Planting Bt Research Articles

Enhancing Cotton Production and Sustainability through Multi-Tier Cropping Systems: Growth, Efficiency, and Profitability Analysis

Intercropping presents an opportunity to optimise land use and resource efficiency in cotton cultivation, particularly for small and marginal farmers facing climate-related challenges and rising input costs. This study explores the potential of intercropping short-duration vegetables with cotton to transform this production system into a more economically viable and sustainable one. The study was conducted in the Cotton Department of Tamil Nadu Agricultural University in Coimbatore during the winter irrigated season, from August to January, in both 2020 and 2021. The growth, yield parameters, equivalent yield (3645 and 4234 kg ha−1), and net return (Rs. 123,434 ha−1 and Rs. 154,034 ha−1) were higher in the intercropping system with the paired row planting of Bt cotton with two rows of cluster bean. Upon comparing sole cropping and the paired row method of planting, it was found that adopting the paired row system of planting Bt cotton with two rows of cluster bean was highly profitable in all aspects of crop production. Therefore, the adoption of paired row cropping systems with compatible intercrops that promote synergistic effects on the main crop should be considered for enhancing overall productivity, as well as sustainability.

An innovative insecticidal approach based on plant protease inhibitor and Bt protoxins inhibits trypsin-like activity in zebrafish

The Leucaena leucocephala trypsin inhibitor (LTI) + Bacillus thuringiensis (Bt) protoxins mix has been proposed as a novel larvicide agent in order to control the vector mosquito of dengue virus, Aedes aegypti, in their aquatic breeding sites. However, use of this insecticide formulation has raised concerns about its impacts on aquatic biota. In this context, this work aimed to assess the effects of LTI and Bt protoxins, separately or in combination, in zebrafish, in regard to the evaluation of toxicity at early life stages and to the presence of LTI inhibitory effects on intestinal proteases of this fish. Results showed that LTI and Bt concentrations (250 mg/L, and 0.13 mg/L, respectively), and LTI + Bt mix (250 mg/L + 0.13 mg/L) - 10 times superior to those with insecticidal action – did not cause death nor did it induce morphological changes during embryonic and larval development (3 to 144 h post-fertilization) of zebrafish. Molecular docking analyses highlighted a possible interaction between LTI and zebrafish trypsin, especially through hydrophobic interactions. In concentrations near to those with larvicidal action, LTI (0.1 mg/mL) was able to inhibit in vitro intestinal extracts of trypsin in female and male fish by 83 % and 85 %, respectively, while LTI + Bt mix promoted trypsin inhibition of 69 % in female and 65 % in male ones. These data show that the larvicidal mix can potentially promote deleterious effects to nutrition and survival in non-target aquatic organisms, especially those with trypsin-like dependent protein digestion.

Managing Practical Resistance of Lepidopteran Pests to Bt Cotton in China

China is one of the major cotton producers globally with small farmers. Lepidopteran pests have always been the main factor affecting cotton production. To reduce the occurrence of and damage caused by lepidopteran pests, China has employed a pest control method focused on planting Bt (Cry1Ac) cotton since 1997. Chinese resistance management tactics for the main target pests, the cotton bollworm and pink bollworm, were also implemented. For polyphagous (multiple hosts) and migratory pests such as the cotton bollworm (Helicoverpa armigera), the "natural refuge" strategy, consisting of non-Bt crops such as corn, soybean, vegetables, peanuts, and other host crops, was adopted in the Yellow River Region (YRR) and Northwest Region (NR). For a single host and weak migration ability pest, such as the pink bollworm (Pectinophora gossypiella), the seed mix refuge strategy yields a random mixture within fields of 25% non-Bt cotton by sowing second-generation (F2) seeds. According to field monitoring results for more than 20 years in China, practical resistance (Bt cotton failure) of target pests was avoided, and there were no cases of Bt (Cry1Ac) failure of pest control in cotton production. This indicated that this Chinese resistance management strategy was very successful. The Chinese government has decided to commercialize Bt corn, which will inevitably reduce the role of natural refuges; therefore, this paper also discusses adjustments and future directions of cotton pest resistance management strategies.

