[Insecticide susceptibility evaluation in Aedes aegypti populations of Caldas, Colombia, in 2007 and 2011]. / Evaluación de la sensibilidad a insecticidas en poblaciones de Aedes aegypti (Diptera: Culicidae) del departamento de Caldas, Colombia, en 2007 y 2011.

INTRODUCTION: Continuous use of insecticides for the control of dengue transmission may lead to decreased susceptibility levels in mosquito vector populations. Timely monitoring is necessary to ensure detection of any potential resistance problems. OBJECTIVE: To determine the susceptibility status of Aedes aegypti to insecticides used in public health in Caldas, Colombia, during 2007 and 2011. MATERIALS AND METHODS: Susceptibility tests to the organophosphates temephos, malathion, fenitrothion and pirimiphos methyl, as well as to the pyrethroid deltamethrin, were carried out using standard World Health Organization and Centers for Disease Control and Prevention protocols. RESULTS: In 2007, resistance to temephos was detected in Ae. aegypti populations from La Dorada with resistance ratios of 11.5 and 13.3, prompting the Caldas Health Department to suspend the use of this larvicide. A reduction in resistance ratios to temephos was observed in 2011, as well as an apparent resistance to pirimiphos methyl. All Ae. aegypti populations tested were susceptible to deltamethrin, malathion and fenitrothion in both years. CONCLUSION: Evaluating the resistance ratios during two distinct periods allowed a decrease in resistance to be detected after suspension of the use of temephos. Surveillance of mosquito populations for changes in susceptibility levels to the insecticides used in dengue control programs is therefore recommended.

Evaluación de la sensibilidad a insecticidas en poblaciones de Aedes aegypti (Diptera: Culicidae) del departamento de Caldas, Colombia, en 2007 y 2011 / Insecticide susceptibility evaluation in Aedes aegypti populations of Caldas, Colombia, in 2007 and 2011

Introducción. El uso continuo de insecticidas para el control de la transmisión del dengue puede generar una reducción en los niveles de sensibilidad de las poblaciones de los mosquitos vectores. La vigilancia oportuna es necesaria para detectar cualquier problema potencial de resistencia. Objetivo. Determinar el estado de la sensibilidad a insecticidas de uso en salud pública en poblaciones de Aedes aegypti del departamento de Caldas, Colombia, en el 2007 y el 2011. Materiales y métodos. Se realizaron pruebas de sensibilidad a los organofosforados temefós, malatión, fenitrotión y metil-pirimifós y al piretroide deltametrina, siguiendo las metodologías estandarizadas de la Organización Mundial de la Salud y de los Centers for Disease Control and Prevention de los Estados Unidos. Resultados. En el 2007 se encontró resistencia al temefós en dos barrios del municipio de La Dorada, con grados de resistencia de 11,5 y 13,3. Por ello, la Dirección Territorial de Salud de Caldas suspendió el uso de este larvicida en dichos barrios. Cuatro años después, en el 2011, se observó una reducción en los grados de resistencia al temefós, así como resistencia al metil-pirimifós. Todas las poblaciones evaluadas fueron sensibles a los insecticidas deltametrina, malatión y fenitrotión en los dos períodos. Conclusión. La cuantificación de los grados de resistencia en dos períodos permitió evidenciar la reducción de la resistencia al temefós después de suspender su uso. Se recomienda mantener la vigilancia de los niveles de sensibilidad de los insecticidas usados en los programas de control de dengue.

Introduction: Continuous use of insecticides for the control of dengue transmission may lead to decreased susceptibility levels in mosquito vector populations. Timely monitoring is necessary to ensure detection of any potential resistance problems. Objective: To determine the susceptibility status of Aedes aegypti to insecticides used in public health in Caldas, Colombia, during 2007 and 2011. Materials and methods: Susceptibility tests to the organophosphates temephos, malathion, fenitrothion and pirimiphos methyl, as well as to the pyrethroid deltamethrin, were carried out using standard World Health Organization and Centers for Disease Control and Prevention protocols. Results: In 2007, resistance to temephos was detected in Ae. aegypti populations from La Dorada with resistance ratios of 11.5 and 13.3, prompting the Caldas Health Department to suspend the use of this larvicide. A reduction in resistance ratios to temephos was observed in 2011, as well as an apparent resistance to pirimiphos methyl. All Ae. aegypti populations tested were susceptible to deltamethrin, malathion and fenitrothion in both years. Conclusion: Evaluating the resistance ratios during two distinct periods allowed a decrease in resistance to be detected after suspension of the use of temephos. Surveillance of mosquito populations for changes in susceptibility levels to the insecticides used in dengue control programs is therefore recommended.

