Characterization of the Activity Spectrum of MON 88702 and the Plant-Incorporated Protectant Cry51Aa2.834_16

The influence of imidacloprid seed treatment on non-ThryvOn and ThryvOn cotton

In the southern United States, thrips are a significant early season pest of cotton. In the United States, in 2022, 98% of cotton acres were infested with thrips, and, of those acres, 45% were treated for thrips. Thrips injury resulted in over $113 million dollars in losses plus control costs to the cotton industry in the United States that year. A new Bacillus thuringiensis trait known as ThryvOn has been commercialized to provide control against thrips. There is ongoing debate about the need for an insecticidal seed treatment to improve thrips control on ThryvOn varieties. Field studies were conducted to determine if the addition of an imidacloprid seed treatment improved efficacy against tobacco thrips and to determine if reduced rates of seed treatments (0, 25, 50, 75, and 100% of the labeled rate) provided benefits for thrips control in ThryvOn cotton. To control for infestation pressure, a complementary greenhouse study was conducted using the same treatments under controlled conditions. Imidacloprid provided only a limited benefit for improved management on ThryvOn cotton in the greenhouse study, but no benefit in the field study. Efforts in pest surveillance should be continued in ThryvOn cotton to allow for foliar applications when warranted based on established thresholds. No conclusions can be drawn about the benefits of an imidacloprid seed treatment for resistance management in ThryvOn cotton from this study, but these data suggest that any benefit would be minimal.

Establishing best practices for insect resistance management: a new paradigm for genetically engineered toxins in cotton expressing Mpp51Aa2

Debate over resistance management tactics for genetically engineered (GE) crops expressing insecticidal toxins is not new. For several decades, researchers, regulators, and agricultural industry scientists have developed strategies to limit the evolution of resistance in populations of lepidopteran and coleopteran pests. A key attribute of many of these events was insecticide resistance management (IRM) strategies designed around a presumed high-dose expression sufficient to kill 99.5% of exposed larvae for some of the main target pests in corn, Zea mays L. and cotton, Gossypium hirsutum L. In contrast, other target pests did not meet this high-dose criterion. Similarly, the recent release of ThryvOn cotton that expresses thysanopteran and hemipteran active Mpp51Aa2.834_16 toxin is not high dose, working on a combination of behavioral and sublethal effects to suppress populations. This unique mode of control has generated considerable uncertainty about what IRM strategies will be most effective to limit field-evolved resistance to this unique spectrum of pests. The goal of this manuscript is to present several knowledge gaps that exist in proposed Mpp51Aa2 IRM plans, focusing on its activity on thrips, Frankliniella spp. Addressing these gaps will be crucial to limit resistance and preserve the benefits that this technology may provide by alleviating reliance on conventional insecticides and seed treatments. Broadly, these considerations will be important for future GE events that are non-high dose but remain valuable components of a more holistic insect management programs that integrate multiple tactics to reduce conventional insecticide use for challenging pests.

Establishing an IPM System for Tarnished Plant Bug (Hemiptera: Miridae) in North Carolina

Prior to 2010, Lygus lineolaris Palisot de Beauvois was a minor pest in North Carolina cotton, Gossypium hirsutum L., but became one of the top pests by 2017. This insect was already a persistent pest in other US cotton-producing regions. Initial work focused on addressing near-term management needs and documenting locally relevant ecology and population dynamics of the pest in North Carolina. Landscape factors were found that correlated with tarnished plant bug incidence. Adult numbers tended to be higher in fragmented fields (more field edges) and nymph numbers were higher near field edges. The minimum required sample for estimating tarnished plant bug populations was studied. Thresholds developed in the Midsouth were proven to be useful in a study between both southeastern Virginia and northeastern North Carolina. Furthermore, an insecticide application sequence was recommended based on efficacy trials, number of expected insecticides, and preserving beneficial insects early in the season. These were evaluated in a study investigating IPM systems approaches. Finally, new management tactics for tarnished plant bug, such as ThryvOn cotton, are being evaluated. As new management strategies and tactics are developed, they will need to be evaluated for their fit in this IPM system.

Prey-mediated effects of Mpp51Aa2-producing cotton on longevity and reproduction of Orius majusculus

Genetically engineered (GE) cotton event MON 88702, producing Mpp51Aa2 (previously mCry51Aa2) from Bacillus thuringiensis (Bt), controls sucking pests, such as Lygus spp. (Hemiptera: Miridae) and thrips (Thysanoptera). Ingesting high doses of the insecticidal protein resulted in adverse effects on life table parameters of beneficial, predatory Orius spp. (Hemiptera: Anthocoridae). This triggered laboratory studies with more realistic food treatments, including different combinations of prey types with and without Bt protein to further characterize risks to this important group of non-target organisms. In this work, exclusive feeding of frozen spider mites (Tetranychus urticae, Acari: Tetranychidae) from Bt cotton confirmed adverse effects on longevity and fecundity of O. majusculus adults. Alternate feeding of Bt protein-containing spider mites and Bt-free Ephestia kuehniella (Lepidoptera: Pyralidae) eggs mitigated effects on longevity, but not on fecundity. When living larvae of Spodoptera littoralis (Lepidoptera: Noctuidae) from Bt cotton were fed to the predators, however, no effects on longevity and reproduction of female O. majusculus were observed, despite the fact that Bt protein concentrations in larvae were almost as high as concentrations in spider mites. When a diverse mix of prey species with various Bt protein concentrations is consumed in the field, it is unlikely that exposure of Orius spp. to Mpp51Aa2 is high enough to exert adverse effects on predator populations. MON 88702 cotton may thus be a valuable tool for integrated management of sucking pests.

