A rapid method for screening mosquito repellents on Anopheles pseudopunctipennis and Aedes aegypti.

One of the main vectors for malaria in Latin America is Anopheles pseudopunctipennis (Theobald), whereas Aedes aegypti (L.) is the primary vector of dengue, yellow fever, Zika and chikungunya viruses. The use of repellents is recommended as a personal protection method against these mosquitoes. However there are very few studies evaluating the effect of repellents on An. pseudopunctipennis. The use of a Petri dish to study repellence has been applied by several authors on flies, cockroaches, kissing bugs and mosquitoes, being a valuable technique for species that are difficult to breed under laboratory conditions, such as An. pseudopunctipennis. In the present study, we evaluated the repellence of the essential oil of the Eucalyptus nitens (Shining gum), its main component (1,8-cineole) and the commercial repellent DEET on An. pseudopunctipennis and Ae. aegypti adult females using the plaque repellency method coupled to EthoVision XT10.1 video-tracking software. Repellent effect and locomotor activity were studied through a repellence index (RI) together with an axis constructed from the behavioural variables obtained using the tracking software. DEET repellent effect was observed at 0.01 mg/mL for Ae. aegypti and 0.01 and 0.1 mg/mL for An. pseudopunctipennis. In addition, the essential oil showed significant repellence at 1 and 10 mg/mL for Ae. aegypti, and 1, 5, 10 and 25 mg/mL for An. pseudopunctipennis. Neither of these species were repelled at any concentration of 1,8-cineole. This is the first study that evaluates these compounds on An. pseudopunctipennis females and quantifies their effects on the activity of both species.

Transcriptomic analysis and molecular docking reveal genes involved in the response of Aedes aegypti larvae to an essential oil extracted from Eucalyptus.

BACKGROUND: Aedes aegypti (L.) is an urban mosquito, vector of several arboviruses that cause severe diseases in hundreds of million people each year. The resistance to synthetic insecticides developed by Ae. aegypti populations worldwide has contributed to failures in vector control campaigns, increasing the impact of arbovirus diseases. In this context, plant-derived essential oils with larvicidal activity could be an attractive alternative for vector control. However, the mode of action and the detoxificant response of mosquitoes to plant derived compounds have not been established, impairing the optimization of their use. METHODS AND FINDINGS: Here we compare gene expression in Ae. aegypti larvae after 14 hrs of exposure to Eucalyptus camaldulensis essential oil with a control group exposed to vehicle (acetone) for the same lapse, by using RNA-Seq. We found differentially expressed genes encoding for cuticle proteins, fatty-acid synthesis, membrane transporters and detoxificant related gene families (i.e. heat shock proteins, cytochromes P450, glutathione transferases, UDP-glycosyltransferases and ABC transporters). Finally, our RNA-Seq and molecular docking results provide evidence pointing to a central involvement of chemosensory proteins in the detoxificant response in mosquitoes. CONCLUSIONS AND SIGNIFICANCE: Our work contributes to the understanding of the physiological response of Ae. aegypti larvae to an intoxication with a natural toxic distilled from Eucalyptus leafs. The results suggest an involvement of most of the gene families associated to detoxification of xenobiotics in insects. Noteworthy, this work provides important information regarding the implication of chemosensory proteins in the detoxification of a natural larvicide. Understanding the mode of detoxification of Eucalyptus distilled compounds could contribute to their implementation as a tool in mosquito control.

Soil presence reduces the control effectiveness of a slow-release formulation of pyriproxyfen on Aedes aegypti (Diptera: Culicidae) larvae.

OBJECTIVE: To assess the influence of soil on the effectiveness of two new slow-release formulations (floating and non-floating) of pyriproxyfen coextruded with low-density polyethylene. METHODS: Two slow-release devices were developed using low-density polyethylene, pyriproxyfen as larvicide and calcium carbonate as filler. A factorial design was used to evaluate the effect of soil presence on the performance of each device. Weekly bioassays were performed. RESULTS: Soil presence affected treatment effectiveness, but this effect was associated with device type. The tablets were effective for nearly 3 months. CONCLUSION: Treatment effectiveness could be reduced because of the loss of pyriproxyfen by several physico-chemical processes such as adsorption into the soil.

