGE rice line expressing endogenous Chilo suppressalis Csu-novel-260 shows significant resistance to target pests. The nontarget insect Apis mellifera is an important pollinator used as a surrogate species for the ecological risk assessment of IRGE plants. To simulate a worst-case scenario, the full-length C. suppressalis and A. mellifera disembodied (dib) cDNAs were cloned. The dib 3'-untranslated regions shared 58.06% nucleotide sequence similarity between C. suppressalis and A. mellifera. No potential Csu-novel-260 binding site in Amdib was detected through the bioinformatics analysis. A dietary RNAi toxicity assay of the impacts of ingested Csu-novel-260 on A. mellifera adults showed that the survival rates of RNAi-treated A. mellifera did not significantly differ from those in the blank control (CK) and negative control (NC) treatments. The Csu-novel-260 uptake by A. mellifera peaked at 8 days postfeeding and then gradually decreased. The Amdib expression was not affected by the RNAi assay days or treatments. These results suggest that A. mellifera adults are not susceptible to high doses of Csu-novel-260 in the dietary RNAi assay and that the impact of miRNA-mediated IRGE plants on A. mellifera is negligible.

Differences in midgut transcriptomes between resistant and susceptible strains of Chilo suppressalis to Cry1C toxin.

BACKGROUND: Chilo suppressalis is a widespread rice pest that poses a major threat to food security in China. This pest can develop resistance to Cry toxins from Bacillus thuringiensis (Bt), threatening the sustainable use of insect-resistant transgenic Bt rice. However, the molecular basis for the resistance mechanisms of C. suppressalis to Cry1C toxin remains unknown. This study aimed to identify genes associated with the mechanism of Cry1C resistance in C. suppressalis by comparing the midgut transcriptomic responses of resistant and susceptible C. suppressalis strains to Cry1C toxin and to provide information for insect resistance management. RESULTS: A C. suppressalis midgut transcriptome of 139,206 unigenes was de novo assembled from 373 million Illumina HiSeq and Roche 454 clean reads. Comparative analysis identified 5328 significantly differentially expressed unigenes (DEGs) between C. suppressalis Cry1C-resistant and -susceptible strains. DEGs encoding Bt Cry toxin receptors, aminopeptidase-P like protein, the ABC subfamily and alkaline phosphatase were downregulated, suggesting an association with C. suppressalis Cry1C resistance. Additionally, Cry1C resistance in C. suppressalis may be related to changes in the transcription levels of enzymes involved in hydrolysis, digestive, catalytic and detoxification processes. CONCLUSION: Our study identified genes potentially involved in Cry1C resistance in C. suppressalis by comparative transcriptome analysis. The assembled and annotated transcriptome data provide valuable genomic resources for further study of the molecular mechanisms of C. suppressalis resistance to Cry toxins.

Cadherin CsCad plays differential functional roles in Cry1Ab and Cry1C intoxication in Chilo suppressalis.

Transgenic rice lines expressing Bacillus thuringiensis (Bt) toxins have been successfully developed for the control of Chilo suppressalis. However, the evolution of insect resistance is a major threat to Bt rice durability. Bt toxins function by binding specific receptors in the midgut of target insects; specifically, cadherin proteins have been identified as Cry toxin receptors in diverse lepidopteran species. Here, we report the functional roles of cadherin CsCad in the midgut of C. suppressalis in Cry1Ab and Cry1C toxicity. We expressed a recombinant truncated CsCad peptide (CsCad-CR11-MPED) in Escherichia coli that included the eleventh cadherin repeat and MPED region. Based on ligand blotting and ELISA binding assays, the CsCad-CR11-MPED peptide specifically bound Cry1Ab with high affinity but weakly bound Cry1C. The CsCad-CR11-MPED peptide significantly enhanced the susceptibility of C. suppressalis larvae to Cry1Ab but not Cry1C. Furthermore, the knockdown of endogenous CsCad with Stealth siRNA reduced C. suppressalis larval susceptibility to Cry1Ab but not Cry1C, suggesting that CsCad plays differential functional roles in Cry1Ab and Cry1C intoxication in C. suppressalis. This information directly enhances our understanding of the potential resistance mechanisms of C. suppressalis against Bt toxins and may assist in the development of effective strategies for delaying insect resistance.

