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The majority of field corn, Zea mays L. in the southeastern United States has been genetically engineered to express insecticidal toxins produced by the soil bacterium, Bacillus thuringiensis (Bt). Field corn is the most important mid-season host for corn earworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), which has developed resistance to all Cry toxins in Bt corn. From 2020 to 2023, corn earworm pupae were collected from early- and late-planted pyramided hybrids expressing Bt toxins and non-Bt near-isolines in North and South Carolina (16 trials). A total of 5,856 pupae were collected across all trials, with 55 and 88% more pupae collected in later-planted trials relative to early plantings in North and South Carolina, respectively. Only 20 pupae were collected from hybrids expressing Cry1F + Cry1Ab + Vip3A20 across all trials. Averaged across trials, Cry1A.105 + Cry2Ab2 hybrids reduced pupal weight by 6 and 9% in North and South Carolina, respectively, relative to the non-Bt near-isoline. Cry1F + Cry1Ab hybrids reduced pupal weight on average by 3 and 8% in North and South Carolina, respectively, relative to the non-Bt near-isoline. The impact of the Bt toxins on pupal weight varied among trials. When combined with data from 2014 to 2019 from previous studies, a significant decline in the percent reduction in pupal weight over time was found in both states and hybrid families. This study demonstrates a continued decline in the sublethal impacts of Bt toxins on corn earworm, emphasizing the importance of insect resistance management practices. [ABSTRACT FROM AUTHOR]

Bioassays were conducted under controlled conditions to determine the response of Spodoptera frugiperda (J. E. Smith) larvae fed with corn materials expressing Bacillus thuringiensis (Bt) insecticidal endotoxins: (1) VT Double Pro® (VT2P) expressing Cry1A.105-Cry2Ab2 proteins and (2) VT Triple Pro® (VT3P) expressing Cry1A.105-Cry2Ab2-Cry3Bb1 proteins. The parameters assessed were: (i) mortality rate, and (ii) growth inhibition (GI) with respect to the control. To conduct this study, larvae were collected from commercial non-Bt corn fields, in four agricultural sub-regions in Colombia, between 2018 and 2020. Fifty-two populations were assessed from the field and neonate larvae from each of the populations were used for the bioassays. The study found that mortality rates in the regions for larvae fed with VT2P corn ranged from 95.1 to 100.0%, with a growth inhibition (%GI) higher than 76.0%. Similarly, mortality rate for larvae fed with VT3P corn were between 91.4 and 100.0%, with a %GI above 74.0%. The population collected in Agua Blanca (Espinal, Tolima; Colombia) in 2020, showed the lowest mortality rate of 53.2% and a %GI of 73.5%, with respect to the control. The population that exhibited the lowest %GI was collected in 2018 in Agua Blanca (Espinal, Tolima, Colombia) with a 30.2%, growth inhibition, with respect to the control. In recent years, the use of plant tissue to monitor susceptibility to fall armyworm has proven to be useful in the resistance management program for corn in Colombia determining that the FAW populations are still susceptible to Bt proteins contained in VT2P and VT3P. [ABSTRACT FROM AUTHOR]

The fall armyworm, Spodoptera frugiperda (J.E. Smith), is a major target pest of Bt crops (e.g., corn, cotton, and soybean) in North and South America. This pest has recently invaded Africa and Asia including China and the invasion has placed a great threat to the food security in many countries of these two continents. Due to the extensive use of Bt crops, practical resistance of S. frugiperda to Cry1F corn (TC 1507) with field control problems has widely occurred in Puerto Rico, Brazil, Argentina, and the mainland United States. Analyzing data generated from decade‐long studies showed that several factors might have contributed to the wide development of the resistance. These factors include (1) limited modes of action of Bt proteins used in Bt crops; (2) cross‐resistance among Cry1 proteins; (3) use of nonhigh dose Bt crop traits; (4) that the resistance is complete on Bt corn plants; (5) abundant in initial Cry1F resistance alleles; and (6) lack of fitness costs/recessive fitness costs of the resistance. The long‐term use of Bt crop technology in the Americas suggests that Bt corn can be an effective tool for controlling S. frugiperda in China. IRM programs for Bt corn in China should be as simple as possible to be easily adopted by small‐scale growers. The following aspects may be considered in its Bt corn IRM programs: (1) use of only "high dose" traits for both S. frugiperda and stalk borers; (2) developing and implementing a combined resistance monitoring program; (3) use "gene pyramiding" as a primary IRM strategy; and (4) if possible, Bt corn may not be planted in the areas where S. frugiperda overwinters. Lessons and experience gained from the global long‐term use of Bt crops should have values in improving IRM programs in the Americas, as well as for a sustainable use of Bt corn technology in China. [ABSTRACT FROM AUTHOR]