Field Evaluation of Cotton Expressing Mpp51Aa2 as a Management Tool for Cotton Fleahoppers, Pseudatomoscelis seriatus (Reuter)

The cotton fleahopper (Pseudatomoscelis seriatus Reuter) is considered a highly economically damaging pest of cotton (Gossypium hirsutum L.) in Texas and Oklahoma. Current control methods rely heavily on the use of foliar-applied chemical insecticides, but considering the cost of insecticides and the critical timeliness of applications, chemical control methods are often not optimized to reduce potential yield losses from this pest. The Bacillus thuringiensis (Bt) Mpp51Aa2 (formerly Cry51Aa2.834_16) protein has proven effective against thrips and plant bugs with piercing and sucking feeding behaviors, but the impact of this toxin on cotton fleahoppers has not been investigated. To evaluate the Mpp51Aa2 trait effectiveness towards the cotton fleahopper, field trials were conducted in 2019, 2020, and 2021, comparing a cotton cultivar containing the Mpp51Aa2 trait to a non-traited isoline cultivar under insecticide-treated and untreated conditions. Populations of cotton fleahopper nymphs and adults were estimated weekly by visually inspecting cotton terminals. Square retention was also assessed during the first week of bloom to provide some insight on how the Bt trait may influence yield. While cotton fleahopper population differences between the traited and non-traited plants were not consistently noted during the pre-bloom squaring period, there was a consistent increase in square retention in cotton expressing Mpp51Aa2 relative to non-traited cotton. Additionally, cotton expressing Mpp51Aa2 offered similar square protection relative to non-traited cotton treated with insecticides for the cotton fleahopper. These findings indicate that the Mpp51Aa2 protein should provide benefits of delayed nymphal growth, population suppression, and increased square retention.

Bacterial Pesticidal Protein Mpp51Aa1 Delivered via Transgenic Citrus Severely Impacts the Fecundity of Asian Citrus Psyllid, Diaphorina citri

The Asian citrus psyllid (ACP) Diaphorina citri vectors the causative agent of citrus greening disease that has the capacity to decimate citrus production. As an alternative and more sustainable approach to manage D. citri than repeated application of chemical insecticides, we investigated the potential use of the bacteria-derived pesticidal protein, Mpp51Aa1, when delivered by transgenic Citrus sinensis cv. Valencia sweet orange or Citrus paradisi cv. Duncan grapefruit. Following confirmation of transcription and translation of mpp51aa1 by transgenic plants, no impact of Mpp51Aa1 expression was seen on D. citri host plant choice between transgenic and control Duncan grapefruit plants. A slight but significant drop in survival of adult psyllids fed on these transgenic plants was noted relative to those fed on control plants. In line with this result, damage to the gut epithelium consistent with that caused by pore-forming proteins was only observed in a minority of adult D. citri fed on the transgenic Duncan grapefruit. However, greater impacts were observed on nymphs than on adults, with a 40% drop in the survival of nymphs fed on transgenic Duncan grapefruit relative to those fed on control plants. For Valencia sweet orange, a 70% decrease in the number of eggs laid by adult D. citri on transgenic plants was noted relative to those on control plants, with a 90% drop in emergence of progeny. These impacts that contrast with those associated with other bacterial pesticidal proteins and the potential for use of Mpp51Aa1-expressing transgenic plants for suppression of D. citri populations are discussed. IMPORTANCE Pesticidal proteins derived from bacteria such as Bacillus thuringiensis are valuable tools for management of agricultural insect pests and provide a sustainable alternative to the application of chemical insecticides. However, relatively few bacterial pesticidal proteins have been used for suppression of hemipteran or sap-sucking insects such as the Asian citrus psyllid, Diaphorina citri. This insect is particularly important as the vector of the causative agent of citrus greening, or huanglongbing disease, which severely impacts global citrus production. In this study, we investigated the potential of transgenic citrus plants that produce the pesticidal protein Mpp51Aa1. While adult psyllid mortality on transgenic plants was modest, the reduced number of eggs laid by exposed adults and the decreased survival of progeny was such that psyllid populations dropped by more than 90%. These results provide valuable insight for potential deployment of Mpp51Aa1 in combination with other control agents for the management of D. citri.

Prey-mediated effects of mCry51Aa2-producing cotton on the predatory nontarget bug Orius majusculus (Reuter)

Genetically engineered (GE) cotton, MON 88702, is protected against certain sucking pests, such as plant bugs and thrips, by producing mCry51Aa2, a modified protein from Bacillus thuringiensis (Bt). Predatory pirate bugs (Orius spp.), natural enemies contributing to biological pest control, are also sensitive to the insecticidal protein when exposed continuously to high concentrations. We evaluated effects of MON 88702 on Orius majusculus when fed prey types with different mCry51Aa2 concentrations. When neonates were provided exclusively Tetranychus urticae spider mites reared on MON 88702 (high mCry51Aa2 content), adverse effects on predator survival and development were confirmed, compared with specimens fed prey from near-isogenic non-Bt cotton. When fed a mixture of T. urticae and Ephestia kuehniella eggs (mCry51Aa2-free), predator life table parameters were similar to the treatment where eggs were fed exclusively. When mCry51Aa2-containing spider mites were provided for a limited time at the beginning or the end of juvenile development, effects were less pronounced. While pirate bug nymphs showed similar consumption rates for prey from Bt and non-Bt cotton, choice experiments revealed a preference for E. kuehniella eggs over spider mites. Lepidopteran larvae (Spodoptera littoralis, high mCry51Aa2 content) or cotton aphids (Aphis gossypii, mCry51Aa2-free) reared on MON 88702 as alternative prey did not result in adverse effects on O. majusculus. Our study suggests limited risk of mCry51Aa2-producing cotton for O. majusculus, because its sensitivity for the Bt protein is relatively low and its natural food consists of diverse prey species with varying concentrations of Bt protein.

