Search Results (81)

Bacillus thuringiensis (Bt) is an efficacious biocontrol bacterium known for producing various toxins, such as crystal toxins, which disrupt the midgut epithelium of pest larvae, leading to larval mortality. However, the development of resistance to Bacillus thuringiensis in pests poses a significant threat to the widespread application of Bt corn. Consequently, we employed high-throughput sequencing of the midgut bacterial 16S ribosomal RNA to characterize the midgut bacteria in four Bt-resistant strains. Specifically, Bt-resistant strains (ACB-FR and ACB-AcR) exhibited lower bacterial diversity compared to ACB-AbR and ACB-IeR. Multivariate analyses and statistical evaluations further demonstrated that the microbiota communities in Bt-resistant pests (AbR, AcR, IeR, and FR) were distinct from those in Bt-susceptible strains. Notably, the genus Klebsiella predominated in BtS, whereas Enterococcus was the genus with peak enrichment in AbR, AcR, IeR, and FR. Bioassays subsequently revealed that Enterococcus enhances the Cry1Ab resistance of ACB larvae. Our investigations indicate that treatment with Bt protein alters the midgut microbiota community of O. furnacalis, and these microbiota differences may potentially modulate the Bt-induced lethality mechanism. Full article

Developing simple and efficient multi-gene expression systems is crucial for multi-trait improvement or bioproduction in transgenic plants. In previous research, an IGG6-based bicistronic system from the nonpathogenic fungus Glarea lozoyensis efficiently expressed multiple enzyme proteins in yeast and maize, and the heterologous enzymes successfully performed their catalytic activity to reconstruct the biosynthetic pathway in the host organism. Unlike enzyme proteins, some heterologous functional proteins (such as insecticidal proteins) are dose-dependent and they need to express sufficient levels to perform their biological functions. It remains unclear whether the IGG6-based bicistronic system can achieve high expression of the functional proteins for practical applications in crops. In this study, two Bacillus thuringiensis (Bt) insecticidal genes, vip3Aa and cry1Ab, were linked via IGG6 to form a bicistron, while two glyphosate resistance genes, gr79epsps and gat, served as monocistronic selectable marker genes. Regenerated maize plants were produced through genetic transformation. RNA and immunoblot analyses revealed that the vip3Aa-IGG6-cry1Ab bicistron was transcribed as a single transcript, which was then translated into two separate proteins. Notably, the transcription and translation of cry1Ab were significantly positively correlated with those of vip3Aa. Through ELISA and leaf bioassay, we identified two transgenic maize lines, VICGG-15 and VICGG-20, that exhibited high insecticidal activity against fall armyworm (FAW; Spodoptera frugiperda) and Asian corn borer (ACB; Ostrinia furnacalis), both of which had high expression of Vip3Aa and Cry1Ab proteins. Subsequent evaluations, including silk, ear, and field bioassays, as well as glyphosate tolerance assessments, indicated that the VICGG-15 plants displayed high resistance to FAW and ACB, and could tolerate up to 3600 g acid equivalent (a.e.) glyphosate per hectare without adversely affecting phenotype or yield. Our finding established that the IGG6-based bicistronic system can achieve high expression of functional proteins in maize, and it is a potential candidate for multi-gene assembly and expression in plants. Full article

