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1.
BMC Genomics ; 22(1): 639, 2021 Sep 04.
Artigo em Inglês | MEDLINE | ID: mdl-34479486

RESUMO

BACKGROUND: Resistance of pest insect species to insecticides, including B. thuringiensis (Bt) pesticidal proteins expressed by transgenic plants, is a threat to global food security. Despite the western corn rootworm, Diabrotica virgifera virgifera, being a major pest of maize and having populations showing increasing levels of resistance to hybrids expressing Bt pesticidal proteins, the cell mechanisms leading to mortality are not fully understood. RESULTS: Twenty unique RNA-seq libraries from the Bt susceptible D. v. virgifera inbred line Ped12, representing all growth stages and a range of different adult and larval exposures, were assembled into a reference transcriptome. Ten-day exposures of Ped12 larvae to transgenic Bt Cry3Bb1 and Gpp34/Tpp35Ab1 maize roots showed significant differential expression of 1055 and 1374 transcripts, respectively, compared to cohorts on non-Bt maize. Among these, 696 were differentially expressed in both Cry3Bb1 and Gpp34/Tpp35Ab1 maize exposures. Differentially-expressed transcripts encoded protein domains putatively involved in detoxification, metabolism, binding, and transport, were, in part, shared among transcripts that changed significantly following exposures to the entomopathogens Heterorhabditis bacteriophora and Metarhizium anisopliae. Differentially expressed transcripts in common between Bt and entomopathogen treatments encode proteins in general stress response pathways, including putative Bt binding receptors from the ATP binding cassette transporter superfamily. Putative caspases, pro- and anti-apoptotic factors, as well as endoplasmic reticulum (ER) stress-response factors were identified among transcripts uniquely up-regulated following exposure to either Bt protein. CONCLUSIONS: Our study suggests that the up-regulation of genes involved in ER stress management and apoptotic progression may be important in determining cell fate following exposure of susceptible D. v. virgifera larvae to Bt maize roots. This study provides novel insights into insect response to Bt intoxication, and a possible framework for future investigations of resistance mechanisms.


Assuntos
Bacillus thuringiensis , Besouros , Praguicidas , Animais , Bacillus thuringiensis/genética , Sobrevivência Celular , Besouros/genética , Endotoxinas/toxicidade , Resistência a Inseticidas , Larva/genética , Controle Biológico de Vetores , Plantas Geneticamente Modificadas/genética , Regulação para Cima , Zea mays/genética
2.
J Econ Entomol ; 114(5): 2096-2107, 2021 Oct 13.
Artigo em Inglês | MEDLINE | ID: mdl-34323975

RESUMO

The western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), is a significant pest of field corn, Zea mays L. (Poales: Poaceae), across the United States Corn Belt. Widespread adoption and continuous use of corn hybrids expressing the Cry3Bb1 protein to manage the western corn rootworm has resulted in greater than expected injury to Cry3Bb1-expressing hybrids in multiple areas of Nebraska. Single-plant bioassays were conducted on larval western corn rootworm populations to determine the level of resistance present in various Nebraska counties. The results confirmed a mosaic of susceptibility to Cry3Bb1 across Nebraska. Larval development metrics, including head capsule width and fresh weight, were measured to quantify the relationship between the level of resistance to Cry3Bb1 and larval developmental rate. Regression and correlation analyses indicate a significant positive relationship between Cry3Bb1 corrected survival and both larval development metrics. Results indicate that as the level of resistance to Cry3Bb1 within field populations increases, mean head capsule width and larval fresh weight also increase. This increases our understanding of western corn rootworm population dynamics and age structure variability present in the transgenic landscape that is part of the complex interaction of factors that drives resistance evolution. This collective variability and complexity within the landscape reinforces the importance of making corn rootworm management decisions based on information collected at the local level.

3.
Pest Manag Sci ; 77(2): 860-868, 2021 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-32946636

RESUMO

BACKGROUND: Western corn rootworm (WCR) pyrethroid resistance has been confirmed in the western US Corn Belt. Toxicological and biochemical studies indicated that multiple mechanisms of resistance might be involved in the resistance trait, such as enhanced metabolism and/or kdr target-site mutation(s) in the voltage-gated sodium channels. To characterize the mechanisms of WCR pyrethroid resistance at the molecular level, pairwise comparisons were made between RNA-Seq data collected from pyrethroid-resistant and -susceptible WCR populations. Gene expression levels and sodium channel sequences were evaluated. RESULTS: Seven transcripts exhibited significantly different expression (q ≤ 0.05) when comparing field-collected pyrethroid-resistant (R-Field) and -susceptible (S-Field) WCR populations. Three of the differentially expressed transcripts were P450s overexpressed in R-Field (9.2-26.2-fold). A higher number (99) of differentially expressed transcripts was found when comparing laboratory-derived pyrethroid-resistant (R-Lab) and -susceptible (S-Lab) WCR populations. Eight of the significant transcripts were P450s overexpressed in R-Lab (2.7-39.8-fold). This study did not detect kdr mutations in pyrethroid-resistant WCR populations. Other differentially expressed transcripts that may play a role in WCR pyrethroid resistance are discussed. CONCLUSION: This study revealed that P450-mediated metabolism is likely to be a major mechanism of WCR pyrethroid resistance, which could affect the efficacy of other insecticides sharing similar metabolic pathways. Additionally, results suggested that although laboratory selection of a pyrethroid-resistant WCR population may help to characterize resistance mechanisms, a field-selected population provided rare and perhaps major variants corresponding to the resistance trait.