BACKGROUND: Using natural populations of Helicoverpa zea from Arizona, we tested the hypotheses that gene flow between Bacillus thuringiensis (Bt) plants and non-Bt plants in a seed mixture of 10% non-Bt corn and 90% Bt corn producing Cry1A.105 and Cry2Ab reduces larval performance on ears from non-Bt plants, or increases performance on ears from Bt plants. RESULTS: Gene flow was not detected in blocks of non-Bt or Bt corn but was extensive in seed mixtures. Analyses of larval weight and abundance over a period of 3 to 4 weeks did not indicate consistent effects of gene flow on development rate and survival. However for non-Bt plants, the ear area damaged and percentage of ears with exit holes were significantly lower in the seed mixtures than blocks. By contrast, the percentage of ears with exit holes and ear damage did not differ significantly between the seed mixtures and blocks for Bt plants. Nearly 100% of the ears were damaged and the damaged area was substantial, showing that H. zea is a major ear-feeding pest in Arizona. Relative to non-Bt corn, the pyramided Bt corn did not significantly reduce the percentage of damaged ears and only reduced the ear area damaged by 21 to 39%, indicating that H. zea may have evolved resistance to Cry1A.105, Cry2Ab, or both. CONCLUSIONS: Our results indicate that gene flow between Bt and non-Bt plants in seed mixtures reduced effective refuge size, and that block refuges may be needed to manage the evolution of H. zea resistance to Bt corn in Arizona. [ABSTRACT FROM AUTHOR]

The northern corn rootworm (NCR), Diabrotica barberi Smith & Lawrence, is an economic pest of maize in the U.S. Corn Belt. The objective of this study was to determine the baseline susceptibility of a laboratory NCR strain to Bt proteins eCry3.1Ab, mCry3A, Cry3Bb1, and Cry34/35Ab1 using seedling, single plant, and diet-toxicity assays. Plant assays were performed in greenhouse using corn hybrids expressing one of the Bt proteins and each respective near-isoline. Diet-toxicity assays, consisting of Bt proteins overlaid onto artificial diet were also conducted. In both plant assays, significantly more larvae survived Cry34/35Ab1-expressing corn compared with all other Bt-expressing corn, and larvae that survived eCry3.1Ab-expressing corn had significantly smaller head capsule widths compared with larvae that survived Cry34/35Ab1-expressing corn. In seedling assays, larvae surviving eCry3.1Ab-expressing corn also had significantly smaller head capsule widths compared with larvae that survived mCry3A-expressing corn. Additionally, larvae that survived mCry3A-expressing corn weighed significantly more than larvae surviving eCry3.1Ab- and Cry34/35Ab1-expressing corn. In single plant assays, no significant differences in larval dry weight was observed between any of the Bt-expressing corn. In diet assays, LC50s ranged from 0.14 (eCry3.1Ab) to 10.6 µg/cm2 (Cry34/35Ab1), EC50s ranged from 0.12 (Cry34/35Ab1) to 1.57 µg/cm2 (mCry3A), IC50s ranged from 0.08 (eCry3.1Ab) to 2.41 µg/cm2 (Cry34/35Ab1), and MIC50s ranged from 2.52 (eCry3.1Ab) to 14.2 µg/cm2 (mCry3A). These results establish the toxicity of four Bt proteins to a laboratory diapausing NCR strain established prior to the introduction of Bt traits and are important for monitoring resistance evolution in NCR field populations. [ABSTRACT FROM AUTHOR]

Transgenic corn has been modified to express a gene derived from the bacterium Bacillus thuringiensis (Bt) to combat lepidopteran pests. Bt proteins and the altered chemical composition of Bt crops may affect the role the soil fauna plays in the decomposition of Bt plants. A 2-y field study and a laboratory feeding experiment using corn leaves were conducted in northeastern China to investigate the effect of Bt corn—consisting of Bt corn (Bt 38) and a near-isoline of non- Bt corn (Z 58)—on the abundance, species richness, morphological traits, community structure, and fitness of soil Collembola. A total of 4,419 collembolans, comprised of 22 species, were recovered in this study. We found that Bt corn cultivation did not significantly affect abundance, species richness, or community structure of Collembola. Some rare isotomids of the genera Desoria Nicolet, 1841 (Collembola: Isotomidae) and Folsomia Willem, 1902 (Collembola: Isotomidae) were only recorded in non- Bt corn varieties and not in Bt corn varieties. Morphological traits, including the number of ocelli, body size, body pigmentation level, furca development, antennal length, and antenna:head ratio of Collembola were not changed by transgenic corn cultivation in the 2-y field study. Our results clearly found that the Bt corn did not affect community characteristics or traits of Collembola during this 2-y field study. [ABSTRACT FROM AUTHOR]

Gene flow between Bt and non-Bt plants can have implications for resistance management. In 2013 and 2014, field trials in Maryland and Louisiana measured gene flow in three refuge systems: (1) structured refuge stand of purple-seeded corn flanked on both sides by stands of yellow corn; (2) seed blend of yellow corn containing purple corn as refuges; and (3) seed blend of purple-seeded corn containing yellow corn as refuges. The presence of cross-pollinated purple kernels was used as a marker to quantify gene flow. In the structured refuge, cross-pollination between Bt and structured refuge plants averaged 5.4% on adjacent rows and decreased significantly moving away from the interface. For refuge system 2, outcrossing of pollen from the refuge plants was < 1% in ears of neighboring Bt plants both within and on adjacent rows. Cross-pollination was generally higher for plants nearest to the refuge plant. In refuge system 3, outcrossing of pollen from neighboring Bt plants caused 18.6% refuge kernels expressing the purple trait. Laboratory bioassay showed that consumption of a meridic diet containing 6% refuge kernel tissue collected from a 95:5% seed blend field caused significant larval growth inhibition of the corn earworm, Helicoverpa zea (Boddie). Overall findings suggest that effects of gene outcrossing from refuge plants to Bt plants in the seed blend systems are likely not a great issue, but significant gene flow from neighboring Bt plants to refuge plants could reduce the number of homozygous susceptible larvae produced and favor survival of heterozygotes. [ABSTRACT FROM AUTHOR]

