Comparison of the insecticide susceptibilities of laboratory strains of Aedes aegypti and Aedes albopictus

A susceptible strain of Aedes albopictus derived from the Gainesville strain (Florida, USA) was established in our laboratory. The larvicidal efficacies of the neurotoxic insecticides temephos, permethrin and the pure cis and trans-permethrin isomers and the microbial insecticide Bacillus thuringiensis israelensis (Bti) against Ae. albopictus were estimated and compared to a susceptible strain of Aedes aegypti. The larvicidal effect of insect growth regulator pyriproxyfen was also evaluated in both mosquito strains. The median lethal concentration/median emergency inhibition values for Ae. aegypti and Ae. albopictus, respectively, were: temephos, 3.058 and 6.632 ppb, permethrin, 3.143 and 4.933 ppb, cis-permethrin, 4.457 and 10.068 ppb, trans-permethrin, 1.510 and 3.883 ppb, Bti, 0.655 and 0.880 ppb and pyriproxyfen, 0.00774 and 0.01642 ppb. Ae. albopictus was more tolerant than Ae. aegypti to all six larvicides evaluated. The order of susceptibility for Ae. aegypti was pyriproxyfen > Bti > trans-permethrin > temephos > permethrin > cis-permethrin and for Ae. albopictus was pyriproxyfen > Bti > trans-permethrin > permethrin > temephos > cis-permethrin. Because both species can be found together in common urban, suburban and rural breeding sites, the results of this work provide baseline data on the susceptibility of Ae. albopictus to insecticides commonly used for controlling Ae. aegypti in the field.

Embryonic development of human lice: rearing conditions and susceptibility to spinosad

The embryonic development of human lice was evaluated according to the changes in the morphology of the embryo observed through the transparent chorion. Based on ocular and appendage development, three stages of embryogenesis were established: early, medium, and late. Influence of temperature and relative humidity (RH) on the laboratory rearing of Pediculus humanus capitis eggs was assessed. The optimal ranges for temperature and RH were 27-31°C and 45-75%. The susceptibility of human louse eggs to insecticide spinosad (a macrocyclic lactone) was assessed by immersion method. The results showed similar susceptibility to spinosad in early, medium, and late stages of head lice eggs. In addition, this study showed similar susceptibility of head and body lice eggs to spinosad, an insecticide that has not been used as pediculicide in Argentina (lethal concentration 50: 0.01%).

The fumigant and repellent activity of aliphatic lactones against Pediculus humanus capitis (Anoplura: Pediculidae)

New alternative insecticides are necessary for the chemical control of head lice. In this study the fumigant knockdown time 50 percent (KT50) and repellency index (RI) of three aliphatic lactones was compared with two essential oils and DDVP, against permethrin-resistance Pediculus humanus capitis from Argentina. In the fumigant assay, none of the lactones were effective compared to the highest activity of eucalyptus (KT50 15.53 m). In the repellency test, the three lactones were equally or more effective (RI ranging from 60.50 to 76.68) than the positive control (piperonal). These lactones are promising as head lice repellents.

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.

Biological effect of 1-dodecanol in teneral and post-teneral Rhodnius prolixus and Triatoma infestans (Hemiptera: Reduviidae)

Topical application of 1-dodecanol was significantly more toxic against teneral first nymphs (1-3 h old) than post-teneral first nymphs (24 h old). The lethal dose ratios were 711,500 for Rhodnius prolixus and 3613 for Triatoma infestans. No significative difference between LD50 was found when 1-dodecanol was injected in recently hatched adult R. prolixus (1-4 h old) nor in older adults (24 h old). These values were similar to those calculated for deltamethrin (an effective triatomicide), showing that 1-dodecanol had no insecticidal properties when it was applied by injection. Topical application of high dose of 1-dodecanol (1 æg/i) on teneral first nymphs of R. prolixus, produced an interruption of the darkening process of the cuticle, and probably in the development of its physiological properties.

Role of enhanced detoxication in a deltamethrin-resistant population of Triatoma infestans (Hemiptera, Reduviidae) from Argentina