OBJECTIF: Evaluer l'influence de la terre sur l'efficacité de deux nouvelles formulations à libération lente (flottante et non flottante) de pyriproxyfène coextrudé avec du polyéthylène de faible densité. MÉTHODES: Deux dispositifs à libération lente ont été développés en utilisant du polyéthylène de faible densité, du pyriproxyfène comme larvicide et du carbonate de calcium comme agent de charge. Un plan factoriel a été utilisé pour évaluer l'effet de la présence de terre sur les performances de chaque dispositif. Des essais biologiques hebdomadaires ont été effectués. RÉSULTATS: La présence de terre a affecté l'efficacité du traitement, mais cet effet était associé au type de dispositif. Les comprimés ont été efficaces pendant près de 3 mois. CONCLUSION: L'efficacité du traitement pourrait être réduite en raison de la perte du pyriproxyfène par plusieurs processus physicochimiques tels que l'adsorption sur la terre.

Effects of Temephos, Permethrin, and Eucalyptus nitens Essential Oil on Survival and Swimming Behavior of Aedes aegypti and Anopheles pseudopunctipennis (Diptera: Culicidae) Larvae.

An essential strategy to deal with mosquito-borne diseases is the control of larvae in their development sites. The mosquitoes Anopheles pseudopunctipennis (Theobald) (Diptera: Culicidae), a malaria vector, and Aedes aegypti (L.) (Diptera: Culicidae), vector of dengue, Zika, yellow fever, and chikungunya viruses, breed in very different habitats. Insecticide treatments of mosquito larvae focus mainly on their lethal effects. However, insecticide degradation or the poor dosage of larvicides will invariably lead to the sublethal exposure of a target (and nontarget) species, the nonlethal effects of these compounds may have important effects on vital insect activities, and therefore their evaluation is necessary. In this study, we assessed the survival and swimming behavior of larvae of Ae. aegypti and An. pseudopunctipennis exposed to increasing concentrations of three larvicides. We found that Ae. aegypti, was more sensitive to the larvicides than An. pseudopunctipennis, we also observed an overall decrease in the movement of those larvae of both species, which survive the treatments. This decrease might have ecological relevance in their natural habitats, increasing the chance to be predated and decreasing their ability to obtain food. Finally, this information will be valuable to assist authorities to make decisions in the implementation of further control programs.

N-substituted methyl maleamates as larvicidal compounds against Aedes aegypti (Diptera: Culicidae).

Severe human arboviral diseases can be transmitted by the mosquito Aedes aegypti (L.), including dengue, chikungunya, zika, and yellow fever. The use of larvicides in containers that can result as potential breeding places and cannot be eliminated is the main alternative in control programs. However, their continuous and widespread use caused an increase in insecticide-resistant populations of this mosquito. The aim of this study was to evaluate the effect of three N-substituted methyl maleamates as larvicides on Ae. aegypti, the N-propyl methyl maleamate (PMM), N-butyl methyl maleamate (BMM), and N-hexyl methyl maleamate (HMM). These compounds could have a different mode of action from those larvicides known so far. We evaluated the larva mortality after 1 and 24 h of exposure and we found that mortality was fast and occurs within the first 60 min. HMM was slightly more effective with LC50 values of 0.7 and 0.3 ppm for 1 and 24 h of exposure and LC95 of 11 and 3 ppm. Our results demonstrate that N-substituted methyl maleamates have insecticidal properties for the control of Ae. aegypti larvae. These compounds could become useful alternatives to traditional larvicides after studying their insecticidal mechanism as well as their toxicity towards non target organisms.

A Video-Tracking Analysis-Based Behavioral Assay for Larvae of Anopheles pseudopunctipennis and Aedes aegypti (Diptera: Culicidae).

