RESUMO
Fall armyworm is one of the main pests of conventional and Bacillus thuringiensis (Bt) corn in many countries in the Americas, Africa, Asia and in Australia. We conducted diet-overlay bioassays to determine the status of susceptibility to four Bt proteins (Cry1A.105, Cry2Ab2, Cry1F and Cry1Ac) in three different populations of fall armyworm from Mexico, and one population from Puerto Rico. Bioassays showed that fall armyworms from Puerto Rico were resistant to Cry1F with a resistance ratio 50 (RR50) higher than 10,000 ng/cm2 and to Cry1Ac with a RR50 = 12.2 ng/cm2, displaying the highest median lethal concentration (LC50) values to all Bt proteins tested. The effective concentration 50 (EC50) values further confirmed the loss of susceptibility to Cry1F and Cry1Ac in this population. However, LC50 and EC50 results with Cry1A.105 and Cry2Ab2 revealed that fall armyworm from Puerto Rico remained largely susceptible to these two proteins. The Mexican populations were highly susceptible to all the Bt proteins tested and displayed the lowest LC50 and EC50 values to all Bt proteins. Our results suggest that Cry1F and Cry1Ac resistance is stable in fall armyworm from Puerto Rico. However, this population remains susceptible to Cry1A.105 and Cry2Ab2. Results with Mexican fall armyworms suggest that possible deployment of Bt corn in Mexico will not be immediately challenged by Bt-resistant genes in those regions.
RESUMO
The fall armyworm, Spodoptera frugiperda (J. E. Smith), is one of the main pests of corn in many areas of the American continent. The reliance on pesticides to control fall armyworm has led to the development of insecticide resistance in many regions. We determined the resistance levels of fall armyworm to insecticides of different modes of action in fall armyworm populations from Puerto Rico and several Mexican states with different insecticide use patterns. Mexican populations that expressed higher resistance ratios (RR50) were: Sonora (20-fold to chlorpyriphos), Oaxaca (19-fold to permethrin), and Sinaloa (10-fold to flubendamide). The Puerto Rico population exhibited a remarkable field-evolved resistance to many pesticides. The RR50 to the insecticides tested were: flubendiamide (500-fold), chlorantraniliprole (160-fold), methomyl (223-fold), thiodicarb (124-fold), permethrin (48-fold), chlorpyriphos (47-fold), zeta-cypermethrin (35-fold), deltamethrin (25-fold), triflumuron (20-fold), spinetoram (14-fold). Spinosad (eightfold), emamectin benzoate and abamectin (sevenfold) displayed lower resistance ratio. However, these compounds are still effective to manage fall armyworm resistance in Puerto Rico. Fall armyworm populations from Mexico show different levels of susceptibility, which may reflect the heterogeneity of the pest control patterns in this country. The status of insecticide resistance in the fall armyworm from Puerto Rico indicates a challenging situation for the control of this pest with these insecticides in the close future. Lessons learned from this research might be applied in regions with recent invasions of fall armyworm in Africa.
Assuntos
Inseticidas , África , Animais , Resistência a Inseticidas , México , Porto Rico , SpodopteraRESUMO
For more than 20 years cotton has been the most widely sown genetically modified (GM) crop in Mexico. Its cultivation has fulfilled all requirements and has gone through the different regulatory stages. During the last 20 years, both research-institutions and biotech-companies have generated scientific and technical information regarding GM cotton cultivation in Mexico. In this work, we collected data in order to analyze the environmental and agronomic effects of the use of GM cotton in Mexico. In 1996, the introduction of Bt cotton made it possible to reactivate this crop, which in previous years was greatly reduced due to pest problems, production costs and environmental concerns. Bt cotton is a widely accepted tool for cotton producers and has proven to be efficient for the control of lepidopteran pests. The economic benefits of its use are variable, and depend on factors such as the international cotton-prices and other costs associated with its inputs. So far, the management strategies used to prevent development of insect resistance to GM cotton has been successful, and there are no reports of insect resistance development to Bt cotton in Mexico. In addition, no effects have been observed on non-target organisms. For herbicide tolerant cotton, the prevention of herbicide resistance has also been successful since unlike other countries, the onset of resistance weeds is still slow, apparently due to cultural practices and rotation of different herbicides. Environmental benefits have been achieved with a reduction in chemical insecticide applications and the subsequent decrease in primary pest populations, so that the inclusion of other technologies-e.g., use of non-Bt cotton- can be explored. Nevertheless, control measures need to be implemented during transport of the bolls and fiber to prevent dispersal of volunteer plants and subsequent gene flow to wild relatives distributed outside the GM cotton growing areas. It is still necessary to implement national research programs, so that biotechnology and plant breeding advances can be used in the development of cotton varieties adapted to the Mexican particular environmental conditions and to control insect pests of regional importance.