Deltamethrin and other pyrethroids have been extensively used in Argentina since 1980, for the chemical control of Triatoma infestans Klug (Hemiptera: Reduviidae). Recently, resistance to deltamethrin was detected in field populations by the survival of bugs exposed by topical application to the diagnostic dose estimated on the CIPEIN susceptible strain. Results of the current study showed low resistant ratios (RRs) to deltamethrin for the resistant populations (RR ranged from 2.0 for San Luis colony to 7.9 for Salta colony). Biochemical studies were made on the most resistant colony (Salta) and the susceptible strain (CIPEIN), in order to establish the importance of degradative mechanisms as a cause of the detected resistance. Esterase activity was measured on 3 days old first instars through phenylthioacetate and a-naphtyl acetate activities. The results showed a significant difference in no cholinesterase esterase activity from susceptible (7.6 ± 0,7 æM S./i.min.) and Salta resistant colony (9.5 ± 0.8 æM S./i.min.). Cytochrome P450 mono-oxygenase (P450) activity was measured on individual insects through ethoxycoumarine deethylase (ECOD) activity using a fluorescence micro plate reader. The dependence of ECOD activity on age and body region of the nymphs, and pH and time of incubation were studied in order to optimize the measurement. As a result, comparative studies were performed on abdomens of 2 days old first instars at pH 7.2 and 4 h incubation time. ECOD activity of first nymphs was significantly lower in the susceptible colony (61.3 ± 9.08 pg ECOD/ insect) than in the resistant one (108.1± 5.7 pg ECOD/ insect). These results suggest that degradative esterases (no-cholinesterase) and mono-oxygenases cytochrome P450, play an important role in the resistance to deltamethrin in Salta colony from Argentina.

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.

Efectividad de lociones capilares sobre poblaciones de Pediculus capitis resistentes a insecticidas / Effectiveness of capilar lotions against insecticide resistant Pediculus capitis populations

Se estudio la influencia de los distintos componentes en la efectividad de lociones experimentales sobre piojos resistentes a insecticidas piretroides. Se encontró que el aumento de la concentración del insecticida D-fenotrina desde 0,2 por ciento (concentración recomendada en lociones comerciales) hasta 0,5 por ciento, no produjo diferencias significativas (p=0,495) en la actividad pediculicida. Por el contrario se encontró un aumento significativo de efectividad de lociones experimentales con d-fenotrina o,2 por ciento al agregar alcohol alifático dodecanol en concentración 10 por ciento. El volteo de piojos expuestos se incrementó desde 23,+- 4,7 por ciento hasta 92,0+- 7,5 por ciento respectivamente. Se encontró además que las lociones conteniendo sólo dodecanol (sin d-fenotrina) producian un volteo significativo de los piojos expuestos (35+-8,5). Se comprobó que el volteo producido por la loción con dodecanol mostraba recuperación parcial a las 18 horas, mientras que la efectividad de las lociones que combinan dodecanol con insecticidas aumentaba al cabo de 18 horas alcanzando 100 por ciento de mortalidad. Se postula que la potenciación de actividad pediculicida demostrada para lociones que combinan dodecanol y d-fenotrina podría deberse a daño cuticular producido por el alcohol que favorecería la penetración del insecticida para ejercer su efecto tóxico

A new tactic for triatoma infestans control: fabrics impregnated with beta-cypermethrin

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 B-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 per cent was found for wool, 80 per cent for rayon-cotton fabrics, and 50 per cent for rayon-polyester fabrics. In addition, b-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 b-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

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.

Evaluación de la B-cipermetrina para el control de Triatoma infestans / Evaluation of -cypermethrin for control of Triatoma infestans

This study assessed the insecticidal effect in the laboratory and in the field of the new pyrethroid -cypermethrin against Triatoma infestans, the vector of Chagas' disease, and compared it with that of deltamethrin. Comparison of the 50% lethal dosis (LD50) of both pyrethroids showed that -cypermethrin is more effective against the nymphs and that deltamethrin is more effective against the adults. Evaluation of the 50% lethal concentration (LC50) of the flowable formulations of both insecticides, placed on different surfaces, showed that their effectiveness on glass is similar, while on a ceramic surface deltamethrin is slightly more effective. The flowable formulations of the two insecticides were tested in 100 infested homes in the province of Santiago del Estero, Argentina. Deltamethrin was applied at a surface concentration of 25 mg/m2 and -cypermethrin at 50 mg/m2. The real surface concentrations of these products were analyzed from filter paper samples placed on walls and ceilings. Gas chromatography revealed good agreement with the target concentrations. In addition, entomological assessments were carried out 60, 90, 180, and 365 days after the treatments. Infestations were found only during the last assessment: in the peridomiciliary area of 10% of the houses treated with -cypermethrin and in 7% of the houses treated with deltamethrin (6% in the peridomiciliary area and 1% inside the house). The results indicate that -cypermethrin's effectiveness in controlling T. infestans when applied at a concentration of 50 mg/m2 is similar to that of deltamethrin applied at a concentration of 25 mg/m2

