Transgenic Bt Maize Research Articles

Impact of dual Bt-transgenic maize (2A7) on soil microbial communities and enzyme activities: A comparative study with control variety Z58

The impacts of transgenic crops on soil microbiology and fertility are critical in determining their biosafety. While transgenic crops can alter soil microbes, their effects are often context-dependent; therefore, the ecological importance of these changes remains a topic of ongoing research. Using high-throughput sequencing, we investigated the effects of Bacillus thuringiensis (Bt) maize expressing the mcry1Ab and mcry2Ab genes (2A7) on soil nutrient dynamics, as well as the diversity and function of soil microbial communities, including bacteria and fungi, within different soil compartments. Our findings revealed a plant-shaped rhizosphere (RS) microbial community as a result of the selective recruitment of microorganisms from the surrounding environment. The transgene insertion had a significant impact on the RS niche, and several species eventually became associated with Z58 and 2A7 plants. For example, Neocosmospora rubicola fungal and Pantoea dispersa bacterial microorganisms were significantly decreased in the dual Bt-transgenic 2A7 rhizosphere but enriched in the Z58 rhizospheres. The activity of soil enzymes such as urease, invertase, and alkaline phosphatase was boosted by Bt-transgenic 2A7. LefSe analysis identified significant bacterial and fungal biomarker species that were responsible for the differential effects of Bt-transgenic 2A7 and control Z58 within rhizosphere soils. Mantel analysis further demonstrated that the root exudates of 2A7 altered nutrient-acquisition enzymes by influencing biomarker taxa. PICRUSt2 functional characterization revealed a significantly higher abundance of the phosphate-starvation-inducible protein in control Z58 than in Bt-transgenic 2A7. Furthermore, taxonomy, alpha (Shannon diversity), and beta diversity analyses all revealed niche-driven microbial profile differentiation. Niche partitioning also had a significant impact on N- and P-related COGs as well. Our findings suggests that Bt-transgenic 2A7 modulates rhizosphere microbial communities by affecting biomarker taxa and soil enzyme activity. These findings will promote sustainable agriculture practices by advancing our knowledge of the ecological effects of Bt crops on soil microbial communities.

Control Efficacy of the Bt Maize Event DBN3601T Expressing Cry1Ab and Vip3Aa Proteins against Beet Armyworm, Spodoptera exigua (Hübner), in China.

The beet armyworm, Spodoptera exigua (Hübner), is a major pest of maize, cotton, soybean, and many other crops globally. Despite the widespread deployment of Bt transgenic maize for pest control worldwide, the efficacy of Bt lepidopteran-resistant transgenic maize in managing S. exigua remains rarely studied. In this study, we quantified the expression level of pyramided Cry1Ab and Vip3Aa toxins in Bt maize (event DBN3601T) and evaluated their control efficiency against S. exigua under both laboratory and field conditions. The enzyme-linked immunosorbent assay (ELISA) results showed that the expression levels of Cry1Ab and Vip3Aa proteins in DBN3601T maize tissues followed a decreasing order as follows: V5-leaf > V8-leaf > VT-tassel > R2-kernel > R1-silk. Diet-overlay assay results showed that the LC50 values of Cry1Ab and Vip3Aa proteins against S. exigua larvae were 11.66 ng/cm2 and 27.74 ng/cm2, respectively, with corresponding GIC50 values at 1.59 ng/cm2 and 7.93 ng/cm2. Bioassay using various tissues of the DBN3601T maize indicated that after 7 days of infestation, mortality rates of neonates and third-instar larvae ranged from 86% to 100% and 58% to 100%, respectively. Mortality was highest on V5 and V8 leaves, followed by R2-kernel, VT-tassel, and R1-silk. Field trials demonstrated that DBN3601T maize exhibited significantly lower larval density, damage rate, and leaf damage score compared to non-Bt maize. Field cage trial showed that the control efficacy of DBN3601T maize at the vegetative stage could reach 98%. These findings provide a theoretical basis for utilizing Bt transgenic maize to enhance the sustainable management of S. exigua in Asia.

Field evaluation the effect of two transgenic Bt maize events on predatory arthropods in the Huang-Huai-Hai summer maize-growing region of China.