Effects of Pb(II) and Zn(II) Contamination on Adsorption, Desorption and Degradation of Cry1Ac Toxin Identical to Bt Transgenic Poplar in Black Soil

Bt transgenic white poplar has been commercially planted in China since 2002, and it showed obvious insect resistance in the field. However, the ecological risk of planting Bt transgenic poplar in a field contaminated with heavy metals has received little attention. The effects of Pb(II) and Zn(II) contamination on the adsorption, desorption and degradation of Bt toxin identical to Bt transgenic poplar in black soil were studied. The results showed that the adsorption of Bt toxin was enhanced and the desorption of Bt toxin was inhibited in black soil by Pb(II) and Zn(II) at concentrations between 0 and 1 mmol/L, and the effect of Pb(II) on Bt toxin was greater than that of Zn(II). In the presence of heavy metal ions, the Cry1Ac toxin molecules are oriented with domain I toward soil particles through the metal ion bridge. The promoting mechanism of Bt toxin adsorption by heavy metal ions in black soil is mainly attributed to cation-controlled electrostatic attraction (CCEA), which is different from patch-controlled electrostatic attraction (PCEA). With the increase in soil concentration from 1 to 4 mg/mL, the adsorption amount of Bt toxin showed a downward trend, and both Pb(II) and Zn(II) had the maximal promotion effect when the soil concentration was 2 mg/mL. The promoting effect of Zn(II) on the adsorption of Bt toxin increased with the increased temperature (5-45 °C), but the promoting effect of Pb(II) was maximal at 25 °C. Both Pb(II) and Zn(II) affected the degradation characteristics of Bt toxin in black soil. For the lead-contaminated black soil, the residual amount of Bt toxin increased in the early stage but decreased in the later stage compared to the control soil. For the zinc-contaminated black soil, the residual amount of Bt toxin decreased compared to the control soil except between the second and tenth days. In this study, it was observed that Bt toxin was degraded rapidly in the early stage, followed by a large amount of released Bt toxin and slow degradation in the middle and late stages.

Evidence of western corn rootworm (Diabrotica virgifera virgifera LeConte) field-evolved resistance to Cry3Bb1 + Cry34/35Ab1 maize in Nebraska.

Western corn rootworm (WCR; Diabrotica virgifera virgifera) field-evolved resistance to transgenic maize expressing the Cry3Bb1 protein derived from Bacillus thuringiensis (Bt) has been confirmed across the United States Corn Belt. Although use of pyramided hybrids expressing Cry3Bb1 + Cry34/35Ab1 has increased in recent years to mitigate existing WCR Bt resistance, susceptibility of Nebraska WCR populations to this rootworm-Bt pyramid has not been assessed. Plant-based bioassays were used to characterize the susceptibility of WCR populations to Cry3Bb1 and Cry3Bb1 + Cry34/35Ab1 maize. Populations were collected from areas of northeastern Nebraska with a history of planting Bt maize that expressed Cry3Bb1 and Cry34/35Ab1. Significant differences in mean corrected survival among populations within Bt hybrids indicated a mosaic of WCR susceptibility to Cry3Bb1 + Cry34/35Ab1 and Cry3Bb1 maize occurred in the landscape. All field populations exhibited some level of resistance to one or both Bt hybrids when compared to susceptible laboratory control populations in bioassays. Most WCR populations exhibited incomplete resistance to Cry3Bb1 + Cry34/35Ab1 maize (92%) and complete resistance to Cry3Bb1 maize (79%). The present study confirms the first cases of field-evolved resistance to Cry3Bb1 + Cry34/35Ab1 maize in Nebraska and documents a landscape-wide WCR Cry3Bb1 resistance pattern in areas characterized by long-term continuous maize production and associated planting of Cry3Bb1 hybrids. Use of a multi-tactic integrated pest management approach is needed in areas of continuous maize production to slow or mitigate resistance evolution to Bt maize. © 2021 Society of Chemical Industry.

Inductive and synergistic interactions between plant allelochemical flavone and Bt toxin Cry1Ac in Helicoverpa armigera