A new method to obtain isofemale lines for monitoring Chilo suppressalis resistance to Bt toxin.

Cost-effective Bt resistance monitoring programmes exist to manage insect resistance to Bt crops. F2 screening is widely used in detecting rare resistant alleles. One way to establish numerous isofemale lines for F2 bioassays is acquiring many field-trapped copulated females. However, it is difficult to obtain sufficient Chilo suppressalis isofemale lines because females have low mating rates and fecundity. We developed a new method to establish C. suppressalis isofemale lines with field-collected egg masses. No significant difference in detection ability was observed in the F2 screen between the old and new methods. Moreover, the new method is economical, convenient and efficient.

Development and relative fitness of Cry1C resistance in Chilo suppressalis.

BACKGROUND: Chilo suppressalis is an important lepidopteran rice pest in the rice-growing areas of China, and the development of transgenic rice expressing the Cry1C insecticidal protein has provided a useful strategy for controlling this pest. However, insect resistance is a major threat to the durability of cry1C rice. Thus, evaluation of the risk of insect resistance before the commercial use of cry1C rice is crucial. RESULTS: This study investigated the development of C. suppressalis resistance to Cry1C protein and the relative fitness of Cry1C-resistant and -susceptible strains on different Bt rice lines. The LC50 value of the Cry1C-resistant strain increased 42.6-fold after 41 generations of selection, and the estimated realized heritability (h2 ) of Cry1C resistance was 0.096 in C. suppressalis. Moreover, the Cry1C-resistant strain displayed high fitness on the cry1C line, but not on the cry1Ab and cry1Ab + cry1C lines and was not cross-resistant to Cry1Ab. CONCLUSIONS: These findings suggest that C. suppressalis has the potential to develop resistance to Cry1C, although the rate of evolution is low. The pyramiding of the cry1A and cry1C genes in Bt rice is an effective strategy for delaying the evolution of resistance in C. suppressalis and sustainably maintaining the utility of Bt rice. © 2017 Society of Chemical Industry.

Morphological and phylogenetic analysis of a microsporidium (Nosema sp.) isolated from rice stem borer, Chilo suppressalis (Walker) (Lepidoptera: Pyralidae).

A new microsporidium was isolated from Chilo suppressalis (Walker) (Lepidoptera: Pyralidae), one of the most important rice pests in China. The morphology and molecular systematics of this novel microsporidium were described in this study. The spores were long oval and measured 3.17 × 1.64 µm on fresh smears. Ultrastructure of the spores was characteristic for the genus Nosema: a diplokaryon, 10-12 polar filament coils of the same type, and posterior vacuole. Small subunit rRNA gene sequence data and phylogenetic analysis further confirmed that the microsporidian species from C. suppressalis belong to the true Nosema sub-group of the genus Nosema. Besides, the microsporidium Nosema sp. CS could cause systemic infection of Bombyx mori and infect silkworms through vertical transmission. Therefore, mulberry field pest control should be carefully monitored, and sanitation of mulberry leaves is essential to control the pebrine disease in sericulture.

Potential resistance management for the sustainable use of insect-resistant genetically modified corn and rice in China.

Many lines of insect-resistant genetically modified (IRGM) corn and rice containing Bacillus thuringiensis (Bt) insecticidal genes have been developed and undergone different environmental biosafety assessments stages in China, showing robust application prospects. The potential of targeted pests to develop resistance to Bt crops is widespread, which threatens the sustainable utility of IRGM corn and rice. In this study, the potential risks of target pest complexes developing resistance to IRGM corn and rice are evaluated. Theoretical and empirical studies implementing precautionary insect resistance management (IRM) strategies to delay resistance evolution are summarized and challenges to IRM are discussed. Additionally, solutions facing these challenges are proposed. Finally, directions for future studies in developing IRGM corn and rice and IRM plans are discussed.