RESUMO
Insecticidal protein genes from the bacterium Bacillus thuringiensis (Bt) are expressed by transgenic Bt crops (Bt crops) for effective and environmentally safe pest control. The development of resistance to these insecticidal proteins is considered the most serious threat to the sustainability of Bt crops. Resistance in fall armyworm (Spodoptera frugiperda) populations from Puerto Rico to transgenic corn producing the Cry1Fa insecticidal protein resulted, for the first time in the United States, in practical resistance, and Bt corn was withdrawn from the local market. In this study, we used a field-collected Cry1Fa corn-resistant strain (456) of S. frugiperda to identify the mechanism responsible for field-evolved resistance. Binding assays detected reduced Cry1Fa, Cry1Ab, and Cry1Ac but not Cry1Ca toxin binding to midgut brush border membrane vesicles (BBMV) from the larvae of strain 456 compared to that from the larvae of a susceptible (Ben) strain. This binding phenotype is descriptive of the mode 1 type of resistance to Bt toxins. A comparison of the transcript levels for putative Cry1 toxin receptor genes identified a significant downregulation (>90%) of a membrane-bound alkaline phosphatase (ALP), which translated to reduced ALP protein levels and a 75% reduction in ALP activity in BBMV from 456 compared to that of Ben larvae. We cloned and heterologously expressed this ALP from susceptible S. frugiperda larvae and demonstrated that it specifically binds with Cry1Fa toxin. This study provides a thorough mechanistic description of field-evolved resistance to a transgenic Bt crop and supports an association between resistance and reduced Cry1Fa toxin binding and levels of a putative Cry1Fa toxin receptor, ALP, in the midguts of S. frugiperda larvae.
Assuntos
Fosfatase Alcalina/metabolismo , Proteínas de Bactérias/toxicidade , Endotoxinas/toxicidade , Proteínas Hemolisinas/toxicidade , Resistência a Inseticidas , Plantas Geneticamente Modificadas/parasitologia , Spodoptera/efeitos dos fármacos , Zea mays/parasitologia , Animais , Toxinas de Bacillus thuringiensis , Proteínas de Bactérias/genética , Endotoxinas/genética , Trato Gastrointestinal/efeitos dos fármacos , Trato Gastrointestinal/enzimologia , Proteínas Hemolisinas/genética , Ligação Proteica , Porto Rico , Spodoptera/fisiologia , Estados UnidosRESUMO
Fall armyworm (FAW) is a damaging pest of many economic crops. Long-term use of chemical control prompted resistance development to many insecticide classes. Many populations were found to be significantly less susceptible to major Bt toxins expressed in transgenic crops. In this study, a FAW strain collected from Puerto Rico (PR) with 7717-fold Cry1F-resistance was examined to determine if it had also developed multiple/cross resistance to non-Bt insecticides. Dose response assays showed that the PR strain developed 19-fold resistance to acephate. Besides having a slightly smaller larval body weight and length, PR also evolved a deep (2.8%) molecular divergence in mitochondrial oxidase subunit II. Further examination of enzyme activities in the midgut of PR larvae exhibited substantial decreases of alkaline phosphatase (ALP), aminopeptidase (APN), 1-NA- and 2-NA-specific esterase, trypsin, and chymotrypsin activities, and significant increases of PNPA-specific esterase and glutathione S-transferase (GST) activities. When enzyme preparations from the whole larval body were examined, all three esterase, GST, trypsin, and chymotrypsin activities were significantly elevated in the PR strain, while ALP and APN activities were not significantly different from those of susceptible strain. Data indicated that multiple/cross resistances may have developed in the PR strain to both Bt toxins and conventional insecticides. Consistently reduced ALP provided evidence to support an ALP-mediated Bt resistance mechanism. Esterases and GSTs may be associated with acephate resistance through elevated metabolic detoxification. Further studies are needed to clarify whether and how esterases, GSTs, and other enzymes (such as P450s) are involved in cross resistance development to Bt and other insecticide classes.
