ABSTRACT The maize weevil (Sitophilus zeamais Motschulsky, 1855; Coleoptera, Curculionidae) is one of the most important pests associated with stored grains. It is controlled almost exclusively with synthetic insecticides. Thus, leading to problems such as pollution and resistance development. Hence an alternative is the use of natural compounds such as edible mushrooms derivates. The aim of this research was to assess, under laboratory conditions, the insecticidal and insectistatic effect of a hydroalcoholic extract of Pleurotus ostreatus (Jacq.) P. Kumm. 1871 against adults of S. zeamais. The parameters assessed were contact and fumigant toxicity, repellency, and antifeedant effect. The highest contact toxicity (57.5% mortality) was achieved with 30 mL extract L-1 solvent. No treatment showed repellent effect; the repellency index (RI) values were higher than 1, and the antifeeding activity < 30%. The fumigant effect showed a maximum of 30% mortality with the highest concentration (300 μL L-1 air). The hydroalcoholic extract of P. ostreatus exerts contact toxicity and interferes with insect reproduction or oviposition of Sitophilus zeamais.

ABSTRACT Insect pests of stored cereals cause losses between 10 and 20%, which requires the search for effective and environmentally friendly control alternatives that pose no threat to human health. The objective of this study was to evaluate under laboratory conditions the insecticidal and insectistatic activity of Eucalyptus globulus and Eucalyptus nitens foliage powder against Sitophilus zeamais. The studied variables were contact and fumigant toxicity and repellent and anti-feed activity. The contact and fumigant toxicity did not exceed 40% mortality in any of the concentrations evaluated, although the concentration of 8.0% affected the progeny, recording 80.9% inhibition of adult insect emergence (F1) in E. globulus and 86.7% inhibition in E. nitens. All the treatments showed repellency and E. nitens recorded a feeding deterrence index (FDI) of 60.5%. It can be concluded that E. globulus and E.nitens powder has potential as a repellent and inhibitor of the life cycle of S. zeamais.

RESUMEN Los insectos plaga de los cereales almacenados causan pérdidas entre 10 y 20%, lo que hace necesaria la búsqueda de alternativas de control efectivas, amigables con el medio ambiente y que no representen riegos para la salud de las personas. El objetivo de la presente investigación fue evaluar, en condiciones de laboratorio, la acción insecticida e insectistática del polvo de follaje de Eucalyptus globulus y Eucalyptus nitens para el control de Sitophilus zeamais. Las variables estudiadas fueron toxicidad por contacto y fumigación y actividad repelente y anti-alimentaria. La toxicidad por contacto y fumigación no superó el 40% de mortalidad en ninguna de las concentraciones evaluadas, aunque el tratamiento de 8,0% afectó la progenie, registrando un 80,9% de inhibición de la emergencia de insectos adultos (F1) para E. globulus y de 86,7% en E. nitens. La totalidad de los tratamientos mostró efecto repelente y el polvo de E. nitens presentó un índice de disuasión de la alimentación (IDA) de 60,5%. Se concluye que el polvo de follaje de E. globulus y E.nitens presenta potencial como repelente e inhibidor del ciclo de S. zeamais.

ABSTRACT Sitophilus zeamais is one of the major pests of stored cereals worldwide and its control is based on the use of synthetic insecticides, but their irrational use has caused environmental pollution and resistance. Essential oils have shown contact and fumigant insecticidal effect and could be an alternative to synthetic compounds. Hence, the insecticidal properties of essential oil of Chenopodium ambrosioides L. were assessed under laboratory conditions against adults of Sitophilus. zeamais. The variables studied were contact and fumigant toxicity, and antifeedant and repellent activity. Mortality by contact toxicity did not exceed 30% in all the treatments evaluated. The highest F1 reduction was observed in the treatment of 4.0% with 41.3% of emergence (58.7% of inhibition). Grain weight loss was lower than 9.0% and maize germination was not affected. All treatments exhibited fumigant activity, while concentrations equal to or lower than 0.5% showed repellent and feeding deterrent effect. It can be concluded that essential oil of Ch. ambrosioides has potential for S. zeamais control.