Comparison of three transgenic Bt rice lines for insecticidal protein expression and resistance against a target pest, Chilo suppressalis (Lepidoptera: Crambidae).

Two transgenic rice lines (T2A-1 and T1C-19b) expressing cry2A and cry1C genes, respectively, were developed in China, targeting lepidopteran pests including Chilo suppressalis (Walker) (Lepidoptera: Crambidae). The seasonal expression of Cry proteins in different tissues of the rice lines and their resistance to C. suppressalis were assessed in comparison to a Bt rice line expressing a cry1Ab/Ac fusion gene, Huahui 1, which has been granted a biosafety certificate. In general, levels of Cry proteins were T2A-1 > Huahui 1 > T1C-19b among rice lines, and leaf > stem > root among rice tissues. The expression patterns of Cry protein in the rice line plants were similar: higher level at early stages than at later stages with an exception that high Cry1C level in T1C-19b stems at the maturing stage. The bioassay results revealed that the three transgenic rice lines exhibited significantly high resistance against C. suppressalis larvae throughout the rice growing season. According to Cry protein levels in rice tissues, the raw and corrected mortalities of C. suppressalis caused by each Bt rice line were the highest in the seedling and declined through the jointing stage with an exception for T1C-19b providing an excellent performance at the maturing stage. By comparison, T1C-19b exhibited more stable and greater resistance to C. suppressalis larvae than T2A-1, being close to Huahui 1. The results suggest cry1C is an ideal Bt gene for plant transformation for lepidopteran pest control, and T1C-19b is a promising Bt rice line for commercial use for tolerating lepidopteran rice pests.

Loss of Genetic Variation in Laboratory Colonies of Chilo suppressalis (Lepidoptera: Crambidae) Revealed by Mitochondrial and Microsatellite DNA Markers.

The Asiatic rice borer, Chilo suppressalis (Walker), is an important insect pest of rice in China. The genetic variation of a set of laboratory colonies of C. suppressalis was compared with their source populations in the wild (laboratory colonies BJCK, BJ1AB, and BJ1AC versus wild population BJW; laboratory colonies FZCK and FZ1CA versus wild population FZW) and was analyzed using eight microsatellite markers and two partial mitochondrial DNA (mtDNA) regions (COI and COII). Results from both analyses revealed similar patterns. Microsatellite DNA analysis showed that the two wild populations (BJW and FZW) harbored more private alleles and had higher levels of gene diversity, and observed and expected heterozygosity, compared with the laboratory colonies. Mitochondrial DNA analysis revealed that the two wild populations (BJW and FZW) had higher numbers of haplotypes compared with the five laboratory colonies. The three Beijing laboratory-reared colonies (BJ1CK, BJ1AB, and BJ1AC) had one fixed haplotype (H04). Most of the pairwise FST values based on mtDNA were high and all pairwise FST comparisons based on microsatellite DNA were significant, which indicated that the significant differences between these colonies and populations. Genetic drift caused by several factors, such as founder effect, small effective population size, rearing protocols, and inbreeding, can contribute to the rapid loss of genetic variation and affect the distribution of alleles and haplotypes. Therefore, it is necessary to increase the sample size of source populations to prevent the loss of genetic variation and genetic differentiation between different colonies.

Homologs to Cry toxin receptor genes in a de novo transcriptome and their altered expression in resistant Spodoptera litura larvae.

Insect resistance threatens sustainability of insecticides based on Cry proteins from the bacterium Bacillus thuringiensis (Bt). Since high levels of resistance to Cry proteins involve alterations in Cry-binding midgut receptors, their identification is needed to develop resistance management strategies. Through Illumina sequencing we generated a transcriptome containing 16,161 annotated unigenes for the Oriental leafworm (Spodoptera litura). Transcriptome mining identified 6 contigs with identity to reported lepidopteran Cry toxin receptors. Using PCR we confirmed their expression during the larval stage and compared their quantitative expression in larvae from susceptible and a field-derived Cry1Ca resistant strain of S. litura. Among reduced transcript levels detected for most tested contigs in the Cry1Ca-resistant S. litura larvae, the most dramatic reduction (up to 99%) was detected for alkaline phosphatase contigs. This study significantly expands S. litura transcriptomic resources and provides preliminary identification of putative receptor genes with altered expression in S. litura resistant to Cry1Ca toxin.