Assuntos
Proteínas de Bactérias/farmacologia , Endotoxinas/farmacologia , Proteínas Hemolisinas/farmacologia , Resistência a Inseticidas/genética , Inseticidas/farmacologia , Organofosfatos/farmacologia , Spodoptera/efeitos dos fármacos , Fosfatase Alcalina/metabolismo , Animais , Toxinas de Bacillus thuringiensis , Proteínas de Bactérias/genética , Sequência de Bases , Resistência a Múltiplos Medicamentos/genética , Complexo IV da Cadeia de Transporte de Elétrons/genética , Complexo IV da Cadeia de Transporte de Elétrons/metabolismo , Endotoxinas/genética , Enzimas/metabolismo , Glutationa Transferase/metabolismo , Proteínas Hemolisinas/genética , Inativação Metabólica , Proteínas de Insetos/metabolismo , Dados de Sequência Molecular , Compostos Organotiofosforados/farmacologia , Fosforamidas/farmacologia , Porto Rico , Spodoptera/genética , Spodoptera/metabolismoRESUMO
Population genetic studies are essential to the better application of pest management strategies, including the monitoring of the evolution of resistance to insecticides and genetically modified plants. Bacillus thuringiensis Berliner (Bt) crops have been instrumental in controlling tobacco budworm, Heliothis virescens (F.) (Lepidoptera: Noctuidae), a pest that has developed resistance to many common insecticides once used for its management. In our study, microsatellite markers were applied to investigate the genetic structure and patterns of gene flow among Brazilian populations of H. virescens from cotton, Gossypium hirsutum L., and soybean, Glycine max (L.) Merr., fields, aiming to propose means to improve its management in the field. In total, 127 alleles were found across nine microsatellites loci for 205 individuals from 12 localities. Low levels of gene flow and moderate to great genetic structure were found for these populations. Host plant association, crop growing season, and geographic origin were not responsible for the genetic structuring among Brazilian populations of H. virescens. Other factors, such as demographic history and seasonal variability of intrapopulation genetic variation, were suggested to be molding the current pattern of genetic variability distribution.