In late 2018, the highly destructive and polyphagous fall armyworm was first detected in China. It is now a major economic threat to corn production. In this article, the main control strategies that are available are reviewed and prospects to manage this pest with Bacillus thuringiensis (Bt) corn in China are discussed. [ABSTRACT FROM AUTHOR]

Western bean cutworm, Striacosta albicosta (Smith; Lepidoptera: Noctuidae) has become a key pest of maize, Zea mays (L.), in Ontario, Canada which is challenging to control due to its lack of susceptibility to most Bt-maize events. Injury by S. albicosta may exacerbate Fusarium graminearum (Schwabe; Hypocreales: Nectriaceae) infection through provision of entry points on the ear. The objectives of this study were to: investigate the relationship between injury by S. albicosta and deoxynivalenol (DON) accumulation; evaluate non-Bt and Bt-maize hybrids, with and without insecticide and fungicide application; and determine optimal insecticide-fungicide application timing for reducing S. albicosta injury and DON accumulation. The incidence of injury by S. albicosta and ear rot severity were found to increase DON concentrations under favorable environmental conditions for F. graminearum infection. Incidence of S. albicosta injury was more important than severity of injury for DON accumulation which may be due to larval consumption of infected kernels. The Vip3A × Cry1Ab event provided superior protection from the incidence and severity of S. albicosta injury compared to non-Bt or Cry1F hybrids. Insecticide application to a Vip3A × Cry1Ab hybrid did not reduce injury further; however, lower severity of injury was observed for non-Bt and Cry1F hybrids when pyrethroids or diamides were applied at early VT or R1 stages. DON concentrations were reduced with application of prothioconazole fungicide tank-mixed with insecticide at late VT (before silk browning) or when insecticide was applied at early VT followed by prothioconazole at R1. The application of an insecticide/fungicide tank-mix is the most efficient approach for maize hybrids lacking high-dose insecticidal proteins against S. albicosta and F. graminearum tolerance. Results demonstrate that reducing the risk of DON accumulation requires a strategic approach to manage complex associations among S. albicosta, F. graminearum and the environment. [ABSTRACT FROM AUTHOR]

Growers that plant Bacillus thuringiensis (Bt) Berliner corn {Zea mays L.) hybrids are required to plant non-Bt corn for resistance management. Refuge in a bag (RIB) is an emerging approach for resistance management where, for some hybrids having multiple Bt traits for a target species, the refuge is planted as a blend of Bt and non-Bt corn. Studies were conducted to evaluate how southwestern corn borer (Diatraea grandiosella Dyar), when infested at different densities and growth stages, affected the yield of infested, non-Bt plants and neighboring Bt plants. Infesting non-Bt corn plants with southwestern corn borer larvae caused significant injury. Both the number of larvae infested on plants and the timing of these infestations affected the number of kernels per ear, total kernel weight, and the weight of individual kernels. Infestation timing was more important than the number of larvae inoculated onto plants, with pretassel infestations causing more yield loss. There was little compensation by Bt plants that were adjacent to infested plants. Thus, the risk of yield loss from stalk tunneling larvae in a refuge in a bag scenario should be directly proportional to the percentage of non-Bt plants and the level of yield loss observed in these non-Bt plants. Because current refuge in a bag systems have five or 10% non-Bt corn plants within the seed unit, the likelihood of substantial yield losses from infestations of corn boring larvae is remote given our results, especially for infes-tations that occur after silking has begun. [ABSTRACT FROM AUTHOR]

Bacillus thuringiensis (Bt) corn, Zea mays L., is highly efficient against the corn borer Sesamia nonagrioides (Lefèbvre) (Lepidoptera: Noctuidae) when the larvae feed only on the transgenic plants. However, when they feed on Bt leaves during only part of their development, thus ingesting sublethal amounts of Bt toxins, some larvae survive. A previous study reported a prolonged development and precocious diapause induction in larvae fed on a diet with sublethal amounts of Cry1Ab protein. To determine whether these effects were accompanied by a modification of the hormonal balance, S. nonagrioides larvae were fed on sublethal amounts of Bt protein provided in Bt leaves or in the diet. The larvae that survived had higher levels of juvenile hormone (JH), whereas their level of ecdysteroids did not increase sufficiently to allow pupation, leading to a longer larval development and more larval molts. This response may be considered a defense mechanism that allows some larvae to survive toxin ingestion; it is similar to the response to insecticidal toxins or viruses observed in other larvae. Changes in the hormone levels in diapausing larvae were undetectable, probably because these changes were masked by the higher level of JH in the hemolymph of diapausing larvae and because of lack of ecdysteroid titer increase, a phenomenon that is usually observed a few days before pupation in nondiapausing larvae. These results should be taken into account in the establishment of non-Bt refuges to prevent development of Bt-resistance in S. nonagrioides populations. [ABSTRACT FROM AUTHOR]