Chilo suppressalis and Sesamia inferens display different susceptibility responses to Cry1A insecticidal proteins.

BACKGROUND: Chilo suppressalis and Sesamia inferens are important lepidopteran rice pests that occur concurrently in rice-growing areas of China. The development of transgenic rice expressing Cry1A insecticidal proteins has provided a useful strategy for controlling these pests. RESULTS: This study evaluated the baseline susceptibilities of C. suppressalis and S. inferens to Cry1A, as well as their responses to selection with Cry1A. Wide geographic variation in susceptibility was observed across all field populations. Within a given population, the LC50 of both Cry1Ab and Cry1Ac against S. inferens was drastically higher than that of C. suppressalis. Large LC50 differences (74.6-fold) were detected between the two species for Cry1Ab in the Poyang population, while small differences (3.6-fold) were detected for Cry1Ac in the Changsha population. The Cry1Ac LC50 of C. suppressalis and S. inferens increased 8.4- and 4.4-fold after 21 and eight selection generations respectively. Additionally, the estimated realised heritabilities (h(2) ) of Cry1Ac tolerance were 0.11 in C. suppressalis and 0.292 in S. inferens. CONCLUSIONS: S. inferens exhibited a significantly lower susceptibility and more rapidly evolved resistance to Cry1A compared with C. suppressalis. Therefore, S. inferens is more likely to evolve increased resistance, which threatens the sustainability of rice expressing Cry1A protein.

Binding site concentration explains the differential susceptibility of Chilo suppressalis and Sesamia inferens to Cry1A-producing rice.

Chilo suppressalis and Sesamia inferens are two important lepidopteran rice pests that occur concurrently during outbreaks in paddy fields in the main rice-growing areas of China. Previous and current field tests demonstrate that the transgenic rice line Huahui 1 (HH1) producing a Cry1Ab-Cry1Ac hybrid toxin from the bacterium Bacillus thuringiensis reduces egg and larval densities of C. suppressalis but not of S. inferens. This differential susceptibility to HH1 rice correlates with the reduced susceptibility to Cry1Ab and Cry1Ac toxins in S. inferens larvae compared to C. suppressalis larvae. The goal of this study was to identify the mechanism responsible for this differential susceptibility. In saturation binding assays, both Cry1Ab and Cry1Ac toxins bound with high affinity and in a saturable manner to midgut brush border membrane vesicles (BBMV) from C. suppressalis and S. inferens larvae. While binding affinities were similar, a dramatically lower concentration of Cry1A toxin binding sites was detected for S. inferens BBMV than for C. suppressalis BBMV. In contrast, no significant differences between species were detected for Cry1Ca toxin binding to BBMV. Ligand blotting detected BBMV proteins binding Cry1Ac or Cry1Ca toxins, some of them unique to C. suppressalis or S. inferens. These data support that reduced Cry1A binding site concentration is associated with a lower susceptibility to Cry1A toxins and HH1 rice in S. inferens larvae than in C. suppressalis larvae. Moreover, our data support Cry1Ca as a candidate for pyramiding efforts with Cry1A-producing rice to extend the activity range and durability of this technology against rice stem borers.

Expression of Cry1Ab protein in a marker-free transgenic Bt rice line and its efficacy in controlling a target pest, Chilo suppressalis (Lepidoptera: Crambidae).

