Héctor Masuh

Eucalyptus essential oil toxicity against permethrin-resistant Pediculus humanus capitis (Phthiraptera: Pediculidae).

During the past decades, chemical control against the head louse Pediculus humanus capitis De Geer has been based in the application of products containing permethrin. The repetitive overuse of pediculicides has resulted in the development of high levels of resistance to one or more of these products worldwide. Essential oils obtained from aromatic plants like Eucalyptus are good and safe alternatives due to their low toxicity to mammals and easy biodegradability. In the present study, we reported the chemical composition of Eucalyptus dunnii and Eucalyptus gunni, and the fumigant activity of five Eucalyptus essential oils and their main compounds against permethrin-resistant head lice from Argentina. The most effective essential oils were Eucalyptus sideroxylon, Eucalyptus globulus ssp globulus, and Eucalyptus globulus ssp maidenii, with knockdown time 50% (KT50) values of 24.75, 27.73, and 31.39xa0min. A linear regression analysis between percentage of 1,8-Cineole and KT50 values of the essential oils showed a significant correlation at a pu2009<u20090.01. Since Eucalyptus essential oils showed to be effective against head lice and are classified as safer compounds, they can be employed into pediculicide formulations.

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 20xa0L 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 35xa0days 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.

Knockdown and larvicidal activity of six monoterpenes against Aedes aegypti (Diptera: Culicidae) and their structure-activity relationships

The relationships between physicochemical parameters of majority components of Eucalyptus essential oils and their insecticide effect were evaluated on Aedes aegypti (L.) (Diptera: Culicidae). The octanol–water partition coefficients of the monoterpenes were estimated by the atom/fragment contribution method and the vapor pressures were determined by our laboratory in previous studies. The larvicidal activity (LC50(ppm)) and knockdown effect (KT50(min)) of each component was determined. The results show that the toxicity of EOs main components of Eucalyptus on adults and larvae of A. aegypti is strongly related to their physicochemical properties (vapor pressure and Log P). However, the interaction of both variables (vapor pressure * Log P) explains the toxicological phenomenon more precisely. The regression models were expressed as follows: KT50(min)u2009=u2009u2009−u200910.9u2009+u20093.7u2009*u2009Logxa0Pu2009+u20091.9u2009*u20091/Pvaporxa0(R2u2009=u20090.80;u2009Fu2009=u200942.5) and LC50(ppm)u2009=u2009u2009−u200994.3u2009+u2009438.6u2009*u2009xa01/Logxa0Pu2009+u20092.8u2009*u2009xa01/Pvaporxa0(Fu2009=u200957.8;u2009R2u2009=u20090.85). The six evaluated components present different functional groups. Therefore, it was considered to evaluate the monoterpenes as a group and separated in two groups: oxygenated monoterpenes (α-terpineol, 4-terpineol, and 1,8-cineole) and terpene hydrocarbons (γ-terpinene, p-cymene, and α-pinene). The results show the regression models for each group as follows: (A) oxygenated terpenes: KT50(min)u2009=u2009−u2009515.3u2009+u20091613.2u2009∗u20091/Logxa0Pu2009+u20095,u20092u2009∗u20091/Pvaporxa0(Fu2009=u20093176.7u2009R2u2009=u20090.99) and LC50(ppm)xa0u2009=u2009u2009−u20091679.4u2009+u20095402.1u2009∗u20091/Logxa0Pu2009+u200912.7u2009∗u2009xa01/Pvaporxa0(Fu2009=u2009282.9;u2009R2u2009=u20090.99). (B) Hydrocarbons terpenes: KT50(min)u2009=u200918.2u2009−u200958.3u2009*u20091/Logxa0Pu2009+u20092.7u2009*u20091/Pvaporxa0(Fu2009=u2009171.7;u2009xa0R2u2009=u20090.97) and LC50(ppm)u2009=u2009−u200921.1u2009+u2009174.9u2009∗u20091/Logxa0Pu2009−u200914.3u2009∗u20091/Pvaporxa0(Fu2009=u2009410.0;u2009R2u2009=u20090.99). The association between the toxic effect of the evaluated monoterpenes against A. aegypti and the physicochemical properties can be better described when they are separated into functional groups (hydrocarbons vs. oxygenated terpenes).

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

BACKGROUNDnThe 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.nnnRESULTSnThe 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).nnnCONCLUSIONnThe 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.

