Bt rice expressing Cry1Ab does not stimulate an outbreak of its non-target herbivore, Nilaparvata lugens

Plant Resistance in Some Modern Soybean Varieties May Favor Population Growth and Modify the Stylet Penetration of Bemisia tabaci (Hemiptera: Aleyrodidae)

Complaints of severe damage by whiteflies in soybean fields containing genetically engineered (GE) varieties led us to investigate the role of transgenic soybean varieties expressing resistance to some insects (Cry1Ac Bt toxin) and to herbicide (glyphosate) on the population growth and feeding behavior of Bemisia tabaci (Gennadius) MEAM1 (Hemiptera: Aleyrodidae). In the laboratory, the whiteflies reared on the GE Bt soybeans had a net reproductive rate (R0) 100% higher and intrinsic rate of population increase (rm) 15% higher than those reared on non-GE soybeans. The increased demographic performance was associated with a higher lifetime fecundity. In electrical penetration graphs, the whiteflies reared on the GE soybeans had fewer probes and spent 50% less time before reaching the phloem phase from the beginning of the first successful probe, indicating a higher risk of transmission of whitefly-borne viruses. Data from Neotropical fields showed a higher population density of B. tabaci on two soybean varieties expressing glyphosate resistance and Cry1Ac Bt toxin. These results indicate that some GE soybean varieties expressing insect and herbicide resistances can be more susceptible to whiteflies than non-GE ones or those only expressing herbicide resistance. Most likely, these differences are related to varietal features that increase host-plant susceptibility to whiteflies. Appropriate pest management may be needed to deal with whiteflies in soybean fields, especially in warm regions, and breeders may want to consider the issue when developing new soybean varieties.

Cry1C rice doesn't affect the ecological fitness of rice brown planthopper, Nilaparvata lugens either under RDV stress or not

The potential risks of Bt rice on non-target arthropods (NTAs) should be evaluated and defined before commercial production. Recently, effects of Bt rice on NTAs under abiotic and biotic stress conditions attracted much attention. Here we reported the effects of Bt rice T1C-19 (Cry1C rice) on the non-target herbivore, Nilaparvata lugens (rice brown planthopper, BPH) with or without RDV (rice dwarf virus) infection conditions. BPH showed no feeding and oviposition preference between Bt rice T1C-19 and its non-Bt parental rice Minghui 63 (MH63), as well as between RDV-infected and RDV-free rice plants. Meanwhile, rice type, RDV infection status, and their interaction had little impacts on the survival, development and fecundity of BPH. By comparison with non-Bt control, Bt rice T1C-19 with or without RDV infection had no significant effects on the life-table parameters of BPH including rm, R0, T, DT and λ. Thus, it could be concluded that Bt rice T1C-19 doesn't affect the ecological fitness of BPH either under RDV stress or not.

Insect-Resistant Genetically Engineered Crops in China: Development, Application, and Prospects for Use

With 20% of the world's population but just 7% of the arable land, China has invested heavily in crop biotechnology to increase agricultural productivity. We examine research on insect-resistant genetically engineered (IRGE) crops in China, including strategies to promote their sustainable use. IRGE cotton, rice, and corn lines have been developed and proven efficacious for controlling lepidopteran crop pests. Ecological impact studies have demonstrated conservation of natural enemies of crop pests and halo suppression of crop-pest populations on a local scale. Economic, social, and human health effects are largely positive and, in the case of Bt cotton, have proven sustainable over 20 years of commercial production. Wider adoption of IRGE crops in China is constrained by relatively limited innovation capacity, public misperception, and regulatory inaction, suggesting the need for further financial investment in innovation and greater scientific engagement with the public. The Chinese experience with Bt cotton might inform adoption of other Bt crops in China and other developing countries.