Genetically engineered crops simultaneously produce defensive allelochemicals and Bacillus thuringiensis (Bt) toxin proteins to kill some of the world's most devastating insect pests. How the two types of toxins, when ingested sequentially or simultaneously, interact at both lethal and sublethal doses in these pests remains underexplored. Here, we examined the toxicological interactions between the Bt toxin Cry1Ac and the flavonoid allelochemical flavone in Helicoverpa armigera. Simultaneous exposure of H. armigera neonates to lethal doses (LC25 ) of Cry1Ac and flavone caused a mortality significantly higher than that of either toxin alone and their expected additive mortality. Preexposure for 24 h to a sublethal dose (LC10 ) of Cry1Ac followed by 6-d simultaneous exposure to the same dose of Cry1Ac plus a lethal dose (1.6 mg/g diets, LC50 ) of flavone resulted in a mortality significantly higher than that of the LC50 dose of flavone alone and the expected additive mortality of the LC50 dose of flavone plus the LC10 dose of Cry1Ac. One-day preexposure to the sublethal dose (LC10 ) of flavone followed by 6-d simultaneous exposure to the LC50 dose (6 ng/cm2 ) of Cry1Ac plus the LC10 dose of flavone yielded a mortality significantly higher than that of the LC50 dose of Cry1Ac but similar to the expected additive mortality of the LC50 dose of Cry1Ac plus the LC10 dose of flavone. The results suggest that Cry1Ac induces and synergizes the toxicity of flavone against H. armigera larvae.

Genetic basis of resistance to the Vip3Aa Bt protein in Helicoverpa zea.

Helicoverpa zea is a destructive pest and target of maize and cotton expressing Cry and Vip3Aa proteins in North America. The efficacy of Cry proteins against H. zea in the USA has been largely compromised by resistance. A rapid shift towards planting Bt cotton and maize producing Vip3Aa will accelerate evolution of resistance to Vip3Aa in H. zea. Research on the genetic basis of Vip3Aa resistance in H. zea is urgently needed, and can provide fundamental information for managing resistance in this pest. Here, we characterize the inheritance of Vip3Aa resistance in H. zea. Susceptibility of a Vip3Aa-susceptible strain (SS), a resistant strain (RR), and progeny from different crosses against Vip3Aa39 was determined. RR was established from an F2 screening of a population from Texas sampled in 2019. RR had a resistance ratio of 45194.1-fold against Vip3Aa39 relative to SS. Maternal effects and sex linkage were absent in RR. The dominance D value, calculated based on median lethal concentration (LC50 ) values, was -1.0 and the effective dominance (DML ), calculated based on a given Vip3Aa39 concentration, was ≤0.0 at concentrations of 0.1-31.6 μg cm-2 . The test using a monogenic mode of inheritance showed that resistance to Vip3Aa in H. zea was largely due to a single gene. Results of this study indicate that Vip3Aa resistance in H. zea is monogenic, autosomal, and recessive. This information is valuable for studying the mechanism of Vip3Aa resistance, monitoring of resistance development, and designing appropriate strategies for preventive management of Vip3Aa resistance. © 2020 Society of Chemical Industry.

Comparing Populations of Western Corn Rootworm (Coleoptera: Chrysomelidae) in Regions With and Without a History of Injury to Cry3 Corn.

Transgenic corn expressing insecticidal proteins derived from the bacterium Bacillus thuringiensis (Bt) is an important pest management tool. Western corn rootworm, Diabrotica virgifera virgifera LeConte, is a key pest of corn in the midwestern United States that has developed field-evolved resistance to all available Bt traits. The first Bt trait to be commercialized for management of rootworm was Cry3Bb1 in 2003, and field-evolved resistance appeared in 2009. In this study, we examined fields in counties where greater-than-expected injury to Cry3 (Cry3Bb1 or mCry3A) corn roots (>1 node) had previously been reported (problem counties) and counties where injury had not been reported (non-problem counties). Four to eight fields were sampled per county in 2015, 2016, and 2017 to quantify rootworm abundance, root injury, Cry3Bb1resistance, and rootworm management strategies. Rootworm abundance, root injury, and resistance to Cry3Bb1 did not differ between county types. Management tactics differed between county types, with problem counties growing more corn, using more soil insecticide, and growing more Cry34/35Ab1 corn. Additionally, a comparison of root injury to Bt and non-Bt corn within fields indicated that farmers derived an economic benefit from planting Bt corn to manage corn rootworm. Our results suggest that rootworm populations are similar between problem and non-problem counties in Iowa due to similar levels of selection pressure on Cry3 corn, but problem county fields have applied more management tactics due to previous rootworm issues in the area.

Impact of Bt Brinjal Cultivation in the Market Value Chain in Five Districts of Bangladesh.