Using Sentinel Plots to Monitor for Changes in Thrips Susceptibility to MON 88702 Cotton Containing the Cry51Aa2.834_16 Bt Protein

Transgenic Bt crops are important tools for growers to manage insect pests, but their durability is threatened by the evolution of insect resistance. Implementing a resistance monitoring program is essential to detect and mitigate resistance. For non-high-dose Bt crops, resistance monitoring is challenging, because insect control is not complete, so targeted insects and insect damage will be present even without resistance. Given these challenges, sentinel plots have been used to monitor for insect resistance to non-high-dose crops by assessing changes in the efficacy of a Bt crop over time relative to a non-Bt control. We optimized a sentinel plot resistance monitoring approach for MON 88702 ThryvOn™ cotton, a new non-high-dose Bt product targeting two sucking pest taxa-Lygus (L. lineolaris and L. hesperus) and thrips (Frankliniella fusca and F. occidentalis)-and report here on the thrips monitoring methods and results. Quantifying thrips immatures was the best metric to characterize the impact of the trait, with at least a 40-60% average reduction of thrips immatures on ThryvOn relative to the control cotton at all sites with higher thrips densities. These data can be used within a ThryvOn resistance monitoring program and represent a case study for establishing a resistance monitoring approach for a non-high-dose trait product.

Cry51Aa Proteins Are Active against Apolygus lucorum and Show a Mechanism Similar to Pore Formation Model

Reduced insecticide spray in crop fields due to the widespread adoption of Bacillus thuringiensis (Bt) crops has favored the population increases of mirid bugs. Cry51Aa proteins are new types of Bt proteins that belong to aerolysin-like β pore-forming proteins with insecticidal activity against hemipteran and coleopteran pests. Here, we studied the activity of Bt Cry51Aa1 and Cry51Aa2 against Apolygus lucorum, an emerging pest in cotton, and their mechanism of action. Cry51Aa1 exhibited almost 5-fold higher toxicity than Cry51Aa2 with LC₅₀ of 11.87 and 61.34 μg/mL, respectively. Protoxins could be activated both in vitro, by trypsin and midgut contents, and in vivo, by A. lucorum midgut. Both Cry51Aa protoxins were processed in two steps, producing pre-activated (∼30 kDa) and final activated (∼25-28 kDa) proteins. Cry51Aa proteins bound to a 25 kDa midgut protein, and Cry51Aa2 showed 2 times higher binding affinity than Cry51Aa1. Incubating Cry51Aa proteins with midgut homogenate resulted in toxin oligomers of 150-200 kDa. Our findings provide a theoretical basis for using Cry51Aa proteins to control A. lucorum and a better understanding of their mode of action.

Standardized Field Trials in Cotton and Bioassays to Evaluate Resistance of Tobacco Thrips (Thysanoptera: Thripidae) to Insecticides in the Southern United States

Foliar-applied insecticide treatments may be necessary to manage thrips in cotton (Gossypium hirsutum L.) under severe infestations or when at-planting insecticide seed treatments do not provide satisfactory protection. The most common foliar-applied insecticide is acephate. Field observations in Tennessee suggest that the performance of acephate has declined. Thus, the first objective was to perform leaf-dip bioassays to assess if tobacco thrips, Frankliniella fusca (Hinds) (Thysanoptera: Thripidae), in cotton production regions have evolved resistance to foliar-applied insecticides. A second objective was to assess the performance of commonly applied foliar insecticides for managing thrips in standardized field trials in Arkansas, Tennessee, Mississippi, and Texas. For both objectives, several insecticides were evaluated including acephate, dicrotophos, dimethoate, lambda-cyhalothrin, imidacloprid, and spinetoram. Field trials and bioassays were completed from 2018 to 2021. Dose-response bioassays with acephate were performed on tobacco thrips field populations and a susceptible laboratory population. Bioassay results suggest that tobacco thrips have developed resistance to acephate and other organophosphate insecticides; however, this resistance seems to be most severe in Arkansas, Tennessee, and the Delta region of Mississippi. Resistance to other classes of insecticides were perhaps even more evident in these bioassays. The performance of these insecticides in field trials was variable, with tobacco thrips only showing consistent signs of resistance to lambda-cyhalothrin. However, it is evident that many populations of tobacco thrips are resistant to multiple classes of insecticides. Further research is needed to determine heritability and resistance mechanism(s).

Safety assessment of Mpp75Aa1.1, a new ETX_MTX2 protein from Brevibacillus laterosporus that controls western corn rootworm

The recently discovered insecticidal protein Mpp75Aa1.1 from Brevibacillus laterosporus is a member of the ETX_MTX family of beta-pore forming proteins (β-PFPs) expressed in genetically modified (GM) maize to control western corn rootworm (WCR; Diabrotica virgifera virgifera LeConte). In this manuscript, bioinformatic analysis establishes that although Mpp75Aa1.1 shares varying degrees of similarity to members of the ETX_MTX2 protein family, it is unlikely to have any allergenic, toxic, or otherwise adverse biological effects. The safety of Mpp75Aa1.1 is further supported by a weight of evidence approach including evaluation of the history of safe use (HOSU) of ETX_MTX2 proteins and Breviballus laterosporus. Comparisons between purified Mpp75Aa1.1 protein and a poly-histidine-tagged (His-tagged) variant of the Mpp75Aa1.1 protein demonstrate that both forms of the protein are heat labile at temperatures at or above 55°C, degraded by gastrointestinal proteases within 0.5 min, and have no adverse effects in acute mouse oral toxicity studies at a dose level of 1920 or 2120 mg/kg body weight. These results support the use of His-tagged proteins as suitable surrogates for assessing the safety of their non-tagged parent proteins. Taken together, we report that Mpp75Aa1.1 is the first ETX-MTX2 insecticidal protein from B. laterosporus and displays a similar safety profile as typical Cry proteins from Bacillus thuringiensis.