Cry2A rice did not affect the interspecific interactions between two rice planthoppers, Nilaparvata lugens, and Sogatella furcifera

Interspecific interactions are complex in agro-ecosystems and could be affected by agricultural technologies including transgenic crop planting. Few studies focused on the effects of Bt crops on the interspecific interactions of non-target organisms. Here we assessed the effects of transgenic cry2A rice (Cry2A rice) on the interspecific interaction between two rice planthoppers, namely, Nilaparvata lugens (the brown planthopper, BPH) and Sogatella furcifera (the white-backed planthopper, WBPH). Cry2A rice showed no significant effects on most biological parameters of these two rice planthoppers, except for wet weight of BPH female adults and development duration of WBPH female nymphs. In contrast, interspecific interactions between BPH and WBPH showed significant impacts on their biological parameters, no matter on Cry2A rice or non-transgenic control. In two-factor analysis combing rice line and interspecific interaction together, the interaction between these two factors did not affect most biological parameters of neither planthopper species, except for development duration of BPH female nymphs and WBPH nymphs (both male and female). Additionally, the egg distributions of BPH and WBPH had no significant differences between Cry2A and non-Cry2A treatments. Results of field experiments showed that Cry2A rice did not affect their population densities at most sampling dates in a five-year survey, and the interaction between BPH and WBPH showed no significant differences in both Cry2A and non-Cry2A rice paddies. In conclusion, our tested Cry2A rice would not affect the interspecific interactions between BPH and WBPH based both laboratory and field results.

Interactive Effects of [CO2] and Temperature on Plant Chemistry of Transgenic Bt Rice and Population Dynamics of a Non-Target Planthopper, Nilaparvata lugens (Stål) under Different Levels of Soil Nitrogen

Gaining a better understanding of the interactive effect of projected atmospheric CO2 level increase and the Earth's rising temperature on plant chemistry (nutritional and defensive characteristics) of transgenic crops is essential when attempting to forecast the responses of target and non-target insects to climate change. In this study, effects of carbon dioxide (CO2; elevated versus ambient), temperature (T; high versus low), and their interactions on leaf nitrogen content (N%) and C:N ratio of transgenic Bt rice and its non-Bt isoline grown under low- and high-N fertilizer were systematically analyzed together with the resulting insect population dynamics of a non-target planthopper Nilaparvata lugens (Stâl) in open-top-chamber experiments. The results indicated that under low-N treatment, elevated CO2 at low T (i.e., eCO2) (compared to ambient CO2 at low T, i.e., CK) significantly decreased N% and Bt-toxin content and significantly increased C:N ratio in leaf sheath and leaf of Bt rice, especially during the tillering stage, whereas inverse effects of high T were shown on the plant chemistry of Bt rice, especially during heading stage. The combination of elevated CO2 and high T (i.e., Combined) (in contrast to CK) significantly increased N% and decreased C:N ratio in leaf sheath of Bt rice during the heading stage under low-N fertilizer, while significantly decreased N% and increased C:N ratio in leaf of Bt rice during the tillering stage, regardless of fertilizer-N level, and significantly increased Bt-toxin content in leaf sheath and leaf during the tillering stage under both low- and high-N. Moreover, no discernable relationships between Bt-toxin content and N% or leaf C:N ratio were observed at any CO2 or N levels evaluated. Furthermore, transgenic treatment, temperature and fertilizer-N level interactions, and CO2 and fertilizer-N level interactions all significantly affected the population dynamics of N. lugens. Specifically, high-N significantly enhanced the population dynamics of N. lugens fed on non-Bt rice grown under eTemp and Bt cultivar significantly reduced the population dynamics of N. lugens under eCO2 regardless of N fertilizer levels. The study demonstrates that the planting of transgenic Bt rice would not increase the risk of increased N. lugens severity under the combined condition of elevated CO2 and increased temperature, particularly under moderate level of N fertility.