Assuntos
Besouros , Inseticidas , Piretrinas , Animais , Besouros/genética , Resistência a Inseticidas/genética , Inseticidas/farmacologia , Piretrinas/farmacologia , Zea mays/genética
4.
Pestic Biochem Physiol ; 164: 165-172, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-32284123

RESUMO

Western corn rootworm (WCR) pyrethroid resistance has been previously reported in the United States (US) western Corn Belt, and cross-resistance and synergism studies suggested that both target site insensitivity and enhanced metabolism may be conferring WCR resistance to pyrethroids. The present study aimed to investigate the potential mechanisms of WCR pyrethroid resistance and to estimate the heritability of the resistance trait. Biochemical assays using model substrates and spectrophotometry revealed 2-4-fold higher activity of P450s and esterases in pyrethroid-resistant WCR populations, whereas the biological activity of glutathione S-transferase was similar between populations tested. No mutation in the voltage-gated sodium channel was detected in pyrethroid-resistant WCR individuals by sequencing PCR products containing the para-homologous L1014, T929, and M918 amino acid positions that are commonly associated with target site mutations in other pyrethroid-resistant insects. A pilot estimation of pyrethroid resistance heritability obtained during laboratory selection of a WCR population suggested a major genetic component of the resistance trait and predicted a 10-fold increase in WCR bifenthrin resistance within ~7 generations of insecticide lethal exposure. Results support earlier indirect evidence that enhanced metabolism may be contributing to WCR resistance to pyrethroids and illustrates the potential of WCR pyrethroid resistance evolution.


Assuntos
Besouros , Inseticidas , Piretrinas , Animais , Resistência a Inseticidas , Larva , Zea mays
5.
Pest Manag Sci ; 76(2): 827-833, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-31414728

RESUMO

BACKGROUND: Field-evolved pyrethroid resistance has been confirmed in western corn rootworm (WCR) populations collected from the United States (US) western Corn Belt. Resistance levels of WCR adults estimated in lab bioassays were confirmed to significantly reduce the efficacy of foliar-applied bifenthrin. The objective of the present study was to investigate the impact of WCR pyrethroid resistance levels on the performance of common soil-applied insecticide formulations (23.4% tefluthrin, 17.15% bifenthrin, and 0.1% cyfluthrin + 2.0% tebupirimphos). Field trials were conducted in 2016 and 2017 in three Nebraska, US, counties (Saunders, Clay, and Keith) where distinct levels of WCR susceptibility to pyrethroids (susceptible, moderately resistant, and highly resistant) had been previously reported in adult and larval bioassays. RESULTS: All soil insecticide treatments effectively protected maize roots from a pyrethroid-susceptible WCR population at Saunders. In contrast, the efficacy of bifenthrin and tefluthrin soil insecticides was significantly reduced at Clay and Keith, where pyrethroid-resistant WCR populations were reported. At Keith, where an additional failure of the cyfluthrin + tebupirimphos soil insecticide was observed, WCR laboratory dose-response bioassays showed a consistent ∼5-fold resistance level to the active ingredients bifenthrin, tefluthrin, and cyfluthrin. CONCLUSION: The efficacy of common soil insecticides used in the US for WCR management was significantly reduced in populations exhibiting relatively low levels of WCR pyrethroid resistance. Using a multitactical approach to manage WCR within an integrated pest management framework may mitigate resistance evolution and prolong the usefulness of WCR insecticides within the system. © 2019 Society of Chemical Industry.


