Norma Casabé

Evaluación de la b -cipermetrina para el control de Triatoma infestans

En este estudio se evaluo en el laboratorio y en el campo el efecto insecticida sobre Triatoma infestans, vector de la enfermedad de Chagas, del nuevo piretroide s-cipermetrina, y se comparo con el de la deltametrina. La comparacion de las dosis letales 50 (DL50) de ambos piretroides indico que la s-cipermetrina es mas efectiva en ninfas y la deltametrina, en adultos. La evaluacion de la concentracion letal 50 (CL50) de las dos formulaciones floables de ambos insecticidas depositados sobre distintos soportes mostro que su efectividad en vidrio es similar. En ceramica, la deltametrina es ligeramente mas efectiva. Los dos insecticidas floables se evaluaron en 100 viviendas infestadas de la provincia de Santiago del Estero, Argentina. La deltametrina floable se aplico a una concentracion superficial de 25 mg/m² y la s-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 analisis por cromatografia de gases mostro buena coincidencia con las concentraciones previstas. Asimismo, se realizaron evaluaciones entomologicas 60, 90, 180 y 365 dias despues de los tratamientos. Solo en la ultima evaluacion se encontro 10% de infestacion en peridomicilios de viviendas tratadas con s-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 s-cipermetrina para controlar a T. infestans cuando se aplica a una concentracion de 50 mg/m² es similar a la de la deltametrina cuando esta se administra a una concentracion de 25 mg/m².

Insecticidal Activity of Pyrethroids Against Triatoma infestans

The insecticide activity of synthetic pyrethroids to Triatoma infestans was tested by topical application. Deltamethrin, fenpropathrin, bioresmethrin, permethrin, Cypermethrin, d-phenothrin and cyphenothrin showed the highest activity.The susceptibility to poisoning of adult insects by these pyrethroids (except bioresmethrin) was increased by cotreatment with profenofos or with piperonyl butoxide (PBO). Assayed pyrethroids synergized by PBO showed similar general structure.The vinyl cyano pyrethroids showed a knockdown effect with a delayed recovery. During 15 days after intoxication with deltamethrin, insect recovery was observed. Recovery blockage by PBO was observed in cyphenothrin and deltamethrin poisoning at low doses.RésuméL’activité insecticide de pyréthrinoides de synthèse a été essayée par application topique sur Triatoma infestans.Deltaméthrine, fénpropathrine, biorésméthrine, permethrine, cyperméthrine, d-phénothrine et cyphénothrine ont montrée la meilleure activité.La susceptibilité à l’intoxication par ces pyréthrinoides des insectes adultes (avec l’exception de biorésmethrine) a été améliorée en ajoutant le profenofos ou le butoxide de pipéronyl (PBO) dans les traitements. Les pyréthrinoides synergisées par PBO ont montrée une structure chimique similaire. Les vinyl cyano piréthrinoides ont montrée l’effect choc accompagné d’une récupération retardée. Pendant 15 jours aprés l’intoxication avec la deltaméthrine, la récupération des insectes a été obtenue.

Evaluation of the flushing out activity of pyrethroids on Triatoma infestans

Tetramethrin, deltamethrin and Cypermethrin formulated as fumigant tablets or spray(ing) solutions showed flushing out activity on Triatoma infestans. Fumes arising from the tablets were analysed by gas chromatography. The proportion of pyrethroid liberated was between 10 and 20% of the original amount formulated. The flushing out activity shown was dependent on the pyrethroid compound, insect stage and sex. In general deltamethrin proved the most active flushing out agent and Cypermethrin the least active. Maximal activity was shown in the combination of nymphs and tetramethrin. Nymphs of Rhodnius prolixus were only flushed out by deltamethrin. In all cases, deltamethrin and Cypermethrin yielded 100% mortality 7 days after exposure to the pyrethroid fumes, while tetramethrin was not a killing agent.RésuméLa tetraméthrine, la deltaméthrine et la cyperméthrine sont des pyréthrinoides que, formulées soit comme tablette fumigène ou comme solutions (spray), ont expurgé des insectes vecteurs de la maladie de Chagas cachés dans des refuges standards. La concentration des pyréthrinoides libérés des tablettes fumigènes, détecté par la Chromatographie gazeuse, a été 10 à 20% l’original. En plus, il a été observé que l’activité d’expurger les insectes (flushing out) produite par les tablettes fumigènes dépend de: type de pyréthrinoide, espèce d’insecte, stade de développement larvaire et sexe. Les résultats observés indiqueraient que la deltaméthrine a l’effet maximal de “flushing out” tandis que l’activité de la cyperméthrine a démontré être sensiblement inférieur. La tetraméthrine a été la plus active sur le 5 éme stade de Triatoma infestans. D’ail leurs, le 5 éme stade de Rhodnius prolixus a été seulement expurgé par la deltaméthrine. Dans tout les cas, la deltaméthrine et la cyperméthrine ont démontré produire un 100% de mortalité sept jours après l’exposition aux pyréthrinoides, autant que la tetraméthrine a été incapable de produire une sensible mortalité.