The use of mixtures of transgenic insecticidal seed and nontransgenic seed to provide an in-field refuge for susceptible insects in insect-resistance-management (IRM) plans has been considered for at least two decades. However, the U.S. Environmental Protection Agency has only recently authorized the practice. This commentary explores issues that regulators, industry, and other stakeholders should consider as the use of biotechnology increases and seed mixtures are implemented as a major tactic for IRM. We discuss how block refuges and seed mixtures in transgenic insecticidal corn, Zea mays L., production will influence integrated pest management (IPM) and the evolution of pest resistance. We conclude that seed mixtures will make pest monitoring more difficult and that seed mixtures may make IBM riskier because of larval behavior and greater adoption of insecticidal corn. Conversely, block refuges present a different suite of risks because of adult pest behavior and the lower compliance with IBM rules expected from farmers. It is likely that secondary pests not targeted by the insecticidal corn as well as natural enemies will respond differently to block refuges and seed mixtures. [ABSTRACT FROM AUTHOR]

The article examines the impact of Bt maize leaf detritus on aquatic invertebrates in headwater streams. It was found that the insect Lepidostoma liba grows slower when it is fed with Bt maize compared to non-Bt maize. There is no significant difference found in total abundance or biomass of benthic macroinvertebrate abundance between Bt and non-Bt streams. Shannon diversity in both streams is low while highly tolerant taxa is dominant in Bt and non-Bt streams.

The article examines the sensitivity of lepidopteran corn pests in India to Cry1Ab insecticidal protein of Bacillus thuringiensis. The sensitivity of corn pests including Chilo partellus, Sesamia inferens, and Helicoverpa armigera is considered essential for resistance management practice. It was found that the multiple populations of these corn pests are susceptible to Cry1Ab. Dose-response concentrations for lethality and growth inhibition are also determined to mark baseline sensitivity.

Polymerase chain reaction–denaturing gradient gel electrophoresis (PCR–DGGE) and sequences of the 16S and 18S rRNA genes were used to access the effects of actively growing Bacillus thuringiensis ( Bt) corn Pioneer 34B24 and Nongda 1246*1482, and plant straw (leaves plus stalks) of Bt hybrid Pioneer 34B24 and Nongda 61 on soil bacterial and fungal communities. Two-way indicator species analysis (TWINSPAN®), and detrended correspondence analysis (DCA) of the DGGE data indicated that neither the actively growing Bt corn nor its straw had any constant apparent effect on the soil bacteria and fungi community structure. The age of the growing plants, or the timing of plant straw decomposition may have more effect on the microbial community than other factors, i.e., the presence of Cry protein, plant hybrid and variety. [ABSTRACT FROM AUTHOR]

Genetically engineered corn ( Zea mays L.) containing a gene from the soil bacterium Bt ( Bacillus thuringiensis) constitutes a large proportion of all corn planted in the United States. In a number of studies, Bt plant residues have been reported to have higher lignin content and to decompose slower than those of non-Bt plants, possibly due to the presence of the Cry endotoxin. We hypothesize that after multiple years of continuous cultivation of Bt corn, the combined results of alleged differences in Bt corn residues and of Cry endotoxin presence will be reflected in soil characteristics, specifically in an increase in soil total carbon (C) and nitrogen (N) levels. We collected soil samples at 0–7.5 cm depth in 2006 from continuous Bt and non-Bt corn treatments in an randomized complete block design experiment with four replications. The experiment was established in 1999 at the Kellogg Biological Station long-term ecological research (LTER) site in southwest Michigan. We found that, after 7 years of Bt cropping, neither total soil C and N nor soil C mineralized during a 35-day incubation were significantly different between Bt and non-Bt corn treatments ( P > 0.05). Total soil C was equal to 7.3 g kg−1 and 7.4 g kg−1, in Bt and non-Bt corn, respectively, with a standard error of the means (SEM) = 0.2, and total N was 0.67 g kg−1 (SEM 0.02) in both treatments. Post-hoc power analysis indicated that, given the number of samples collected in this study and the observed level of variability, the minimal differences between the Bt and non-Bt treatments that could be detected as statistically significant at α = 0.05 with a power of 0.80 were equal to 1.0 g kg−1, 0.14 g kg−1 and 0.125 g kg−1 for total C, total N, and soil C mineralized during a 35-day incubation, respectively. The results indicate that continuous Bt corn production during a 7-year period did not lead to sizeable changes in total soil C and N. [ABSTRACT FROM AUTHOR]

Field studies were conducted over a 3-yr period to investigate the potential effects of cultivating transgenic maize hybrids containing a Cry1F insect-resistant protein on nontar get arthro- pod abundance. The narrow spectrum of activity of CryiF against a subset of lepidopteran pest species would not suggest broad-spectrum effects on nontarget arthropods. However, because of the insecticidal nature of Bt proteins, an alternate hypothesis is that some nontargets may be affected by exposure to the protein. To examine this hypothesis at the field level, monitoring for nontarget organism abundance was initiated at four locations across the U.S. Corn Belt from 2004 through 2006. At each location, paired fields (≈0.8 ha each) of commercial Cry1F maize hybrids and isogenic noiitransgenic control hybrids were planted. Sampling methods used to monitor nontarget organisills included visual surveillance, sticky cards, pitfall traps, and litterbags. Data were analyzed using multivariate analyses to look for a general community level response to the treatments. Analysis of variance was conducted on individual taxa to detect differences distinct from the primary (ommunity response. Community level analyses of the nontarget arthropod abundance showed no significant impact on community abundance when comparing Bt with non-Bt maize fields. Anal) ses of the individual taxa also showed no significant differences in abundance between Bt and noii-Bt fields. Results of these studies confirm earlier laboratory testing and support the hypothesis that Cry1F niaize does not produce adverse effects on nontarget arthropods occurring in maize fields. [ABSTRACT FROM AUTHOR]