Aedes aegypti (L.) is the primary vector of dengue, yellow fever, Zika, and chikungunya viruses, whereas Anopheles pseudopunctipennis (Theobald) is the principal vector for malaria in Latin America. The larval stage of these mosquitoes occurs in very different development habitats, and the study of their respective behaviors could give us valuable information to improve larval control. The aim of this study was to set up a bioassay to study basic larval behaviors using a video-tracking software. Larvae of An. pseudopunctipennis came from two localities in Salta Province, Argentina, while Ae. aegypti larvae were of the Rockefeller laboratory strain. Behaviors of individual fourth-instar larvae were documented in an experimental petri dish arena using EthoVision XT10.1 video-tracking software. The overall level of movement of larval An. pseudopunctipennis was lower than that for Ae. aegypti, and, while moving, larval An. pseudopunctipennis spent significantly more time swimming near the wall of the arena (thigmotaxis). This is the first study that analyzes the behavior of An. pseudopunctipennis larvae. The experimental system described here may be useful for future studies on the effect of physiological, toxicological, and chemosensory stimuli on larval behaviors.

Repellent and Larvicidal Activity of the Essential Oil From Eucalyptus nitens Against Aedes aegypti and Aedes albopictus (Diptera: Culicidae).

Dengue, chikungunya, and yellow fever are important vector-borne diseases transmitted by female mosquitoes when they feed on humans. The use of repellents based on natural products is an alternative for personal protection against these diseases. Application of chemicals with larvicidal activity is another strategy for controlling the mosquito population. The repellent and larvicidal activities of the essential oil from Eucalyptus nitens were tested against Aedes aegypti and Aedes albopictus, the main vectors of these arboviruses. The essential oil was extracted by hydrodistillation and then analyzed by gas chromatography-mass spectrometry. The main components of Eucalyptus nitens essential oil were found to be terpenes such as 1,8-cineole and p-cymene, followed by ß-triketones and alkyl esters. The repellent activity of the essential oil against both species was significantly higher when compared with the main component, 1,8-cineole, alone. These results indicate that the repellent effect of E. nitens is not due only to the main component, 1,8-cineole, but also that other compounds may be responsible. Aedes aegypti was found to be more tolerant to the essential oil larvicidal effects than Ae. albopictus (Ae. aegypti LC50 = 52.83 ppm, Ae. albopictus LC 50 = 28.19 ppm). The repellent and larvicidal activity could be associated to the presence of cyclic ß-triketones such as flavesone, leptospermone, and isoleptospermone.

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

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.

The use of Aedes aegypti larvae attractants to enhance the effectiveness of larvicides.

Aedes aegypti (L.) is an important dengue, chikungunya, and yellow fever vector. Immature stages of this species inhabit human-made containers placed in residential landscapes, and the application of larvicides inside containers that cannot be eliminated is still considered a priority in control programs. Larvicidal efficacy is influenced by several factors, including the formulation used, the water quality, and the susceptibility of larvae, among others. If an attractant can be incorporated into a slow-release larvicide formulation, it will be feasible to direct the larvae into the source of insecticide and thereby improving its efficacy. We studied the influence of 1-octen-3ol and 3-methylphenol on the rate of Ae. aegypti larvae mortality using the larvicides Bacillus thuringiensis var. israelensis (Bti), temephos, and spinosad. These chemicals were combined with the larvicides mixed with agar during the bioassays. Mortality was registered every 10 min, and a lethal time 50 (LT50) was calculated. The inclusion of the Ae. aegypti larvae attractants with the larvicides into a solid agar matrix improved their efficiency obtaining a strong and marked reduction in the LT50 compared with the use of larvicides alone.

Oviposition Behavior in Aedes aegypti and Aedes albopictus (Diptera: Culicidae) in Response to the Presence of Heterospecific and Conspecific Larvae.