Assuntos
Besouros , Animais , Resistência a Inseticidas , Inseticidas , Larva , Nebraska , Piretrinas , Solo , Zea mays
6.
J Econ Entomol ; 112(6): 2737-2743, 2019 12 09.
Artigo em Inglês | MEDLINE | ID: mdl-31550358

RESUMO

The northern corn rootworm, Diabrotica barberi Smith & Lawrence (Coleoptera: Chrysomelidae), is one of the most important insect pests in the U.S. Corn Belt. Efforts to obtain eggs from wild northern corn rootworm populations using techniques developed for other rootworm species have been unsuccessful due to lack of oviposition. In 2016, we evaluated four oviposition media in choice tests within each of three female densities in 30.5 × 30.5 × 30.5 cm BugDorm cages. The number of eggs laid per female was significantly affected by female density and the interaction of female density × oviposition media, but oviposition was relatively poor in all oviposition media (1.2 eggs per female when averaging the three female densities and all oviposition media). Single females were also evaluated in nonchoice assays in 6 cm × 6 cm × 8 cm clear plastic boxes and averaged up to 108 eggs per female depending on the oviposition media. In 2017, the cumulative number of eggs laid per female in boxes with one female was not significantly different from the number of eggs laid per female in boxes with 3 females. In 2018, the cumulative number of eggs laid per female was not significantly different between female densities of 1, 3, 5, or 10 females per box. Total egg production per box therefore increased as female density increased. More than 27,000 wild northern corn rootworm eggs were collected from just 190 females when collected relatively early in the field season. We now have an efficient and robust system for obtaining eggs from wild northern corn rootworm females.


Assuntos
Besouros , Animais , Feminino , Oviposição , Plantas Geneticamente Modificadas , Zea mays
7.
Sci Rep ; 9(1): 6713, 2019 04 30.
Artigo em Inglês | MEDLINE | ID: mdl-31040345

RESUMO

The western corn rootworm (Diabrotica virgifera virgifera LeConte) (WCR) is a major insect pest of corn (Zea mays L.) in the United States (US) and is highly adaptable to multiple management tactics. A low level of WCR field-evolved resistance to pyrethroid insecticides has been confirmed in the US western Corn Belt by laboratory dose-response bioassays. Further investigation has identified detoxification enzymes as a potential part of the WCR resistance mechanism, which could affect the performance of insecticides that are structurally related to pyrethroids, such as organophosphates. Thus, the responses of pyrethroid-resistant and -susceptible WCR populations to the commonly used pyrethroid bifenthrin and organophosphate dimethoate were compared in active ingredient bioassays. Results revealed a relatively low level of WCR resistance to both active ingredients. Therefore, a simulated aerial application bioassay technique was developed to evaluate how the estimated resistance levels would affect performance of registered rates of formulated products. The simulated aerial application technique confirmed pyrethroid resistance to formulated rates of bifenthrin whereas formulated dimethoate provided optimal control. Results suggest that the relationship between levels of resistance observed in dose-response bioassays and actual efficacy of formulated product needs to be further explored to understand the practical implications of resistance.


Assuntos
Besouros/efeitos dos fármacos , Resistência a Inseticidas , Inseticidas/administração & dosagem , Controle de Pragas/métodos , Piretrinas/farmacologia , Aeronaves , Animais , Simulação por Computador , Dimetoato/administração & dosagem , Dimetoato/farmacologia , Relação Dose-Resposta a Droga , Inseticidas/farmacologia , Nebraska , Oxazinas/farmacologia , Piretrinas/administração & dosagem , Zea mays
8.
J Econ Entomol ; 112(3): 1354-1364, 2019 05 22.
Artigo em Inglês | MEDLINE | ID: mdl-30753514

RESUMO

The southern corn rootworm, Diabrotica undecimpunctata howardi Barber (Coleoptera: Chrysomelidae), was exposed over multiple generations to vacuolar (v)ATPase-A double-stranded (ds)RNA, first as adults and later, as neonate larvae. During adult selection, high mortality and lower fecundity were observed in the RNAi-selected cages after beetles were exposed to sublethal dsRNA concentrations that varied between LC40 and LC75. During larval selection, a delay in adult emergence and effects on population growth parameters were observed after neonates were exposed to sublethal dsRNA concentrations that varied between LC50 and LC70. Some of the parameters measured for adult emergence such as time to reach maximum linear adult emergence, time elapsed before attaining linear emergence, termination point of the linear emergence, and total days of linear emergence increase, were significantly different between RNAi-selected and control colonies for at least one generation. Significant differences were also observed in population growth parameters such as growth rate, net reproductive rate, doubling time, and generation time. After seven generations of selection, there was no indication that resistance evolved. The sublethal effects caused by exposures of southern corn rootworm to dsRNAs can affect important life history traits and fitness especially through delays in adult emergence and reduction in population growth. Although changes in susceptibility did not occur, the observation of sublethal effects suggests important responses to potential selection pressure. Assuming resistance involves a recessive trait, random mating between susceptible and resistant individuals is an important factor that allows sustainable use of transgenic plants, and delays in adult emergence observed in our studies could potentially compromise this assumption.