Eggplant (brinjal) is a popular vegetable that provides an important source of income for small, resource-poor Bangladeshi farmers. The biggest constraint to brinjal production is the eggplant fruit and shoot borer (EFSB). This study was conducted in 2019 in five districts in Bangladesh and examined the impacts of using genetically engineered, insect-resistant brinjal (Bt brinjal) on its value and marketing. Based on a survey of Bt and non-Bt farmers, results indicate that Bt brinjal provided an average of 19.6% higher yield and 21.7% higher revenue compared to non-Bt varieties. On a per tonne basis, the revenue benefit of using Bt brinjal was 1.7%, reflecting different levels of acceptability among trade buyers and consumers. Some were prepared to pay higher prices for Bt brinjal compared to non-Bt brinjal because the fruit was less damaged, while others paid a price discount because the Bt brinjal was not available in preferred local varieties. Labor use, expressed in 8-h days, for harvesting, grading, and packaging of Bt brinjal was 14% higher for Bt brinjal, reflecting the increased yields of Bt brinjal. 83.1% of Bt brinjal growers were satisfied with the yields obtained, and 80.6% were satisfied with the quality of fruit. This contrasts with non-Bt brinjal growers where 58.7% were satisfied with their yields and 28% indicated that a large portion of their fruit was infested, not a concern for Bt brinjal. Three-quarters of Bt brinjal growers planned to plant Bt brinjal next season because of the apparent benefits achieved of higher yields, revenue and fruit quality. Many also highlighted the benefits of reduced insecticides. Of the non-Bt growers, 39.6% had not heard of Bt brinjal. However, after hearing more about the impact of the technology, 71.4% of them indicated they planned to grow Bt brinjal next season. These findings suggest there are significant benefits of Bt brinjal and highlight the importance of making the technology available in more varieties that are suitable to local conditions and consumer preferences. Additional studies are warranted to corroborate these findings and explore in more detail the factors influencing decisions made by farmers and consumers regarding Bt brinjal.

Critical factors influencing biotech corn adoption of farmers in the Philippines in relation with the 2015 GMO Supreme Court ban

Abstract This study investigated 21 factors influencing biotech corn adoption of 111 corn farmers in Pampanga, Philippines, in relation with the 2015 GMO Supreme Court ban. Results of the statistical tests using ordinal logistic regression and thematic analyses showed that four factors were prioritized by the farmers over the rest of the available influential factors regarding their crop adoption decision making process. ‘Satisfaction in planting biotech corn’ ranked first among the four identified factors relative to the sampled farmers, followed by ‘knowledge about the ban on planting biotech corn and Bt eggplant’, then by ‘knowledge about biotech corn’, and lastly ‘personal experiences in planting biotech corn’. The study also demonstrated how the farmers' sources of information (external and internal) can be factored into their entire decision making process. Data generated from this study can be directly utilized by policy makers and agriculturists to increase the awareness of non-biotech farmers to emerging technologies such as biotech corn and other biotech crops.

Helicoverpa zea (Lepidoptera: Noctuidae) Oviposition and Larval Vertical Distribution in Bt Cotton Under Different Levels of Nitrogen and Irrigation

In some Bt cotton (Gossypium hirsutum L.) varieties, bollworm (Helicoverpa zea Boddie) larval behavior differs from non-Bt varieties. Laboratory assays indicate bollworm larvae can detect Bt proteins, which may cause behavioral differences. Plant stress from factors including fertility and water availability causes changes in plant physiology and Bt expression. Our objective was to determine whether nitrogen and irrigation influenced bollworm behavior in Bt cotton by recording the vertical distribution of eggs and larvae over time. We conducted small plot experiments with Cry1Ac + Cry1F cotton in 2016 and 2017 with three nitrogen rates, along with irrigated and nonirrigated treatments during 2017. Bollworm locations were determined by in-field examination of 10-20 cotton plants per plot over 6-8 wk. The location of each egg and larva was recorded by node, with instar estimation of each larva. Oviposition was higher in in plots receiving nitrogen; first and second instars were also more common in plots receiving nitrogen or irrigation, whereas older instars had similar numbers among treatments. Oviposition was more evenly distributed throughout the canopy earlier in the sampling period than during later weeks, with more eggs in the top third of the canopy in only three of 14-wk. Early instars were also evenly distributed throughout the canopy. Later, instars moved to the middle portions of the canopy, away from bottom nodes, and did not move toward the terminal. Understanding bollworm behavior can inform both crop scouting and resistance management decisions.