Computational approach to understand molecular mechanism involved in BPH resistance in Bt- rice plant

In silico approach was utilised to identify differentially expressed key hub genes during BPH infestation on Bt rice plant, under laboratory conditions. Re-analysis of GSE74745 data with in-house R scripts and STRING database reveals that only 5 key hub genes, namely Os05g0176100, Os06g0683200, Os07g0208500, Os07g0252400 and Os07g0424400, belonging to cellulose synthase family, are differentially expressed and have confidence score ≥0.9 among themselves. Conserve domain analysis of all proteins encoded via these 5 key hub genes reveals that they have a common cellulose synthase domain, in which "Plant-Conserved Region" (PCR) is highly conserved. After binding with other domains of cellulose synthase proteins or other accessory proteins, like sucrose synthase, PCR serves as a metabolic channel to deliver UDP-Glucose, which is the main substrate for cellulose synthesis, into the active site of cellulose synthase and initiate cellulose synthesis. Simulation study of recently solved topological model of PCR [PDB ID: 5JNP] and molecular docking studies of PCR with UDP-glucose reveals that, during BPH infestation, in nearby phloem tissue where BPH suck sap, there is an increase interaction of UDP-glucose with PCR and other accessory proteins which in turn increases both the stability of PCR and the production of cellulose, finally causing callose deposition at that site and hence causing longer nymphal developmental period and lower fertility of BPH infested on Bt rice. In near future, these differentially identified 5 hub genes could be possible targets for controlling BPH infestation in rice plant under field conditions and increasing rice yield globally.

Bt rice could provide ecological resistance against nontarget planthoppers

Genetically engineered (GE) rice lines expressing Lepidoptera-active insecticidal cry genes from the bacterium Bacillus thuringiensis (Bt) have been developed in China. Field surveys indicated that Bt rice harbours fewer rice planthoppers than non-Bt rice although planthoppers are not sensitive to the produced Bt Cry proteins. The mechanisms underlying this phenomenon remain unknown. Here, we show that the low numbers of planthoppers on Bt rice are associated with reduced caterpillar damage. In laboratory and field-cage experiments, the rice planthopper Nilapavata lugens had no feeding preference for undamaged Bt or non-Bt plants but exhibited a strong preference for caterpillar-damaged plants whether Bt or non-Bt. Under open-field conditions, rice planthoppers were more abundant on caterpillar-damaged non-Bt rice than on neighbouring healthy Bt rice. GC-MS analyses showed that caterpillar damage induced the release of rice plant volatiles known to be attractive to planthoppers, and metabolome analyses revealed increased amino acid contents and reduced sterol contents known to benefit planthopper development. That Lepidoptera-resistant Bt rice is less attractive to this important nontarget pest in the field is therefore a first example of ecological resistance of Bt plants to nontarget pests. Our findings suggest that non-Bt rice refuges established for delaying the development of Bt resistance may also act as a trap crop for N. lugens and possibly other planthoppers.

The rice planthopper parasitoid Anagrus nilaparvatae is not at risk when feeding on honeydew derived from Bacillus thuringiensis (Bt) rice

BACKGROUND

Honeydew is a sugar-rich excretion produced by sap-feeding Sternorrhyncha and is an important source of carbohydrates for natural enemies, especially for parasitoids. Honeydew derived from genetically modified (GM) crops can contain amounts of the transgene product. Thus, it is a possible route of exposure for natural enemies feeding on honeydew. In the present study, the potential effects of Nilaparvata lugens honeydew derived from Cry1C and Cry2A rice on different life-table parameters and parasitism dynamics of the egg parasitoid Anagrus nilaparvatae were evaluated under laboratory and field conditions. Furthermore, the Bacillus thuringiensis (Bt) levels and the sugar and amino acid composition of honeydew were analyzed.

RESULTS

Results indicated that A. nilaparvatae was exposed to Bt proteins by feeding on N. lugens honeydew produced from Bt rice. However, honeydew derived from the tested Cry1C and Cry2A rice lines did not affect the development, longevity, emergence rate and fecundity of A. nilaparvatae. Also, the parasitism dynamics in the field remained unaffected. In addition, the sugar and amino acid composition of N. lugens honeydew was not significantly altered for the tested Bt rice lines compared with the parental non-Bt plant.