Peptide mediated, enhanced toxicity of a bacterial pesticidal protein against southern green stink bug

The damage caused by stink bugs that feed on agricultural crops accounts for such significant losses that transgenic plant resistance to stink bugs would be highly desirable. As the level of toxicity of the Bacillus thuringiensis-derived, ETX/Mtx2 pesticidal protein Mpp83Aa1 is insufficient for practical use against the southern green stink bug Nezara viridula, we employed two disparate approaches to isolate peptides NvBP1 and ABP5 that bind to specific proteins (alpha amylase and aminopeptidase N respectively) on the surface of the N. viridula gut. Incorporation of these peptides into Mpp83Aa1 provided artificial anchors resulting in increased gut binding, and enhanced toxicity. These peptide-modified pesticidal proteins with increased toxicity provide a key advance for potential future use against N. viridula when delivered by transgenic plants to mitigate economic loss associated with this important pest.

Sampling Optimization and Crop Interface Effects on Lygus lineolaris Populations in Southeastern USA Cotton

Tarnished plant bug, Lygus lineolaris (Hemiptera: Miridae), is an economically damaging pest in cotton production systems across the southern United States. We systematically scouted 120 commercial cotton fields across five southeastern states during susceptible growth stages in 2019 and 2020 to investigate sampling optimization and the effect of interface crop and landscape composition on L. lineolaris abundance. Variance component analysis determined field and within-field spatial scales, compared with agricultural district and state, accounted for more variation in L. lineolaris density using sweep net and drop cloth sampling. This result highlights the importance of field-level scouting efforts. Using within-field samples, a fixed-precision sampling plan determined 8 and 23 sampling units were needed to determine L. lineolaris population estimates with 0.25 precision for sweep net (100 sweeps per unit) and drop cloth (1.5 row-m per unit) sampling, respectively. A spatial Bayesian hierarchical model was developed to determine local landscape (<0.5 km from field edges) effects on L. lineolaris in cotton. The proportion of agricultural area and double-crop wheat and soybeans were positively associated with L. lineolaris density, and fields with more contiguous cotton areas negatively predicted L. lineolaris populations. These results will improve L. lineolaris monitoring programs and treatment management decisions in southeastern USA cotton.

Biology, Ecology, and Pest Management of the Tarnished Plant Bug, Lygus lineolaris (Palisot de Beauvois) in Southern Row Crops

Simple Summary

The tarnished plant bug, Lygus lineolaris, is a polyphagous, sap-feeder that causes significant economic damage in several field crops, especially cotton (Gossypium hirsutum L.) in the mid-southern United States. In 2020, it was reported that 4.8 million acres of cotton were infested by Lygus spp. in the United States. A broad host range, polyphagous feeding behavior and high mobility of this pest along with resistance development to conventional pesticides helped them establish as a significant pest of concern for cotton growers in the mid-south. Since the publication of a review by Layton (2000) on damage caused by Lygus lineolaris, many new research studies have been published on the Lygus biology, ecology, and integrated pest management strategies. A comprehensive review paper that summarizes these latest research developments and Lygus management strategies will be useful for researchers and cotton growers. In this review, we report and discuss the latest developments in Lygus research and the new control strategies that have been developed in the last two decades.

Abstract

The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), (Hemiptera: Miridae) is considered the most damaging pest of cotton (Gossypium hirsutum L.) in the mid-southern United States, although it is established throughout the United States, southern Canada, and northern Mexico. The introduction of transgenic crops for the control of moths in the Heliothine complex and eradication of the boll weevil, Anthonomus grandis, from much of the United States led to greatly reduced pesticide use in cotton fields, which allowed L. lineolaris to emerge as a new primary pest of cotton in the mid-southern United States. Since the publication of a review by Layton (2000) on damage caused by Lygus lineolaris, many new studies have been published on the changes in host range, population dynamics, sampling methods and thresholds, cultural practices, sex pheromones and attractant blends, novel pesticides and insecticide resistance mechanisms, olfactory and feeding behaviors, introduction of biological control agents, host-plant resistance mechanisms, and new molecular and genetic tools for integrated pest management of Lygus species in cotton and other important crops. Here, we review and discuss the latest developments in L. lineolaris research in the last two decades.

Biosafety of bee pollinators in genetically modified agro-ecosystems: Current approach and further development in the EU

Bee pollinators are an important guild delivering a fundamental input to European agriculture due to the ecological service they provide to crops in addition to the direct economic revenues from apiculture. Bee populations are declining in Europe as a result of the effects of several environmental stressors, both natural and of anthropic origin. Efforts are ongoing in the European Union (EU) to improve monitoring and management of pollinator populations to arrest further declines. Genetically modified (GM) crops are currently cultivated in a limited area in Europe, and an environmental risk assessment (ERA) is required prior to their authorization for cultivation. The possible impacts of GM crops on pollinators are deemed relevant for the ERA. Existing ecotoxicological studies indicate that traits currently expressed in insect-resistant GM plants are unlikely to represent a risk for pollinators. However, new mechanisms of insect resistance are being introduced into GM plants, including novel combinations of Cry toxins and double strand RNA (dsRNA), and an ERA is required to consider lethal and sublethal effects of these new products on nontarget species, including insect pollinators. The evaluation of indirect effects linked to the changes in management practices (e.g. for herbicide-tolerant GM crops) is an important component of EU regulations and a requirement for ERA. This paper reviews current approaches used to test the sensitivity of pollinators to GM plants and their products to determine whether sufficient data are being provided on novel GM plants to satisfy EU risk assessment requirements. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

A novel Bacillus thuringiensis isolate toxic to cotton pink bollworm (Pectinophora gossypiella Saunders)

