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.

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.

Susceptibility and resistance to insecticides of Chagas disease vector

Chemical control of Chagas disease vectors appears to be the best pratical way to reduce the incidence of the disease. DDT was intially tested in the 1950s for the campaigns of control of Chagas disease vectors. Its low level of effectiveness against triatomine caused the failure of these control actions. HCH was then introduced in the southem cone and Dieldrin in the north of Latinoamerica. Starting in the late 1960s anticholinesterasic organophosphorus and carbamate compounds were introduced in the control of Chagas vectors. The use of pyrethoriod compounds began in 1980. This family of insecticides is now the most important tool in triatomines control because of its favorable toxicological properties. Other types of insecticides also studied for Chagas vector control were the insect growth regulators and the antifeeding compounds. Because of the mode of action of these insecticides they are now considered just a potential complement of neurotoxic insecticides for integrated programmes of Triatomines control. Innovative formulations such as fumigant canister and insecticidal paints have been successfully developed in Latinoamerica with the World Health Organization support. Resistance to insecticides of triatomines is not a great problem in Chagas vectors. However, some resistant strains to pyrethroids have been found in Rhodnius prolixus from Venezuela and in Triatoma infestans from Brazil. Some cases of T. infestans incipient resistance to deltamethrin have been detected in Argentina. According to the control tools now available it is possible to expect the interruption of vector transmission of Chagas disease in the near future.

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.

Localización de actividad esterásica en geles de poliacrilamida usando etilésteres como sustratos / Locating of esterase activity in polyacrylamide gels using ethyl-esters subtrates

El procedimiento propuesto para la localización de carboxiesterasas en gel de poliacrilamida está adaptado de la técnica colorimétrica de Talcott. Se basa en el acoplamiento de la hidrólisis de etil-carboxiésteres debido a esterasas, a la reducción de un colorante de tetrazolio. Se obtienen resultados satisfactorios usando diferentes sustratos de interés general y toxicológico como el acetato de etilo, malonato de etilo, ftalato de etilo y malatión. Se ensayaron preparados enzimáticos de insectos con este procedimiento y dieron en cada caso nuevos patrones de esterasas. Usado independientemente o en combinación con el método de tinción de alfa-naftil acetado y fast blue B, provee un mayor conocimiento sobre la especificidad de este grupo complejo de enzimas

Modo de acción de insecticidas en Triatoma infestans / Mode of action of insecticides in Triatoma infestans

Se analizan la acción ovicida de compuestos sintéticos (clorados, fosforados, carbamatos y piretroideos) en insectos -especialmente en Triatoma infestans-; la metodología de evaluación toxicológica de insecticida y ovicidas en el laboratorio (inmovilización del insecto, aplicación del tóxico y tratamiento estadístico de los resultados, técnicas de medición de la acción ovicida) y factores intervinientes en ella. También se describen los pasos básicos del proceso de intoxicación de insectos (Triatoma infestans): penetración por cutícula (modo de entrada de insecticidas de contacto, cinética de la penetración de insecticidas, factores intervinientes en la velocidad de penetración y penetración por tráquea); mecanismos metabólicos de insecticidas (metabolismo activante y detoxificante); y, sitio de acción de los insecticidas (ataque a un centro vital) o lesión bioquímica. Se concluye destacando la necesidad de profundizar los conocimientos sobre los temas expuestos