CONCLUSION

The quality of honeydew derived from the tested Bt rice lines as a food resource for natural enemies was maintained. © 2018 Society of Chemical Industry.

Does Bt rice pose risks to non-target arthropods? Results of a meta-analysis in China

Transgenic Bt rice expressing the insecticidal proteins derived from Bacillus thuringiensis Berliner (Bt) has been developed since 1989. Their ecological risks towards non-target organisms have been investigated; however, these studies were conducted individually, yielding uncertainty regarding potential agroecological risks associated with large-scale deployment of Bt rice lines. Here, we developed a meta-analysis of the existing literature to synthesize current knowledge of the impacts of Bt rice on functional arthropod guilds, including herbivores, predators, parasitoids and detritivores in laboratory and field studies. Laboratory results indicate Bt rice did not influence survival rate and developmental duration of herbivores, although exposure to Bt rice led to reduced egg laying, which correctly predicted their reduced abundance in Bt rice agroecosystems. Similarly, consuming prey exposed to Bt protein did not influence survival, development or fecundity of predators, indicating constant abundances of predators in Bt rice fields. Compared to control agroecosystems, parasitoid populations decreased slightly in Bt rice cropping systems, while detritivores increased. We draw two inferences. One, laboratory studies of Bt rice showing effects on ecological functional groups are mainly either consistent with or more conservative than results of field studies, and two, Bt rice will pose negligible risks to the non-target functional guilds in future large-scale Bt rice agroecosystems in China.

Combined influence of Bt rice and rice dwarf virus on biological parameters of a non-target herbivore, Nephotettix cincticeps (Uhler) (Hemiptera: Cicadellidae)

The advent of genetically modified (GM) Bt rice creates the possibility of interactions among Bt crops, crop pathogens and non-target herbivores. In particular, information on how pathogen-infected Bt-expressing plants will influence non-target herbivores is necessary to predict the sustainability of GM cropping systems. Laboratory bioassays were conducted to evaluate the potential combined impacts of rice dwarf virus (RDV) and two Bt rice lines, T1C-19 (Cry1C) and T2A-1 (Cry2A), on non-target green rice leafhopper (GRLH), Nephotettix cincticeps (Uhler) (Hemiptera: Cicadellidae). In the first experiment, GRLHs feeding preference tests on Bt rice lines compared to a parental control rice line, MH63, were conducted. As rice plants were uninfected with RDV, GRLHs generally preferred the control MH63 line over the two Bt lines during the initial 8 h, with no significant preference during the following 64 h. As rice plants were infected with RDV, there were no clear preferences between the Bt rice lines and the control MH63 line. In the second experiment, we assessed the combined influence of RDV-infection status and Bt rice lines on GRLH biological parameters. Egg duration, adult weights, and male adult longevity were significantly affected on RDV-infected Bt rice. Other parameters, egg hatching rate, nymph survival and fecundity were not significantly influenced. We infer that interaction effect among two testing Bt rice lines and RDV will not lead to enlarged pest populations, thus demonstrating that growing these two Bt rice lines will poses negligible risk to GRLH in sustainable rice agroecosystems. Long-term field experiments to monitor the population dynamics of GRLHs at large scale need to be carried out to confirm the current results.