Densidades y Daños de Insectos Plaga en Algodonero Convencional y Bt en la Comarca Lagunera, México

The genetically modified cotton expressing Cry toxins from the bacteria Bacillus thuringiensis (transgenic or Bt cotton) was introduced to Mexico in 1996, achieving a high degree of adoption by cotton producers, due to its high effectiveness against lepidopteran pests, which resulted in a reduction of the use of insecticides and a significant increase in crop yields. This study was conducted to determine and compare the populations and levels of damage of the main insect pests in commercial conventional (non-Bt cotton) and transgenic cotton (Bt cotton) fields in the Comarca Lagunera, Mexico during 2016, after 20 years of planting Bt cotton. In four fields of each type of cotton samplings were carried out from June 30 to August 27 to evaluate densities and damages of bollworm, Helicoverpa zea (Boddie); beet armyworm, Spodoptera exigua (Hubner); pink bollworm, Pectinophora gossypiella (Saunders); boll weevil, Anthonomus grandis (Boheman); conchuela, Chlorochroa ligata (Say); and sweetpotato whitefly, Bemisia tabaci (Gennadius). Bollworm and beet armyworm populations were significantly lower in Bt cotton than in conventional cotton, with reductions from 70-100% and 90-98%. Damage to squares and bolls by these two pests were lower in Bt cotton than in conventional cotton, with reductions from 82 to 84%. The pink bollworm and tobacco budworm were not detected in any type of cotton. Damage to cotton bolls by boll weevils and conchuelas were low and did not differ between types of cotton. Sweetpotato whitefly populations did not differ between types of cotton and increased at the end of the crop season. These results show that Bt cotton (Bollgard II) expressing Cry1Ac and Cry2Ab toxins continues to be effective against bollworm and beet armyworm; while the pink bollworm and tobacco budworm are practically eradicated from this region. The Bt cotton showed no effectiveness against sweetpotato whitefly, boll weevil, and conchuela, as was to be expected because they are non-target pests.

Effects of transgenic Bt rice on the active rhizospheric methanogenic archaeal community as revealed by DNA-based stable isotope probing.

This study aimed to investigate the influence of planting Cry1Ab/Cry1Ac gene expressing rice (Bt rice) on rhizospheric active methanogenic archaeal communities. The nontransgenic parental line was used as the control (Ck rice). DNA-based stable isotope probing (DNA-SIP) technology traced the rhizospheric active methanogens at the tillering stage. The results revealed significantly lower CH4 emission flux from Bt soil than that from Ck soil during the whole growth period. The active methanogenic community composition remained stable. The RC-I lineage (77·9-79·8%) and Methanosaetaceae (13·9-15·1%) were the predominant active methanogens in Bt and Ck rice rhizospheres. However, the abundance of functionally active methanogens in the Bt rice rhizosphere was significantly reduced. Lower levels of root exudates (that included carbohydrate and organic acids) from Bt rice were also detected at the tillering stage. This study found that the genetic modification of rice reduced the potential methanogenic substrates came from plant-derived root exudates, which represented an important factor in reducing CH4 generation and active methanogenic archaeal abundance in Bt rhizosphere soil. The effect of genetically modified (GM) insect-resistant crops on soil micro-organisms has become an issue of public concern, especially the indirect effect of plant metabolisms caused by the insertion of foreign genes. Methanogenesis, which is regarded as a critical ecological process in paddy soil, is influenced by plant root exudates; these are mainly derived from photosynthesis. The variations in root exudates across the Bt and Ck rice suggested the indirect influence of foreign gene insertion. DNA-SIP successfully traced the active methanogenic archaeal populations assimilating 13 C-labelled photosynthetic carbon and found a strong influence of planting Bt rice on active methanogens. As a consequence, we proposed that analysis of functionally active micro-organisms is more suitable for monitoring and predicting the environmental influence of GM plants.

Factors Associated With Willingness to Plant Non-Bt Maize Refuge and Suggestions for Increasing Refuge Compliance