Assuntos
Fluxo Gênico , Mariposas/genética , Animais , Brasil , Variação Genética , Gossypium , Repetições de Microssatélites , Glycine maxRESUMO
The fungi Nomuraea rileyi and Isaria tenuipes (=Paecilomyces tenuipes) are ecologically obligate, widespread pathogens of lepidopterans. Bioassays were carried out to evaluate the activity of oil-suspended conidia of N. rileyi and I. tenuipes against larvae of Spodoptera frugiperda, Spodoptera exigua, Helicoverpa zea, and Heliothis virescens. The tests consisted of two bioassay sets. In the first set, conidia of N. rileyi and I. tenuipes were suspended in water+Tween 80, and in vegetable (canola, soybean) and mineral (proprietary mixture of alkanes and cyclic paraffins) oils, and tested against S. frugiperda. Both fungi were highly compatible with oils and caused mortalities near 100% in all oil treatments; the lowest LT(50) values were 4.7 days for N. rileyi in mineral oil and 6.0 days for I. tenuipes in soybean oil. The second set included additional fungal strains and oil formulations (mineral, canola, sunflower, olive and peanut oils) tested against larvae of S. exigua, S. frugiperda, H. zea and H. virescens. The highest activity was that of N. rileyi in mineral oil against Spodoptera spp., with LT(50) values of 2.5 days (strain ARSEF 135) and 3 days (strain ARSEF 762) respectively. For two different isolates of I. tenuipes the lowest LT(50) values (5.1-5.6 days respectively) were obtained with mineral oil formulations against Spodoptera spp. and H. zea respectively. Additionally, we tested both fungi against prepupae of all four lepidopteran species. Mortalities with I. tenuipes against S. exigua ranged from 90% to 100% (strains ARSEF 2488 and 4096); N. rileyi caused 95% mortality on S. frugiperda. The activity of formulations depended on host species and oil used; Spodoptera spp. was more susceptible to these fungi than Heliothis and Helicoverpa. The results indicate that a comprehensive evaluation of these entomopathogens in agriculture using oil application technologies is advisable, particularly, in organic and sustainable settings.
Assuntos
Lepidópteros/microbiologia , Controle Biológico de Vetores/métodos , Saccharomycetales/patogenicidade , Animais , Bioensaio , Larva/microbiologiaRESUMO
The adoption of cotton producing insecticidal proteins of Bacillus thuringiensis, commonly referred to as Bt cotton, around the world has proven to be beneficial for growers and the environment. The effectiveness of this important genetically-modified crop can be jeopardized by the development of resistance to Bt cotton by pests it is meant to control, with the possibility that this phenomenon could develop in one country and spread to another by means of insect migration. To preserve the effectiveness of this agricultural biotechnology, regulatory agencies have developed plans to mitigate the development of resistance, and research institutions constantly monitor for shifts in Bt-susceptibility in important pests. If Bt-resistance is detected, this finding needs to be corroborated by an independent laboratory according to current regulatory requirements; a process that presents numerous challenges. We investigated the biological activity of Bt-incorporated diet on Helicoverpa virescens L. after it was stored for several days at different temperatures. Diet stored up to nine days at different temperatures (-14 to 27 degrees C) produced the same biological effect on H. virescens as freshly-prepared diet. Elevating the temperature of Bt stock solution to 76 degrees C as compared to 26 degrees C yielded significantly higher reading of apparent Cry1Ac concentration from MVP II, but not enough to elicit a significant biological response when these stock solutions were incorporated into insect artificial diet. These findings are important particularly when the confirmation of resistance is done at a distant location, such as Mexico, or when diet is shared between laboratories, and must be stored for later use, as in the case of international collaboration.
Assuntos
Bacillus thuringiensis/fisiologia , Proteínas de Bactérias/toxicidade , Toxinas Bacterianas/toxicidade , Endotoxinas/toxicidade , Monitoramento Ambiental/métodos , Proteínas Hemolisinas/toxicidade , Resistência a Inseticidas/efeitos dos fármacos , Inseticidas/toxicidade , Cooperação Internacional , Mariposas/efeitos dos fármacos , Animais , Toxinas de Bacillus thuringiensis , Proteínas de Bactérias/genética , Toxinas Bacterianas/genética , Dieta , Endotoxinas/genética , Gossypium , Proteínas Hemolisinas/genética , Resistência a Inseticidas/genética , Larva/efeitos dos fármacos , Larva/crescimento & desenvolvimento , México , Mariposas/crescimento & desenvolvimento , Controle Biológico de Vetores/métodos , Plantas Geneticamente Modificadas , Temperatura , Fatores de Tempo , Estados UnidosRESUMO
Se reporta un estudio de cohorte analítico para evaluar factores pronósticos en 34 pacientes con timoma y miastenia gravis, a los cuales se les realizó timectomía, entre enero de 1984 y diciembre de 1998, 22 femeninos y 12 masculinos, con un promedio de edad de 49,7 años. De acuerdo con la clasificación clínica de Masaoka, 14 pertenecieron al estadio I, 2 al II, 12 al III y 6 al IV. Histológicamente 17 fueron mixtos, 9 corticales, 5 medulares y 3 carcinomas tímicos bien diferenciados. Según la clasificación de Osserman 5 enfermos se encontraban en el grupo IIa, 23 en el IIb y 6 en el IV. La vía de acceso fue la esternotomía media. Los pacientes con tumores invasivos recibieron radioterapia y poliquimioterapia adyuvante. El índice de remisión de los síntomas miasténicos al año fue de 53,1 (por ciento). Hubo 3 fallecidos en el período posoperatorio y 7 tardíamente. El timoma cortical y, en general, los tumores invasivos fueron los de peores resultados. Los factores que más se relacionaron con el pronóstico por su influencia sobre el intervalo libre de enfermedad y la supervivencia a largo plazo, fueron el estadio clínico del tumor, el tipo hístico y el tipo de miastenia.