Understanding of the mating and dispersal behavior of the western corn rootworm, Diabrotica virgifera virgifera (LeConte), is essential to predicting potential resistance to Bt corn technologies recently deployed to combat this pest. To quantify movement of male beetles, field studies were conducted during 2006 and 2007 in commercial Bt cornfields that included the Environmental Protection Agency-mandated 20% refuge acreage. Wing traps containing a single virgin female beetle were placed along transects throughout these fields. Male beetles were collected from the sticky bottoms of traps to compare the mean number of beetles captured at the different transect distances. Gut contents of each captured male were assayed with protein test strips to determine if the Bt protein (Cry3Bb1) was present. This provided an estimate of the distances traveled by males to reach virgin females. These data indicated that the mean number of males captured ≈200 m from refuge corn was not significantly different than the mean number of males captured close to the refuge (<22 m). Complementary field observations were conducted to determine how far newly emerged female beetles moved before mating and the time of day mating occurs. Results indicated that females do not move far from the site of emergence before mating and do not mate within the first 4 h of adult life. The implications of these data for movement and mating patterns of adult rootworms in Bt/refuge environments are discussed. [ABSTRACT FROM AUTHOR]

Effects of Bt corn on post-harvest residues' decomposition, soil microflora, and soil fauna were studied in two field experiments in the Czech Republic. At each experiment location, Bt corn and a non-Bt conventional corn hybrid with a similar genetic background were each planted on half of a field, which was repeated at both locations for 3 years. Field microcosms containing litter bags of Bt or non-Bt corn post-harvest residues and matching field soils were exposed in field plots in completely randomized blocks and sampled after 3, 6, and 18 months. Decomposition of litter bag content, microbial biomass, PLFA profile, and abundance of soil fauna in whole microcosms were determined. No significant effects of Bt corn were recorded for the investigated parameters. In the laboratory, either fresh post-harvest residues or post-harvest residues exposed to soil for 90 days from the above field experiment were used to study the effect of Bt corn on population growth of Enchytraeus crypticus (Oligochaeta: Enchytraedae). Significant (about 30%) reductions of E. crypticus population growth in fresh Bt corn litter in comparison with non-Bt corn were observed. However, this was not observed in litter exposed to soil for 90 days. In conclusion, Bt corn may have a deleterious effect on decomposers in the laboratory, but this effect was minor and restricted to the initial stages of decomposition and undetectable in long-term field experiments. [ABSTRACT FROM AUTHOR]

Rootworm control tactics have recently expanded to include transgenic maize, which express insecticidal proteins from Bacillus thuringiensis (Bt) to reduce larval injury and protect yield potential. Exceptional root protection, increased grower efficiency and improved safety have led to rapid adoption of this technology in the USA. As a result, there is a recognized need for resistance management programmes aimed at delaying rootworm resistance. An essential component of resistance management programmes is the development and implementation of effective resistance monitoring techniques. Five test populations of Diabrotica virgifera virgifera (LeConte) were used to evaluate the sensitivity of two techniques used to describe population susceptibility to the Bt proteins expressed in event DAS-59122-7 maize: a diet bioassay employing purified proteins applied to artificial diet and a novel technique using sub-lethal measures of larval development on seedling maize. Test populations included Rochelle-US, an unselected susceptible colony, three populations composed of 5%, 25% or 50% Rochelle-S mixed with Rochelle-US, and the Rochelle-S selected colony. Rochelle-S was derived from the same founding population as Rochelle-US, but selected for survival on DAS-59122-7 maize. Selections identified a minor trait conferring increased tolerance, and greenhouse plant efficacy evaluations confirmed that after 10 generations of selection with no random mating, Rochelle-S caused significantly more root injury to DAS-59122-7 than Rochelle-US. Rochelle-S present at 5% of the test population resulted in measurable but not significant increase in injury to DAS-59122-7 maize. The diet bioassay was relatively insensitive to the susceptibility differences between the Rochelle-US and Rochelle-S populations. Neither LC50 nor EC50 estimates produced statistically significant differentiation between test populations with 0%, 5%, 25% or 50% Rochelle-S. The sub-lethal assay clearly identified differences between Rochelle-S and Rochelle-US and an increased rate of larval development was measurable when the test population contained only 5% of Rochelle-S. [ABSTRACT FROM AUTHOR]