Southern U.S. growers who plant Bt maize (Zea mays L.) must plant a separate non-Bt refuge to maintain Bt susceptibility to pests. North Carolina maize growers were surveyed for intention to plant non-Bt maize refuge, understanding of the importance of refuge, and for their perceptions on actions that would encourage refuge plantings. Identical surveys were conducted and compared before and after a short verbal presentation during 2014 on the logic and necessity of planting refuge. An identical survey was given during 2016, but without a verbal presentation and growers were not asked about actions to encourage planting of refuge. Survey responses from 2014 and 2016 were compared and 2016 survey responses were investigated for possible correlations to environmental factors, such as planted crop area and demographic factors by county. Only 38.3 to 44.3% growers indicated they were planning to plant refuge, and 22 to 29.4% were uncertain about this. Additionally, the verbal county meeting presentation did not increase grower intention to plant more refuge. Although this medium increased understanding directly following the presentation, understanding did not change two years later. Total cropland and farm size were most consistently correlated with intention to plant refuge and understanding of the importance of planting refuge. Future efforts to increase compliance and maintain Bt susceptibility in southern U.S. states like North Carolina should focus on reaching smaller-sized growers. Furthermore, the seed industry could also focus on improved breeding, seed availability, and marketing efforts toward companion non-Bt refuge hybrids, as this was popular with growers.

IPM Use With the Deployment of a Non-High Dose Bt Pyramid and Mitigation of Resistance for Western Corn Rootworm (Diabrotica virgifera virgifera).

Recent detection of western corn rootworm resistance to Bt (Bacillus thuringiensis) corn prompted recommendations for the use of integrated pest management (IPM) with planting refuges to prolong the durability of Bt technologies. We conducted a simulation experiment exploring the effectiveness of various IPM tools at extending durability of pyramided Bt traits. Results indicate that some IPM practices have greater merits than others. Crop rotation was the most effective strategy, followed by increasing the non-Bt refuge size from 5 to 20%. Soil-applied insecticide use for Bt corn did not increase the durability compared with planting Bt with refuges alone, and both projected lower durabilities. When IPM participation with randomly selected management tools was increased at the time of Bt commercialization, durability of pyramided traits increased as well. When non-corn rootworm expressing corn was incorporated as an IPM option, the durability further increased. For corn rootworm, a local resistance phenomenon appeared immediately surrounding the resistant field (hotspot) and spread throughout the local neighborhood in six generations in absence of mitigation. Hotspot mitigation with random selection of strategies was ineffective at slowing resistance, unless crop rotation occurred immediately; regional mitigation was superior to random mitigation in the hotspot and reduced observed resistance allele frequencies in the neighborhood. As resistance alleles of mobile pests can escape hotspots, the scope of mitigation should extend beyond resistant sites. In the case of widespread resistance, regional mitigation was less effective at prolonging the life of the pyramid than IPM with Bt deployment at the time of commercialization.

ABCs of Insect Resistance to Bt.

ABCs of Insect Resistance to Bt.

Transgenic Bt rice has adverse impacts on CH4 flux and rhizospheric methanogenic archaeal and methanotrophic bacterial communities

The effect of transgenic insect-resistant crops on soil microorganisms has become an issue of public concern. The goal of this study was to firstly realize the variation of in situ methane (CH4) emission flux and methanogenic and methanotrophic communities due to planting transgenic Bt rice (Bt) cultivar. CH4 emitted from paddy soil was collected by static closed chamber technique. Denaturing gradient gel electrophoresis and real-time PCR methods were employed to analyze methanogenic archaeal and methanotrophic bacterial community structure and abundance. Results showed that planting Bt rice cultivar effectively reduced in situ CH4 emission flux and methanogenic archaeal and methanotrophic bacterial community abundance and diversity. Data analysis showed that in situ CH4 emission flux increased significantly with the increase of methanogenic archaeal abundance (R 2 = 0.839, p < 0.001) and diversity index H′ (R 2 = 0.729, p < 0.05), whereas was not obviously related to methanotrophic bacterial community. Our results suggested that the lower in situ CH4 emission flux from Bt soil may result from lower methanogenic archaeal community abundance and diversity, lower methanogenic activity and higher methanotrophic activity. Moreover, our results inferred that specific functional microorganisms may be a more sensitive indicator than the total archaeal, bacterial or fungal population to assess the effects of transgenic insect-resistant plants on soil microorganisms.