RESUMEN Sitophilus zeamais Motschulsky es a nivel mundial una de las principales plagas de los cereales almacenados y su control se basa en insecticidas sintéticos, pero su uso irracional ha provocado contaminación del ambiente y resistencia. Los aceites esenciales han mostrado efecto insecticida de contacto y fumigante por lo que podrían constituir una alternativa a los compuestos sintéticos. Por este motivo se evaluaron, en condiciones de laboratorio, las propiedades insecticidas del aceite esencial de Chenopodium ambrosioides L. contra adultos de S. zeamais. Las variables evaluadas fueron toxicidad por contacto y fumigación, y actividad antialimentaria y repelente. La mortalidad por contacto no superó el 30% en todos los tratamientos evaluados. La mayor reducción de la F1 se observó en el tratamiento de 4,0% con 41,3% de emergencia (58,7% de inhibición). La pérdida de peso de los granos fue menor a 9,0% y la germinación del maíz no se vio afectada. Todos los tratamientos mostraron actividad fumigante y las concentraciones iguales o superiores a 0,5% tuvieron efecto repelente y antialimentario. Se concluye que el aceite esencial de Ch. ambrosioides presenta potencial para el control de S. zeamais.

ABSTRACT The pepper tree (Schinus molle L.) has secondary metabolites with insecticidal activity. The objective of this study was to assess under laboratory conditions the insecticidal and insectistatic activity of fruit powder and essential oil of S. molle against Sitophilus zeamais. In contact toxicity bioassays, the highest mortality was observed with essential oil at a concentration of 8.0%, recording 96.3% of dead insects with an LC50 of 3.82 mL essential oil 100 g-1 maize (3.82%). Powder at the same concentration showed a 63.8 % of mortality with an LC50 of 7.95 g powder 100 g-1 maize (7.95%). None of the treatments affected germination or grain weight loss. The essential oil at a concentration of 8.0% caused a complete inhibition of F1 resulting in 0% of adult insects. All treatments had repellent effects. The highest antifeeding effect observed with the essential oil was recorded at a concentration of 16.0% with a 72.2% of inhibition. It was concluded that both powder and essential oil of S. molle show contact insecticidal toxicity as well as repellent and antifeeding effects against S. zeamais.

RESUMEN El pimiento boliviano (Schinus molle L.) es un árbol del cual se han identificado metabolitos secundarios con actividad insecticida. El objetivo fue evaluar, en condiciones de laboratorio, la actividad insecticida e insectistática del polvo y aceite esencial de frutos de S. molle sobre Sitophilus zeamais. En los bioensayos de toxicidad por contacto la mayor mortalidad se obtuvo con el aceite esencial al 8,0 % con 96,3% de insectos muertos con una CL50 de 3,82 mL aceite esencial 100 g-1 maíz (3,82%). A la misma concentración el polvo mostró un 63,8% de mortalidad y una CL50 de 7,95 g polvo 100 g-1 maíz (7,95%). Ambos tratamientos no afectaron significativamente la germinación ni la pérdida de peso del grano. El aceite esencial en la concentración de 8,0% provocó una completa inhibición en la emergencia mostrando una F1 de 0% de insectos adultos. Todos los tratamientos fueron repelentes y el mayor efecto antialimentario del aceite esencial se registró con la concentración de 16% con 71,2% de inhibición. Se concluyó que el polvo y aceite esencial de S. molle presentan toxicidad insecticida por contacto y efecto repelente e inhibidor de la alimentación sobre S. zeamais.