Aedes aegypti (Diptera: Culicidae): evaluation of natural long-lasting materials containing pyriproxyfen to improve control strategies.

Natural materials such as beeswax or a paraffin/stearin mixture containing pyriproxyfen and used as a slow release formulation may convert any breeding place into a larvicidal ovitrap for Aedes aegypti (L.) control. Effectiveness and residual activity of beeswax and paraffin/stearin 1:1 discs containing from 10(-5) to 10(-1) % pyriproxyfen and sticked at the bottom of plastic jars were evaluated for adult emergence inhibition (EI) on late 3rd or early 4th instar A. aegypti larvae. At the initial time t = 0, the EI was 100% for vessels containing beeswax or paraffin/stearin 1:1 discs containing up to 10(-4)% pyriproxyfen. For the lowest pyriproxyfen concentration of 10(-5)%, paraffin/stearin mixture gave a higher EI% value than beeswax (100 and 50%, respectively). Jars were kept at room temperature, and water was totally replaced every 15 days. Bioassays for residual activity repeated monthly showed that at 30 days and for pyriproxyfen 10(-5) % and both matrices, the EI values were low and comparable to control values. For pyriproxyfen 10(-4) %, EI remained above 95% for at least 90 days and around 75% up to 180 days. The EI values are always higher for paraffin/stearin mixture than for beeswax. For all other higher concentrations, 100% EI was obtained at least during 300 days. In a semi-field trial, paraffin/stearin/sand O-rings (2:1:2), containing pyriproxyfen 1%, were sunken in 200-l water-storage tanks and held outdoors in a shadow place. After 72 h, a 250-ml aliquot was taken (t = 0) obtaining 100 % EI. Water level was completed to 200 l every 15 days and bioassays repeated monthly as before. Residual activity remains with 100% EI at least for 6 months.

A new ovitrap made of slow release natural materials containing pyriproxyfen for Aedes aegypti (Diptera:Culicidae) control.

ABSTRACT This initial study is aimed to measure the performance of incorporating pyriproxyfen in natural materials with low environmental impact to obtain slow release formulations that can be used as larvicidal or autocidal ovitraps avoiding hatched Aedes aegypti (L.) eggs to emerge as adults. Hollow candles made of beeswax or paraffin:stearin 1:1 mixture containing pyriproxyfen 0.01 and 0.05% were prepared and used as holding water containers for larval bioassay. Pyriproxyfen was released quickly into the larvae-breeding water. Ae. aegypti larvae were introduced immediately after the addition of tap water to the hollow candles (t = 1 min) or after 1, 4, and 8 h. More than 40% of the larvae did not emerge as adults for t = 1 min, reaching 80-100% when the larvae were added after 1 or 4 h, respectively. The hollow candles were kept at room temperature, and water was replaced every 15 d. Bioassays performed every 30 d showed that the residual activity obtained for both matrices and both concentrations of pyriproxyfen was higher than 360 d, with 100% inhibition of adult emergence.

Field comparison of thermal and non-thermal ultra-low-volume applications using water and diesel as solvents for managing dengue vector, Aedes aegypti.

OBJECTIVES: To compare the effectiveness on Aedes aegypti (Linneo) (Diptera: Culicidae) of a larvicide-adulticide ULV formulation applied by a thermal or a cold fogger using different solvents. METHODS: We applied, in field conditions, a ULV formulation containing pyriproxyfen and permethrin, using a thermal and a cold fogger and water or diesel as solvent. We determined the effectiveness of these applications on Ae. aegypti adults and larvae by different bioassays and measuring Breteau, house and adult indices. RESULTS: When water was used as solvent, the treatments applied with the cold or the thermal foggers were equally effective on adult mortality (close to 90%) and adult emergence inhibition (% EI) (close to 70%). When the thermal fogger was used with water as solvent, the adult mortality outside the houses (85%) was higher, but not significantly different, than with diesel (65%). The contrary happens inside (22%vs. 58%), while there were no differences in %EI. Adult and larval indices behaved similarly in all areas, with a slight tendency for the treatments applied using water as solvent to be more effective. CONCLUSIONS: Water-based formulations are equally or more effective than the one applied with diesel as solvent. The use of water as solvent will not only improve the effectiveness of this formulation but also reduce the environmental impact and costs of spraying compared to the use of diesel.