Effect of Bt Broccoli or Plants Treated With Insecticides on Ovipositional Preference and Larval Survival ofPlutella xylostella(Lepidoptera: Plutellidae)

The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), a major pest of cruciferous crops throughout the world, has demonstrated an ability to develop resistance to many different classes of insecticides, including proteins from Bacillus thuringiensis that are expressed in plants (Bt plants). The ovipositional preferences and larval survival of strains (resistant strain, RR; heterozygous strain, RS; susceptible strain, SS) of P. xylostella to Cry1Ac-expressing broccoli or broccoli plants treated with lambda-cyhalothrin or spinosad were studied under greenhouse condition. Numbers of eggs per plant did not differ between Bt broccoli and non-Bt broccoli for Bt-RR, Bt-RS, and Bt-SS adults. Ovipositing adults (spinosad-RR, spinosad-RS, and spinosad-SS) also could not discriminate between spinosad-treated and untreated plants, and oviposition did not increase over the 13 d after spinosad treatment. For broccoli treated with lambda-cyhalothrin at the diagnostic dose of 20 ppm, all three insect strains (lc-RR, lc-RS, and lc-SS) had constant oviposition over time based on linear regressions. At the field dose of 80 ppm, the lc-RR strain had constant oviposition over time. The lc-SS susceptible strain had increasing oviposition over time, but the oviposition pattern on the nonsprayed broccoli also increased over time. Susceptible females layed fewer eggs on plants sprayed with lambda-cyhalothrin than on unsprayed plants. A residue-persistence test showed that spinosad and lambda-cyhalothrin could effectively control SS P. xylostella larvae for 7-9 d after application. These results are discussed in relation to their potential impact on insecticide resistance management strategies.

Bt maize and integrated pest management ‐ a European perspective

The European corn borer (Ostrinia nubilalis), the Mediterranean corn borer (Sesamia nonagrioides) and the western corn rootworm (Diabrotica virgifera virgifera) are the main arthropod pests in European maize production. Practised pest control includes chemical control, biological control and cultural control such as ploughing and crop rotation. A pest control option that is available since 1996 is maize varieties that are genetically engineered (GE) to produce insecticidal compounds. GE maize varieties available today express one or several genes from Bacillus thuringiensis (Bt) that target corn borers or corn rootworms. Incentives to growing Bt maize are simplified farm operations, high pest control efficiency, improved grain quality and ecological benefits. Limitations include the risk of resistance evolution in target pest populations, risk of secondary pest outbreaks and increased administration to comply with licence agreements. Growers willing to plant Bt maize in the European Union (EU) often face the problem that authorisation is denied. Only one Bt maize transformation event (MON810) is currently authorised for commercial cultivation, and some national authorities have banned cultivation. Spain is the only EU member state where Bt maize adoption levels are currently delivering farm income gains near full potential levels. In an integrated pest management (IPM) context, Bt maize can be regarded as a preventive (host plant resistance) or a responsive pest control measure. In any case, Bt maize is a highly specific tool that efficiently controls the main pests and allows combination with other preventive or responsive measures to solve other agricultural problems including those with secondary pests.

Advances in effects of insecticidal crystal proteins released from transgenic Bt crops on soil ecology

With the large scale cultivation of transgenic crops expressing Bacillus thuringiensis (Bt) insecticidal crystal proteins in the world, the problem of environmental safety caused by these Bt crops has received extensive attention. These insecticidal crystal proteins can be released into the soil continuously in the growing period of Bt plants. If their accumulation of the insecticidal crystal proteins exceeds consumption by insect larvae and degradation by the environmental factors, these insecticidal crystal proteins could constitute a hazard to non-target insects and soil microbiota. There are three main ways to release insecticidal crystal proteins into soil for Bt plants: root exudates, pollen falling, and crop reside returning. The Bt insecticidal crystal proteins released into soil can be adsorbed rapidly by active soil particles and the absorption equilibrium attained within 1-3 h. The adsorption protects Bt insecticidal crystal proteins against soil microbial degradation or enzyme degradation, which leads to remarkable prolong of the persistence of insecticidal activity. The change of soil microorganism species is an important index for evaluating the effect of Bt plants on soil ecology. The research showed that these insecticidal crystal proteins released by the Bt plant root exudates or Bt organism had no toxicity to the soil earthworms, nematodes, protozoa, bacteria and fungi; however, it could reduce the mycelium length of the arbuscular mycorrhizal fungi (AMF) and restrain AMF to form invasion unit. The influencing degree of Bt protein on soil enzyme activity varied with the releasing modes or growth period of Bt crops. Bt Cry1Ab protein can be taken up from soil by parts of following crops; however, different results were obtained with different commercial kits. To better understand the soil ecological evaluation about the insecticidal crystal proteins released from transgenic Bt crops, this review provides a comprehensive overview about the release, adsorption and residue of Bt insecticidal crystal proteins in soil, as well as their effects on soil protozoa, soil microorganism, soil enzyme activity and following crops.