Assuntos
Besouros , ATPases Vacuolares Próton-Translocadoras , Animais , Endotoxinas , Larva , Plantas Geneticamente Modificadas , Crescimento Demográfico , RNA de Cadeia Dupla , Zea mays
9.
PLoS One ; 13(11): e0208266, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-30496268

RESUMO

Repeated use of field corn (Zea mays L.) hybrids expressing the Cry3Bb1 and mCry3A traits in Nebraska has selected for field-evolved resistance in some western corn rootworm (WCR; Diabrotica virgifera virgifera LeConte) populations. Therefore, this study was conducted to characterize spatial variation in local WCR susceptibility to Cry3Bb1 and mCry3A traits in Keith and Buffalo counties, Nebraska, and determine the relationship between past management practices and current WCR susceptibility. Adult WCR populations were collected from sampling grids during 2015 and 2016 and single-plant larval bioassays conducted with F1 progeny documented significant variation in WCR susceptibility to Cry3Bb1 and mCry3A on different spatial scales in both sampling grids. At the local level, results revealed that neighboring cornfields may support WCR populations with very different susceptibility levels, indicating that gene flow of resistant alleles from high trait survival sites is not inundating large areas. A field history index, comprised of additive and weighted variables including past WCR management tactics and agronomic practices, was developed to quantify relative selection pressure in individual fields. The field history index-Cry3 trait survivorship relationship from year 1 data was highly predictive of year 2 Cry3 trait survivorship when year 2 field history indices were inserted into the year 1 base model. Sensitivity analyses indicated years of trait use and associated selection pressure at the local level were the key drivers of WCR susceptibility to Cry3 traits in this system. Retrospective case histories from this study will inform development of optimal resistance management programs and increase understanding of plant-insect interactions that may occur when transgenic corn is deployed in the landscape. Results from this study also support current recommendations to slow or mitigate the evolution of resistance by using a multi-tactic approach to manage WCR densities in individual fields within an integrated pest management framework.


Assuntos
Proteínas de Bactérias/genética , Besouros/fisiologia , Endotoxinas/genética , Proteínas Hemolisinas/genética , Doenças das Plantas/parasitologia , Plantas Geneticamente Modificadas/genética , Zea mays/genética , Animais , Toxinas de Bacillus thuringiensis , Suscetibilidade a Doenças , Nebraska , Controle Biológico de Vetores , Plantas Geneticamente Modificadas/parasitologia , Zea mays/parasitologia
10.
J Econ Entomol ; 111(1): 209-217, 2018 02 09.
Artigo em Inglês | MEDLINE | ID: mdl-29267968

RESUMO

Colaspis crinicornis Schaeffer (Coleoptera: Chrysomelidae) primarily occurs in the Great Plains, United States. Although C. crinicornis has historically been considered a non-pest and is rarely found in agricultural systems, population densities of this species have been increasing in corn, Zea mays L., and soybean, Glycine max (L.) Merrill, over the last decade in southeastern Nebraska. As part of a comprehensive project to understand the life history and pest potential of C. crinicornis, a field study was conducted to: understand adult seasonality of C. crinicornis using emergence cages and whole-plant-count sampling in cornfields and sweep-net sampling in soybean fields; confirm voltinism and the overwintering stage; and evaluate the potential of larvae to cause economic injury to corn roots. Data indicate that C. crinicornis is univoltine in southeastern Nebraska and overwinters as medium-large larvae at least 20 cm deep in the soil. Adults were present from June through August with peak emergence in July. The C. crinicornis lifecycle is similar to related Colaspis species. Root injury to corn was minor at population densities encountered in the field, and therefore, C. crinicornis is unlikely to cause economic loss. C. crinicornis may be an example of an insect species that has exploited open niches in crops that have been created by changes in agricultural and pest management practices. The lifecycle and polyphagous nature of the insect, annual crop rotation, the shift to minimum tillage, and replacement of insecticides with Bacillus thuringiensis Berliner (Bt) traits may have collectively facilitated establishment and increased survival in agroecosystems.


Assuntos
Besouros/fisiologia , Herbivoria , Zea mays , Animais , Besouros/crescimento & desenvolvimento , Larva/crescimento & desenvolvimento , Larva/fisiologia , Traços de História de Vida , Nebraska , Raízes de Plantas/crescimento & desenvolvimento , Dinâmica Populacional , Estações do Ano , Zea mays/crescimento & desenvolvimento
11.
J Econ Entomol ; 110(6): 2545-2553, 2017 12 05.
Artigo em Inglês | MEDLINE | ID: mdl-29045668