To illustrate the impact of genetically modified (GM) Bt maize on the natural enemy communities in the Huang-Huai-Hai summer maize-growing region in China, the abundance of 7 common predator taxa (Geocoris pallidipennis Costa, Harmonia axyridis (Pallas), lacewings, Orius sauteri (Poppius), Propylea japonica (Thunberg), spiders, and Staphylinidae) was quantitatively evaluated by comparing Bt-Cry1Ab DBN9936 and Bt-Cry1Ab/Cry2Aj Ruifeng 125 events to their near non-Bt isolines during the growing season from 2016 to 2019. A total of 10,302, 19,793, 13,536, and 5,672 individuals were observed during 4 years, and the abundance of each taxa on Bt maize varied between sample dates among those arthropod taxa. Shannon-Wiener diversity index of predator communities from 7 taxa showed very similar temporal dynamics and principal response curve analyses to examine community-level effects showed no significant differences in predator abundance in Bt maize compared with non-Bt maize. We conclude that the 2 Bt maize hybrids did not adversely affect the predator community in the Huang-Huai-Hai summer maize-growing region of China.

Toxic Effects of Bt-(Cry1Ab+Vip3Aa) Maize on Storage Pest Paralipsa gularis (Zeller).

Paralipsa gularis (Zeller) is a storage pest; however, in recent years it has evolved into a considerable maize pest during the late growth stage in the border region between China and other Southeast Asian countries. Bt transgenic insect-resistant maize is an effective measure in controlling a wide range of lepidopteran pests, but there is a lack of research on the toxic effects of storage pests. We tested the toxicity of Bt-Cry1Ab, Vip3Aa, and their complex proteins against P. gularis via bioassay and investigated the efficiency of Bt-(Cry1Ab+Vip3Aa) maize in controlling P. gularis during the late growth stage of maize in the period 2022-2023. The bioassay results show that the susceptibilities of P. gularis to the two Bt proteins and their complex proteins were significantly different. The LC50 values of DBNCry1Ab ("DBN9936" event), DBNVip3Aa ("DBN9501" event), DBN Cry1Ab+Vip3Aa ("DBN3601T" event), and Syngenta Cry1Ab+Vip3Aa ("Bt11" event × "MIR162" event) were 0.038 μg/g, 0.114 μg/g, 0.110 μg/g, and 0.147 μg/g, and the GIC50 values were 0.014 μg/g, 0.073 μg/g, 0.027 μg/g, and 0.026 μg/g, respectively. Determination of the expression content of the insecticidal protein in different tissues of Bt-(Cry1Ab+Vip3Aa) maize shows that the total Bt protein content in different tissues was in the following order: stalk > bract > cob > kernel. However, the bioassay results show that the mortalities of P. gularis feeding on Bt-(Cry1Ab+Vip3Aa) maize in different tissues at different growth stages were all above 93.00%. The field trial indicates that the occurrence density of larvae and plant damage rate for conventional maize were 422.10 individuals/100 plants and 94.40%, respectively, whereas no larvae were found on Bt-(Cry1Ab+Vip3Aa) maize. In summary, this study implies that Bt-(Cry1Ab+Vip3Aa) maize has a high potential for control of P. gularis, providing a new technical measure for the management of the pest.

Gut bacterial community and gene expression alterations induced by transgenic Bt maize contribute to insecticidal activity against Mythimna separata

Gut bacterial community and gene expression alterations induced by transgenic Bt maize contribute to insecticidal activity against Mythimna separata

Effects of Insect-Resistant Maize HGK60 on Community Diversity of Bacteria and Fungi in Rhizosphere Soil.

The influence of biotech crops on microbial communities in rhizosphere soil is an important issue in biosafety assessments. The transgenic maize HGK60 harboring the Bt cry1Ah gene enhanced the resistance to lepidopteran pests, while the ecological risk of HGK60 maize on rhizosphere microorganisms is unclear. In this study, we comprehensively analyzed the diversity and composition of bacterial and fungal communities in the rhizosphere soil around Bt maize HGK60 and the near-isogenic non-Bt maize ZD958 at four growth stages via a high-throughput sequencing technique. The results showed that HGK60 maize unleashed temporary effects on the bacterial and fungal diversity and richness during the study plant's development, which would be restored after one cycle of plant cultivation due to the application of the same agricultural management. The differences of bacterial and fungal communities were marked by seasonality, while the different growth stage was the important factor as opposed to the cultivar contributing to the shifts in the bacterial and fungal communities' structure. This study will provide useful information regarding the impact of Bt transgenic maize on the soil microbiome and a theoretical basis for the development of a safety assessment approach for Bt maize in China.