Volatile compounds secreted by Brindley's glands of adult Triatoma infestans: identification and biological activity of previously unidentified compounds

ABSTRACT Volatile emissions of adult male Triatoma infestans were collected on non-polar SPME fibers and analyzed by gas chromatography linked to a mass spectrometer. A complex mixture of 16 short-chain esters and acids were identified. The composition of short-chain aliphatic acids (ethanoic to nonanoic acids) was similar to previously reported results. The most abundant aliphatic acid was 2-methylpropanoic acid, constituting 18% of the total volatile content. Also abundant were the esters 2- and 3-methylbutyl 2-methylpropanoate, which constituted 30% and 22%, respectively, of the total volatile content. A similar pattern of compounds was observed in the volatiles secreted by dissected male Brindleys glands; however, in this case, 2- and 3-methylbutan-1-ol were detected which were not found in live insect volatile emissions. Large variability in volatile composition was also observed among the glands excised from different insects. Electroantennographic (EAG) evaluation of the components of Brindleys gland showed significant responses for 2- and 3-methylbutyl 2-methylpropanoate compared to controls. The mixture of volatiles secreted by excised Brindleysglands and the isolated 2- and 3-methylbutyl 2-methylpropanoate had repellent effects on both male and female T. infestans, possibly associated with a defensive strategy.

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.

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

ABSTRACT n 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.

Biological and Chemical Characterization of a New Larvicide Ovitrap Made of Plastic With Pyriproxyfen Incorporated for Aedes aegypti (Diptera: Culicidae) Control

Abstract Aedes aegypti (L.) is a species of international concern because of its ability to transmit serious human arboviral diseases including yellow fever, dengue, and chikungunya, which have spread to all continents. Ovitraps are containers constructed to imitate Aedes’ natural breeding sites and have been used for many decades as a sensitive and inexpensive surveillance tool for detecting the presence of container-inhabiting mosquitoes. In addition to their value for vector surveillance, various ovitrap devices have been evaluated as tools for suppressing Ae. aegypti populations. In this study, we performed a biological and chemical characterization of a new ovitrap prototype manufactured by injection molding of low-density polyethylene (LDPE) with the larvicide pyriproxyfen. Our research shows that pyriproxyfen was immediately released from the LDPE into the water of the ovitrap and led to an emergence inhibition of 100% for over 30 weeks. In addition, ovitraps continued to show a high larvicidal activity after over 20 washes. Pyriproxyfen was detectable in the water after 20 s and reached a peak after 24 h. Our results show that this ovitrap can be an effective, inexpensive, and low-maintenance tool for Ae. aegypti surveillance and control.

A floral‐derived attractant for Aedes aegypti mosquitoes

The reproductive success of Aedes aegypti (L.) (Diptera: Culicidae) is strongly dependent on the availability of carbohydrates in the environment and the ability of the mosquitoes to locate them. The most significant source of carbohydrates for mosquitoes is nectar from flowering plants, which mosquitoes locate by their volatile compounds. The aim of our work was to identify plant volatile compounds that elicit a behavioral response in Ae. aegypti, which may be included in a mosquito trap for surveillance and/or control purposes. Landing‐preference bioassays were performed with plants of three species—Plectranthus neochilus Schltr. (Lamiaceae), Tagetes patula L. (Asteraceae), and Lobularia maritima (L.) Desv. (Brassicaceae)—as lures and toxic sugar baits as landing markers. Mosquitoes landed only on L. maritima. Freshly cut inflorescences of L. maritima elicited a positive flight response in both sexes of mosquitoes. The analysis of the compounds in the static head space of L. maritima was performed by solid phase microextraction (SPME). Of the single volatile compounds tested, acetophenone was attractive and 1‐octanol caused a flight aversive response. These findings are relevant as there are no reported plant‐derived compounds attractive to A. aegypti. As both the male and female mosquitoes sugar feed, traps baited with plant odors are able to lure the whole adult population, making it an interesting option for including in future mosquito surveillance traps.

New spot-on formulation containing chlorpyrifos for controlling horn flies on cattle: laboratory model of insecticide release and field trial.

A highly viscous formulation containing chlorpyrifos (RET) was evaluated under laboratory, pre-field, and field conditions, and compared against ear tags with organophosphorus insecticides. Laboratory bioassays were performed using Musca domestica L. and a thin layer chromatography (TLC) plate of reversed phase silica gel modeling a lipophilic surface. Insects were exposed to the insecticide vapors of both formulations, directly and indirectly to test for lateral diffusion. Knockdown time 50% (KT50) values were determined as toxicological indicators of insecticide release. Minimum KT50 values of the direct effect of both formulations on horn flies were reached 4xa0weeks after being applied. The KT50 effect of migrated insecticides showed that RET formulation had a maximal effectiveness between the fourth and tenth last week. The KT50 effect of the insecticide migrating from ear tags decreased during the last 2xa0weeks of the experiment, and the KT50 effect of the laterally migrated insecticide was significantly higher for the RET formulation during this period. A pre-field bioassay was performed by exposing pieces of rabbit leather with both formulations and recording the KT50. At the end of the experiment, the KT50 effect of laterally migrated insecticide was significantly higher for the RET formulation. Regarding vapor emission, as a general trend the KT50 effect of ear tags was greater than for the RET formulation. To evaluate the horn fly infestation in the field bioassays, photographs of the animal were taken. The results shows that RET provided significant control for 11xa0weeks while the ear tags provided protection until the 12th week.