In mosquitoes, location of suitable sites for oviposition requires a set of visual, tactile, and olfactory cues that influences females before laying their eggs. The ability of gravid females to distinguish among potential oviposition sites that will or will not support the growth, development, and survival of their progeny is critical. Aedes aegypti (L.) and Aedes albopictus (Skuse) share ecological niches, being highly competitive in larval stage. We studied the oviposition behavior of both species in the presence of larvae of one or the other species (heterospecific or conspecific larvae). The number of eggs laid by gravid females on oviposition sites (water with different or the same species of Aedes larvae) were compared. The presence and density of heterospecific or conspecific larvae had a positive or negative effect on the ovipositional responses, measured as an oviposition activity index. For both species, the oviposition was not affected by heterospecific larvae with densities between 10 and 100 larvae in water, but a strong attractant behavior was observed for a density of 500 larvae in water. For Ae. albopictus in the presence of larvae of the same species (conspecific oviposition), we observed an attractant effect for larvae density of 10 but not for 100 or 500 larvae in water. Instead, for Ae. aegypti, we observed attraction only for 100 larvae, not for 10 or 500 larvae. Results presented here provide an additional insight about oviposition behavior responses of gravid females in the presence of conspecific and heterospecific larvae in breeding sites.

Behavioral Response of Aedes aegypti (Diptera: Culicidae) Larvae to Synthetic and Natural Attractants and Repellents.

Aedes aegypti (L.) (Diptera: Culicidae) is the key vector of three important arboviral diseases: dengue, yellow fever, and chikungunya. Immature stages of this species inhabit human-made containers placed in residential landscapes. In this study, we evaluated a few compounds in a sensitive behavioral assay with Ae. aegypti larvae. The orientation of larvae to different compounds was surveyed using a performance index (PI). The PI represents the response to each odorant, where a value of +1 is indicative of full attraction and -1 represents complete repulsion. The widely used insect repellent N, N-diethyl-m-toluamide elicited a significantly negative PI, as did acetophenone and indole. A yeast extract, a known food source, elicited a significantly positive PI, as did 2-methylphenol, 1-octen-3-ol, 3-methylphenol, and fish food. On the other hand, no response was observed for the essential oil of Eucalyptus grandis x Eucalyptus camaldulensis at the concentration evaluated. Pretreatment of larvae with N-ethylmaleimide and ablation of the antennae resulted in a suppression of behavioral responses. The overall mobility of ablated larvae was indistinguishable from unablated controls, and absence of any visible locomotor dysfunction was observed. This work is a contribution to the study of the chemical ecology of disease vectors with the aim of developing more efficient tools for surveillance and control.Natural and synthetic compounds attractive to Ae. aegypti larvae should be incorporated into integrated pest management programs through the use of baited traps or by improving the efficacy of larvicides commonly used in control campaigns.

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: KT 50(min) = - 10.9 + 3.7 * Log P + 1.9 * 1/Pvapor (R(2) = 0.80; F = 42.5) and LC 50(ppm) = - 94.3 + 438.6 * 1/Log P + 2.8 * 1/Pvapor (F = 57.8; R(2) = 0.85). 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: KT 50(min) = - 515.3 + 1613.2 * 1/Log P + 5, 2 * 1/Pvapor (F = 3176.7 R(2) = 0.99) and LC 50(ppm) = - 1679.4 + 5402.1 * 1/Log P + 12.7 * 1/Pvapor (F = 282.9; R(2) = 0.99). (B) Hydrocarbons terpenes: KT 50(min) = 18.2 - 58.3 * 1/Log P + 2.7 * 1/Pvapor (F = 171.7; R(2) = 0.97) and LC 50(ppm) = - 21.1 + 174.9 * 1/Log P - 14.3 * 1/Pvapor (F = 410.0; R(2) = 0.99). 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).

Post-control surveillance of Triatoma infestans and Triatoma sordida with chemically-baited sticky traps.