Impact of Transgenic Cry1Ab/2Aj Maize on Abundance of Non-Target Arthropods in the Field.

Transgenic Bacillus thuringiensis (Bt) maize has broad prospects for application in China. Before commercialization, it is necessary to assess possible ecological impacts, including impacts on non-target arthropods (NTAs) in the field. In the present study, transgenic Bt maize expressing cry1Ab/2Aj and its corresponding non-transformed near isoline were planted under the same environmental and agricultural conditions, and arthropods in the field were collected during the three main growth stages of maize. In a one year trial, the results showed the composition of NTA communities in the transgenic and control maize fields were similar. There were no significant differences for community-level parameters of species richness (S), Shannon–Wiener diversity index (H′), evenness index (J) and Simpson’s dominant concentration (C) between the two types of maize fields. Likewise, a Bray–Curtis dissimilarity and distance analysis showed that Cry1Ab/2Aj toxin exposure did not increase community dissimilarities between Bt and non-Bt maize plots and that the structure of the NTAs community was similar on the two maize varieties. Furthermore, planting of the transgenic cry1Ab/2Aj maize did not affect the density or composition of non-target decomposers, herbivores, predators, parasitoids and pollinator guilds. In summary, our results showed that planting of Bt maize producing Cry1Ab/Cry2Aj proteins do not adversely affect population dynamics and diversity of NTAs.

A 6-year field monitoring of fall armyworm, Spodoptera frugiperda, in transgenic Bt maize in Brazil

A 6-year field monitoring study was designed to compare the presence of fall armyworm Spodoptera frugiperda (J. E. Smith), leaf injury, its parasitoids, 100 seed weight, and seed yield of Bt maize hybrids approved for commercialization in the Brazilian market. Field trials were planted in two municipalities, divided into two periods, from 2011 to 2014 (period I), and due to the approval of different Bt hybrids, from 2015 to 2016 (period II). Treatments were Bt, non-Bt maize and all non-Bt maize sprayed with insecticide methomyl. Six Bt-maize hybrids were planted, expressing the following proteins: Cry1Ab, Cry1F, Cry1A.105 (Cry1Ab +Cry1Ac +Cry1F), Cry2Ab2a and Vip3. In 2015 and 2016 Bt Powercore was planted due to its commercial approval. The number of S. frugiperda larvae for most Bt hybrids was lower than on non-Bt hybrids, except for Fórmula TL and Herculex in period II, in both municipalities. In period I, Bt hybrids VT, VT 2 and Viptera showed almost no injury on their leaves, despite the high number of fall armyworm larvae found in plants. Different parasitoids emerged from larvae from Bt and non Bt hybrids: Archytas sp., Campoletis sp., Chelonus sp., Eiphosoma sp. and Ophion luteus. The average 100 seed weight was higher in municipality from Sete Lagoas for all Bt hybrids, non-Bt hybrids and non-Bt hybrids sprayed with methomyl, when compared to Nova Porteirinha during period I. Fórmula TL, non-Bt Fórmula TL sprayed with methomyl, and non-Bt Fórmula TL showed the lowest seed yield in both municipalities and periods.

Transgenic Bt maize in South-and Central America: the pros and cons

The official authorization for planting Bt maize in most Central and South American countries was granted more than 20 years ago. This permission has raised concerns, has revealed inconsistencies in the information provided for farmers, has shown unknowns, motivating comments, and produced publications, often not scientific. Given the theoretical impact on environment, economy, and health, and the development of fall army worm´s resistance, despite the existing research capacity in these countries, the scientific literature is scarce, probably due to lack of funding and influence by the holders of the patents and the producers and traders of seeds of transgenic maize. The aim of this review is to debate the benefits and disadvantages originated by the sowing of the maize hybrids that contain any of the different Cry´s of the bacteria Bacillus thuringiensis. The documents reviewed do not elucidate conclusions; it will be necessary to wait years to define if the transgenic maize plantings represented a benefit for the growers and consumers of this plant species, which originated in these areas. However, at this moment an existing balance between the benefits and the risks of Bt maize plantings could be deduced.