RESUMO

RNA interference is a powerful tool against corn rootworm. Adults and neonates of southern corn rootworm, Diabrotica undecimpunctata howardi Barber (Coleoptera: Chrysomelidae), were exposed to the LC50 of vATPase-A and Snf7 double-stranded RNAs (dsRNAs), and the effects on female fecundity, egg viability, male fitness as measured by sperm viability and mating capacity, larval recovery along with dry weight, and instar determination 10 d after exposure to dsRNA, were determined. Significant reductions were observed for a number of parameters in dsRNA-exposed rootworms relative to control treatments. Female fecundity and larval recovery were significantly reduced after exposure to both dsRNAs. In addition, larval dry weight and recovery of 2nd and 3rd instars along with dry weight for 3rd instars were significantly reduced after neonate exposure to vATPase-A dsRNA. Neither dsRNA affected male capacity to mate or sperm viability after exposure to the respective LC50s. After 10 d of feeding on untreated corn roots, neonates that survived exposure for 2 d to the vATPase-A dsRNA LC50 exhibited lower dry weight than the control. There was significant gene knockdown in adult males and females after exposure for 5 d to LC50 of vATPase-A and Snf7 dsRNAs. The parameters are discussed in terms of fitness and possible outcomes after deployment of corn hybrids expressing dsRNAs.


Assuntos
Besouros/fisiologia , Controle de Insetos , Proteínas de Insetos/genética , Interferência de RNA , RNA de Cadeia Dupla/farmacologia , Adenosina Trifosfatases/genética , Adenosina Trifosfatases/metabolismo , Animais , Besouros/crescimento & desenvolvimento , Feminino , Fertilidade , Proteínas de Insetos/metabolismo , Larva/crescimento & desenvolvimento , Larva/fisiologia , Masculino , Óvulo/crescimento & desenvolvimento , Óvulo/fisiologia , Comportamento Sexual Animal , Espermatozoides/fisiologia
12.
PLoS One ; 12(6): e0179311, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-28628635

RESUMO

Recently, resistance to the pyrethroid bifenthrin was detected and confirmed in field populations of western corn rootworm, Diabrotica virgifera virgifera LeConte from southwestern areas of Nebraska and Kansas. As a first step to understand potential mechanisms of resistance, the objectives of this study were i) to assess adult mortality at diagnostic concentration-LC99 to the pyrethroids bifenthrin and tefluthrin as well as DDT, ii) estimate adult and larval susceptibility to the same compounds as well as the organophosphate methyl-parathion, and iii) perform synergism experiments with piperonyl butoxide (PBO) (P450 inhibitor) and S,S,S-tributyl-phosphorotrithioate (DEF) (esterase inhibitor) in field populations. Most of the adult field populations exhibiting some level of bifenthrin resistance exhibited significantly lower mortality to both pyrethroids and DDT than susceptible control populations at the estimated LC99 of susceptible populations. Results of adult dose-mortality bioassays also revealed elevated LC50 values for bifenthrin resistant populations compared to the susceptible control population with resistance ratios ranging from 2.5 to 5.5-fold for bifenthrin, 28 to 54.8-fold for tefluthrin, and 16.3 to 33.0 for DDT. These bioassay results collectively suggest some level of cross-resistance between the pyrethroids and DDT. In addition, both PBO and DEF reduced the resistance ratios for resistant populations although there was a higher reduction in susceptibility of adults exposed to PBO versus DEF. Susceptibility in larvae varied among insecticides and did not correlate with adult susceptibility to tefluthrin and DDT, as most resistance ratios were < 5-fold when compared to the susceptible population. These results suggest that both detoxifying enzymes and target site insensitivity might be involved as resistance mechanisms.


Assuntos
Besouros , Resistência a Inseticidas/efeitos dos fármacos , Inseticidas , Piretrinas , Zea mays/parasitologia , Animais , Bioensaio , Besouros/crescimento & desenvolvimento , Ciclopropanos , DDT , Sinergismo Farmacológico , Hidrocarbonetos Fluorados , Larva , Dose Letal Mediana , Compostos Organotiofosforados , Butóxido de Piperonila
13.
Transgenic Res ; 26(3): 419-428, 2017 06.
Artigo em Inglês | MEDLINE | ID: mdl-28326506