This study aimed to explore the effects of dietary fiber level and breed on the growth performance, nutrient utilization, intestinal morphology, slaughter performance, and meat quality of finishing pigs using fermented corn straw (FCS) as the fiber source. The experiment employed a 2 × 4 factorial design, selecting 96 Songliao Black (SLB) and Duroc × Landrace × Yorkshire (DLY) crossbred finishing pigs (a total of 192 pigs, with an initial body weight of 60.52 ± 4.59 kg) randomly assigned by breed to four dietary treatment groups (A: 2.92% crude fiber; B: 4.82% crude fiber; C: 6.86% crude fiber; D: 9.01% crude fiber). The results showed that DLY finishing pigs had higher final weight (FW), average daily gain (ADG), and average daily feed intake (ADFI) in both finishing stages 1 and 2 compared to SLB pigs (p < 0.05), while the ratio of feed to weight gain (F/G) showed no significant differences (p > 0.05). Compared to the basal diet, increasing the dietary fiber level to 4.82% improved FW and ADG in both SLB and DLY finishing pigs (p < 0.05) and reduced F/G (p < 0.05). Additionally, SLB finishing pigs had lower ether extract (EE) digestibility but higher crude fiber (CF) and acid detergent fiber (ADF) digestibility than DLY (p < 0.05). Dietary fiber level and breed exhibited an interaction effect on dry matter (DM) and crude protein (CP) digestibility in finishing pigs (p < 0.05). At a dietary fiber level of 4.82%, villus height, crypt depth in the jejunum, and cecal volatile fatty acid (VFA) concentrations were increased in both SLB and DLY finishing pigs (p < 0.05). Dietary fiber level and breed showed an interaction effect on cecal VFA production in finishing pigs (finishing stage 1; p < 0.05). The dietary fiber level of 4.82% increased loin eye area (LA) (p < 0.05) and decreased backfat thickness (BT) (p < 0.05) in both SLB and DLY finishing pigs. Dietary fiber level and breed had an interaction effect on LA in finishing pigs (p < 0.05). SLB pigs had higher muscle redness (a*), shear force, and contents of crude protein (CP), EE, saturated fatty acid (SFA), and polyunsaturated fatty acids (PUFA) than DLY (p < 0.05). Increasing the dietary fiber level improved pH_24h and reduced drip loss and shear force in both SLB and DLY finishing pigs (p < 0.05). Dietary fiber level and breed showed an interaction effect on pig meat color and drip loss (p < 0.05). In conclusion, FCS is a beneficial source of dietary fiber for SLB and DLY pigs. Its proper addition can enhance the growth performance, carcass traits, and meat quality in fattening pigs. Full article

The corn earworm, Helicoverpa zea (Boddie), causes persistent ear damage to corn grown in the southeastern United States region. Increased levels of ear damage have been associated with mycotoxin contamination in addition to yield loss. Corn hybrids expressing proteins from the Bacillus thuringiensis (Bt) may provide corn earworm control. A selection of hybrids expressing various Bt traits were evaluated in field experiments across Georgia over two years to assess their efficacy for corn earworm control, grain yield and quality protection, and grain mycotoxin mitigation. Ear damage was significantly reduced only by Bt hybrids expressing the Vip3Aa20 protein. The remaining Bt hybrids expressing Cry proteins provided only marginal control. Ear damage had a variable effect on grain yield and was not correlated with grain aflatoxin contamination. In contrast, grain fumonisin contamination was positively associated with earworm damage. These results indicate Bt hybrids that effectively reduce corn earworm damage may also assist in reducing fumonisin contamination and possibly yield loss. Full article

The impact of Bacillus thuringiensis (Bt) corn straw returning on the soil ecosystem has attracted significant attention. In this study, taking the homologous conventional corn 5422 as a control, we explored the effects of Bt corn (5422Bt1 and 5422CBCL) straw return after five consecutive cycles on soil nutrients, enzyme activities, and microbial communities. The results showed that in the 5422Bt1 treatment, the levels of available phosphorus (AP), total nitrogen (TN), and sucrose enzyme (SUC) activities significantly increased. In the 5422CBCL treatment, organic matter (OM), alkaline nitrogen (AN), and AP contents, as well as SUC and acid phosphatase (ACP) activities, significantly decreased, while available potassium (AK) and TN contents significantly increased. Through Illumina high-throughput sequencing, it was found that the OTU abundance of soil fungi and bacteria changed after straw returning, and there were no significant differences in alpha diversity (α-diversity) among the three treatments. Redundancy analysis (RDA) indicated that soil nutrients and enzyme activities also affect the soil microbial communities. In summary, Bt corn straw returning affects soil nutrients, enzyme activities, and the structure of microbial communities. Overall, this study revealed the impact of continuous Bt corn straw returning on the soil ecosystem, providing a theoretical basis for subsequent studies. Full article

The hindwing geometry, aspect ratio, and numerical modeling of susceptible, Bt-Corn- and rotation-resistant western corn rootworm (WCR) wings was investigated. All variants had similar hindwing geometries and aspect ratio (AR: 6–7). These AR values correspond to wings suited to lower altitude flights of a shorter distance. These AR values are characteristic of wings that can carry heavier loads and are capable of precision flying. Numerical modeling using the finite element method (FEM) showed that the Bt-Corn-resistant and rotation-resistant WCR hindwings could potentially resist higher wind speeds with minimal deformations compared to conspecific susceptible WCR. Understanding the physiology and dispersal of resistant WCR enables a better understanding of how these variants spread their alleles across large scale agricultural landscapes. This may have important implications for integrated resistant management strategies for WCR. Full article