Analysis of metabolites and metabolic mechanism in Bt transgenic and non-transgenic maize

The gas chromatography-mass spectrometry was used to isolate and identify metabolites of non-transgenic and Bacillus thuringiensis transgenic maize. The non-targeted metabolomics technique was used to analysis the metabolic pathway and mechanism of two kinds of maize. The methanol was used as extractant and the N,O-bis(trimethylsilyl) trifluoroacetamide was used as derivatization reagent. 38 kinds of metabolites were isolated and identified from non-transgenic maize, and 61 kinds of metabolites were isolated and identified in Bacillus thuringiensis transgenic maize. The specific metabolites between non-transgenic and Bacillus thuringiensis transgenic maize were analyzed. The metabolic pathway of specific metabolites was analyzed by KEGG annotation. The metabolic mechanism of non-transgenic maize and Bacillus thuringiensis transgenic maize was explored. The result indicated there were more metabolites involved in metabolic pathways in Bacillus thuringiensis transgenic maize than in non-transgenic maize, and tricarboxylic acid cycle and energy metabolism pathways of Bacillus thuringiensis transgenic maize are found to be higher than that of non-transgenic maize. The metabolic pathway of Bacillus thuringiensis transgenic maize conforms to the biological activity law.

AMF Inoculation Can Enhance Yield of Transgenic Bt Maize and Its Control Efficiency Against Mythimna separata Especially Under Elevated CO2.

The promotion and application of transgenic Bt crops provides an approach for the prevention and control of target lepidopteran pests and effectively relieves the environmental pressure caused by the massive usage of chemical pesticides in fields. However, studies have shown that Bt crops will face a new risk due to a decrease in exogenous toxin content under elevated carbon dioxide (CO2) concentration, thus negatively affecting the ecological sustainability of Bt crops. Arbuscular mycorrhizal fungi (AMF) are important beneficial microorganisms that can effectively improve the nutrient status of host plants and are expected to relieve the ecological risk of Bt crops under increasing CO2 due to global climate change. In this study, the Bt maize and its parental line of non-transgenic Bt maize were selected and inoculated with a species of AMF (Funneliformis caledonium, synonyms: Glomus caledonium), in order to study the secondary defensive chemicals and yield of maize, and to explore the effects of F. caledonium inoculation on the growth, development, and reproduction of the pest Mythimna separata fed on Bt maize and non-Bt maize under ambient carbon dioxide concentration (aCO2) and elevated carbon dioxide concentration (eCO2). The results showed that eCO2 increased the AM fungal colonization, maize yield, and foliar contents of jasmonic acid (JA) and salicylic acid (SA), but decreased foliar Bt toxin content and Bt gene expression in Bt maize leaves. F. caledonium inoculation increased maize yield, foliar JA, SA contents, Bt toxin contents, and Bt gene expression in Bt maize leaves, and positively improved the growth, development, reproduction, and food utilization of the M. separata fed on non-Bt maize. However, F. caledonium inoculation was unfavorable for the fitness of M. separata fed on Bt maize, and the effect was intensified when combined with eCO2. It is indicated that F. caledonium inoculation had adverse effects on the production of non-Bt maize due to the high potential risk of population occurrence of M. separata, while it was just the opposite for Bt maize. Therefore, this study confirms that the AMF can increase the yield and promote the expression levels of its endogenous (JA, SA) and exogenous (Bt toxin) secondary defense substances of Bt maize under eCO2, and finally can enhance the insect resistance capacity of Bt crops, which will help ensure the sustainable utilization and safety of Bt crops under climate change.

Ovipositional responses of Spodoptera frugiperda on host plants provide a basis for using Bt-transgenic maize as trap crop in China

Spodoptera frugiperda, the pest fall armyworm (FAW), is widespread in more than 100 countries. To date, planting insect-resistant transgenic crops is one of the main control methods in its native countries. In this study we evaluated Bt-transgenic maize (Bt maize) and non-transgenic (conventional) maize and six other host plants in greenhouse pot experiments and field trials for oviposition preference by the Chinese populations of FAW. In laboratory trials, female moths preferred to oviposit on maize with no significant preference between conventional and Bt maize. However, after conventional and transgenic maize were exposed to FAW larvae and damaged, oviposition was significantly higher on transgenic maize than on the conventional one. Field trials showed that for plants less damaged at an early stage (seedling stage), oviposition of FAW on transgenic and conventional maize was significantly higher than that on wheat, sorghum, foxtail millet, peanut and soybean while showing no significant difference between transgenic or conventional maize. FAW adults mainly laid eggs on Bt maize, while the larval density and leaf damage rating or percentage of damaged plants were significantly lower than on conventional maize. Larval density and its damage on conventional maize were significantly higher than that on Bt maize and the other five hosts. Thus, maize is a highly preferred and suitable host for S. frugiperda feeding and ovipositing, and Bt maize can be used as trap crop to protect other crops.