RESUMO

Greater than expected injury by western corn rootworm (WCR) (Diabrotica virgifera virgifera LeConte) to Cry3Bb1 expressing maize hybrids (Zea mays L.) has been reported in southwestern Nebraska. Affected areas of some fields are often associated with high pH calcareous soils where maize growth is poor and iron chlorosis is common. As part of a comprehensive study to understand potential causes of unexpected injury, experiments were conducted during 2013 and 2014 to ascertain whether the calcareous soil conditions and associated poor maize growth negatively affect the expression of Cry3Bb1. Quantitative determination of Cry3Bb1 protein expression levels in root tissues was carried out on plants at V5-V6 growth stage using the enzyme-linked immunosorbent assay. Cry3Bb1 and non-Bt near isoline maize hybrids were artificially infested with Cry3Bb1-susceptible WCR eggs to measure survival and efficacy of Cry3Bb1 maize in calcareous and non-calcareous soils. Results showed that there was not a significant difference in expression of Cry3Bb1 protein between plants from calcareous and non-calcareous soils (18.9-21.2 µg/g fresh weight). Western corn rootworm survival was about sevenfold greater from the non-Bt isoline than Cry3Bb1 maize indicating that Cry3Bb1 performed as expected when infested with a Cry3Bb1 susceptible rootworm population. When survival from calcareous and non-calcareous soils was compared, no significant differences were observed in each soil. A significant positive correlation between soil pH and expression of Cry3Bb1 protein in roots was detected from samples collected in 2014 but not in 2013. No such correlation was found between soil pH and survival of WCR. Results suggest that Cry3Bb1 expression levels were sufficient to provide adequate root protection against WCR regardless of soil environment, indicating that lowered Cry3Bb1 expression is not a contributing factor to the greater than expected WCR injury observed in some southwestern Nebraska maize fields.


Assuntos
Besouros/fisiologia , Endotoxinas/genética , Plantas Geneticamente Modificadas/genética , Solo/química , Zea mays/genética , Animais , Regulação da Expressão Gênica de Plantas , Concentração de Íons de Hidrogênio , Nebraska , Raízes de Plantas/genética , Raízes de Plantas/crescimento & desenvolvimento , Plantas Geneticamente Modificadas/crescimento & desenvolvimento , Zea mays/crescimento & desenvolvimento
14.
Pest Manag Sci ; 73(9): 1883-1899, 2017 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-28195683

RESUMO

BACKGROUND: Cases of western corn rootworm (WCR) field-evolved resistance to Cry3Bb1 and other corn rootworm (CRW) control traits have been reported. Pyramid products expressing multiple CRW traits can delay resistance compared to single trait products. We used field studies to assess the pyramid CRW corn products, SmartStax (expressing Cry3Bb1 and Cry34Ab1/Cry35Ab1) and SmartStax PRO (expressing Cry3Bb1, Cry34Ab1/Cry35Ab1 and DvSnf7), at locations with high WCR densities and possible Cry3Bb1 resistance, and to assess the reduction in adult emergence attributable to DvSnf7 and other traits. Insect resistance models were used to assess durability of SmartStax and SmartStax PRO to WCR resistance. RESULTS: SmartStax significantly reduced root injury compared to non-CRW-trait controls at all but one location with measurable WCR pressure, while SmartStax PRO significantly reduced root injury at all locations, despite evidence of Cry3Bb1 resistance at some locations. The advantage of SmartStax PRO over SmartStax in reducing root damage was positively correlated with root damage on non-CRW-trait controls. DvSnf7 was estimated to reduce WCR emergence by approximately 80-95%, which modeling indicated will improve durability of Cry3Bb1 and Cry34Ab1/Cry35Ab1 compared to SmartStax. CONCLUSION: The addition of DvSnf7 in SmartStax PRO can reduce root damage under high WCR densities and prolong Cry3Bb1 and Cry34Ab1/Cry35Ab1 durability. © 2017 Society of Chemical Industry.


Assuntos
Doenças das Plantas , Zea mays/genética , Zea mays/fisiologia , Animais , Bioensaio , Besouros/fisiologia , Plantas Geneticamente Modificadas
15.
J Econ Entomol ; 109(1): 1-12, 2016 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-26362989

RESUMO

Transgenic Bt maize that produces less than a high-dose has been widely adopted and presents considerable insect resistance management (IRM) challenges. Western corn rootworm, Diabrotica virgifera virgifera LeConte, has rapidly evolved resistance to Bt maize in the field, leading to local loss of efficacy for some corn rootworm Bt maize events. Documenting and responding to this resistance has been complicated by a lack of rapid diagnostic bioassays and by regulatory triggers that hinder timely and effective management responses. These failures are of great concern to the scientific and agricultural community. Specific challenges posed by western corn rootworm resistance to Bt maize, and more general concerns around Bt crops that produce less than a high-dose of Bt toxin, have caused uncertainty around current IRM protocols. More than 15 years of experience with IRM has shown that high-dose and refuge-based IRM is not applicable to Bt crops that produce less than a high-dose. Adaptive IRM approaches and pro-active, integrated IRM-pest management strategies are needed and should be in place before release of new technologies that produce less than a high-dose. We suggest changes in IRM strategies to preserve the utility of corn rootworm Bt maize by 1) targeting local resistance management earlier in the sequence of responses to resistance and 2) developing area-wide criteria to address widespread economic losses. We also favor consideration of policies and programs to counteract economic forces that are contributing to rapid resistance evolution.