A marker-free Bt transgenic rice line, mfb-MH86, was recently developed in China, which contains a cry1Ab gene driven by a ubiquitin promoter. This Bt gene confers resistance to a range of lepidopteran species, including the striped stem borer, Chilo suppressalis (Walker). The expression of Cry1Ab protein in mfb-MH86 leaves, stems and leaf sheaths (hereinafter referred to as stems), and roots was evaluated throughout the rice-growing season using an enzyme-linked immunosorbent assay. In addition, mfb-MH86 resistance to C. suppressalis, a major pest of rice, was evaluated in a laboratory bioassay with field-collected rice stems. Cry1Ab protein levels of mfb-MH86 were highest in leaves (9.71-34.09 µg/g dry weight [DW]), intermediate in stems (7.66-18.51 µg/g DW), and lowest in roots (1.95-13.40 µg/g DW). In all tissues, Cry1Ab levels in mfb-MH86 were higher in seedling and tillering stages than in subsequent growth stages. In the laboratory bioassay, mortality of C. suppressalis after 6 d of feeding on mfb-MH86 stems was 100% throughout the rice-growing season; mortality of C. suppressalis when feeding on stems of the nontransformed isoline, MH86, ranged from 15.0 to 38.3%. The results indicate that Cry1Ab protein levels in mfb-MH86 stems are sufficient to protect plants against C. suppressalis throughout the rice-growing season. Although our results are promising, further comprehensive evaluations of mfb-MH86, including field surveys, will be needed before commercial use.

[Occurrence dynamics of migratory pest insects Cnaphalocrocis medinalis and Sogatella furcifera in transgenic Bt rice field in Xing'an County of Guangxi Province].

An investigation was conducted in Xing' an County of Guangxi Province in 2010 to study the occurrence and damage characteristics of two unique migratory pest insects, rice leaffolder (Cnaphalocrocis medinalis) and white-backed planthopper (Sogatella furcifera), in a transgenic Bt rice (cv. HH1 with dual Cry1Ab+Cry1Ac genes) field, taking the corresponding non-transgenic parent (cv. MH63) field as the control. No significant differences were observed in the abundance of C. medinalis eggs and larvae in the two fields, but the percentage of fold-leaf plants and the fold-leaf rate per plant were significantly lower in transgenic Bt rice field than in the control, suggesting that transgenic Bt rice had higher resistance against the target pest insect C. medinalis. As for S. furcifera, its occurrence dynamics of nymphs, adults (including macro- and brachypterous forms), and whole population had no significant differences between the two fields, but the abundance of the nymphs and brachypterous adults at the peak stage of S. furcifera occurrence was obviously higher in transgenic Bt rice field than in the control, while the macropterous abundance was in adverse. The sex ratio of female of the macropterous adults at the late growth stage of rice was generally lower in transgenic Bt rice field than in the control. These results suggested that under the background of large area commercial production of transgenic Bt rice, the occurrence and harm of the non-target pest insect S. furcifera could become more complicated.

Population dynamics of Sesamia inferens on transgenic rice expressing Cry1Ac and CpTI in southern China.

Genetically modified insect-resistant rice lines containing the cry1Ac gene from Bacillus thuringiensis (Bt) or the CpTI (cowpea trypsin inhibitor) gene developed for the management of lepidopterous pests are highly resistant to the major target pests, Chilo suppressalis (Walker), Cnaphalocrocis medinalis (Guenée), and Scirpophaga incertulas (Walker), in the main rice-growing areas of China. However, the effects of these transgenic lines on Sesamia inferens (Walker), an important lepidopterous rice pest, are currently unknown. Because different insect species have varying susceptibility to Bt insecticidal proteins that may affect population dynamics, research into the effects of these transgenic rice lines on the population dynamics of S. inferens was conducted in Fuzhou, southern China, in 2005 and 2006. The results of laboratory, field cage, and field plot experiments show that S. inferens has comparatively high susceptibility to the transgenic line during the early growing season, with significant differences observed in larval density and infestation levels between transgenic and control lines. Because of a decrease in Cry1Ac levels in the plant as it ages, the transgenic line provided only a low potential for population suppression late in the growing season. There is a correlation between the changing expression of Cry1Ac and the impact of transgenic rice on the population dynamics of S. inferens during the season. These results indicate that S. inferens may become a major pest in fields of prospective commercially released transgenic rice, and more attention should be paid to developing an effective alternative management strategy.