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.

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.

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

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.

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.

Sensitivity of Aedes aegypti adults (Diptera: Culicidae) to the vapors of Eucalyptus essential oils.

Vapors of essential oils extracted from various species of Eucalyptus (E. gunnii, E. tereticornis, E. grandis, E. camaldulensis, E. dunnii, E. cinerea, E. saligna, E. sideroxylon, E. globulus ssp. globulus, E. globulus ssp. maidenii, E. viminalis and the hybrids E. grandisxE. tereticornis and E. grandisxE. camaldulensis) and their major components were found to be toxic to Aedes aegypti adults, the yellow fever mosquito. An aliquot of each oil was placed in a cylindrical test chamber and the number of knocked-down mosquitoes was recorded as function of time. Knockdown time 50% was then calculated. Results showed that E. viminalis had the fastest knockdown time at of 4.2 min, on the same order as dichlorvos, a standard knockdown agent. A correlation was observed between the content of 1,8-cineole in the Eucalyptus essential oils and the corresponding toxic effect. The correlation between KT(50) values and calculated vapor pressures of the essential oil components showed that the fumigant activity of simple organic compounds in insects is correlated with their volatility.

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.

Efficacy of a new combined larvicidal-adulticidal ultralow volume formulation against Aedes aegypti (Diptera: Culicidae), vector of dengue.

A new ultralow volume formulation (ULV) containing permethrin as an adulticidal active ingredient and the insect growth regulator (IGR) pyriproxyfen as a larvicide was developed and its efficacy evaluated in a field trial in Wanda, Misiones (Argentina). Two separate study areas were sprayed: one with a ULV formulation of permethrin 15% plus pyriproxyfen 3% and the other with permethrin 15% only. A third untreated area was kept as a control. Sentinel cages containing adult mosquitoes and jars containing Aedes aegypti larvae III/IV were placed in treated and control areas. The residual activity of the formulations was tested using 20 L water containers. The adulticide effect of permethrin 15% + pyriproxyfen 3% formulation was similar to the permethrin 15% formulation, however, the inhibition of adult emergence in the treatment with permethrin 15% never exceeded 20%, whereas the inhibition of adult emergence in the treatment with permethrin 15% plus pyriproxyfen 3% showed initial values of 96% maintaining this high level of inhibition up to 35 days after ULV spraying. Larval indexes (House and Breteau indexes) showed that a greater, long-lasting effect was obtained with the permethrin 15% plus pyriproxyfen 3% formulation.

Effectiveness of pyriproxyfen and diflubenzuron formulations as larvicides against Aedes aegypti.

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 (microg/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.

Aedes aegypti (Diptera: Culicidae): monitoring of populations to improve control strategies in Argentina.

To study the seasonal fluctuations of populations of Aedes aegypti (L.), to improve control strategies, or to monitor chemical control interventions, a lightweight, inexpensive ovitrap made of black plastic, pail-shaped, stackable, and provided with a wood tongue depressor was used. Field assays were performed in the northeast and northwest part of Argentina. In a 1-year trial performed in Tartagal (Salta), almost 100% of the ovitraps were highly positive, collecting a total of 1,000/2,000 eggs during March and the first part of April. A focal treatment in the corresponding neighborhood, performed at this time, immediately began to reduce positive ovitraps in spite of the high temperatures registered, rising again in November after winter season. Another field trial was performed in the whole urban area of Iguazú (Misiones). Mosquito populations were evaluated after three weekly ultra low volume (ULV) applications with an EC formulation of permethrin in water. The number of positive ovitraps diminished from 49% to 10% after the treatments. The last one performed in Wanda (Misiones) showed that positive ovitraps inside the dwellings aided in determining reinfestation rates after an intervention with a smoke-generating formulation containing beta-cypermethrin. The work performed in three different situations in urban areas at high risk of dengue can be considered a preliminary assay to establish the effective performance of simple ovitraps, allowing the Vector Control Service of the Argentinian Ministry of Health its use to improve surveillance and control strategies.

Aedes aegypti resistance to temephos in Argentina.

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.

Larvicidal effect of Eucalyptus grandis essential oil and turpentine and their major components on Aedes aegypti larvae.

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 (alpha- and beta-pinene and 1,8-cineole) was determined. Gas chromatography-mass spectroscopy analysis of E. grandis essential oil revealed that its major components are alpha-pinene and 1,8-cineole. Similar analysis of turpentine obtained by distillation of the resin pitch of conifers showed that alpha- and beta-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 alpha- and beta-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 alpha-pinene in E. grandis and alpha- and beta-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.