BACKGROUND: Chagas disease prevention critically depends on keeping houses free of triatomine vectors. Insecticide spraying is very effective, but re-infestation of treated dwellings is commonplace. Early detection-elimination of re-infestation foci is key to long-term control; however, all available vector-detection methods have low sensitivity. Chemically-baited traps are widely used in vector and pest control-surveillance systems; here, we test this approach for Triatoma spp. detection under field conditions in the Gran Chaco. METHODOLOGY/PRINCIPAL FINDINGS: Using a repeated-sampling approach and logistic models that explicitly take detection failures into account, we simultaneously estimate vector occurrence and detection probabilities. We then model detection probabilities (conditioned on vector occurrence) as a function of trapping system to measure the effect of chemical baits. We find a positive effect of baits after three (odds ratio [OR] 5.10; 95% confidence interval [CI(95)] 2.59-10.04) and six months (OR 2.20, CI(95) 1.04-4.65). Detection probabilities are estimated at p ≈ 0.40-0.50 for baited and at just p ≈ 0.15 for control traps. Bait effect is very strong on T. infestans (three-month assessment: OR 12.30, CI(95) 4.44-34.10; p ≈ 0.64), whereas T. sordida is captured with similar frequency in baited and unbaited traps. CONCLUSIONS/SIGNIFICANCE: Chemically-baited traps hold promise for T. infestans surveillance; the sensitivity of the system at detecting small re-infestation foci rises from 12.5% to 63.6% when traps are baited with semiochemicals. Accounting for imperfect detection, infestation is estimated at 26% (CI(95) 16-40) after three and 20% (CI(95) 11-34) after six months. In the same assessments, traps detected infestation in 14% and 8.5% of dwellings, whereas timed manual searches (the standard approach) did so in just 1.4% of dwellings only in the first survey. Since infestation rates are the main indicator used for decision-making in control programs, the approach we present may help improve T. infestans surveillance and control program management.

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.

Validation of models to estimate the fumigant and larvicidal activity of Eucalyptus essential oils against Aedes aegypti (Diptera: Culicidae).

The aim of this work is to validate the pre-existing models that relate the larvicidal and adulticidal activities of the Eucalyptus essential oils on Aedes aegypti. Previous works at our laboratory described that the larvicidal activity of Eucalyptus essential oils can be estimated from the relative concentration of two main components (p-cymene and 1,8-cineole) and that the adulticidal effectiveness can be explained, to a great extent, by the presence of large amounts of the component 1,8-cineole in it. In general, the results show that the higher adulticidal effect of essential oils the lower their larvicidal activity. Fresh leaves was harvested and distilled. Once the essential oil was obtained, the chemical composition was analysed, evaluating the biological activity of 15 species of the genus Eucalyptus (Eucalyptus badjensis Beuzev and Welch, Eucalyptus badjensis × nitens, Eucalyptus benthamii var Benthamii Maiden and Cambage, Eucalyptus benthamii var dorrigoensis Maiden and Cambage, Eucalyptus botryoides Smith, Eucalyptus dalrympleana Maiden, Eucalyptus fastigata Deane and Maiden, Eucalyptus nobilis L.A.S. Johnson and K.D.Hill, Eucalyptus polybractea R. Baker, Eucalyptus radiata ssp radiata Sieber ex Spreng, Eucalyptus resinifera Smith, Eucalyptus robertsonii Blakely, Eucalyptus robusta Smith, Eucalyptus rubida Deane and Maiden, Eucalyptus smithii R. Baker). Essential oils of these plant species were used for the validation of equations from preexistent models, in which observed and estimated values of the biological activity were compared. The regression analysis showed a strong validation of the models, re-stating the trends previously observed. The models were expressed as follows: A, fumigant activity [KT(50(min)) = 10.65-0.076 × 1,8-cineole (%)](p < 0.01; F, 397; R (2), 0.79); B, larval mortality (%)((40 ppm)) = 103.85 + 0.482 × p-cymene (%) - 0.363 × α-pinene (%) - 1.07 × 1,8-cineole (%) (p < 0.01; F, 300; R (2), 0.90). These results confirmed the importance of the mayor components in the biological activity of Eucalyptus essential oils on A. aegypti. However, it is worth mentioning that two or three species differ in the data estimated by the models, and these biological activity results coincide with the presence of minor differential components in the essential oils. According to what was previously mentioned, it can be inferred that the model is able to estimate very closely the biological activity of essential oils of Eucalyptus on A. aegypti.

Chemical composition and fumigant toxicity of the essential oils from 16 species of Eucalyptus against Haematobia irritans (Diptera: Muscidae) adults.