Abstract: Andricus quercuslaurinus Melika & Pujade-Villar (Hymenoptera: Cynipidae) is a gall wasp from the branches (asexual reproduction) and leaves (sexual reproduction) of the Quercus affinis Scheidw. oak in Acaxochitlán, Hidalgo, Mexico. Severe infestations on the leaves cause a delay in growth and, given time, the death of trees with large levels of damage. This study evaluated the effectiveness of the pesticides Imidacloprid, Spirotetramat, Acephate and Abamectin when applied through foliar spray on the adult population of wasps that oviposit on the leaves, as well as on the eggs and larvae of the oak galls. Acephate prevented oviposition on the treated foliage. The least number of oak galls was found on the trees treated with Acephate; furthermore, they had no larvae. On the other hand, Spirotetramat had not been evaluated for the control of Cynipidae; alongside Imidacloprid, these pesticides were effective in reducing the survival of eggs and larvae. Spraying the pesticides Acephate (1.20 kg·ha-1), Spirotetramat (0.75 L·ha-1), and Imidacloprid (1.00 L·ha-1) on Q. affinis foliage are options to be considered for the control of A. quercuslaurinus given their significant effects (P = 0.05) on the mortality of the eggs with regard to the control.

Resumen: Andricus quercuslaurinus Melika y Pujade-Villar (Hymenoptera: Cynipidae) es una avispa agalladora de ramas (generación asexual) y hojas (generación sexual) del encino Quercus affinis Scheidw. en Acaxochitlán, Hidalgo, México. Las infestaciones severas en ramas causan retraso del crecimiento y, eventualmente, la mortalidad de árboles que tienen niveles altos de daño. En este trabajo se evaluó la efectividad de los insecticidas Imidacloprid, Espirotetramat, Acefato y Abamectina aplicados mediante aspersión foliar sobre la población de avispas adultas que ovipositan en las hojas, así como sobre los huevos y larvas en las agallas. El Acefato evitó la oviposición sobre el follaje tratado. El menor número de agallas se encontró en los árboles tratados con Acefato; además, no tuvieron larvas. Por otra parte, el Espirotetramat no había sido evaluado para el control de cinípidos y junto con el Imidacloprid fueron efectivos para reducir la supervivencia de huevos y larvas. La aspersión de los insecticidas Acefato (1.20 kg·ha-1), Espirotetramat (0.75 L·ha-1) e Imidacloprid (1.00 L·ha-1) al follaje de Q. affinis son opciones a considerar para el control de A. quercuslaurinus, debido a los efectos significativos (P = 0.05) en la mortalidad de huevos con respecto al testigo.

The maize weevil (Sitophilus zeamais Motschulsky) is one of most important pest of stored seeds worldwide, but its current control method is based on the use of synthetic insecticides, usually leading to undesirable problems such as insecticide residues on treated food, human intoxications, and insect resistance development. Therefore the search of friendly alternative methods is required. The aim of this study was to assess, under laboratory conditions, the insecticidal properties of Peumus boldus Molina, Laurelia sempervirens (Ruiz & Pav.) Tul., and Laureliopsis philippiana (Looser) Schodde essential oils against S. zeamais. The phytochemical analysis of the three essential oils showed 1,8-cineole, safrole and methyleugenol as the common components; all of them documented with insecticidal activity from essential oils from other plant species. The highest toxicity (100% mortality) of these three oils acting as a contact insecticide was observed at 24 h exposure at 4% concentration. The estimated LC50 values for P. boldus, L. sempervirens, and L. philippiana were 0.37, 1.02, and 0.28 μL g-1, respectively. Peumus boldus exhibited the highest fumigant activity with 100% adult mortality at 30 μL oil L-1 air. At ≥ 0.5% (v/w) concentration, all essential oils showed repellent activity. These three essential oils showed a promissory insecticidal activity against the maize weevil.

In the State of Mexico, cut rose (Rosa x hybrida) grown under greenhouse conditions has as a commercial constraint the low phytosanitary quality of its flower buds. To improve this quality, three growth regulators containing cytokinins (two commercial products and one prepared at a dose of 0.001 ppm from a technical-grade growth regulator, all at three frequencies of application) and CP* Floral Protector (FP) were evaluated in cut Rosa x hybrid 'Polo' grown under greenhouse conditions in Villa Guerrero, State of Mexico. A completely randomized experimental design with 20 treatments and four replications in a factorial arrangement was used. Treatments were applied to flower buds of 0.5 cm in diameter with closed sepals. Evaluations were made according to commercial harvest criteria when the petals begin to separate from the center of the flower. The FP and application of growth regulators increased bud diameter and length (P ≤ 0.05), but there was no effect on peduncle length or the number of days to harvest. FP use prevented insect damage and increased the number of export-quality buds. CP® floral protector and growth regulators improve the quality of cut roses.