Variation among conventional cultivars could be used as a criterion for environmental safety assessment of Bt rice on nontarget arthropods

The current difficulty facing risk evaluations of Bacillus thuringiensis (Bt) crops on nontarget arthropods (NTAs) is the lack of criteria for determining what represents unacceptable risk. In this study, we investigated the biological parameters in the laboratory and field population abundance of Nilaparvata lugens (Hemiptera: Delphacidae) on two Bt rice lines and the non-Bt parent, together with 14 other conventional rice cultivars. Significant difference were found in nymphal duration and fecundity of N. lugens fed on Bt rice KMD2, as well as field population density on 12 October, compared with non-Bt parent. However, compared with the variation among conventional rice cultivars, the variation of each parameter between Bt rice and the non-Bt parent was much smaller, which can be easily seen from low-high bar graphs and also the coefficient of variation value (C.V). The variation among conventional cultivars is proposed to be used as a criterion for the safety assessment of Bt rice on NTAs, particularly when statistically significant differences in several parameters are found between Bt rice and its non-Bt parent. Coefficient of variation is suggested as a promising parameter for ecological risk judgement of IRGM rice on NTAs.

Effects of Transgenic Bt Rice on Nontarget Rhopalosiphum maidis (Homoptera: Aphididae)

The effects of three transgenic Bacillus thuringiensis (Bt) rice lines, KMD1, KMD2, and G8-7, on biological parameters and population dynamics of nontarget insect, Rhopalosiphum maidis (Fitch) (Homoptera: Aphididae), were investigated in the laboratory and field. No significant differences were found between Bt and non-Bt rice lines for aphid survival. The developmental time of R. maidis that fed on KMD1 and KMD2 did not differ significantly from those of the individuals feeding on the parental variety Xiushui11, but significantly prolonged developmental time was observed on G8-7 as compared with its parental variety Xiushui110. Aphid fecundity was significantly higher on Bt than on parental rice. A 2-yr field survey indicated that Bt rice did not significantly affect the population dynamics of R. maidis in comparison with non-Bt rice. Additionally, guttation droplets of Bt rice and aphids feeding on Bt rice were analyzed for presence of Cry1Ab using ELISA. No Cry1Ab protein was found in aphid adults feeding on Bt rice lines both in the laboratory and field. By using the guttation droplets from the top of rice seedlings, we designed a novel method to collect phloem sap, and found that relatively low concentrations were detected in the guttation droplets from Bt rice lines. In conclusion, although the Bt rice lines tested in this study stimulate the fecundity of R. maidis, the aphid population density did not increase in Bt rice fields.

Effects of transgenic cry1Ie maize on non-lepidopteran pest abundance, diversity and community composition

Non-lepidopteran pests are exposed to, and may be influenced by, Bt toxins when feeding on Bt maize that express insecticidal Cry proteins derived from Bacillus thuringiensis (Bt). In order to assess the potential effects of transgenic cry1Ie maize on non-lepidopteran pest species and ecological communities, a 2-year field study was conducted to compare the non-lepidopteran pest abundance, diversity and community composition between transgenic cry1Ie maize (Event IE09S034, Bt maize) and its near isoline (Zong 31, non-Bt maize) by whole plant inspections. Results showed that Bt maize had no effects on non-lepidopteran pest abundance and diversity (Shannon-Wiener diversity index, Simpson's diversity index, species richness, and Pielou's index). There was a significant effect of year and sampling time on those indices analyzed. Redundancy analysis indicated maize type, sampling time and year totally explained 20.43 % of the variance in the non-lepidopteran pest community composition, but no association was presented between maize type (Bt maize and non-Bt maize) and the variance. Nonmetric multidimensional scaling analysis showed that sampling time and year, rather than maize type had close relationship with the non-lepidopteran pest community composition. These results corroborated the hypothesis that, at least in the short-term, the transgenic cry1Ie maize had negligible effects on the non-lepidopteran pest abundance, diversity and community composition.

