Susana Licastro

LARVICIDAL EFFECT OF EUCALYPTUS GRANDIS ESSENTIAL OIL AND TURPENTINE AND THEIR MAJOR COMPONENTS ON AEDES AEGYPTI LARVAE

ABSTRACT In the search for new alternatives for the control of Aedes aegypti the larvicidal activity of Eucalyptus grandis essential oil and pine resin essential oil (turpentine) and their major components (α- and β-pinene and 1,8-cineole) was determined. Gas chromatography–mass spectroscopy analysis of E. grandis essential oil revealed that its major components are α-pinene and 1,8-cineole. Similar analysis of turpentine obtained by distillation of the resin pitch of conifers showed that α- and β-pinene are the only major components. Third and early 4th instars of the CIPEIN-susceptible strain of Ae. aegypti were exposed to acetonic solutions of E. grandis essential oil, turpentine, and their major components for 24 h. Turpentine, with an LC50 of 14.7 ppm, was more active than the essential oil of E. grandis (LC50: 32.4 ppm). Larvicidal activity of the essential oil components showed that α- and β-pinene present low LC50 values (15.4 and 12.1 ppm, respectively), whereas pure 1,8-cineole showed an LC50 of 57.2 ppm. These results suggest that α-pinene in E. grandis and α- and β-pinene in turpentine serve as the principal larvicidal components of both oils. Results obtained on larvicidal effects of essential oil of Eucalyptus grandis and turpentine could be considered a contribution to the search for new biodegradable larvicides of natural origin.

Aedes aegypti Resistance to Temephos in Argentina

ABSTRACT Monitoring of resistance of Aedes aegypti to temephos was implemented in the provinces of Formosa and Misiones, Argentina, as a response to the need to improve the vigilance for the dengue vector in areas of high risk of dengue. Eggs collected in each locality were reared, and susceptibility to temephos was assayed using larval bioassays. A weak decrease in susceptibility of larvae to temephos was observed in Clorinda and Puerto Iguazú, indicating an incipient resistance with a resistance ratio of 3. No control failures have been observed yet, and this program should allow the early detection of a real problem in our country.

Effectiveness of Pyriproxyfen and Diflubenzuron Formulations as Larvicides Against Aedes aegypti

ABSTRACT The efficacy of technical pyriproxyfen and diflubenzuron was evaluated at the laboratory level against Aedes aegypti, where we achieved adult emergence inhibition (EI50) values of 0.048 and 1.59 ppb (µg/liter), respectively. We compared these data with values obtained for temephos. We prepared emulsifiable concentrate formulations of pyriproxyfen and diflubenzuron in the laboratory and obtained EI50 values of 0.01 and 0.02 ppb, respectively. We also obtained 100% adult emergence inhibition with 0.1% slow-release sand formulations of pyriproxyfen and diflubenzuron. In a simulated field study, the granular sand formulations of pyriproxyfen, diflubenzuron, and temephos remained active for over 4 mo. In a field study, a 0.2% granular formulation of diflubenzuron and 1% temephos showed a similar performance.

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.

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.

Thermal behaviour and biological activity against Aedes aegypti (Diptera: Culicidae) of permethrin and pyriproxyfen in a smoke-generating formulation.

BACKGROUND The most common ways to control dengue vector Aedes aegypti (L.) are larval source reduction in domestic habitats and ground application of small quantities of aerosol insecticide (ultralow volume). Nevertheless, these actions have been shown repeatedly to be ineffective in controlling Ae. aegypti populations. RESULTS The efficacy of a new smoke-generating formulation containing pyriproxyfen and permethrin was evaluated in the laboratory. Smoke-generating tablets containing each insecticide individually or combined were prepared, and the recovery of the insecticides from the smoke was determined. Recovery values of over 90% were obtained for pyriproxyfen, and around 50% for permethrin. The biological efficacy of pyriproxyfen released in the smoke was evaluated in the laboratory, on late third-instar or early fourth-instar Ae. aegypti larvae, using different concentrations of pyriproxyfen and exposure times. Adult emergence inhibition (EI) values of 100% were obtained at 30 min, and a dose-dependent effect was observed at 5 min. The effect of pyriproxyfen released in the smoke was due to direct contact with the larvicide in the water rather than by inhalation of the fumes. The efficacy of permethrin released in the fumes was also evaluated as knockdown effect (KT(50)) on adults for a tablet containing permethrin alone or permethrin plus pyriproxyfen. There was no significant difference in KT(50) values obtained for permethrin (KT(50) = 19.9 min) and permethrin plus pyriproxyfen (KT(50) = 19.4 min). CONCLUSION The excellent laboratory performance of this new formulation on immature stages and adults indicates that a smoke-generating tablet containing pyriproxyfen and permethrin could be a new tool for controlling mosquitoes.

A new strategy for Aedes aegypti (Diptera: Culicidae) control with community participation using a new fumigant formulation.