EFFECTIVENESS OF TRANSGENIC BT MAIZE TO CONTROL Helicoverpa armigera (LEPIDOPTERA: NOCTUIDAE)

The caterpillar Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), identified in Brazil in 2013, greatly worries farmers because of its destructive power. The technology of transgenic plants that induces resistance to insects is a great ally for controlling caterpillars. In this study we compared the performance of transgenic Bt maize in the controlling of different larval instars of H. armigera in semi-field seedlings. There were tested the following genotypes: (1) Non-Bt maize Iso-hybrid (Control); (2) Cry1F; (3) Cry1F+ Cry1A.105 + Cry2Ab2; (4) Cry1A.105 + Cry2Ab2; (5) Cry1Ab + Cry1F; (6) Cry1Ab + Vip3Aa20. The experimental design was organized in randomized blocks with eight replications, each consisting of a pot with 5 plants artificially infested with larvae of 2nd, 3rd or 4th instar. At 1, 3, 7, 10 and 14 days after infestation, plants were evaluated for defoliation. In the 3rd instar larvae bioassay, there was high predation by birds, but until seven days after infestation all transgenic maize were efficient to the pest. All transgenic Bt maize were effective in the control of tested H. armigera larvae instars.

Landscape-level feedbacks in the demand for transgenic pesticidal corn in the Philippines

We introduce a novel econometric approach to estimate economic pest control feedbacks within agroecological systems, using discrete choice endogenous sorting models. We apply this approach to deployment of transgenic Bt maize in the Philippines. We show with basic theory how areawide pest suppression from largescale Bt maize deployment attenuates farmers' demand for this technology. Econometric results support this hypothesis and imply long-run demand for the Bt trait is price-inelastic, contrasting with price-elastic demand estimated from a model without feedback. Investigating whether this feedback truly derives from areawide pest suppression, we analyze farmers' pest infestation expectations and find expected damages are significantly reduced by higher areawide Bt deployment. We discuss implications of these findings and other potential applications of the econometric approach to study coupled biological and economic systems.

COMPARISON OF EAR DAMAGE CAUSED BY CATERPILLAR PESTS IN TRANSGENIC (BT) MAIZE HYBRIDS AND CONVENTIONAL MAIZE HYBRIDS

The use of transgenic (Bt) maize hybrids has been an important tool to minimize ear damages caused by the caterpillar pests Helicoverpa zea and Spodoptera frugiperda (Lepidoptera: Noctuidae). The objective of this work was to evaluate ear damages caused by caterpillar pests in maize hybrids with Bt technologies and in their respective conventional versions (non-Bt) for control of caterpillar pests that attack maize ears in the state of São Paulo, Brazil. Experiments were carried out in four regions of the state, in two summer crops (2009/10 and 2010/11), using a randomized block design with 6x2 factorial arrangements. The first factor was the hybrids and the second factor was the use or not of Bt technology. During harvesting, the percentage of damaged ears was evaluated and damage scores were attributed to a sample of 20 ears per plot. It was found that: (i) YieldGard and Total Liberty (both Cry 1Ab), Herculex (Cry 1F), VTPRO (Cry 1A.105 + Cry2Ab2) and Viptera (VIP3Aa20) technologies, regardless of the hybrid and the season crop, significantly reduce the ear damages and the percentage of damaged ears; (ii) hybrids expressing the Cry 1Ab protein are more damaged by caterpillar pests compared with other technologies; and (iii) there is great variability among hybrids when expressing toxins, even among those hybrids with the same Bt event.