The development and status of Bt rice in China

Multiple lines of transgenic rice expressing insecticidal genes from the bacterium Bacillus thuringiensis (Bt) have been developed in China, posing the prospect of increases in production with decreased application of pesticides. We explore the issues facing adoption of Bt rice for commercial production in China. A body of safety assessment work on Bt rice has shown that Bt rice poses a negligible risk to the environment and that Bt rice products are as safe as non-Bt control rice products as food. China has a relatively well-developed regulatory system for risk assessment and management of genetically modified (GM) plants; however, decision-making regarding approval of commercial production has become politicized, and two Bt rice lines that otherwise were ready have not been allowed to enter the Chinese agricultural system. We predict that Chinese farmers would value the prospect of increased yield with decreased use of pesticide and would readily adopt production of Bt rice. That Bt rice lines may not be commercialized in the near future we attribute to social pressures, largely due to the low level of understanding and acceptance of GM crops by Chinese consumers. Hence, enhancing communication of GM crop science-related issues to the public is an important, unmet need. While the dynamics of each issue are particular to China, they typify those in many countries where adoption of GM crops has been not been rapid; hence, the assessment of these dynamics might inform resolution of these issues in other countries.

Transgenic cry1C or cry2A rice has no adverse impacts on the life-table parameters and population dynamics of the brown planthopper, Nilaparvata lugens (Hemiptera: Delphacidae)

BACKGROUND

Transgenic rice producing the insecticidal protein from Bacillus thuringiensis Berliner (Bt) is protected from damage by lepidopteran insect pests. However, one of the main concerns about Bt rice is the potential impact on non-target herbivores. In the present study, the ecological impacts of two Bt rice lines, T1C-19 expressing Cry1C protein and T2A-1 expressing Cry2A protein, on the non-target herbivore brown planthopper (BPH), Nilaparvata lugens (Stål), were evaluated under laboratory and field conditions. The purpose was to verify whether these Bt rice lines could affect the performance of BPH at individual and population scales.

RESULTS

Laboratory results showed that most of the fitness parameters (development duration, survival rate, fecundity, fertility, amount of honeydew excreted) of BPH were not significantly affected by the two tested Bt rice lines, although the development duration of fourth-instar nymphs fed on T1C-19 was distinctly longer compared with that on T2A-1 and non-Bt rice plants. Five life-table parameters did not significantly differ among rice types. Two-year field trials also revealed no significant difference in population dynamics of BPH among rice types.

CONCLUSION

It is inferred that the tested Bt rice lines are unlikely to affect the population growth of BPH.

The effects of triazophos applied to transgenic Bt rice on the nutritional indexes, Nlvg expression, and population growth of Nilaparvata lugens Stål under elevated CO₂

The brown planthopper, Nilaparvata lugens (Stål) (Hemiptera: Delphacidae), is a typical pest in which population resurgence can be induced by insecticides. Warmer global temperatures, associated with anthropogenic climate change, are likely to have marked ecological effects on terrestrial ecosystems. However, the effects of elevated CO2 (eCO2) concentrations on the resurgence of N. lugens that have been treated with pesticides used for transgenic Bt rice cultivation are not fully understood. The present study investigated changes in the protein content, soluble sugar content, free amino acid level, vitellogenin (Nlvg) mRNA expression, and the population growth of N. lugens on transgenic Bt rice (TT51) following triazaophos foliar spray under conditions of eCO2. The results showed that the protein content in the fat bodies and ovaries of N. lugens adult females in TT51 treated with 40 ppm triazophos under eCO2 was significantly higher than under ambient CO2 (aCO2) and was also higher than that in females feeding on the non-transgenic parent (MH63) under aCO2 at different days after emergence (DAEs). The soluble sugar content and free amino level of adult females in TT51 treated with 40 ppm triazophos under eCO2 was significantly higher than under aCO2 and was also higher than in MH63 under aCO2 at 1 and 3 DAE. The Nlvg mRNA expression level of N. lugens adult females in TT51 treated with 40 ppm triazophos under eCO2 was significantly higher than under aCO2 and was also higher than in MH63 under aCO2 at 1 and 3 DAE. The population number of N. lugens in TT51 treated with 40 ppm triazophos under eCO2 was significantly higher than under aCO2 and was also higher than in MH63 under aCO2. The present findings provide important information for integrated pest management with transgenic varieties and a better understanding of the resurgence mechanism of N. lugens under eCO2.