Assuntos
Proteínas de Bactérias/farmacologia , Besouros/efeitos dos fármacos , Endotoxinas/farmacologia , Proteínas Hemolisinas/farmacologia , Inseticidas/farmacologia , Zea mays/crescimento & desenvolvimento , Animais , Bacillus thuringiensis/genética , Toxinas de Bacillus thuringiensis , Resistência a Inseticidas , Controle Biológico de Vetores , Plantas Geneticamente Modificadas/genética , Plantas Geneticamente Modificadas/crescimento & desenvolvimento , Zea mays/genética
16.
PLoS One ; 10(11): e0142299, 2015.
Artigo em Inglês | MEDLINE | ID: mdl-26566127

RESUMO

Pyrethroid insecticides have been used to control larvae or adults of the western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, a key pest of field corn in the United States. In response to reports of reduced efficacy of pyrethroids in WCR management programs in southwestern areas of Nebraska and Kansas the present research was designed to establish a baseline of susceptibility to the pyrethroid insecticide, bifenthrin, using susceptible laboratory populations and to compare this baseline with susceptibility of field populations. Concentration-response bioassays were performed to estimate the baseline susceptibility. From the baseline data, a diagnostic concentration (LC99) was determined and used to test adults of both laboratory and field populations. Larval susceptibility was also tested using both laboratory and field populations. Significant differences were recorded in adult and larval susceptibility among WCR field and laboratory populations. The highest LC50 for WCR adults was observed in populations from Keith 2 and Chase Counties, NE, with LC50s of 2.2 and 1.38 µg/vial, respectively, and Finney County 1, KS, with 1.43 µg/vial, as compared to a laboratory non-diapause population (0.24 µg/vial). For larvae, significant differences between WCR field and laboratory populations were also recorded. Significant differences in mortalities at the diagnostic bifenthrin concentration (LC99) were observed among WCR adult populations with western Corn Belt populations exhibiting lower susceptibility to bifenthrin, especially in southwestern Nebraska and southwestern Kansas. This study provides evidence that resistance to bifenthrin is evolving in field populations that have been exposed for multiple years to pyrethroid insecticides. Implications to sustainable rootworm management are discussed.


Assuntos
Besouros/efeitos dos fármacos , Inseticidas/toxicidade , Piretrinas/toxicidade , Zea mays/parasitologia , Animais , Besouros/fisiologia , Resistência a Inseticidas , Kansas , Larva/efeitos dos fármacos , Larva/fisiologia , Nebraska
17.
J Econ Entomol ; 108(2): 742-51, 2015 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-26470186

RESUMO

Transgenic plants have been widely adopted by growers to manage the western corn rootworm, Diabrotica virgifera virgifera LeConte, in field corn. Because of reduced efficacy in some Nebraska fields after repeated use of Cry3Bb1-expressing hybrids, single plant bioassays were conducted in 2012 and 2013 to characterize the susceptibility of western corn rootworm populations to the rootworm-active proteins Cry3Bb1, mCry3A, and Cry34/35Ab1. Results demonstrate that there are heritable differences in susceptibility of Nebraska western corn rootworm populations to rootworm-active Bt traits. Proportional survival and corrected survival data coupled with field histories collectively support the conclusion that a level of field resistance to Cry3Bb1 has evolved in some Nebraska populations in response to selection pressure and that cross-resistance exists between Cry3Bb1 and mCry3A. There was no apparent cross-resistance between Cry34/35Ab1 and either Cry3Bb1 or mCry3A. The potential implications of these results on current and future corn rootworm management strategies are discussed.


Assuntos
Proteínas de Bactérias , Besouros , Endotoxinas , Proteínas Hemolisinas , Inseticidas , Animais , Toxinas de Bacillus thuringiensis , Resistência a Inseticidas , Larva , Nebraska , Plantas Geneticamente Modificadas , Zea mays/genética
18.
J Econ Entomol ; 108(3): 1260-70, 2015 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-26470254

RESUMO

Seed blends containing various ratios of transgenic Bt maize (Zea mays L.) expressing the mCry3A+eCry3.1Ab proteins and non-Bt maize (near-isoline maize) were deployed alone and in combination with a soil applied pyrethroid insecticide (Force CS) to evaluate the emergence of the western corn rootworm, Diabrotica virgifera virgifera LeConte, in a total of nine field environments across the Midwestern United States in 2010 and 2011. Northern corn rootworm, Diabrotica barberi Smith & Lawrence emergence was also evaluated in four of these environments. Both western and northern corn rootworm beetle emergence from all Bt treatments was significantly reduced when compared with beetle emergence from near-isoline treatments. Averaged across all environments, western corn rootworm beetle emergence from 95:5, 90:10, and 80:20 seed blend ratios of mCry3A+eCry3.1Ab: near-isoline were 2.6-, 4.2-, and 6.7-fold greater than that from the 100:0 ratio treatment. Northern corn rootworm emergence from the same seed blend treatments resulted in 2.8-, 3.2-, and 4.2-fold more beetles than from the 100:0 treatment. The addition of Force CS (tefluthrin) significantly reduced western corn rootworm beetle emergence for each of the three treatments to which it was applied. Force CS also significantly delayed the number of days to 50% beetle emergence in western corn rootworms. Time to 50% beetle emergence in the 100% mCry3A+eCry3.1Ab treatment with Force CS was delayed 13.7 d when compared with western corn rootworm beetle emergence on near-isoline corn. These data are discussed in terms of rootworm resistance management.