Oils extracted from various species of Eucalyptus (Eucalyptus badjensis Beuzev & Welch, Eucalyptus badjensis x Eucalyptus nitens, Eucalyptus benthamii variety dorrigoensis Maiden & Cambage, Eucalyptus botryoides Smith, Eucalyptus dalrympleana Maiden, Eucalyptus fastigata Deane & Maiden, Eucalyptus nobilis L.A.S. Johnson & K. D. Hill, Eucalyptus polybractea R. Baker, Eucalyptus radiata ssp. radiata Sieber ex Spreng, Eucalyptus resinifera Smith, Eucalyptus robertsonii Blakely, Eucalyptus rubida Deane & Maiden, Eucalyptus smithii R. Baker, Eucalyptus elata Dehnh, Eucalyptus fraxinoides Deane & Maiden, E. obliqua L'Hér) were obtained by hydrodistillation. The chemical composition of essential oils was determined by gas chromatography coupled to mass spectrometry. Essential oils were mainly composed of 1,8-cineole, alpha-pinene, alpha-terpineol, 4-terpineol, and p-cymene. Vapors from these essential oils and their major components were found to be toxic to Haematobia irritans (L.) (Diptera: Muscidae) adults. An aliquot of each oil was placed in a cylindrical test chamber, and the number of knocked down flies was recorded as a function of time. Knockdown time 50% was then calculated. Results showed that essential oil of E. polybractea had the highest knockdown activity of 3.44 min. A correlation was observed between the content of 1,8-cineole in the Eucalyptus essential oils and the corresponding toxic effect.

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.

Insecticidal activity of essential oils from eleven Eucalyptus spp. and two hybrids: lethal and sublethal effects of their major components on Blattella germanica.

The aim of the current study was to evaluate the fumigant activity of the essential oils from 11 species of the genus Eucalyptus and two of their hybrids on first instar of Blattella germanica L. The fumigant activity and repellence of the four major monoterpene components of these essential oils also were tested. Fumigant activity was evaluated by exposing nymphs to the vapors emitted by 50 microl of essential oil or monoterpene in a closed container. The lowest knockdown time 50% (KT50) values, expressed in minutes, were elicited by the essential oils of the Eucalyptus grandis X Eucalyptus tereticornis (57.9) hybrid, Eucalyptus sideroxylon A. Cunn (62.0), E. grandis X Eucalyptus camaldulensis (63.8) hybrid, Eucalyptus viminalis Labill (64.1), Eucalyptus dunnii Maiden (64.5), and Eucalyptus grandis (Hill) ex Maiden (68.7). The KT50 values for the remaining essential oils ranged between 74.5 (E. saligna Smith) and 161.4 min (E. tereticornis Smith). The essential oil from the hybrid E. grandis X E. tereticornis was 3.7 times less toxic than dichlorvos (positive control). The KT50 values of monoterpenes were 38.8 for alpha-pinene, 55.3 for 1,8-cineole, 175.6 for p-cymene, and 178.3 for gamma-terpinene. Alpha-pinene was 2.5 times less toxic than dichlorvos. There was a strong positive correlation between the fumigant activity of essential oils and their corresponding 1,8-cineole and alpha-pinene concentration. Repellency was quantified using a video tracking system. Two concentrations of monoterpenes were studied (7 and 70 microg/cm2). All compounds produced a light repellent effect but only when applied at 70 microg/cm2. In all cases, the repellent effect was less than that produced by the broad-spectrum insect repellent N,N-diethyl-3-methylbenzamide (positive control).

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% (KT(50)) values were determined as toxicological indicators of insecticide release. Minimum KT(50) values of the direct effect of both formulations on horn flies were reached 4 weeks after being applied. The KT(50) effect of migrated insecticides showed that RET formulation had a maximal effectiveness between the fourth and tenth last week. The KT(50) effect of the insecticide migrating from ear tags decreased during the last 2 weeks of the experiment, and the KT(50) 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 KT(50). At the end of the experiment, the KT(50) effect of laterally migrated insecticide was significantly higher for the RET formulation. Regarding vapor emission, as a general trend the KT(50) 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 11 weeks while the ear tags provided protection until the 12th week.