Abstract Chrysodeixis includens, is an important Plusiinae pest that feeds on soybean, beans, and cotton. This species has a genetic structure determined by molecular markers in populations collected in soybean crops in Brazil and has developed resistance to insecticides. This had led to an increased interest in the genetic diversity of its populations in Argentina. This study aimed to characterize the fitness parameters and mating compatibility of geographically distant C. includens populations and on different host plants in Argentina. Intra- and inter-population crosses revealed that C. includens populations from Tucumán and Santiago del Estero provinces did not present any evidence of prezygotic and postzygotic incompatibilities, suggesting that both populations collected from soybean plants belonged to a single wide-ranging species. Prezygotic and postzygotic incompatibilities were detected between populations collected from different crops (soybean and bean). These incompatibilities may be caused by the different nutrients that each plant species renders, or the specific pest control strategies which may affect C. includens behavior. Studies of the genetic structure of C. includens populations based on mating isolation on other crops, as well as of the impact of management strategies on the specie, will increase understanding of the reproductive compatibility revealed by the present study.

Lufenuron is a chitin synthesis inhibitor used for controlling several pest insects. The German cockroach, Blattella germanica, is a cosmopolitan insect of medical and economic importance. Resistance to insecticides has been worldwide reported in this species. The objective of this work was to evaluate the effect of lufenuron in two colonies of B. germanica, one susceptible to insecticides (CIPEIN) and another pyrethroid-resistant (JUBA). Experimental populations from each colony were exposed to flter papers treated with 50 mg of lufenuron/m2. Controls were exposed to flter papers treated with solvent alone. After seven weeks, the average size of both lufenuron-treated populations was 1.33 ± 0.7 individuals, while the average size of control populations were 206.5 ± 39.5 (CIPEIN) and 136.5 ± 43.5 (JUBA) individuals. This drastic effect suggests that lufenuron could be used as an alternative for the control of pyrethroid-resistant German cockroaches. Future studies should explore the toxicity of lufenuron on other populations of B. germanica resistant to pyrethroids or other insecticides.

Lufenurón es un inhibidor de la síntesis de quitina usado para controlar diversas plagas de insectos. La cucaracha alemana, Blattella germanica, es un insecto cosmopolita de importancia médica y económica. Existen numerosos reportes de resistencia a insecticidas en poblaciones de B. germanica alrededor del mundo. El objetivo de este trabajo fue evaluar el efecto de lufenurón en dos colonias de B. germanica, una susceptible a insecticidas (CIPEIN) y otra resistente a deltametrina (JUBA). Se expusieron poblaciones experimentales de ambas colonias a papeles de fltro tratados con 50 mg de lufenurón/m2. Los controles fueron expuestos a papeles de fltro tratados con solvente solo. Al cabo de siete semanas, las dos poblaciones expuestas a lufenurón presentaron el mismo tamaño promedio (1,3 ± 0,7 individuos); mientras que los tamaños promedio de las poblaciones controles fueron 206,5 ± 39,5 (CIPEIN) y 136,5 ± 43,5 individuos (JUBA). Este drástico efecto sobre el tamaño poblacional sugiere que lufenurón podría ser usado como una alternativa para controlar cucarachas alemanas resistentes a deltametrina. A la vista de estos resultados, se debería explorar la toxicidad de lufenurón en otras poblaciones de B. germanica resistentes a piretroides u otros insecticidas.

Chrisopids are economically significant predators of several agricultural pests. In Argentina, the species recorded of Chrysoperla Steinmann, 1964 are C. externa (Hagen, 1861), C. asoralis (Banks, 1915), C. argentina (González Olazo & Reguilón, 2002) and C. defreitasi (Brooks, 1994). Chrysoperla asoralis and C. argentina have been associated with citric, olive, maize and cotton crops. In the present note, we record for the first time these two species in La Plata and neighboring areas within the Buenos Aires province, in association with the sweet pepper, Capsicum annuum L.

Los crisópidos son depredadores, económicamente importantes, de varias plagas de la agricultura. En Argentina, las especies registradas dentro del género Chrysoperla Steinmann, 1964 son C. externa (Hagen, 1861), C. asoralis (Banks, 1915), C. argentina (González Olazo & Reguilón, 2002) y C. defreitasi (Brooks, 1994). Chrysoperla argentina y C. asoralis han sido citadas asociadas con cultivos de cítricos, olivos, maíz y algodón. En la presente nota registramos, por primera vez, estas dos especies en la zona del Gran La Plata, Provincia de Buenos Aires, en asociación con el pimiento, Capsicum annuum L.