Synergism between cis-permethrin and benzoyl phenyl urea insect growth regulators against Aedes aegypti larvae.

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.

Laboratory and scaled up evaluation of cis-permethrin applied as a new ultra low volume formulation against Aedes aegypti (Diptera: Culicidae).

Ultra low volume (ULV) aerial spraying is a common methodology for spatial treatments for Aedes aegypti (L.) control. Previous studies from our laboratory indicated that the cis isomer of permethrin has an excellent efficacy for vector control, in particular for Triatoma infestans. It was of interest to determine the efficacy of this pure isomer in a ULV water-based formulation for adult A. aegypti control, since both vectors usually are found together in South America. A method is presented to make a quick measure at laboratory level of the knock down effect (KT50) of a new EC water-based formulation of cis-permethrin, in a small Peet Grady chamber of 0.34 m3, with a specially designed glass sprayer. A deltamethrin standard ULV formulation "CISLIN" was used for comparison. cis-Permethrin showed a significantly lower KT50 value than deltamethrin (7.50 and 9.65 min, respectively). When the mosquitoes were introduced into the chamber 10 min after spraying KT50 values were almost equal (15.59 and 15.88 min, respectively). In scaled up bioassays the ULV formulation of cis-permethrin showed 100% mortality of A. aegypti adult mosquitoes at the beginning of the treatment (t=0) and some mortality at 1h post treatment of freshly introduced mosquitoes. It was concluded that cis-permethrin could be an excellent tool for control of A. aegypti and other vectors of medical importance, with fewer side effects and better cost-effectiveness than with the cyanopyrethroids.

Field evaluation of a smoke-generating formulation containing beta-cypermethrin against the dengue vector in Argentina.

Previous results from laboratory and prefield assays obtained by our laboratory indicated that the fumigant canister CIPEIN PF-7 (Bolate) a smoke-generating formulation containing 5% beta-cypermethrin, has excellent performance as an adulticide for Aedes aegypti control. A field trial was carried out to evaluate the effectiveness of CIPEIN PF-7 to control adult mosquitoes of Ae. aegypti inside houses. The trial was carried out in Colonia Delicia, a locality of 4,750 inhabitants, located in Misiones, a subtropical area in northeastern Argentina, an area highly infested with Ae. aegypti and at risk to dengue. One fumigant canister was applied in each house, which remained closed for 1 h and was then ventilated for 15 min by opening doors and windows. Taking into account the time spent in the fumigation activities, the rate of the treatment was around 20 houses per worker per day. Cages with adult mosquitoes and plastic cups with water containing mosquito larvae were put in various places of the houses. There was 100% initial mortality in each case after treatment with the fumigant canister. The residual effect showed 100% mortality of adults exposed 2 h for at least 3 days after treatment and 100% mortality of larvae 1 day after treatment. House and Breteau indices before the treatment were 51% and 106, respectively, falling to 23% and 44 after treatment. The potential for using this new tool in geographic areas very difficult to reach or as a quick alternative to control Ae. aegypti inside the houses, especially during dengue epidemics, is discussed.

Thermal decomposition and isomerization of cis-permethrin and beta-cypermethrin in the solid phase.

The stability to heart of cis-permethrin and beta-cypermethrin in the solid phase was studied and the decomposition products identified. Samples heated at 210 degrees C in an oven in the dark showed that, in the absence of potassium chlorate (the salt present in smoke-generating formulations of these pyrethroids), cis-permethrin was not isomerized, although in the presence of that salt, decomposition was greater and thermal isomerization occurred. Other salts of the type KXO3 or NaXO3, with X being halogen or nitrogen, also led to a considerable thermal isomerization. Heating the insecticides in solution in the presence of potassium chlorate did not produce isomerization in any of the solvents assayed. Salt-catalysed thermal cis-trans isomerization was also found for other pyrethroids derived from permethrinic or deltamethrinic acid but not for those derived from chrysanthemic acid. The main thermal degradation processes of cis-permethrin and beta-cypermethrin decomposition when potassium chlorate was present were cyclopropane isomerization, ester cleavage and subsequent oxidation of the resulting products. Permethrinic acid, 3-phenoxybenzyle chloride, alcohol, aldehyde and acid were identified in both cases, as well as 3-phenoxybenzyl cyanide from beta-cypermethrin. A similar decomposition pattern occurred after combustion of pyrethroid fumigant formulations.