Transgenic Bacillus thuringiensis (Bt) corn, Zea mays L., has been widely used to manage a corn borer complex in the mid-southern region of the United States. The sugarcane borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae), has become a dominant cornstalk boring species in some areas of this region, especially in Louisiana. Therefore, management of sugarcane borer resistance to Bt corn is critical to ensure the long-term sustainability of Bt corn for the region. This study screened 280 two-parent family-lines of sugarcane borer from four geographical populations in Louisiana during 2005 to determine whether Bt resistance allele frequency in sugarcane borer is sufficiently low to meet the rare resistance assumption of the current "high dose/refuge" resistance management strategy for Bt corn. These sugarcane borer family-lines were examined for Bt resistance by using novel F2 screening procedures. No major Bt resistance alleles were detected in these four populations. The estimated frequency of major Bt resistance alleles was <0.0027, with a 95% probability and a detection power of 94%. The estimated minor resistance allele frequency was 0.0063, with a 95% CI of 0.0025-0.0117. During a previous study, a major Bt resistance allele was detected in one individual from 213 family-lines of another Louisiana population of sugarcane borer. Combining these data with the current screen, the frequency of major Bt resistance alleles across the five populations was 0.001, with a 95% credibility interval of 0.0001-0.0028 and a detection power of 95%. Major Bt resistance allele frequencies in Louisiana sugarcane borer populations seem to be low, and they should support the rare resistance allele requirement of the high dose/refuge strategy. [ABSTRACT FROM AUTHOR]

The use of Bt maize could directly or indirectly affect non-target organisms. Assessment of the impacts of Bt crops is hampered by the lack of even the most basic checklist of the species present in most systems. In South Africa the maize agroecosystem is of particular interest because of the large area planted with Bt maize (Event MON810) for the control of Busseola fusca (Fuller) (Lepidoptera: Noctuidae) and Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) populations. The aims of this study were to determine the diversity of Lepidoptera species that feed on or are closely associated with maize, and to assess the possible effects of Bt maize on the incidence of Lepidoptera damage under field conditions. Field surveys were conducted at 24 sites during the 2004/2005 and 2005/2006 cropping seasons. Fifteen species of Lepidoptera were recorded on maize. Six of these species were recorded to feed on Bt maize. Limited information is available on host plants and biology of some of these species. The incidences of Lepidoptera-infested plants and infestation levels were generally lower in Bt fields than in non-Bt fields possibly indicating that these species may be affected by Bt maize. Results showed that B. fusca larvae were able to survive on Bt maize at low population levels. On the basis of exposure and risk of resistance development, Helicoverpa armigera and Acantholeucania loreyi can be considered to be important non-target lepidopteran herbivores on maize in South Africa. [ABSTRACT FROM AUTHOR]

Foliar applications of fertilizer phosphorus (P) could improve use efficiency by minimizing soil applications. Nine experiments were conducted in 2002 and 2003 to determine foliar P rates and appropriate growth stages for application. Treatments comprised of 10 factorial combinations of three foliar P application timings and four rates of foliar P. Foliar application times were V4 (collar of fourth leaf visible), V8 (collar of eighth leaf visible), and VT (last branch of the tassel completely visible but silks not yet emerged) corn growth stages. Foliar P rates were 0, 2, 4, and 8 kg ha-1. Foliar P applied at the VT growth stage improved grain and forage P concentration, which was reflected in increased grain yield in some of the experiments. A foliar P rate of 8 kg ha-1 improved yield to some extent and forage and grain P concentration more than the smaller rates. The results suggest that foliar P could be used as an efficient P-management tool in corn when applied at the appropriate growth stage and rate. [ABSTRACT FROM AUTHOR]

The European corn borer, Ostrinia nubilalis (Hübner), is one of the most important insect pests in corn, Zea mays L. Transgenic corn cultivars expressing Bacillus thuringiensis (Bt) toxin provide a promising crop protection strategy against European corn borer; however, management is needed to avoid resistance development of the target pest species. The aim of this work was to establish the baseline susceptibility of different European corn borer populations in Germany to be able to forecast a possible development of resistance at an early stage. To standardize test procedures for future resistance management, the efficiency of Cry1Ab toxins from different suppliers and different production was assessed. Furthermore, two different test methods, surface treatment and the incorporation method, were compared with regard to their practicability and efficiency. Neither method provided significant differences in the baseline susceptibility of populations from different German regions. Overall, the data suggested little differentiation among German populations in terms of their susceptibility to Bt toxin and their genetic background. Future monitoring could therefore use a single European corn borer population as a representative for southwestern Germany. However, toxins from different suppliers and different production batches produced a vast range of LC50 values. Changes because of different toxin batches may be mistaken as a change in baseline susceptibility or even as the start of a resistance development. Thus, it is important throughout insect resistance management that the same toxin batches will be available for baseline susceptibility bioassays and for future tests. [ABSTRACT FROM AUTHOR]

Dispersal of the southwestern corn borer, Diatraea grandiosella Dyar, was examined by release and recapture of dye-marked adults and by capture of feral adults in and around 50-ha center pivot irrigated fields of Bacillus thuringiensis (Bt) maize. Pheromone and blacklight traps were used to capture the adults, In 1999, 2000, and 2001, a total of 177, 602, and 1,292 marked males, and 87, 231, and 1,045 marked females were released in four irrigated Bt maize fields, respectively. Recapture beyond release point was 2.13, 6.17, 3.16, and 17.91% for males and 0, 0, 2.23, and 4.18% for females in the four field, respectively. One male was recaptured over native vegetation outside the field perimeter, and one was caught in a neighboring maize field, 457 m from the release point. An exponential decay function explained recapture of marked adults across the dispersal distance. More than 90% of adults were recaptured within 300 m of the release point. Large numbers of feral adults were captured throughout the study fields and over native vegetation between fields. The feral adult dispersal could be described with a linear model. Virgin females (38% marked and 14% feral) were captured throughout the study fields. The recapture of marked insects suggests that the dispersal was limited. However, capture of feral adults throughout Bt maize fields indicates that the actual dispersal may be more extensive than indicated by recapture of marked adults. Potential refuge sources for the feral adults were 587-1,387 m from the edge of the fields. There seems to be some dispersal of D. grandiosella from the nontransgenic "refuge" fields into the transgenic fields, which may allow for some genetic mixing of the Bt-resistant and -susceptible insects to help suppress potential evolution of pest resistance to transgenic maize. However, it is not clear whether the dispersed recorded in this study is sufficient to support the current resistance management strategy for corn borers. [ABSTRACT FROM AUTHOR]