In this study, we report a novel indigenous Bacillus thuringiensis (Bt) isolate, T26, which showed spores and crystals under scanning electron microscope and pathogenicity against the pink bollworm (Pectinophora gossypiella Saunders) in artificial diet based bioassay. SDS-PAGE analysis of the spore-crystal mixture of the Bt isolate, T26 revealed presence of three major protein bands of approximate molecular weights of 80, 55 and 40 kDa. The draft genome assembly consists of 56 scaffolds with an entire draft genome size of 5,054,095 bp. NCBI blast analysis revealed that assembled draft genome is spread over in a chromosome (4,818,543 bp) and one plasmid (235,552 bp). NCBI Prokaryotic Genome Annotation Pipeline (PGAP) showed presence of 5033 coding gene sequences and 159 RNAs genes. None of the known lepidopteran active genes (cry1, cry2 and cry9) could be detected with PCR or with whole genome sequence analysis using Bt toxin scanner tool or CryProcessor tool. Thus, presence of protein crystals and toxicity towards cotton pink bollworm and absence of any known cry/vip/cyt type of genes in draft genome indicates it is a novel type of Bt isolate. Further investigation of this genome sequence along with protein sequencing will lead to understand the novel factors responsible for its virulence and could be a useful tool for the insect resistance management in pink bollworm.

Resistance monitoring to four insecticides and mechanisms of resistance in Lygus lineolaris Palisot de Beauvois (Hemiptera: Miridae) populations of southeastern USA cotton

BACKGROUND

Economically damaging infestations of the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), have become more frequent in Virginia and North Carolina cotton since 2013 and 2010, respectively. Foliar insecticide use has increased dramatically in response. Efficacy data (LC₅₀ ) are needed to evaluate L. lineolaris susceptibility and resistance levels (RR₅₀ ) to commonly used and recommended insecticides for managing this pest in the southeastern USA.

RESULTS

Elevated resistance levels to acephate and bifenthrin were measured in L. lineolaris populations collected from wild and cultivated hosts in Virginia, North Carolina and northern Alabama when compared to a susceptible laboratory population. High levels of bifenthrin resistance were observed in 2018 and 2019. Mixed-function oxidase and esterase (EST) inhibitors, piperonyl butoxide and S,S,S-Tributyl phosphotrithioate, respectively, had a synergistic effect on bifenthrin with resistant populations of L. lineolaris. Bifenthrin-resistant L. lineolaris populations expressed elevated levels of cytochrome P450 (CYP₄₅₀ ) monooxygenase and general EST activity. Results suggest that insecticide resistance is present in some locations and that CYP₄₅₀ and EST activity in L. lineolaris contribute to pyrethroid resistance in the southeastern USA.

CONCLUSIONS

Results can serve as a baseline for continued monitoring of L. lineolaris insecticide resistance and inform insecticide resistance management strategies that help southeastern USA cotton producers to minimize inputs and slow resistance development. © 2020 Society of Chemical Industry.

Understanding the potential impact of continued seed treatment use for resistance management in Cry51Aa2.834_16 Bt cotton against Frankliniella fusca

Transgenic cotton expressing Cry51Aa2.834_16 Bt toxin (hereafter referred to as MON 88702) has the potential to be an important tool for pest management due to its unique activity against tobacco thrips, Frankliniella fusca. Unlike other Bt toxins targeting lepidopteran cotton pests, MON 88702 does not cause direct mortality but has an antixenotic effect that suppresses F. fusca oviposition. Previous work has shown neonicotinoid seed treated (NST) crops have similar behavioral effects on thrips. This study used non-choice and common garden experiments to examine how the presence of MON 88702 cotton and soybean (another F. fusca host) with and without NSTs might alter F. fusca infestation distributions. In a no-choice environment, significant larval establishment differences were observed, with untreated soybean plants becoming most heavily infested. In choice experiments, plants expressing MON 88702 or were neonicotinoid treated had significantly lower larval establishment. Larval density decreased as dispersal distance increased, suggesting reproductive decisions were negatively related to distance from the release point. Understanding how F. fusca responds to MON 88702 in an environment where adults can choose among multiple host plants will provide valuable context for projections regarding design of MON 88702 resistance refuges. Reduced larval establishment on NST cotton and soybean suggests that area-wide use of NSTs could reduce the number of susceptible F. fusca generated in unstructured crop refuges for MON 88702. These results also suggest that although the presence of NST MON 88702 could suppress reproduction and resistance selection, over time this benefit could erode resulting in increased larval establishment on NST cotton and soybean due to increased frequency of neonicotinoid resistant F. fusca populations.

Evaluation of Current Tarnished Plant Bug (Hemiptera: Miridae) Thresholds in Transgenic MON 88702 Cotton Expressing the Bt Cry51Aa2.834_16 Trait

The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), is an important pest of cotton in many areas of the southern United States. An experiment was conducted at two locations in Mississippi during 2016 and 2017 to evaluate action thresholds for tarnished plant bug on a novel Bacillus thuringiensis cotton that expresses the Cry51Aa2.834_16 toxin. Treatments included the current action threshold, a 2× threshold, and treatments where insecticides were only applied during the early season (preflower) or only during late season (during flowering) based on the current action thresholds. These were compared to an untreated control and a weekly insecticide use regime that received weekly insecticide sprays. All treatments were imposed on both Bt Cry1Aa2.834_16 cotton and a nontraited cotton. The Bt Cry1Aa2.834_16 trait reduced the number of tarnished plant bugs and injury, and improved yields compared to nontraited cotton. For all spray treatments except the weekly insecticide use regime, yields were greater for the Bt Cry51Aa2.834_16 cotton than the nontraited cotton. In terms of thresholds, Bt Cry1Aa2.834_16 cotton sprayed based on current action thresholds resulted in similar yields to the weekly insecticide use regime of both cotton types. In contrast, the 2× threshold resulted in lower yields than the current threshold for both cotton types. Though thresholds intermediate to the currently recommended action threshold and the 2× threshold were not tested, these data suggest that currently recommended action thresholds appear appropriate for Bt Cry51Aa2.834_16 cotton. These results suggest that this trait will be an important component of current IPM programs in cotton where tarnished plant bug is an important pest.