Soybean is the most important crop in Argentina and Rachiplusia nu (Gueneé) (Lepidoptera: Noctuidae) is one of its main pests. In this study, the toxicity of five pyrethroids applied topically and by exposure to films on filter paper was evaluated on third instar larvae from a laboratory strain and a field population of R. nu. Four cyanopyrethroids and one non-cyanopyrethroid (permethrin) were tested. All cyanopyrethroids showed the same order of increasing toxicity, regardless of the form of application and origin of the larvae: cypermethrin < ?-cyhalothrin < deltamethrin < ß-cyfluthrin. Knock down Dose 50% and Knock down Time 50% values increased as a function of the solubility of cyanopyrethroids in water. Permethrin showed a different behavior: it was the most toxic insecticide for the laboratory strain when applied topically, but the least toxic when larvae were exposed to filter papers. In general, the pyrethroids were more toxic for laboratory larvae than for the field ones. After calculating Resistance Factor (RF) values, low-moderate resistance to permethrin, cypermethrin and ?-cyhalothrin was observed in the experiments with topical application. However, exposure to films on filter papers failed to detect resistance. There was not correlation between the RF values obtained by both methods. These results suggest that the population of R. nu studied here has low-moderate resistance to some pyrethroids, and that topical application is a more appropriate method for quantifying resistance than exposure to insecticide films on filter paper.

La soja es el cultivo más importante en la República Argentina y Rachiplusia nu (Gueneé) (Lepidoptera: Noctuidae), una de sus principales plagas. En este estudio se evaluó la toxicidad de cuatro cianopiretroides y un no-cianopiretroide, aplicados en forma tópica o por exposición a filmes sobre papeles de filtro, en ninfas del tercer estadio de una cepa de laboratorio y una población de campo de R. nu. Todos los cianopiretroides mostraron el mismo orden de toxicidad creciente, independientemente de la forma de aplicación y del origen de las larvas: cipermetrina < ?-cihalotrina < deltametrina < ß-ciflutrina. Los valores de Dosis de Volteo para el 50% (DV50) y de Tiempo de Volteo para el 50% (TV50) aumentaron en función de la solubilidad de los cianopiretroides en agua. El no-cianopiretroide permetrina mostró un comportamiento diferente: fue el insecticida más tóxico para la cepa de laboratorio cuando se hizo una aplicación tópica, pero el menos tóxico cuando las larvas fueron expuestas a filmes sobre papeles de filtro. En general, todos los piretroides fueron más tóxicos para las larvas criadas en laboratorio que para las provenientes del campo. La estimación de los valores de Factor de Resistencia (FR) permitió establecer que la población de campo presentaba resistencia moderada o baja a permetrina, cipermetrina y ?-cihalotrina, cuando los insecticidas fueron aplicados en forma tópica. Sin embargo, no se detectó resistencia cuando se realizó la exposición en papeles de filtro tratados. No hubo correlación entre los valores de FR obtenidos por ambos métodos. Estos resultados sugieren que la población de campo de R. nu estudiada, presentaba resistencia moderada a algunos piretroides, y que la aplicación tópica es un método más apropiado que la exposición a filmes sobre papeles de filtro para cuantificar la resistencia.

A traça-do-tomateiro, Tuta absoluta (Meyrick), é uma das pragas chaves no tomateiro na Argentina. O controle químico tem sido o principal método de controle empregado a partir da sua dispersão nos anos 70. Contudo, tem-se observado uma redução na eficácia de alguns dos inseticidas recomendados a partir da década de 80. O objetivo deste trabalho foi estudar a toxicidade de três inseticidas amplamente usados no controle químico de T. absoluta (abamectina, deltametrina e metamidofós) em larvas de uma população susceptível de laboratório (CASTELAR) e duas populações colectadas em casa de vegetação (ROSARIO e BELLA VISTA). Inseticidas foram diluídos em acetona e aplicados topicamente na região dorsal mediana do abdome de larvas no segundo dia do quarto estágio larval. Para cada inseticida estimou-se o LD50 e calculou-se o Nível de Resistência (NR = LD50 de cada população de casa de vegetação/LD50 população de laboratório). As populações de ROSARIO e BELLA VISTA mostraram os seguintes NRs: > 68.38 para deltametrina; 2.48 e 3.49 para abamectina, respetivamente; e 0.79 e 0.86 para metamidofós, respetivamente. A resistência a deltametrina observada em ROSARIO pode ser resultante da alta pressão seletiva exercida pelos piretróides nessa localidade. A resistência incipiente a abamectina detectada em BELLA VISTA pode ter sido causado pelo uso freqüente do inseticida nessa localidade ou pode estar associada à variação natural.