Assuntos
Proteínas de Bactérias/farmacologia , Besouros/efeitos dos fármacos , Endotoxinas/farmacologia , Proteínas Hemolisinas/farmacologia , Controle Biológico de Vetores , Zea mays/crescimento & desenvolvimento , Animais , Bacillus thuringiensis/genética , Toxinas de Bacillus thuringiensis , Besouros/crescimento & desenvolvimento , Besouros/fisiologia , Ciclopropanos/farmacologia , Hidrocarbonetos Fluorados/farmacologia , Inseticidas/farmacologia , Larva/efeitos dos fármacos , Larva/crescimento & desenvolvimento , Larva/fisiologia , Zea mays/genética
19.
Environ Entomol ; 44(6): 1553-61, 2015 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-26314034

RESUMO

A field study was conducted to increase our understanding of diel activity patterns of Colaspis brunnea (F.) and Colaspis crinicornis Schaeffer (Coleoptera: Chrysomelidae) in key crop habitats. Within 24-h periods, C. brunnea was sampled in clover fields (primarily red clover, Trifolium pretense (L.), with some sweet clover, Melilotus officinalis (L.) Pallas, and downy brome, Bromus tectorum (L.)) and soybean, Glycine max (L.) Merrill, fields, using a sweep-net, while whole-plant-count sampling was used to monitor C. crinicornis densities in field corn, Zea mays (L.). Sweep-net captures of C. brunnea were significantly greater at night than during the day, suggesting possible vertical movement within the canopy during a 24-h period. Colaspis crinicornis densities on corn plants were fairly constant throughout a 24-h period, but beetle activity (e.g., walking, mating) was significantly greater at night than during the day. Results suggest that both Colaspis species may be exhibiting similar increases in activity at night that facilitates movement from more protected to more exposed areas within a habitat. It is unclear what mechanisms drive this diel pattern, but vegetation architecture and associated interactions with environmental conditions may play a role. Sweep-netting in clover or soybean fields and use of whole-plant-counts in cornfields were effective sampling methods for Colaspis adults. However, because activity and behaviors of Colaspis beetles were influenced by time of day in this study, use of a consistent sampling time within a diel period would be recommended for future population studies or integrated pest management decision-making.


Assuntos
Comportamento Animal/fisiologia , Ritmo Circadiano , Besouros/fisiologia , Animais , Bromus , Locomoção , Melilotus , Nebraska , Densidade Demográfica , Soja , Especificidade da Espécie , Trifolium , Zea mays
20.
J Insect Sci ; 152015.
Artigo em Inglês | MEDLINE | ID: mdl-26106090

RESUMO

The chrysomelid beetle Colaspis crinicornis Schaeffer (Coleoptera: Chrysomelidae) occurs primarily in the Great Plains region of the United States. Little is known about the biology and ecology of this species, but over the last decade, it has become increasingly common in the corn, Zea mays L., and soybean, Glycine max (L.) Merrill, agroecosystem of southeastern Nebraska. As part of a larger comprehensive project to understand the natural history and pest potential of this species, laboratory experiments were conducted to study the developmental biology, morphological characters of immature stages, and the effect of adult diet on consumption, longevity, and fecundity. Females readily deposited egg clusters in the soil, and percentage egg hatch was high under laboratory conditions. Larvae and pupae were confirmed to be soil-dwelling stages. C. crinicornis has relatively short egg, pupal, and adult stages with the majority of its life cycle spent in the larval stage. Results of choice and no-choice adult feeding experiments indicate that diets of corn or soybean leaves did not significantly affect consumption, longevity, or fecundity of adult C. crinicornis, suggesting that corn and soybean leaves are similarly suitable food sources for adults. The ability to effectively utilize tissues from very different plant families as adult food sources suggests that C. crinicornis is polyphagous in the field.


Assuntos
Besouros/fisiologia , Soja/parasitologia , Zea mays/parasitologia , Animais , Besouros/anatomia & histologia , Besouros/crescimento & desenvolvimento , Feminino , Fertilidade , Larva/anatomia & histologia , Larva/crescimento & desenvolvimento , Longevidade , Masculino , Pupa/anatomia & histologia , Pupa/crescimento & desenvolvimento , Solo
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