This paper presents an analytical cohort study to evaluate prognostic factors in 34 patients with thymona and myasthemia gravis whom thymectomy from January 1984 to December 1998. Twenty two were females and 12 males aged 49,7 years of age as average. According to Masaoka´s clinical classification, 14 patients were at stage I; two at stage II, 12 at stage III and 6 at stage IV. From the histological viewpoint, 17 were mixed thymona, 9 cortical thymonas, 5 medullar thymonas and 3 well-differentiated thymic carcinomas. According to Osswerman´s classification, 5 patients were included in group IIa, 23 in group IIb and 6 in group IV. The access pathway was median sternotomy. Remission index of myasthemic symptoms after a year was 53.1 percent. there were 3 deaths in the postoperative period and 7 died later. Cortical thymona and in general, invasive tumors showed the worst results. The most related factors to prognosis because of their influence over the disease-free interval and the long term survival were the clinical staging of tumor, the hystic type and the type of myasthemia(AU)
Assuntos
Humanos , Masculino , Feminino , Adulto , Timectomia/métodos , Timoma/cirurgia , Neoplasias do Timo/diagnóstico , Miastenia Gravis/tratamento farmacológico , Estudos de Coortes , SobrevivênciaRESUMO
El cáncer de páncreas constituye la quinta causa de muerte por cáncer. En la actualidad se considera que la única posibilidad de curación para la enfermedad es la pancreatoduodenectomía. En el trabajo se expone un estudio prospectivo realizado con 18 pacientes operados, desde octubre de 1996 hasta enero del 2000, con el diagnóstico de tumor periampular. En la serie se halló que la afección se asocia frecuentemente con la diabetes mellitus y que los tipos hísticos más diagnosticados fueron el adenocarcinoma de páncreas y el ampuloma. La colangiopancreatografía retrógrada endoscópica fue el estudio complementario más útil, y alcanzó una sensibilidad del 94 porciento en el diagnóstico. Se encontró una relación directa entre el volumen de sangre trasfundido perioperatoriamente y la mortalidad. La morbilidad global fue de 50 porciento. La mortalidad ha disminuido en relación con años anteriores. La supervivencia a largo plazo sigue siendo baja(AU)
Pancreatic cancer is the fifth cause of death from cancer. Pancreaticoduodenectomy is considered as the only possibility of cure for this disease at present. A prospective study conducted among 18 patients with the diagnosis of periampullar tumor that were operated on from October, 1996, to January, 2000, is presented. It was found that the affection is frequently associated with diabetes mellitus and that the most diagnosed histic types were pancreatic adenocarcinoma and ampuloma. The endoscopic retrograde cholangiopancreatography was the most useful complementary study and reached a sensitivity of 94 percent in the diagnosis. It was observed a direct relationship between the perioperatively transfused blood volume and mortality. Total morbidity was 50 percent. Mortality has decreased in comparison with pevious years. Long-term survival is still low(AU)