The relation between viscosity and penetration of some diethyl p-substituted phenyl phosophorothionates and oil carriers into the cuticle of Triatoma infestans

Abstract The penetration rate of a series of O,O -diethyl p -substituted phenyl phosphorothionates was measured in the conenose bug Triatoma infestans . The influence of some physicochemical parameters was studied. No correlation was observed with π constant but a good linear relationship was obtained with the relative viscosity of the compounds. The penetration rates were also measured with parathion formulated with a series of paraffinic compounds as carriers. An increased penetration of the formulated parathion was observed. A good correlation was established between the viscosity of the oily carriers and the penetration rates in the different formulations. Parathion formulated with an oily vehicle showed an enhanced insecticide effect.

Cholinesterases and eserine-resistant esterases in the developing embryo of Triatoma infestans and its role as targets for inhibition in the ovicide action of parathion

Abstract 1. Activity of eserine-resistant esterases was found during all the embryonic development of Triatomainfestans. 2. The ontogenesis of esterases and cholinesterases was established by disc gel electrophoresis. Bands were classified as corresponding to aryl plus acetylesterases, carboxyesterases, acetylcholinesterases and butyrylcholinesterases according to the specificity to substrate and its inhibition by paraoxon. 3. Biochemical measurement of esterases after treatment of eggs with parathion showed partial inhibition of eserine-resistant esterases and cholinesterases. Disc gel electrophoresis revealed complete inhibition of bands corresponding to acetylcholinesterases and carboxyesterases and partial inhibition of butyrylcholinesterases. In vitro incubation with 10−5 M paraoxon caused similar inhibition of the esteratic bands. 4. Eggs of T. infestans rolled on 3.2 μg/cm2 of parathion (2 × LC50) developed fully but failed to hatch. A later acetylcholinesterase whose electrophoretic band was strongly visible at the hatching time was suggested as a possible critical target of the delayed ovicide action.

Fenitrothion toxicity in Triatoma infestans synergized by quercetin or thymol blue

Quercetin and thymol blue were shown to synergize the toxicity of fenitrothion to Triatoma infestans with synergistic ratios of 1.89 and 2.65 respectively. These synergistic ratios were statistically significant at P < 0.05. Both compounds inhibited glutathione S-transferases (GST) in vitro, with pI 50 values of 6.1 and 5.1 respectively. Quercetin or thymol blue caused in-vivo GST inhibition without affecting non-specific esterase (NSE) or acetylcholinesterase (AChE) activity. Incubation of [ 14 C]fenitrothion with T. infestans or rabbit liver GST produced desmethylfenitrothion as the major metabolite, which was specifically diminished in the presence of 0.3 mM quercetin. [ 14 C]Fenitrothion toxicokinetics study showed a significant decrease (P < 0.05) in radioactivity due to polar metabolites when insects were pre-treated with quercetin. These facts suggest that both assayed chemicals may be active in synergizing fenitrothion toxicity due to their ability to prevent the detoxification of organophosphorus insecticides by GSH conjugation.

Assay of pyrethroid-hydrolysing esterases using (1,R)-cis-3-(2,2-dibromovinyl)-2,2-dimethyl cyclopropane carboxylates as substrates

1. p-Nitrophenyl-, alpha-naphthyl-, and beta-naphthyl-(1,R)-cis-3-(2,2-dibromovinyl)2,2-dimethyl cyclopropane carboxylates are proposed as pyrethroid-like substrates for the detection of pyrethroid esterases (PyEs). 2. The substrates have been used in a spectrophotometric assay of PyEs and in a staining method to locate PyEs on polyacrylamide electrophoresis.