Feeding behavior of Frankliniella fusca on seedling cotton expressing Cry51Aa2.834_16 Bt toxin

BACKGROUND

Tobacco thrips, Frankliniella fusca (Hinds), is a pest of cotton. Currently, growers rely on neonicotinoid seed treatments to control F. fusca. However, the occurrence of neonicotinoid-resistant F. fusca populations has created new challenges for their management. Development of thrips-active Cry51Aa2.834_16 Bacillus thuringiensis (Bt) toxin expressed in MON 88702 cotton will be an important new tactic for thrips management. Previous studies have shown that MON 88702 causes limited mortality of F. fusca adults and larvae but reduces infestations on seedling cotton by suppressing oviposition from colonizing adults. This suggests that the toxin affects host preference of adult F. fusca. Knowledge of the effect of this trait on F. fusca feeding behavior provides a more complete understanding of MON 88702 activity. Using electropenetrography, we compared the feeding behaviors of adult F. fusca females on MON 88702 cotton and a non-Bt isoline cotton over 2 h. The number of probes, proportion of probes resulting in ingestion, total duration of ingestion, and duration of ingestion per event were measured.

RESULTS

On MON 88702 seedlings, F. fusca probed and ingested fewer times than those on non-Bt cotton. Probes on MON 88702 were less likely to lead to ingestion than on non-Bt cotton. The total duration of ingestion and duration of ingestion per event did not differ between treatments.

CONCLUSION

The results show that MON 88702 has an antifeedant effect on F. fusca, which provides insight into behavioral responses driving MON 88702 aversion and anti-oviposition documented in previous studies. © 2020 Society of Chemical Industry.

Sublethal Endpoints in Non-target Organism Testing for Insect-Active GE Crops

Historically, genetically engineered (GE) plants that have incorporated genes conferring insect protection have primarily used Cry proteins derived from Bacillus thuringiensis (Bt) to achieve their insecticidal phenotype. As a result, regulators have developed a level of familiarity and confidence in reviewing plants incorporating these insecticidal proteins. However, new technologies have been developed that produce GE plants that incorporate pest protection by triggering an RNA interference (RNAi) response or proteins other than Bt Cry proteins. These technologies have new modes of action. Although the overall assessment paradigm for GE plants is robust, there are ongoing discussions about the appropriate tests and measurement endpoints needed to inform non-target arthropod assessment for technologies that have a different mode of action than the Bt Cry proteins. As a result, increasing attention is being paid to the use of sublethal endpoints and their value for environmental risk assessment (ERA). This review focuses on the current status and history of sublethal endpoint use in insect-active GE crops, and evaluates the future use of sublethal endpoints for new and emerging technologies. It builds upon presentations made at the Workshop on Sublethal Endpoints for Non-target Organism Testing for Non-Bt GE Crops (Washington DC, USA, 4-5 March 2019), and the discussions of government, academic and industry scientists convened for the purpose of reviewing the progress and status of sublethal endpoint testing in non-target organisms.

Novel mechanism of thrips suppression by Cry51Aa2.834_16 Bt toxin expressed in cotton

BACKGROUND

Genetically engineered (GE) crops that express insecticidal traits have improved the sustainability of insect pest management worldwide, but many important pest orders are not controlled by commercially available toxins. Development of the first transgenic thysanopteran- and hemipteran-active Bacillus thuringiensis (Bt) Cry51Aa2.834_16 toxin expressed in MON 88702 cotton will significantly expand the diversity of pests controlled in the crop. Here, we examined MON 88702 cotton activity against two thrips species within the same genera, Frankliniella fusca and Frankliniella occidentalis. We used a multi-component cotton tissue assay approach to understand effects on adult longevity, fecundity, and larval development.

RESULTS

We found that in no-choice assays, cotton plants expressing MON 88702 suppress oviposition, when compared to a non-Bt cotton. MON 88702 did not kill a large proportion of F. fusca larvae or adults but killed most F. occidentalis larvae. Time series experiments with F. occidentalis larvae documented significant developmental lags for MON 88702 exposed individuals. We also found that female thrips preferred to oviposit on non-Bt cotton when provided a choice.

CONCLUSION

Together these results describe the activity of MON 88702 against thrips. They document clear differences in toxin performance between different thrips species and throughout the insects' life cycle. Most importantly, we show that MON 88702 was associated with reduced oviposition via behavioral avoidance to the toxin. This is a novel mechanism of action for pest control for a Bt crop plant. Together, these results provide a basis to describe the mechanism of population control for MON 88702 cotton. © 2019 Society of Chemical Industry.

Genome-wide markers reveal temporal instability of local population genetic structure in the cotton fleahopper, Pseudatomoscelis seriatus (Hemiptera: Miridae)

BACKGROUND

The cotton fleahopper, Pseudatomoscelis seriatus (Reuter) (Hemiptera: Miridae), is a pest of upland cotton, Gossypium hirsutum L. (Malvales: Malvaceae), that attacks pre-floral buds (squares), leading to abscission and yield losses. In the Brazos Valley cotton production area of Texas (USA), P. seriatus exhibits a seasonal pattern of host use. In spring, eggs hatch from stems of the overwintering host, woolly croton, Croton capitatus Michx. (Malpighiales: Euphorbiaceae). During the growing season, individuals feed on a variety of host plants, including cotton. Adults return to woolly croton at season end to oviposit. We investigated if genetic differentiation exists between populations infesting cotton and those infesting alternative hosts, and whether woolly croton serves as a year-end site of admixture that could be suitable as a natural refuge for the purposes of insect resistance management. We combined high-throughput DNA sequencing with fine-scale spatio-temporal sampling to test (i) whether a population genomic approach would recover patterns of genetic variation consistent with earlier studies and (ii) if local genetic population structure was robust to seasonal changes in local habitat over time.

RESULTS

We found high gene flow among populations of P. seriatus collected from different host plants in the Brazos Valley. We also identified temporal instability of the local population genetic structure, including the near complete loss of a genotypic group that had been previously abundant.