The purpose of this study was to assess the persistence and accumulation of the CrylAb protein, in soil as a result of sustained planting of genetically modified Bacillus thuringiensis (Bt) corn hybrids. Soil samples were collected from agricultural fields in five corn-growing regions of the United States where Bt corn hybrids (MON 810: or Btll) had been planted forat least 3 consecutive yr. At each site,, soil samples were collected during the corn-growing period (postanthesis) and again within 6 wk after harvest. Multiple soil specimens from matched Bt cornfields and nearby, non-Bt control fields were analyzed by diet-incorporation insect bioassay, using growth inhibition (GI) of the European corn borer (Ostrinia nubilalis) as the toxicity endpoint. Positive control soil samples containing CrylAb protein at the GI50 level (0.05 μg/g soil) were analyzed In tandem with test and control samples to verify that the bioassay was able to detect low levels of CrylAb protein. The limit of detection for CrylAb protein in soil was 0.03 μg/g soil. The presence of CrylAb protein in soil was assessed by statistical comparison of the insect toxicity (GI) of soils collected from Bt and non-Bt (control) cornfields. Only one soil sample, collected postanthesis in a Bt cornfield that had also been treated with carbofuran insecticide, showed insect toxicity. This toxicity was below the GI50 level, and no toxicity was detected in the soil collected from the same plot shortly after harvest Therefore, there is no evidence of persistence or accumulation of CrylAb protein in soils from fields planted for at least three consecutive growing seasons with Bt corn hybrids. [ABSTRACT FROM AUTHOR]

Corn and soybean are two important crops in the Delmarva (Delaware, Maryland and Virginia) peninsula region. Both crops are attacked by corn earworm (CEW), Helicoverpa zea (Boddie). The larvae cause significant ear damage to corn serving as a primary nursery for CEW populations which shift to soybean later in the season. In soybean, CEW larvae cause serious yield losses if not controlled by insecticides. Many farmers in the Delmarva region have been increasing the acreage they grow with genetically engineered corn hybrids that contain insecticidal proteins expressed by the genes of Bacillus thurngiensis sub sp. kurstaki (Bt) as an alternative to the application of chemical insecticides. A study was conducted to investigate the use of Bt corn as a trap crop for the management of CEW in soybean. Bt corn was planted as a trap crop in a ten percent of the area of soybean as a peripheral trap, trap in the middle and trap in the intermittent rows in soybean. CEW moths were attracted and observed on the newly formed silks of the ears of Bt corn in all types of traps including peripheral trap, trap in the middle and trap in the intermittents rows planted in soybean. CEW eggs were also observed on the silk of transgenic corn. The moths, eggs and larvae (CEW) were hardly observed in soybean grown as a main crop. Clearly, we were able to divert the CEW adults on Bt corn from soybean. The number of CEW eggs was significantly higher in the peripheral trap and trap in the intermittent rows compared with trap in the middle of the plots, suggesting that Bt corn planted as a peripheral trap crop could be more practicable and effective for the farmers in reducing the CEW damage in soybean. [ABSTRACT FROM AUTHOR]

Genetically modified (GM) crops have met with widespread approval among scientists and policy makers in the United States, but public approval of GM crops, both domestically and abroad, is progressing much more slowly. An underlying cause of public wariness may be that both nations and individual consumers do not perceive significant benefits to themselves from GM crops, while fearing the risks they may incur. In this study, an economic analysis is conducted to determine whether the benefits of one type of GM corn, Bt corn (genetically modified to resist damage from the ECB and Southwestern corn borer), outweigh the potential risks; and who the “winners” and “losers” are among stakeholder groups that may be affected by Bt corn. It is found that Bt corn growers, consumers, and industry all benefit from Bt corn adoption, though the purported health and environmental benefits of reducing chemical pesticide usage through Bt corn are negligible. Though the aggregated public benefit is large, the welfare gain to individual consumers is small and may not make up for perceived risks. While environmental and health risks of Bt corn are unlikely, the potential market risks—impacting both the organic corn market and total U.S. corn exports—are found to be significant. Currently, distributional analysis is not a part of regulatory decision making of Bt corn in the United States; yet it may help to explain why decision makers at both the government and individual-consumer levels have failed to embrace Bt corn and other GM crops. [ABSTRACT FROM AUTHOR]

The insecticidal proteins in genetically modified hybrid Bt corn(Zea mays spp.) reduce insect damage, which in turn can reduce infection of the grain by mycotoxigenic fungi. Lower levels of Fusarium mycotoxins, fumonisin, and deoxynivalenol in Bt corn could have significant market and health impacts, both in the United States and around the world. These impacts are foregone losses through market rejection, human health losses, and animal health losses. We estimate that at current planting levels, Bt corn saves farmers in the United States about$17 million annually through reduced fumonisin and deoxynivalenol damage alone. Though not extensively grown in developing countries, the benefits there in mycotoxin reduction could be even more significant, particularly in regions where corn is a staple in the human diet. [ABSTRACT FROM AUTHOR]