En este estudio se evaluó en el laboratorio y en el campo el efecto insecticida sobre Triatoma infestans, vector de la enfermedad de Chagas, del nuevo piretroide ß-cipermetrina, y se comparó con el de la deltametrina. La comparación de las dosis letales 50 (DL50) de ambos piretroides indicó que la ß-cipermetrina es más efectiva en ninfas y la deltametrina, en adultos. La evaluación de la concentración letal 50 (CL50) de las dos formulaciones floables de ambos insecticidas depositados sobre distintos soportes mostró que su efectividad en vidrio es similar. En cerámica, la deltametrina es ligeramente más efectiva. Los dos insecticidas floables se evaluaron en 100 viviendas infestadas de la provincia de Santiago del Estero, Argentina. La deltametrina floable se aplicó a una concentración superficial de 25 mg/m2 y la ß-cipermetrina, de 50 mg/m2. Las concentraciones superficiales reales de ambos productos se analizaron por medio de papeles de filtro colocados en paredes y techos. El análisis por cromatografía de gases mostró buena coincidencia con las concentraciones previstas. Asimismo, se realizaron evaluaciones entomológicas 60, 90, 180 y 365 días después de los tratamientos. Solo en la última evaluación se encontró 10% de infestación en peridomicilios de viviendas tratadas con ß-cipermetrina y 7% en las viviendas tratadas con deltametrina (6% en el peridomicilio y 1% en el domicilio). Los resultados indican que la efectividad de la ß-cipermetrina para controlar a T. infestans cuando se aplica a una concentración de 50 mg/m2 es similar a la de la deltametrina cuando esta se administra a una concentración de 25 mg/m2

Estudios sobre la seguridad en el uso del pote fumígeno insecticida CIPEIN PF-5 / Investigation on the security in the use of the fumigant canister insecticide CIPEIN PF-5

El CIPEIN PF-5 es una formulación insecticida experimental, especialmente desarrollada para el control químico de los vectores del Mal de Chagas. Su composición consiste en una mezcla fumígena (90.9%w/w) y tres principios activos: lindano (4%), diclhorvos (5%) y deltametrina (0.1%). Este pote fumígeno insecticida, demostró una excelente selectividad contra insectos. En tres especies de animales vertebrados diferentes no se detectaron síntomas de intoxicación ni inhibición de la acetilcolinesterasa, después de haber sido expuestos durante 2 horas a los humos insecticidas liberados por dos potes fumígenos, en un galpón de 264 metros cúbicos. Esta concentración ambiental de principios de principios activos fue suficiente para matar al 100%de los insectos expuestos (vinchucas, moscas y cucarachas). Los residuos de insecticidas en las superficies del galpón experimental resultaron entre 0.24-0.54 *g/cm* y después de 15 días no fueron detectables. Luego de 15 min. de ventilación del ambiente, la concentración de insecticida en el aire no fue detectable (< 0.1ppm). Los residuos de insecticidas superficiales, sobre los operarios fumigadores, son menores que 0.003 *g/cm*. El residuo carbonoso de los potes fumígenos combustionados presentó sólo un resto de lindano de 0.64%. El resultado del monitoreo bioquímico y clínico, de las personas expuestas laboralmente al CIPEIN PF-5, no mostró diferencias significativas con personas no expuestas. La presente evaluación toxicológica del pote fumígeno sugiere que se trata de un formulado selectivo contra las vinchucas y otros insectos, y lo suficientemente seguro bajo condiciones de uso normales, para el hombre y otros vertebrados

Relación entre la actividad de esterasas y la resistencia a malatión en una cepa de Tribolium Castaneum / Relation activity from enterase and t.castaneum malathion resistant

Se estudiaron comparativamente las esterasas de las cepas de Tribolium castaneum ULP (suceptible) y ML (resistente a malatión). La actividad de esterasas que hidrolizan acetato de * y ß naftol presentes en homogenatos de T. castaneum fue mayor en la cepa susceptible ML, mientras que la actividad frente al acetato de tiofenilo fue similar en ambas cepas. La distribución subcelular de la actividad esterástica frente al PTA mostró diferencias en ambas cepas. En los homogenatos de insectos de la cepa susceptible se observó que a mayor velocidad de centrifugación el sobrenadante resultó considerablemente más activo en la hidrólisis de acetato de tiofenilo. Se supone que ese resultado se debe a la presencia de un inhibidor endógeno no dializable, de peso molecular tal que puede ser parcialmente precipitado a 10.000g y en mayor medida a 100.000g. Los zimogramas de esterasas no inhibibles por eserina separadas por electroforesis en gel de poliacrilamida y reveladas con * y ß naftilacetato, mostraron, en todos los casos, una única banda que fue clasificada como aril o acetil esterasa. Los resultados descriptos encuadran en la teoría de la aliesterasa mutada, postulada para casos de resistencia al malatión, descriptos en otas especies de insectos

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