Potential of transgenic Bt-maize for management of Elasmopalpus lignosellus

The Lepidoptera insects are responsible for large losses in maize production in Brazil, and stand out those that attack seedlings, such as lesser cornstalk borer, Elasmopalpus lignosellus (Zeller). The objective of this work was to compare the performance of transgenic Bt maize in the control of the E. lignosellus caterpillar in the maize seedlings phase in two trials. In the first trial six treatments were tested: (1) Conventional Non-Bt maize; (2) Conventional Non-Bt maize with insecticide application; (3) transgenic maize expressing the Cry1Ab genes; (4) Cry1F; (5) Cry1A.105 + Cry2Ab2; (6) Cry1A.105 + Cry2Ab2 + Cry1F. The experimental design was randomized blocks, where each treatment was repeated 4 times in plots of 22.5 m2. Ten consecutive plants with third instar larvae of E. lignosellus in the seedling stage were artificially infested. Only the Non-Bt maize (Control) was affected by the E. lignosellus caterpillar, but all the treatments presented tillering, galleries and holes in the stem. In the second assay the genotypes used were seeded on 11/23/2012, and the damages of 3rd instar caterpillars of E. ligosellus (Zeller) were evaluated. The treatments were: (1) Conventional Non-Bt maize (Control); (2) transgenic maize expressing the Cry1F + Cry1A.105 + Cry2Ab2 genes; (3) Cry1A.105 + Cry2Ab2; (4) Vip3Aa20; (5) Vip3Aa20 + Cry1Ab; (6) Cry1F; (7) Cry1Ab + Cry1F. The plots were formed by a line spaced in 0.7 m of 2 m, with 10 plants, with barriers to prevent the exit of artificially infested insects. In the first and second assays, non-Bt maize with or without insecticide application were affected by E. lignosellus caterpillars. However, Bt transgenic maize was not harmed by E. lignosellus caterpillars, except the Vip3Aa20 treatment. Bt transgenic plants were poorly damaged by E. lignosellus in the seedling and leaf stage.

Short communication: The rate of release of Cry1Ab protein from Bt maize leaves into water

Transgenic Bt maize plants are genetically modified to contain genes of Bacillus thuringiensis that encode for δ-endotoxins (Cry1Ab protein) that have insecticidal properties. These endotoxins target certain lepidopteran pests of maize. There are several entry routes by which Cry proteins enter the aquatic ecosystem in which aquatic organisms are exposed to these proteins. The main route is through plant debris such as leaves, stalks and postharvest detritus that are transported by means of run-off, rain and wind. While several studies have been conducted on the fate of Cry1Ab protein in terrestrial ecosystems, little is known of the release rates of Cry1Ab proteins from maize plant tissues that end up in aquatic ecosystems. In this study, leaves of Bt-maize and its isoline were submerged in containers filled with deionised or borehole water for a period of 16 days, and kept at 3 different temperatures (10±1, 21±1 and 30±1°C). Samples were collected at 1, 2, 4, 8, 16, 24, 48, 96, 192 and 384 h post submersion and analysed for Cry protein content using enzyme-linked immunosorbent assay (ELISA). The release of Cry protein from submerged maize leaves was influenced by temperature, and duration of immersion. An increase in Cry protein levels in the water was observed from the first hour onwards in both water types until the end of the experiment. The highest concentration of Cry protein was found at 30°C. This study showed that temperature and time period influence the release rate of Cry proteins from dried leaf matter into the aquatic environment.

Arbuscular mycorrhizal fungi alter the food utilization, growth, development and reproduction of armyworm (Mythimna separata) fed on Bacillus thuringiensis maize.

BackgroundThe cultivation of Bt maize (maize genetically modified with Bacillus thuringiensis) continues to expand globally. Arbuscular mycorrhizal fungi (AMF), an important kind of microorganism closely related to soil fertility and plant nutrition, may influence the ecological risk of target lepidopteran pests in Bt crops.MethodsIn this study, transgenic Bt maize (Line IE09S034 with Cry1Ie vs. its parental line of non-Bt maize cv. Xianyu335) was inoculated with a species of AMF, Glomus caledonium (GC). Its effects on the food utilization, reproduction and development of armyworm, Mythimna separata, were studied in a potted experiment from 2017 to 2018.ResultsGC inoculation increased the AMF colonization of both modified and non-modified maize, and also increased the grain weight per plant and 1,000-grain weight of modified and non-modified maize. However, the cultivation of Bt maize did not significantly affect the AMF colonization. The feeding of M. separata with Bt maize resulted in a notable decrease in RCR (relative consumption rate), RGR (relative growth rate), AD (approximate digestibility), ECD (efficiency of conversion of digested food) and ECI (efficiency of conversion of ingested food) parameters in comparison to those observed in larvae fed with non-Bt maize in 2017 and 2018, regardless of GC inoculation. Furthermore, remarkable prolongation of larval life span and decreases in the rate of pupation, weight of pupa, rate of eclosion, fecundity and adult longevity of M. separata were observed in the Bt treatment regardless of GC inoculation during the two-year experiment. Also, when M. separata was fed with Bt maize, a significant prolongation of larval life and significant decreases in the pupal weight, fecundity and adult longevity of M. separata were observed when inoculated with GC. However, it was just the opposite for larvae fed with non-Bt maize that was inoculated with GC. The increased percentage of larval life-span, the decreased percentages of the food utilization, and the other indexes of reproduction, growth, and development of M. separata fed on Bt maize relative to non-Bt maize were all visibly lower when under GC inoculation in contrast to the CK.DiscussionIt is presumed that Bt maize has a marked adverse impact on M. separata development, reproduction and feeding, especially when in combination with the GC inoculation. Additionally, GC inoculation favors the effectiveness of Bt maize against M. separata larvae by reducing their food utilization ability, which negatively affects the development and reproduction of the armyworm. Thus, Bt maize inoculated with AMF (here, GC) can reduce the severe threats arising of armyworms, and hence the AMF inoculation may play an important ecological functions in the field of Bt maize ecosystem, with potentially high control efficiency for the target lepidopteran pests.