Blended refuges for corn-expressing toxins from Bacillus thuringiensis (Bt) Berliner controls have been approved in the United States as an alternative resistance management approach to structured refuge. This study examined the impact of blended refuges up to 30% non-Bt seed on the corn earworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), larval numbers, and kernel injury, and its effect on corn grain yield and test weights. The percentage of infested ears, larval numbers, and kernel injury of the 20% blend were not significantly different from the non-Bt and nonblended Bt for the Cry1A.105 + Cry2Ab + Cry1Fa2 treatment, but infested ears, larval numbers, and kernel injury of the nonblended Cry1A.105 + Cry2Ab treatment was lower than the comparable non-Bt hybrids, with the 20% blend being intermediate. The nonblended Cry1A.105 + Cry2Ab + Vip3Aa20 had virtually no larvae in ears and no kernel injury. Ear infestation, larval numbers, and kernel injury of the non-Bt blends with Vip3Aa20 were proportional to the percentage of non-Bt seed in the blend, and all infested ears were from the non-Bt refuge plants. Grain yield and test weight were not significantly different among nonblended or blended treatments of any Bt product tested. Results indicate losses of grain yield and test weight by corn earworm in seed blends up to 30% non-Bt seed are unlikely with infestation levels observed in this study. Full article

Asian corn borer (ACB), Ostrinia furnacalis, is an important agricultural pest affecting maize production in southwestern China, but knowledge of the toxic effect of Bt maize on the pest has been insufficient until now. In this study, we determined the susceptibility of ACB to Cry1Ab, Vip3Aa, and their complex proteins and evaluated the efficacy of Chinese domestic Bt-(Cry1Ab+Vip3Aa) maize (“DBN3601T” event) against the pest in Yunnan Province of southwestern China. The susceptible bioassay indicated that the LC₅₀ values of the Cry1Ab and Cry1Ab+Vip3Aa proteins expressed by the Bt maize varieties against ACB larvae were 51.42 and 46.85 ng/g, respectively; however, the ACB larva was insensitive to the Vip3Aa protein. The Cry1Ab+Vip3Aa protein contents in V6–V8 leaves, VT tassels, R1 silks, R2 kernels, R3 stalks and R3 cobs of the Bt-(Cry1Ab+Vip3Aa) maize were 114.20, 30.69, 3.77, 8.92, 11.09 and 10.99 μg/g, respectively. The larval feeding test indicated that the Bt-(Cry1Ab+Vip3Aa) maize was more toxic to the early instar larvae, and the survival time of larvae fed on the leaves was the shortest, while it survived the longest on stalks. The identification of maize resistance levels in the field showed that both larval density and plant damage score of Bt-(Cry1Ab+Vip3Aa) maize were significantly lower than those in conventional maize. It is concluded that the Bt-(Cry1Ab+Vip3Aa) maize can be used for control of the ACB in southwestern China. Full article

Insecticides based on baculoviruses have become an alternative for pest control in different agricultural crops. The aim of this study was to assess the biological activity of the bioinsecticide Cartugen^™ (SfMNPV: Baculoviridae: Alphabaculovirus) on larvae of Spodoptera frugiperda J. E. Smith (Lepidoptera: Noctuidae) resistant to Bt corn expressing the insecticidal proteins Cry1A.105+Cry2Ab2+Cry1F. In addition, we assessed the efficiency of SfMNPV on S. frugiperda control in the field from natural infestation of the pest during two agricultural seasons. The results showed that no larvae survived 10 days after being inoculated with Bt and non-Bt corn leaves contaminated with 1.50 × 10¹⁰ occlusion bodies (OBs)/L (equivalent to the recommended dose of the product). However, when using doses equivalent to 50% (7.50 × 10⁹ OBs/L) and 25% (3.75 × 10⁹ OBs/L), the larval mortality ranged from 21.12% to 46.55%, respectively. Although larvae resistant to the Cry1A.105+Cry2Ab2+Cry1F proteins, when exposed to 50% of the SfMNPV dose (7.50 × 10⁹ OBs/L), showed reductions in larval weight (52 to 67% reduction), pupal weight (32 to 59% reduction), and total fecundity (67 to 86% reduction) compared to the control. Furthermore, doses above 25% (3.75 × 10⁹ OBs/L⁻¹) caused a population decrease in the growth of the species in both Bt and non-Bt corn according to the fertility life table. In the field, at 7 and 10 DAA (days after application), corn plants sprayed with SfMNPV (1.50 × 10¹⁰ OBs/L) showed reductions in leaf damage according to the Davis scale. However, from 14 to 21 DAA, there was an increase in leaf damage in corn leaves from both treatments, with or without the application of SfMNPV. This shows that SfMNPV may be an important strategy in the integrated management and resistance management of S. frugiperda. Full article

The fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), is one of the most important insect pests affecting corn crops worldwide. Although planting transgenic corn expressing Bacillus thuringiensis (Bt) toxins has been approved as being effective against FAW, its populations’ resistance to Bt crops has emerged in different locations around the world. Therefore, it is important to understand the interaction between different Bt proteins, thereby delaying the development of resistance. In this study, we performed diet-overlay bioassays to evaluate the toxicity of Cry1Ab, Cry1Ac, Cry1B, Cry1Ca, Cry1F, Cry2Aa, Cry2Ab, Vip3Aa11, Vip3Aa19, and Vip3Aa20, as well as the interaction between Cry1Ab-, Cry1F-, Cry2Ab-, and Vip3Aa-class proteins against FAW. According to our results, the LC₅₀ values of Bt proteins varied from 12.62 ng/cm² to >9000 ng/cm² (protein/diet), among which the Vip3Aa class had the best insecticidal effect. The combination of Cry1Ab and Vip3Aa11 exhibited additive effects at a 5:1 ratio. Cry1F and Vip3Aa11 combinations exhibited additive effects at 1:1, 1:2, and 5:1 ratios. The combination of Cry1F and Vip3Aa19 showed an antagonistic effect when the ratio was 1:1 and an additive effect when the ratio was 1:2, 2:1, 1:5, and 5:1. Additionally, the combinations of Cry1F and Vip3Aa20 showed antagonistic effects at 1:2 and 5:1 ratios and additive effects at 1:1 and 2:1 ratios. In addition to the above combinations, which had additive or antagonistic effects, other combinations exhibited synergistic effects, with variations in synergistic factors (SFs). These results can be applied to the establishment of new pyramided transgenic crops with suitable candidates, providing a basis for FAW control and resistance management strategies. Full article

The European corn borer (Ostrinia nubilalis, Hübner) has been managed successfully in North America since 1996 with transgenic Bt-corn. However, field-evolved resistance to all four available insecticidal Bt proteins has been detected in four provinces of Canada since 2018. Evidence suggests resistance may be spreading and evolving independently in scattered hotspots. Evolution and spread of resistance are functions of gene flow, and therefore dispersal, so design of effective resistance management and mitigation plans must take insect movement into account. Recent advances in characterizing European corn borer movement ecology have revealed a number of surprises, chief among them that a large percentage of adults disperse from the natal field via true migratory behavior, most before mating. This undermines a number of common key assumptions about adult behavior, patterns of movement, and gene flow, and stresses the need to reassess how ecological data are interpreted and how movement in models should be parameterized. While many questions remain concerning adult European corn borer movement ecology, the information currently available is coherent enough to construct a generalized framework useful for estimating the spatial scale required to implement possible Bt-resistance prevention, remediation, and mitigation strategies, and to assess their realistic chances of success. Full article

The fall armyworm (JE Smith) (Spodoptera frugiperda) is a polyphagous pest targeted by selected Cry and Vip3A insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) that are produced in transgenic Bt corn and cotton. Available evidence suggests that sublethal larval exposure to Cry1Ac increases flight activity in adult Spodoptera spp. However, it is not known whether this effect is also observed in survivors from generally lethal exposure to Cry1Ac. Moreover, while multiple cases of field-evolved resistance to Bt proteins have been described in the native range of S. frugiperda, the effect of resistance on flight behavior has not been examined. Long-distance migratory flight capacity of S. frugiperda is of concern given its ongoing global spread and the possibility that migrants may be carrying resistance alleles against pesticides and Bt crops. In this study, we used rotational flight mills to test the effects of generally lethal exposure to Cry1Ac in susceptible and sublethal exposure in Cry1F-resistant S. frugiperda strains. The results detected altered pupal weight after larval feeding on diet containing Cry proteins, which only translated in significantly increased tendency for longer flights in female moths from the susceptible strain. This information has relevant implications when considering current models and assumptions for resistance management of Bt crops. Full article

