Toxicity of pyrethroids and repellency of diethyltoluamide in two deltamethrin-resistant colonies of Triatoma infestans Klug, 1834 (Hemiptera: Reduviidae)

The aim of the currrent investigation was to evaluate (a) the toxicity of three pyrethroids (deltamethrin, lambda-cyhalothrin, and tetramethrin); (b) the effect of these insecticides on the locomotor activity; and (c) the repellent effect of N,N-diethyl-m-toluamide (DEET) on two deltamethrin-resistant strains of Triatoma infestans from Argentina (El Chorro and La Toma), and one susceptible strain. The resistance ratios (RRs) obtained for the La Toma strain were: > 10,769, 50.7, and > 5.2 for deltamethrin, lambda-cyhalothrin, and tetramethrin respectively. The RRs for the El Chorro strain were: > 10,769, 85.8, and > 5.2 for deltamethrin, lambda-cyhalothrin, and tetramethrin respectively. The hyperactivity usually caused by the three pyrethroids was in both the deltamethrin-resistant strains compared to the susceptible reference strain. No differences were observed in the repellent effect of DEET between the three groups. These results indicate that the deltamethrin-resistant insects have a cross resistance to lambda-cyhalothrin and tetramethrin, and are also resistant to the first symptom of pyrethroid poisoning (hyperactivity). However, the sensorial process related to DEET repellency does not appear to be altered.

Historia de las células: el camino hacia las unidades mínimas de la vida y su origen; las perspectivas de crear vida en los laboratorios / Cell history: the way of units minimum life and its origin

Este texto nos lleva a explorar cómo aparecieron las primeras células y cómo poblaron el planeta, modificándolo y dando origen a todas las formas de vida que hoy existen...

Insecticide resistance in Argentine populations of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae)

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.

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.

Resistencia a insecticidas en Blattella Germánica de Buenos Aires / Resistance to insecticides in Blatella germanica from Buenos Aires

Se determinó la línea base de susceptibilidad a delta deltametrina, cipermetrina, cxlorpirifós y fenitrotión en ninfas del primer estadio de la cucaracha alemana, Blatella germanica, provenintes de una población susceptible a insecticidas mantenida en laboratorio (cepa CIPEIN). En base a los valores de DL50, se observó el siguiente orden decrteciente de toxicidad: deltametrina > clorpirifós > cipewrmetrina fenitrotión. La DL99 de cada uno de estos insecticiodas fue aplicada a la descendencia de individuos recolectados en cuatro sitios de Buenos Aires y a individuos de una cepa resistente a deltametrina criada en laboratorio desde 1994. En todos los casos, al menos un insecticida produjop menor mortalidad que la observada en la cepa susceptible, sigiriendo la excistencia de resistencia. Se obtuvieron valores de DL50 y los Grados de Resistencia (GR) a deltametrina para cada muestra. En todos los casos se observó resistencia a este insecticida, con GR que variaron entre 7,3 y 75,4.

Aspectos moleculares de la resistencia a insecticidas / Molecular basic of insecticide resistance

El surgimiento de resistencia en poblaciones de insectos es uno de los efectos indeseables asociados al uso de insecticidas, y es un buen ejemplo del modo en que ocurren los procesos microevolutivos. En 1908 se documentó por primera vez la existencia de insectos resistentes a insecticidas. Ahora se conocen casos de resistencia en más de 500 especies de artrópodos. Los principales mecanismos que confieren resistencia a insecticidas son penetración cuticular reducida, metabolismo degradativo aumentado y reducción en la susceptibilidad de los sitios de acción. Los métodos de la biología molecular permiten identificar las bases moleculares de esos mecanismos. El propósito de este artículo es reseñar el conocimiento disponible acerca de la biología molecular de la resistencia a insecticidas: mutaciones puntuales en genes de acetilcolinesterasa (Drosophila melanogaster) y del receptor de GABA (varias especies), inserciones en genes de transferasas (D. melanogaster) y del citocromo P450 (D. melanogaster), amplificación de genes de esterasas (Myzus persicae y Culex pipiens / quinquefasciatus complex), cambios que afectan la expresión del gen del citocromo P450 (Musca domestica), y una mutación ligada al gen del canal de sodio dependiente de voltaje (M. domestica)

Incoordination, paralysis and recovery after pyrethoid treatment on nymphs III of Triatoma infestans (Hemiptera: reduviidae)

Symptons of poisoning for deltamethrin and cis-permethrin on nymphs III of Triatoma infestans were described. The time required for incoordination and paralysis were determined. Deltamethrin was equal or more rapid in the onset of the first (accordingly to dose), and cis-permethrin in the onset of the second one. There were no significant differences between incoordination doses 50 per cent (IncD50s) at different times for the two pyrethroids. They showed equivalent incoordination power, but the nymphs treated with deltamethrin recovered slighly more rapid and in greater amount than the nymphs treated with cis-permethrin. The recovery was inhibited by the simultaneus application of piperonyl butoxide. This suggests that biotransformation by mixed-function microsomal oxidases are involved in the process of recovery.