Comparing Gene Expression Profiles Between Bt and non-Bt Rice in Response to Brown Planthopper Infestation

Bt proteins are the most widely used insecticidal proteins in transgenic crops for improving insect resistance. We previously observed longer nymphal developmental duration and lower fecundity in brown planthopper (BPH) fed on Bt rice line KMD2, although Bt insecticidal protein Cry1Ab could rarely concentrate in this non-target rice pest. In the present study, we performed microarray analysis in an effort to detect Bt-independent variation, which might render Bt rice more defensive and/or less nutritious to BPH. We detected 3834 and 3273 differentially expressed probe-sets in response to BPH infestation in non-Bt parent Xiushui 11 and Bt rice KMD2, respectively, only 439 of which showed significant differences in expression between rice lines. Our analysis revealed a shift from growth to defense responses in response to BPH infestation, which was also detected in many other studies of plants suffering biotic and abiotic stresses. Chlorophyll biosynthesis and basic metabolism pathways were inhibited in response to infestation. IAA and GA levels decreased as a result of the repression of biosynthesis-related genes or the induction of inactivation-related genes. In accordance with these observations, a number of IAA-, GA-, BR-signaling genes were downregulated in response to BPH. Thus, the growth of rice plants under BPH attack was reduced and defense related hormone signaling like JA, SA and ET were activated. In addition, growth-related hormone signaling pathways, such as GA, BR, and auxin signaling pathways, as well as ABA, were also found to be involved in BPH-induced defense. On the other side, 51 probe-sets (represented 50 genes) that most likely contribute to the impact of Bt rice on BPH were identified, including three early nodulin genes, four lipid metabolic genes, 14 stress response genes, three TF genes and genes with other functions. Two transcription factor genes, bHLH and MYB, together with lipid transfer protein genes LTPL65 and early nodulin gene ENOD93, are the most likely candidates for improving herbivore resistance in plants.

Acquisition of Cry1Ac protein by non-target arthropods in Bt soybean fields

Soybean tissue and arthropods were collected in Bt soybean fields in China at different times during the growing season to investigate the exposure of arthropods to the plant-produced Cry1Ac toxin and the transmission of the toxin within the food web. Samples from 52 arthropod species/taxa belonging to 42 families in 10 orders were analysed for their Cry1Ac content using enzyme-linked immunosorbent assay (ELISA). Among the 22 species/taxa for which three samples were analysed, toxin concentration was highest in the grasshopper Atractomorpha sinensis and represented about 50% of the concentration in soybean leaves. Other species/taxa did not contain detectable toxin or contained a concentration that was between 1 and 10% of that detected in leaves. These Cry1Ac-positive arthropods included a number of mesophyll-feeding Hemiptera, a cicadellid, a curculionid beetle and, among the predators, a thomisid spider and an unidentified predatory bug belonging to the Anthocoridae. Within an arthropod species/taxon, the Cry1Ac content sometimes varied between life stages (nymphs/larvae vs. adults) and sampling dates (before, during, and after flowering). Our study is the first to provide information on Cry1Ac-expression levels in soybean plants and Cry1Ac concentrations in non-target arthropods in Chinese soybean fields. The data will be useful for assessing the risk of non-target arthropod exposure to Cry1Ac in soybean.

Arthropod abundance and diversity in transgenic Bt soybean

Before the commercialization of any insect-resistant genetically modified crop, it must be subjected to a rigorous premarket risk assessment. Here, possible effects of growing of transgenic Cry1Ac soybean on arthropod communities under field conditions were assessed for 2 yr and quantified in terms of arthropod community indices including the Shannon-Weaver diversity index, richness index, and dominance index. Our results showed no significant differences of diversity, richness, or dominant indices for Bt soybean compared with the recipient cultivar, conventional soybean, or sprayed conventional soybean. Conventional soybean treatment with insecticide had an adverse effect on the arthropod community after spraying, but arthropod community diversity recovered quickly. Bt soybean had no negative effect on the dominant distribution of subcommunities, including sucking pests, other pests, predators, parasitoids, and others except for lepidopteran pests. The dominance distribution of lepidopteran pests decreased significantly in Bt soybean because of the significant decrease in the numbers of Spodoptera litura (F.) and Ascotis selenaria Schiffermüller et Denis compared with the recipient cultivar. Our results showed that there were no negative effects of Cry1Ac soybean on the arthropod community in soybean field plots in the short term.