Impacts of Bt maize inoculated with rhizobacteria on development and food utilization of Mythimna separata

AbstractThe current trend of increasing proportion of cultivation of transgenic Bt crops is pushing towards dramatic destabilization of the agroecosystem, thus raising severe concerns about the sustainability of transgenic Bt crops as an effective management tool for the control of target insect pests in the future. Rhizobacteria is the key biological regulator to ameliorate soil‐nitrogen utilization efficiency of crop plants, especially transgenic Bt crops. A laboratory study quantified the impacts of transgenic Bt maize (Line IE09S034 with Cry1Ie vs. non‐Bt maize cv. Xianyu335) inoculated with Azospirillum brasilense (AB) and Azotobacter chroococcum (AC) on the growth, development and food utilization of a target lepidopteran insect, Mythimna separata. The results showed that the inoculation of rhizobacteria significantly prolonged the larval lifespan and pupal duration, increased RCR and AD, reduced pupal weight, pupation rate, fecundity, RGR, ECD and ECI, and shortened adult longevity of M. separata fed on transgenic Bt maize, while exact opposite trends were found in these measured indexes of growth, development and food utilization for M. separata fed on non‐Bt maize inoculated with AB and AC compared with the buffer control in both years. Thus, the results clearly depicted that the inoculation of rhizobacteria had opposite influences on the growth, development and food utilization of M. separata fed on transgenic Bt maize. Presumably, rhizobacteria inoculation can be used to stimulate plant–soil‐nitrogen uptake and promote plant growth for transgenic Bt maize and non‐Bt maize, simultaneously increasing Bt toxin production and enhancing resistance efficiency against target lepidopteran pests for transgenic Bt maize.

Bt-induced hormesis in Bt-resistant insects: Theoretical possibility or factual concern?

The biphasic dose-response of a stressor where low amounts of a toxicant may stimulate some biological processes is a recent focus of attention in insecticide ecotoxicology. Nonetheless, the importance and management consequences of this phenomenon of pesticide-induced hormesis remain largely unrecognized. Curiously, the potential induction of hormesis by insecticidal proteins such as Bacillus thuringiensis toxins (i.e., Bt toxins), a major agriculture pest management tool of widespread use, has been wholly neglected. Thus, we aimed to circumvent this shortcoming while assessing the potential occurrence of hormesis induced by the Bt toxin Cry1Fa in its main target pest species – the fall armyworm Spodoptera frugiperda. Concentration-response bioassays were carried out in a Bt-susceptible and a Bt-resistant population providing the purified Cry1Fa toxin in artificial diet and recording the insect demographic parameters. As significant hormetic effect was detected in both populations with a significant increase in the net reproductive rate and the intrinsic rate of population growth, the potential occurrence of Bt-induced hormesis was subsequently tested providing the insects with leaves from transgenic Bt maize expressing the toxic protein. The performance of the Bt-resistant insects was not different in both maize genotypes, indicating that the leaf expression of the Bt protein did not promote hormesis in the resistant insects. Thus, despite the Bt-induced hormesis detected in the purified protein bioassays, the phenomenon was not detected with current levels of Bt expression in maize minimizing the risk of this additional efficacy constraint besides that of field occurrence of Bt resistance.