En el Estado de México, la rosa de corte (Rosa x hybrida) que se produce en invernadero tiene como limitante comercial la baja calidad fitosanitaria de los botones florales. Para incrementar dicha calidad, se evaluaron en Villa Guerrero, Estado de México tres reguladores del crecimiento que contienen citocininas (dos comerciales y uno preparado a la dosis de 0.001 ppm a partir del regulador de crecimiento grado técnico; todas con tres frecuencias de aplicación) y el Protector Floral CP* (PF) en Rosa x hybrida 'Polo' de corte en invernadero. Se utilizó un diseño experimental completamente al azar con 20 tratamientos y cuatro repeticiones en arreglo factorial. Los tratamientos se aplicaron a botones florales de 0.5 cm de diámetro con los sépalos cerrados. Las evaluaciones se hicieron de acuerdo al criterio comercial de punto de corte cuando los pétalos empezaban a separarse del centro de la flor. El PF y la aplicación de reguladores del crecimiento incrementaron el diámetro y longitud del botón (P ≤ 0.05), pero no hubo efecto en la longitud del pedúnculo ni en los días al corte. El uso del PF previno daños por insectos e incrementó el número de botones con calidad de exportación. El protector floral CP* y los reguladores del crecimiento mejoran la calidad de la rosa de corte.

The spider mite, Tetranychus urticae Koch., is one of the most important pests of cut rose (Rosa x hybrida) in the State of México and, its primary control it's through the use of acaricides, such as propargite; the producers initially used it with satisfactory results and currently it does not control this pest anymore. In order to estimate the level of resistance to that acaricide, in 2007, its response to this acaricide was assessed in populations from Coatepec Harinas, Tenancingo, Villa Guerrero and Zumpahuacán, State of México. In each locality at least 4 000 nymphs and 2 000 adults were collected in the cut rose cultivation in greenhouses and were reproduced to F1 for the bioassays. The dose range that eliminated 0 to 100% of the treated individuals was determined (biological window). Subsequently, from five to seven concentrations were included covering the range. Five repetitions were made, four in different consecutive days. Spider mite populations from Coatepec Harinas (RR95= 7.9X, Villa Guerrero (RR95= 1.3 X and Zumpahuacán (RR95= 11X) are considered susceptible to propargite; while the population of Tenancingo (RR95= 90. IX) is considered resistant to the acaricide.

Resumen La araña roja, Tetranychus urticae Koch., es una de las plagas más importantes de la rosa de corte, (Rosa x hybrida), en el Estado de México y su combate se realiza principalmente mediante el uso de acaricidas como el propargite; mismo que los productores usaron inicialmente con resultados satisfactorios y actualmente no controla esta plaga. Con el objetivo de estimar el nivel de resistencia a dicho acaricida, en el año 2007 se evaluó su respuesta a dicho acaricida en poblaciones provenientes de Coatepec Harinas, Tenancingo, Villa Guerrero y Zumpahuacán, Estado de México. De cada localidad se recolectaron al menos 4000 ninfas y 2 000 adultos en el cultivo de rosa de corte bajo invernadero y se reprodujeron hasta F1 para realizar los bioensayos. Se determinó el rango de dosis que eliminaba el 0 al 100% de los individuos tratados (ventana biológica). Posteriormente se incluyeron de cinco a siete concentraciones que cubrieron dicho rango. Se realizaron cinco repeticiones cuatro en días consecutivos diferentes. Las poblaciones de araña roja provenientes de Coatepec Harinas (RR95= 7.9x), Villa Guerrero (RR95=1.3x) y Zumpahuacán (RR95= 11 x) se consideran susceptibles a propargite; mientras que la población de Tenancingo (RR95 = 90.1 x) se considera resistente a dicho acaricida.