Genetically modified MON 89034 corn (Zea mays L.) expressing Bacillus thuringiensis (Bt) insecticidal proteins, viz. Cry1A.105 and Cry2Ab2, is a biotechnological option being considered for the management of the major corn pest in Indonesia, the Asian corn borer (Ostrinia furnacalis (Guenée) (Lepidoptera: Crambidae)). As a part of a proactive resistance-management program for MON 89034 corn in Indonesia, we assessed the baseline susceptibility of field-collected populations of O. furnacalis to Cry1A.105 and Cry2Ab2 proteins. Dose–response bioassays using the diet-dipping method indicated that the lethal concentration (LC₅₀) values of Cry1A.105 and Cry2Ab2 in 24 different field populations of O. furnacalis ranged from 0.006 to 0.401 µg/mL and from 0.044 to 4.490 µg/mL, respectively, while the LC₉₅ values ranged from 0.069 to 15.233 µg/mL for Cry1A.105 and from 3.320 to 277.584 µg/mL for Cry2Ab2. The relative resistance ratios comparing the most tolerant field populations and an unselected laboratory population were 6.0 for Cry1A.105 and 2.0 for Cry2Ab2 based on their LC₅₀ values. Some field populations were more susceptible to both proteins than the unselected laboratory population. The LC₉₉ and its 95% fiducial limits across the field populations were calculated and proposed as candidate diagnostic concentrations. These data provide a basis for resistance monitoring in Bt Corn and further support building resistance-management strategies in Indonesia. Full article

Fall armyworm (FAW), Spodoptera frugiperda, invaded the south of China in December 2018 and has since posed a huge threat to crop production in China. However, transgenic Bacillus thuringiensis (Bt) corn can efficiently control the damage caused by FAWs. In fact, the Chinese government has issued biosafety certificates for several Bt corn hybrids expressing any one of four Bt proteins, Vip3A, Cry1F, Cry1Ab, and Cry2Ab, or combinations thereof, to control FAWs. These Bt corn events are soon to be commercialized in China. Therefore, it is necessary to monitor and evaluate whether the FAW has developed resistance to any of the Bt corn hybrids planted in fields in China. To address this issue, we collected 11 geographical populations of FAWs and determined the sensitivity of each to the aforementioned four purified Bt proteins as assessed by diet surface overlay bioassays. The ranges for the 50% lethal concentration (LC₅₀) of the four Bt proteins to all FAW populations were as follows: 11.42–88.33 ng/cm² (for Vip3A), 111.21–517.33 (Cry1F), 135.76–1108.47 (Cry1Ab), and 994.42–5492.50 (Cry2Ab). The corresponding ranges for the 50% growth inhibition concentrations (GIC₅₀) were 1.43–14.86, 2.35–138.97, 1.58–464.86, and 25.01–1266.07 ng/cm². The lethal effects and growth inhibition effects of the four Bt proteins on FAW were in the same order of Vip3A > Cry1F > Cry1Ab > Cry2Ab. A comparison with published LC₅₀ values of Bt proteins towards sensitive FAW populations revealed that all 11 FAW populations in this study were sensitive to Vip3A, Cry1F, and Cry1Ab. This study provides foundational data for monitoring and controlling the resistance of Bt corn to FAW in China. Full article

The wide occurrence of resistance to Cry1A and Cry2A insecticidal toxins from Bacillus thuringiensis (Bt) in the corn earworm/bollworm Helicoverpa zea (Boddie) leaves the Vip3A toxin produced during the vegetative stage of Bt as the only fully active toxin expressed in transgenic crops to control H. zea in the U.S.A. During 2021, the first unexpected survival of H. zea and injury (UXI) on a maize hybrid expressing Cry1A.105, Cry2Ab2, and Vip3Aa in Louisiana, U.S.A. were observed in two sentinel plots used for resistance monitoring. A follow-up intensive investigation was conducted with two H. zea populations established from larvae collected from the two UXI plots. The main goal of this study was to reveal if the unexpected damage was due to resistance development in the insect to the Bt toxins expressed in the maize hybrid. Diet-overlay bioassays showed that the two populations were highly resistant to Cry1A.105, moderately resistant to Cry2Ab2, but still highly susceptible to Vip3Aa when compared to a reference susceptible strain. In 10 d assays with detached ears, the larvae of the two UXI populations exhibited survival on ears expressing only Cry toxins but presented near 100% mortality on maize hybrids containing both cry and vip3A transgenes. Multiple field trials over three years demonstrated that natural H. zea populations in Louisiana were highly resistant to maize expressing only Cry toxins but remained susceptible to all tested hybrids containing cry and vip3A genes. Altogether, the results of this study suggest that the observed UXIs in Louisiana were associated with a resistance to Cry toxins but were not due to a resistance to Vip3A. The possible causes of the UXIs are discussed. The results generated and procedures adopted in this study help in determining thresholds for defining UXIs, assessing resistance risks, and documenting field resistance. Full article