The tomato leafminer, Tuta absoluta (Meyrick), is one of the key pests of tomato in Argentina. Since its dispersal in the 1970s, chemical control has been the main method of controlling it. However, reduced efficacy of some of the recommended insecticides has been observed since the 1980s. The aim of this work was to study the toxicity of three insecticides widely used in chemical control of T. absoluta (abamectin, deltamethrin and methamidophos) on larvae from a laboratory susceptible population (CASTELAR) and two greenhouse populations (ROSARIO and BELLA VISTA). Insecticides were dissolved in acetone and topically applied to the mid-dorsal abdominal region of two-day old 4th instar larvae. LD50 values were estimated and the Resistance Ratio (RR) for each insecticide was calculated (RR = LD50 value of each greenhouse population/LD50 value of the susceptible population). ROSARIO and BELLA VISTA populations showed the following RRs values: > 68.38 for deltamethrin; 2.48 and 3.49 for abamectin, respectively; and 0.79 and 0.86 for metamidophos, respectively. Deltamethrin resistance observed in ROSARIO could be due to the high selective pressure exerted by pyrethroids in this location. Deltamethrin resistance in BELLA VISTA is more difficult to explain, because pyrethroids were scarcely used in the greenhouse where the insects were sampled. The incipient abamectin resistance detected in the BELLA VISTA population could result from the frequent use of this insecticide in this location, although natural variation can not be discarded.

Triatoma infestans is the most important vector of Chagas’ disease in Argentina. Experiences from Argentine national campaigns have shown indoor spraying to control triatomine bugs is both expensive and difficult. An alternative control method may be the use of pyrethroid- impregnated fabrics (PIFs), which could be both a practical and cheap complement to conventional control measures. In this study, a formulation of emulsifiable concentrate of beta-cypermethrin [a-cyano-3-phenoxybenzyl-3- (2,2-dichlorovinyl) -2,2-dimethylcyclopropanecarboxilate] pyrethroid was used to impregnate different fabrics. The fabrics were then tested for their efficacy and persistence in killing Triatoma infestans. Insects attempting to penetrate or grasp the fabric in search of blood meals were poisoned by the exposure to the absorbed pyrethroid. Laboratory bioassays showed that the insecticidal effect of the PIFs with a dosage of 0.2 g/m² lasted longer on wool than on cotton or rayon. Eight months after impregnation, a residual efficacy of 100% was found for wool, 80% for rayon-cotton fabrics, and 50% for rayon- polyester fabrics. In addition, beta-cypermethrin-impregnated fabrics showed a better repellency effect than did fabrics impregnated with either deltamethrin or cypermethrin. For field trials, fabrics were impregnated either in the laboratory or "in situ" at a dosage of 1 g beta-cypermethrin/m² and then dried. The PIFs were placed inside homes, either under the roof or under the bed mattress. The field trials showed the PIF approach to be very effective in keeping dwellings free of triatomine bugs for at least one year and found a high degree of acceptability among the houses’ residents.

Triatoma infestans es el principal vector de la enfermedad de Chagas en Argentina. La experiencia adquirida en las campañas nacionales de este país ha demostrado que la fumigación de los domicilios para controlar los triatómidos es cara y difícil. Un método de control alternativo que podría ser un complemento práctico y barato de las medidas de control convencionales sería el empleo de telas impregnadas de piretroides. Los insectos que intentaran penetrar la tela o caminaran sobre ella en busca de comida serían intoxicados por la exposición al piretroide absorbido. En este estudio se utilizó un concentrado emulsionado del piretroide beta-cipermetrina [alfa-ciano-3-fenoxibencil-3- (2,2-diclorovinil) -2,2-dimetil-ciclopropano-carboxilato] para impregnar diferentes telas y después se investigó su eficacia y persistencia para matar a Triatoma infestans. Los bioensayos de laboratorio revelaron que, con una dosis de beta-cipermetrina de 0,2 g/m², el efecto insecticida era más duradero en la lana que en el algodón o el rayón. Ocho meses después de la impregnación, se registró una eficacia residual de 100% en la lana, de 80% en las telas de rayón y algodón y de 50% en las de rayón y poliéster. Además, las telas impregnadas de beta-cipermetrina presentaron mayor efecto repelente que las impregnadas de deltametrina o cipermetrina.En los estudios de campo, después de ser impregnadas in situ con una dosis de beta-cipermetrina de 1 g/m² y secadas, las telas fueron colocadas en el interior de las casas, debajo de los colchones o clavadas al techo. Estos estudios de campo demostraron que el método era muy eficaz para mantener los domicilios sin triatómidos durante al menos un año y que tenía un alto grado de aceptación por parte de los moradores.