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.

Impacts of Bt rice expressing Cry1C or Cry2A protein on the performance of nontarget leafhopper, Nephotettix cincticeps (Hemiptera: Cicadellidae), under laboratory and field conditions

Transgenic rice expressing Bacillus thuringiensis Berliner (Bt) protein can effectively control target insects including stem borers and leaf folders. However, the potential effects of Bt rice on nontarget organisms including nontarget herbivores have not been fully evaluated. In the current study, ecological fitness parameters of the nontarget herbivore, Nephotettix cincticeps (Uhler) (Hemiptera: Cicadellidae), fed on T1C-19 (Cry1C) or T2A-1 (Cry2A) rice were compared with non-Bt rice (MH63) under laboratory conditions. A 2-yr field trial was also conducted to monitor the population dynamics of N. cincticeps in the Bt and control rice plots using the vacuum-suction machine and yellow sticky card traps. Laboratory results showed that there were no significant differences in some of biological parameters including egg developmental duration, adult fresh weight, adult longevity, and oviposition period when N. cincticeps fed on Bt or non-Bt rice was compared. However, the survival rate of N. cincticeps nymphs fed on T2A-1 Bt rice plants was significantly higher than that on the control. When N. cincticeps fed on T1C-19 Bt rice plants, its nymphal duration was significantly longer and fecundity significantly lower compared with those fed on both T2A-1 Bt and non-Bt rice plants; the preoviposition period of N. cincticeps fed on T1C-19 and T2A-1 Bt rice was also significantly shorter than those on non-Bt rice. Nonetheless, both seasonal density and population dynamics of N. cincticeps adults and nymphs were similar between Bt (T1C-19 and T2A-1) and non-Bt rice plots under field conditions. In conclusion, our results indicate that our two tested Bt rice lines would not lead to higher population of N. cincticeps. Long-term experiments to monitor the population dynamics of N. cincticeps at large scale need to be carried out to confirm the current results.

Impact of six transgenic Bacillus thuringiensis rice lines on four nontarget thrips species attacking rice panicles in the paddy field

As a key component of ecological risk assessments, nontarget effects of Bacillus thuringiensis (Bt) rice have been tested under laboratory and field conditions for various organisms. A 2-yr field experiment was conducted to observe the nontarget effects of six transgenic rice lines (expressing the Cry1Ab or fused protein of Cry1Ab and Cry1Ac) on four nontarget thrips species including Frankliniella intonsa (Trybom), F. tenuicornis (Uzel), Haplothrips aculeatus (F.), and H. tritici (Kurd), as compared with their rice parental control lines. Two sampling methods including the beat plate and plastic bag method were used to monitor the population densities of the four thrips species for 2 yr. The results showed that the seasonal average densities of four tested thrips species in Bt rice plots were significantly lower than or very similar to those in the non-Bt rice plots depending on rice genotypes, sampling methods, and years. Among all six tested Bt rice lines, transgenic B1 and KMD2 lines suppressed the population of these tested thrips species the most. Our results indicate that the tested Bt rice lines are unlikely to result in high population pressure of thrips species in comparison with non-Bt rice. In some cases, Bt rice lines could significantly suppress thrips populations in the rice ecosystem. In addition, compatibility of Bt rice, with rice host plant resistance to nontarget sucking pests is also discussed within an overall integrated pest management program for rice.