The potential negative effects of transgenic Bt corn on the monarch butterfly, Danaus plexippus, requires quantification of the presence of D. plexippus in the field and of the effect of Bt corn tissues on oviposition and larval survival. During a 2-year field study, D. plexippus females laid similar number of eggs on Asclepias syriaca in corn fields and on A. syriaca growing in roadside habitats parallel to corn fields. In 1999 and 2000 similar number of D. plexippus larvae were observed on A. syriaca in corn fields and roadside habitats, whereas a greater proportion of A. syriaca in corn fields were infested by at least one D. plexippus larva in 2000. Similar number of eggs were laid in transgenic Bt and non-Bt corn fields, indicating that females did not avoid leaves dusted with anthers and 6–72 Bt pollen grains/cm2. Similar number of D. plexippus larvae were found in and near Bt corn fields compared to non-Bt corn fields following corn anthesis. In 2000, transgenic Event MON810 Bt corn pollen and anthers had no measurable effects on D. plexippus oviposition or larval survival. [Copyright &y& Elsevier]

European corn borer Ostrinia nubilalis Hu¨bner (Lepidoptera: Crambidae) larvae that have completed development on Event 176 Bt corn hybids have either survived exposure to sublethal doses of Cry1Ab Bt toxin or exploited plant tissues that do not express the toxin. To evaluate the impact of such exposure on larval establishment and survival, Event 176 plants with and without tassels and a non-Bt isoline were infested with O. nubilalis egg masses during anthesis. On the non-Bt plants, larval establishment occurred primarily on pollen collecting in the leaf axils, silks and ears. In contrast, almost no larvae were recovered from leaf axils of the Bt treatments and at least 50% fewer larvae were recovered from the silks and ears during the first 2 weeks after infestation relative to the non-Bt plants. The larvae recovered from Bt treatments weighed significantly less than those observed in the non-Bt isoline at 4 weeks after infestation. By the eighth week, the larval weights of all three treatments were similar in three of four different field tests, suggesting that second generation larvae have the ability to compensate for initial exposure to sublethal doses of Bt toxin. In laboratory assays involving exposure of neonate larvae to silks of Event 176 and non-Bt corn, survival of neonate O. nubilalis was not different although larval weights were significantly reduced (2- to 6-fold). These results suggest that second generation larvae completing development on Event 176 corn do not completely avoid exposure to the Bt toxin, although those that do survive are able to compensate for these sublethal effects. The implication of these results is that Event 176 hybrids do not appear to satisfy requirements for high dose that are recommended for resistance management purposes. [Copyright &y& Elsevier]

Abstract Widespread use of transgenic crops that express an insecticidal endotoxin from Bacillus thuringiensis increases the risk of evolution of resistance by the European corn borer and other insect pests. To delay resistance evolution, the high-dose/refuge strategy is being implemented for Bt maize and Bt cotton. We develop a general modelling framework to understand the invasion and spread of alleles conferring resistance. We show that at least three processes are involved in explaining the effectiveness of the high-dose/refuge strategy: the intensity of selection, assortative (non-random) mating due to spatial subdivision, and variation in male mating success also due to spatial subdivision. Understanding these processes leads to a greater range of possible resistance management tactics. For example, efforts to encourage adults to leave their natal fields may have the unwanted effect of speeding rather than slowing resistance evolution. Furthermore, when Bt maize causes high mortality to susceptible target pests, spraying insecticides in refuges to reduce pest populations may not greatly disrupt resistance management. [ABSTRACT FROM AUTHOR]

We present the first evidence that transgenic Bacillus thuringiensis (Bt) corn pollen naturally deposited on Asclepias syriaca; common milkweed, in a corn field causes significant mortality of Danaus plexippus L. (Lepidoptera: Danaidae) larvae. Larvae feeding for 48 h on A. syriaca plants naturally dusted with pollen from Bt corn plants suffered significantly higher rates of mortality at 48 h (20±3%) compared to larvae feeding on leaves with no pollen (3±3%), or feeding on leaves with non-Bt pollen (0%). Mortality at 120 h of D. plexippus larvae exposed to 135 pollen grains/cm2 of transgenic pollen for 48 h ranged from 37 to 70%. We found no sub-lethal effects on D. plexippus adults reared from larvae that survived a 48-h exposure to three concentrations of Bt pollen. Based on our quantification of the wind dispersal of this pollen beyond the edges of agricultural fields, we predict that the effects of transgenic pollen on D. plexippus may be observed at least 10 m from transgenic field borders. However, the highest larval mortality will likely occur on A. syriaca plants in corn fields or within 3 m of the edge of a transgenic corn field. We conclude that the ecological effects of transgenic insecticidal crops need to be evaluated more fully before they are planted over extensive areas. [ABSTRACT FROM AUTHOR]

The article reports on the decreasing compliance rates of farmers to comply with procedures in the prevention of pesticide resistant insects in the U.S. According to a report of Gregory Jaffe of the Centre for Science in the Public Interest (CSPI), there were 28% of farmers who provide refuges that were too small while 34% were too far away in 2008. The article mentions that farmers planting Bt corn are asked to supply insect refuges nearby containing conventional corn and other plants.