El sistema tradicional para producir botones florales de rosa de corte es ineficiente en las zonas productoras del estado de México, ya que muy pocos de ellos logran una alta calidad. El presente trabajo tuvo el objetivo de evaluar el uso de protectores florales solos o impregnados con fitohormonas (giberelinas o citocininas) para aumentar la calidad del botón floral. El protector floral impidió el ingreso de trips al botón floral e incrementó la calidad del botón floral tanto en la variedad Black Magic como en la Polo. El protector floral solo y con giberelinas contribuyó a aumentar la calidad del botón floral. Las citocininas utilizadas para impregnar tanto el botón floral como el protector floral aumentaron la calidad del botón en dosis óptima de 0,001 mg·L-1; sin embargo, dosis iguales o mayores a 100 mg·L-1 dañaron la estructura floral.

The present study was conducted to assess the use of floral protectors alone or impregnated with phytohormones (gibberellins or cytokinins) to increase bud quality. The floral protectors prevented the entry of thrips to the flower bud and increased the flower bud quality in the varieties Black Magic and Polo. The floral protector alone and gibberellin impregnated contributed to increase the quality of the floral buds. Cytokinins used to impregnate both the bud and the protector increased the quality of the floral buds at the optimal dosage of 0.001 mg·L-1; however, doses equal or above 100 mg·L-1 damaged the floral structure.

Gynaikothrips ficorum (Marchal) is a pest of the laurel tree in urban zones and insecticides are possibly used for its control, but its initial response to these products is unknown. Therefore susceptibility of various populations of this species was determined (Texcoco, Córdoba and Tlayacapan) to the insecticides permethrin, cypermethrin, diazinón, malathion, methyl oxydemeton, methyl parathion, endosulfán and methomyl. The Texcoco population was used as reference to make comparisons of the response. At 24 h of exposure, the confidence levels of the CL50 of the three populations overlapped in the insecticides cypermethrin, diazinón, malathion and methyl oxydemeton; but they did not overlap in Córdoba and Tlayacapan with Texcoco, for permethrin, methyl parathion, endosulfán and methomyl. For Córdoba and Tlayacapan with cypermethrin, the resistance proportion (RP50) was 0.88 and 0.53'; with diazinón, 0.3 and 0.29'; with malathion 1.04 and 1.02'; with methyl oxydemoton 0.74 and 7.18'; with methyl parathion 8.4 and 4.63'; with endosulfán 1.19 and 0.2', and with methomyl 0.11 and 0.53'. At 95 % mortality, only in Tlayacapan and for endosulfán (RP95=0.03), the fiducial limits did not overlap with the other two populations. The values obtained at 48 h of exposure followed the same tendencies found at 24 h. These response values correspond to a susceptible state and can be used as comparison reference.

Gynaikothrips ficorum (Marchal) es una plaga del laurel en zonas urbanas y posiblemente se usan insecticidas para su control, pero se desconoce su respuesta inicial a éstos. Por tanto, se determinó la susceptibilidad de varias poblaciones de esta especie (Texcoco, Córdoba y Tlayacapan) a los insecticidas permetrina, cipermetrina, diazinón, malatión, oxidemetón metílico, paratión metílico, endosulfán y metomil. La población Texcoco se usó como referencia para hacer comparaciones de la respuesta. A las 24 h de exposición, los límites de confianza de la CL50 de las tres poblaciones se traslaparon en los insecticidas cipermetrina, diazinón, malatión y oxidemetón metílico; pero no se traslaparon en Córdoba y Tlayacapan con Texcoco, para permetrina, paratión metílico, endosulfán y metomil. Para Córdoba y Tlayacapan con cipermetrina, la proporción de resistencia (PR50) fue 0.88 y 0.53'; con diazinón 0.3 y 0.29'; con malatión 1.04 y 1.02'; con oxidemetón metílico 0.74 y 0.9'; con permetrina 5 y 7.18'; con paratión metílico 8.4 y 4.63'; con endosulfán 1.19 y 0.2', y con metomil 0.11 y 0.53'. A nivel del 95 % de mortalidad, sólo en Tlayacapan y para endosulfán (PR95 =0.03), los límites fiduciales no se traslaparon con las otras dos poblaciones. Los valores obtenidos a las 48 h de exposición siguieron las mismas tendencias encontradas a las 24 h. Estos valores de respuesta corresponden a un estado susceptible y se podrán usar como referencia de comparación.