ABSTRACT Dengue and dengue hemorrhagic fever are mosquito-borne viral diseases that coincide with the distribution of Aedes aegypti (L.), the primary vector in the tropical and semitropical world. With no available vaccine, controlling the dengue vector is essential to avoid epidemics. This study evaluates the efficacy of a new smoke-generating formulation containing pyriproxyfen and permethrin in Puerto Libertad, Misiones, Argentina. A fumigant tablet (FT) was applied inside the houses by the community members and compared with a professional application. A treatment combining the application of fumigant tablets indoors and ultralow volume fumigation outdoors was also assessed. The community perceptions and practices about dengue disease and the acceptance of this new nonprofessional FT were evaluated through surveys. Results show >90% adult emergence inhibition and 100% adult mortality with these treatments. More than 80% of the residents applied the FT and preferred participating in a vector control program by using a nonprofessional mosquito control tool, instead of attending meetings and workshops promoting cultural changes.

Droplet size and efficacy of an adulticide–larvicide ultralow‐volume formulation on Aedes aegypti using different solvents and spray application methods

BACKGROUND When cases of dengue are reported or the density of adult Aedes aegypti (L.) becomes too high, ultralow-volume (ULV) application of insecticides is the recommended control method. The droplet size of an aerosol insecticide influences its efficiency in killing adult mosquitoes. Many studies have been carried out to determine the optimum droplet size that maximises vector control efforts, but only a few have determined droplet-size spectra for specific equipment using different solvents and comparing thermal and non-thermal aerosols. RESULTS The present study showed that the droplet size for a water-based adulticide-larvicide formulation was larger than for the same formulation diluted in gasoil or biodiesel. No significant differences in adult mortality were observed between sprayers and solvents, but efficacy decreased with distance from the sprayer nozzle. Adult emergence inhibition was more than 90% when using water as a solvent for both thermal and cold foggers, and the efficacy did not decrease with distance from the sprayer nozzle. On the other hand, oil-based solvents became less effective with distance. CONCLUSION The use of water as a solvent with both thermal and cold foggers improves the efficacy of the studied formulation containing permethrin as adulticide and pyriproxyfen as larvicide in scaled-up assays. Moreover, it reduces the environmental impact and costs of spraying by comparison with formulations using oil solvents.

Sublethal Effect of Pyriproxyfen Released from a Fumigant Formulation on Fecundity, Fertility, and Ovicidal Action in Aedes aegypti (Diptera: Culicidae)

ABSTRACT Dengue and dengue hemorrhagic fever are mosquito-borne viral diseases that coincide with the distribution of Aedes aegypti (L.), the primary vector in the tropical and semitropical world. With no available vaccine, controlling the dengue vector is essential to prevent epidemics. The effects of the insect growth regulator pyriproxyfen on Ae. aegypti adults that survived a treatment with a sublethal dose were investigated in the laboratory, including effects on their reproductive potential. Pyriproxyfen was released from a fumigant formulation at a dose causing 20 or 40% emergence inhibition (%EI). Females were dissected before and after blood feeding and the basal follicle number was counted. There were no differences between the control and treated group on the basal follicle number for both doses used. Fertility and fecundity were reduced at a concentration of EI40 but no at EI20. There was no ovicidal effect of pyriproxyfen by immersion of eggs in treated water neither when the females laid their eggs on a pyriproxyfen-treated surface. This work shows that sublethal doses of pyriproxyfen can have effects on fertility and fecundity of Ae. aegypti females, which together with its larvicidal activity could contribute to an overall decrease in a given population.

SYNERGISM BETWEEN CIS-PERMETHRIN AND BENZOYL PHENYL UREA INSECT GROWTH REGULATORS AGAINST AEDES AEGYPTI LARVAE

ABSTRACT Emulsifiable concentrate formulations of 2 insect growth regulator (IGR) benzoyl ureas (novaluron and diflubenzuron) and the pyrethroid cis-permethrin were individually bioassayed against late 3rd- or early 4th-stage larvae of susceptible Aedes aegypti. The emergence inhibition 50% were 0.038, 0.048, and 0.179 ppb for novaluron, diflubenzuron, and cis-permethrin, respectively. We also tested 1:1 (v:v) mixtures of cis-permethrin and benzoyl ureas. Emergence inhibition 50% for novaluron plus cis-permethrin and diflubenzuron plus cis-permethrin were 0.030 and 0.037, respectively, with combination indexes of 0.49 and 0.56, indicating a synergistic interaction between these insecticides. The percentage of larval mortality produced by 0.5 ppb of the mixtures of cis-permethrin and each IGR was compared to the addition of larval mortality produced in separated experiments by 0.25 ppb of each component, after 5, 9 and 13 days of continuous exposure. In all bioassays, the novaluron plus cis-permethrin mixture produced a significantly higher larvicidal effect (P < 0.05) compared with the individual contribution of each compound. The diflubenzuron plus cis-permethrin mixture showed significantly higher larval mortality (P < 0.05) compared with the contributive effect of each insecticide after 9 and 13 days of exposure, but there was no significant difference after 5 days of exposure.