CONCLUSION

We support the status of woolly croton as a natural refuge that promotes year-end gene flow between genotypes infesting cotton and those infesting alternative hosts. © 2019 Society of Chemical Industry.

Genome Editing, Gene Drives, and Synthetic Biology: Will They Contribute to Disease-Resistant Crops, and Who Will Benefit?

Genetically engineered crops have been grown for more than 20 years, resulting in widespread albeit variable benefits for farmers and consumers. We review current, likely, and potential genetic engineering (GE) applications for the development of disease-resistant crop cultivars. Gene editing, gene drives, and synthetic biology offer novel opportunities to control viral, bacterial, and fungal pathogens, parasitic weeds, and insect vectors of plant pathogens. We conclude that there will be no shortage of GE applications totackle disease resistance and other farmer and consumer priorities for agricultural crops. Beyond reviewing scientific prospects for genetically engineered crops, we address the social institutional forces that are commonly overlooked by biological scientists. Intellectual property regimes, technology regulatory frameworks, the balance of funding between public- and private-sector research, and advocacy by concerned civil society groups interact to define who uses which GE technologies, on which crops, and for the benefit of whom. Ensuring equitable access to the benefits of genetically engineered crops requires affirmative policies, targeted investments, and excellent science.

Behavioral Responses of Thrips (Thysanoptera: Thripidae) and Tarnished Plant Bug (Hemiptera: Miridae) to a New Bt Toxin, Cry51Aa2.834_16 in Cotton

Thrips (Thysanoptera: Thripidae) and tarnished plant bug, Lygus lineolaris (Hemiptera: Miridae), are among the most important insect pests of cotton, Gosssypium hirsutum, in the mid-southern United States. These pests are currently managed primarily by insecticides; however, a new Bt toxin, Cry51Aa2.834_16 is under evaluation for control of thrips and tarnished plant bug. Experiments were conducted to evaluate the behavioral response of thrips and tarnished plant bug to Bt Cry51Aa2.834_16. Adult thrips avoided Bt Cry51Aa2.834_16 cotton in field choice tests and in separate field tests of Bt and non-Bt cotton not treated with insecticides. In a greenhouse choice test, approximately twice as many adult thrips and eggs were found on non-Bt compared with Bt Cry51Aa2.834_16 cotton. Similarly, in a field test of nontreated Bt Cry51Aa2.834_16 and non-Bt cotton, 68% of adult thrips collected were found on non-Bt cotton. In cotton that was not sprayed with insecticides, Bt Cry51Aa2.834_16 did not affect the distribution of tarnished plant bug within the canopy, although more square and flower injury was caused by tarnished plant bug in non-Bt cotton. Adult tarnished plant bug exhibited a nonpreference for diet containing lyophilized Bt Cry51Aa2.834_16 leaves and for excised Bt Cry51Aa2.834_16 squares in choice tests with non-Bt squares. The behavioral responses of these pests when exposed to this new Bt toxin will play a key role in the efficacy and potential resistance management strategies if this new technology is incorporated in an overall cotton insect pest management system.

Quantitative Differences in Feeding Behavior of Lygus lineolaris (Hemiptera: Miridae) on Transgenic and Nontransgenic Cotton

Lygus lineolaris (Palisot de Beauvois) is one of the most important pests on cotton in the United States. Previous research showed that transgenic cotton plants expressing the Bacillus thurigiensis (Bt) crystalline protein Cry51Aa2.834_16 (designated MON 88702) have insecticidal effects on nymphal L. lineolaris. The present study is the first to examine effects of a Bt-expressing cotton on feeding by a heteropteran like L. lineolaris. We compared stylet probing behaviors of third-instar nymphs on pin-head squares (i.e., buds <3 mm wide) of MON 88702 cotton versus nontransgenic (control) DP393 plants using AC-DC electropenetrography. Waveforms were quantified based on appearances previously characterized and correlated with adult L. lineolaris feeding behaviors; nymphal and adult waveforms had the same appearance. Generalized third-instar feeding included maceration of tissues during cell rupturing (waveform CR), tasting/testing during a waveform called transition (T), and ingestion (I); all were similar between MON 88702 and DP393 plants. However, the number of events and duration of each waveform were different between treatments. Relative to nymphs on DP393, those on MON 88702 spent more time overall in stylet probing, due to increased number of maceration events per probe and longer durations of tasting/testing, per waveform event, per probe, and per insect; yet, ingestion events were shorter and more frequent. These findings support that MON 88702 cotton plants were less palatable and/or preorally digestible to L. lineolaris nymphs than DP393, suggesting antixenosis for MON 88702. Transgenic cotton antixenosis could positively affect cotton pest management by reducing feeding of L. lineolaris nymphs and protecting crop yield.

Effects of Planting Date on Thrips (Thysanoptera: Thripidae) in Cotton

At-plant applications of insecticides are the most common method to manage thrips in upland cotton, Gossypium hirstutum L. Because the primary pest species, tobacco thrips, Frankliniella fusca (Hinds), has developed resistance to commonly used neonicotinoid insecticides used in producing cotton, alternative control options are needed for sustainable thrips management programs. A 3-year study (2015-2017) showed that densities of thrips, feeding injury from thrips, cotton growth, and yield varied among 10 planting dates. Densities of thrips were lowest in seedling cotton planted after mid-May in all years. Thrips injury ratings in all years were highest in cotton planted in April, lowest in cotton planted in June, and below intermediate injury (intermediate corresponded to a 3 on the 0-5 scale) levels in cotton planted after mid-May. Cotton planted during May, rather than in April or June, had the highest yield potential, regardless of variety. Results of the study indicated that altering planting date could potentially be useful in mitigating injury and losses from thrips in upland cotton.