Spiromesifen is an insecticide that inhibits the synthesis of lipids and, in Mexico, its use against the Tomato-Potato Psyllid, Bactericera cockerelli (Sulc), on chili pepper (Capsicum annum), tomato (Lycopersicon sculentum) and potato (Solanum tuberosum) began in 2005; however more information is needed to understand its toxicity on this insect pest. The aim of this research was to determine the toxicity of spiromesifen against each of the biological stages of tomato-potato psyllid, its effect on fertility and viability of eggs deposited by treated females, as well as the female preference to lay eggs on treated and non treated plants. The relative toxicity at 95% mortality (highest LC95 value /LC95 value of the respective biological stage) of spiromesifen in egg, nymph 1, nymph 2, nymph 3, nymph 4, and nymph 5 were 517.5; 31316.2; 2950.1; 315.6; 18.2 and 1-fold, respectively. There were no differences in the toxicity of spiromesifen between adult males and females. The number of laid eggs was reduced as the spiromesifen concentration used to treat female increased and egg hatch was reduced in all tested doses. In the "no choice" test, females deposited 38.6 ± 2.01 eggs by leaf of non treated chili pepper type jalapeño, while in the treated with 360 mg L-1 we observed 0.3 ± 0.08 eggs by leaf. In the "choice" test, the oviposition decreased as the dose increased. There were no eggs on plants treated with 2400 mg L-1 of spiromesifen.

In two field-collected populations of de Bemisia tabaci (Gennadius) B biotype previously selected with the neonicotinoid insecticide thiamethoxam (NEO-R, NEO-N), and a population susceptible to insecticides (SUSC), the level of response to the insecticide thiametoxam, as well as the life and fertility tables were determined. At LC95, the NEO-R population showed a resistance ratio (RR95) value of 8.8-fold, an intrinsic rate of increase (r m) of 0.72. The fitness of the NEO-R and NEO-N populations in relation to the SUSC was 1.5 and 2.0, respectively. The RR95 value for NEO-N was 1.9-fold; it's r m value was 0.082, while in the SUSC population was 0.041. The developmental time of egg and adult were longer in NEO-R population, while the nymph and pupa lasted longer in the NEO-N and SUSC populations. The developmental time was different in the three NEO-R, NEO-N, and SUSC populations with 19.7 d (315.84 degree days or dd), 15.7 d (250.4 dd) and 18.5 d (296.6 d), respectively. The populations previously selected with thiamethoxam did not reproduce faster than their susceptible counterpart.

The rational use of insecticides requires previous evaluation of the effectiveness of the chemicals to be used. This may reduce the use of non-effective products and prevent rising production costs and pollution. To facilitate bioassays in the laboratory, susceptibility values (LD50) of 64 insecticides and acaricides for 33 species of arthropods are presented. These LD50 could be used to determine susceptibility or resistance of these species in México.

La utilización racional de insecticidas contra una plaga en un cultivo determinado requiere de la evaluación previa de la efectividad de los productos a emplear. Esto puede disminuir el uso de productos no efectivos que encarecen la producción y contaminan el medio. Para facilitar los bioensayos en el laboratorio, se presentan los valores de susceptibilidad (DL50) para 64 insecticidas y acaricidas en 33 especies de artrópodos. Estos DL50 se podrían usar para determinar susceptibilidad o resistencia de esas especies en México.

The tomato-potato psyllid, Bactericera cockerelli (Sulc.), is one of the most important pests of chili pepper (Capsicum spp.), tomato (Lycopersicon esculentum Mill.), and potato (Solanum tuberosum L.) in México. Insecticides are used for its control, and the farmers perceive that their biological effectiveness is not satisfactory. In nymphs, LC50, LC95, confidence limits at 95%, values of resistance ratio at a level of LC50 (RR50) and LC95 (RR95) to six insecticides were determined in one susceptible and two field-collected populations (El Huizache, State of San Luis Potosí, and Arteaga-Galeana of Coahuila and Nuevo León). All the populations were susceptible to fenpropathrin, abamectin, cyfluthrin, dimetoate, esfenvalerate, and pyriproxyfen. It is documented that the lack of biological effectiveness in field is not due to resistance to insecticides.

El salerillo, Bactericera cockerelli (Sulc) es una de las plagas más importante del chile (Capsicum spp.), jitomate (Lycopersicon esculentum Mill.) y papa (Solanum tuberosum L.) en México. Para su control se usan insecticidas y los agricultores perciben que su eficacia biológica no es satisfactoria. En ninfas se determinaron los valores de CL50, CL95, límites de confianza al 95% y valores de proporción de resistencia a nivel de CL50 (RR50) y CL95 (RR95) a seis insecticidas en una población susceptible y dos de campo (El Huizache, Estado de San Luis Potosí, y Arteaga-Galeana de Coahuila y Nuevo León). Todas las poblaciones fueron susceptibles a fenpropatrín, abamectina, cyfluthrín, dimetoato, esfenvalerato y pyriproxyfen. Se documenta que la falta de eficacia biológica en campo no se debe a la resistencia a insecticidas.

Abstract: Bollgard II® cotton expresses the δ-endotoxins Cry1Ac and Cry2Ab of Bacillus thuringiensis Berliner, controls larvae of Helicoverpa zea (Boddie), and will probably be used in the near future in Mexican agriculture. However, the initial susceptibility to this toxin in populations of H. zea is unknown. The objective of the present study was to determine the susceptibility to the δ-endotoxin Cry2Ab in neonate larvae of five populations (one susceptible and four field populations) of H. zea. The observed mortality levels were low (<43%) in the evaluated doses (≤5 μg mL-1). The estimated concentration necessary to prevent 50% of the exposed larvae from reaching the third instar or inhibition of development of 50% of treated larvae (ID50) varied from 0.017 to 0.086 μg mL-1, while the ID95 varied from 1.06 to 1.93 μg mL-1. The concentration that reduced or inhibited 50% of the weight of treated larvae (IP50) varied from 0.013 to 0.025 μg mL-1, and the IP95 from 0.5 to 1.48 μg mL-1. The obtained toxicity values to δ-endotoxin Cry2Ab in larvae of H. zea are considered as initial response or reference point, given that this toxin is still not used in the field and will serve to estimate the proportion of change over time once Bolgard II® is used in México.

Resumen: El algodonero Bollgard II® expresa las δ-endotoxinas Cry1Ac y Cry2Ab de Bacillus thuringiensis Berliner, controla larvas de Helicoverpa zea (Boddie) y es probable que en un futuro cercano se empiece a utilizar en la agricultura mexicana. Sin embargo, se desconoce la susceptibilidad inicial a esta toxina en poblaciones de H. zea. El objetivo de este estudio fue determinar la susceptibilidad a la δ-endotoxina Cry2Ab en larvas neonatas de cinco poblaciones (una susceptible y cuatro de campo) de H. zea. Los niveles de mortalidad observados fueron bajos (<43%) en las dosis evaluadas (≤5 μg mL-1). La concentración estimada de toxina necesaria para impedir que 50% de las larvas expuestas llegara al tercer ínstar o inhibición de desarrollo del 50% de larvas tratadas (ID50) varió de 0.017 a 0.086 μg mL-1, mientras que la ID95 varió de 1.06 a 1.93 μg mL-1. La concentración que redujo o inhibió 50% del peso de larvas tratadas (IP50) varió de 0.013 a 0.025 μg mL-1, y la IP95 de 0.5 a 1.48 μg mL-1. Los valores que se obtuvieron de toxicidad a la δ-endotoxina Cry2Ab en larvas de H. zea se consideran como respuesta inicial o punto de referencia, dado que dicha toxina aún no se utiliza en campo y servirán para estimar la proporción de cambio a través del tiempo una vez que el algodonero Bollgard II® se utilice en México.