First transgenic trait for control of plant bugs and thrips in cotton

BACKGROUND

Plant bugs (Lygus spp.) and thrips (Thrips spp.) are two of the most economically important insect pest groups impacting cotton production in the USA today, but are not controlled by current transgenic cotton varieties. Thus, seed or foliar-applied chemical insecticides are typically required to protect cotton from these pest groups. Currently, these pests are resistant to several insecticides, resulting in fewer options for economically viable management. Previous publications documented the efficacy of transgenic cotton event MON 88702 against plant bugs and thrips in limited laboratory and field studies. Here, we report results from multi-location and multi-year field studies demonstrating efficacy provided by MON 88702 against various levels of these pests.

RESULTS

MON 88702 provided a significant reduction in numbers of Lygus nymphs and subsequent yield advantage. MON 88702 also had fewer thrips and minimal injury. The level of control demonstrated by this transgenic trait was significantly better compared with its non-transgenic near-isoline, DP393, receiving insecticides at current commercial rates.

CONCLUSION

The level of efficacy demonstrated here suggests that MON 88702, when incorporated into existing IPM programs, could become a valuable additional tool for management of Lygus and thrips in cotton agroecosystems experiencing challenges of resistance to existing chemical control strategies. © 2018 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Field Study Investigating Cry51Aa2.834_16 in Cotton for Control of Thrips (Thysanoptera: Thripidae) and Tarnished Plant Bugs (Hemiptera: Miridae)

Field experiments were conducted in 2016 and 2017 in Tennessee to evaluate the effects of a novel Bacillus thuringiensis (Bt)-transgenic toxin, Bt Cry51Aa2.834_16, on thrips (Thysanoptera: Thripidae) and tarnished plant bug, Lygus lineolaris (Palisot De Beauvois) (Hemiptera: Miridae), in cotton. Protection from thrips injury with the Bt trait was as good or better than an insecticide-based approach. The use of the Bt trait resulted in reduced numbers of immature tarnished plant bug, particularly large nymphs, and partial protection from plant bug injury. Cotton that expressed Bt Cry51Aa2.834_16 had greater yields than the non-Bt isoline when insecticides were not used. Although Bt Cry51Aa2.834_16 reduced the need for insecticide applications, foliar-applied insecticide applications were needed to provide adequate plant protection from tarnished plant bug. The currently recommended treatment thresholds for tarnished plant bug performed similarly well for Bt Cry51Aa2.834_16 and non-Bt isolines. Insecticide applications for tarnished plant bug increased fiber quality, while Bt Cry51Aa2.834_16 had minor effects. The Bt-transgenic toxin Cry51Aa2.834_16 is expected to reduce the need for insecticide applications targeting thrips and tarnished plant bug and could be a valuable addition to an overall insect management program in cotton.

Temporal efficacy of neonicotinoid seed treatments against Frankliniella fusca on cotton

BACKGROUND

Reports of neonicotinoid seed treatment (NST) failure against Frankliniella fusca in the mid-south and southeastern USA led to the discovery of widespread resistance in these insect populations. Previous studies of NSTs in other crops have shown the concentration of the insecticide to change over time, which could reduce its efficacy. To understand this temporal effect in cotton with F. fusca, our study examined how plant age alters the effects of NSTs (imidacloprid, imidacloprid + thiodicarb and thiamethoxam) by examining larval establishment at multiple seedling ages during the period of cotton seedling susceptibility to this insect. Additionally, we used F. fusca populations with differing neonicotinoid sensitivity levels to understand how resistance impacts this changing efficacy.

RESULTS

Greenhouse studies showed that larval numbers were significantly greater on older NST-grown cotton seedlings. The population with elevated neonicotinoid resistance had a more rapid increase in larval number on thiamethoxam-treated plants over time.

CONCLUSION

NSTs reduce the number of F. fusca larvae on younger seedlings, but this effect declines as seedlings age. The duration of efficacy is shorter against neonicotinoid-resistant populations. Neonicotinoid resistance in cotton-infesting F. fusca populations may be accelerated by this time-dependent decrease in efficacy, which likely encourages low-dose exposure to these insecticides. © 2018 Society of Chemical Industry.

Within-Plant Distribution and Dynamics of Thrips Species (Thysanoptera: Thripidae) in Cotton

A 2-yr study in cotton (Gossypium hirsutum L.) was conducted to determine the abundance and species composition of thrips (Thysanoptera: Thripidae) on different plant parts throughout the season in Alabama, Georgia, North Carolina, South Carolina, and Virginia. Plant parts sampled included seedlings, terminals with two expanded leaves, leaves from the upper, middle, and lower sections of the canopy, white flowers, and medium-sized bolls. Adult thrips were significantly more abundant on seedlings and flowers in 2014, and on flowers followed by seedlings and leaves from the middle canopy in 2015. Immature thrips were significantly more abundant on seedlings, followed by flowers in 2014, and on seedlings followed by leaves from the lower canopy and flowers in 2015. Across locations and plant parts, thrips consisted of Frankliniella tritici (Fitch) (46.8%), Frankliniella fusca Hinds (23.5%), Frankliniella occidentalis (Pergande) (17.1%), Neohydatothrips variabilis (Beach) (7.4%), Thrips tabaci (Lindeman) (1.8%), and other species (3.4%). Frankliniella fusca represented 86.7% of all thrips on seedlings, while F. tritici was more abundant on terminals (51.6%), squares (57.5%), and flowers (75.1%). Across all leaf positions, F. fusca was the most abundant species (28.8%), followed by F. tritici (19.2%), N. variabilis (18.8%), F. occidentalis (12.9%), and T. tabaci (5.2%), as well as other species (15.0%). As neonicotinoid insecticides remain a primary tool to manage seedling infestations of F. fusca, our data indicate that mid- to late-season applications of neonicotinoid insecticides targeting other insect pests will intensify selection pressure for resistance on F. fusca, the primary pest of seedling cotton.