Seasonal variation in the chemical composition and larvicidal activity against Aedes aegypti L. of essential oils from Brazilian Amazon.

Arthropod-borne viral diseases are important public health threats in tropical countries. In the Americas, diseases such as Dengue, Zika, Chikungunya, Mayaro, and Yellow fever, which are mainly transmitted by Aedes aegypti L. are responsible for high rates of morbidity and mortality in the populations. The incidence of those viruses has increased in the last few years, due to the decrease of vector control programs, as well as, the resistance of this vector in front of many products that have been used in this proposal. Plant-based products such as essential oils are a promising alternative for Ae. aegypti control. In this context, the present work aims to investigate the seasonality effect on the larvicidal potential and safety of essential oils from 4 endemic plants of the Brazilian Amazon, as well as to verify their larvicidal activity and safety. The species were collected in the rainy and dry periods (Eugenia uniflora L., Lantana camara L., Ocimum basilicum L., Plectranthus neochilus Schlrt.). The essential oils were extracted by hydrodistillation and chemical composition was determined by gas chromatography coupled to mass spectrometry. The larvicidal activity was performed according to the methodology recommended by the World Health Organization. The safety of the oil use was evaluated against two non-target organisms: Artemia salina Leach and Danio rerio Hamilton Buchanan. Essential oils of E. uniflora, L. camara, O. basilicum, P. neochilus, presented as major compounds, in both collection periods, the substances Curzerene, Germacrene D, Methyl chavicol and, Caryophyllene, respectively. However, showed a qualitative and quantitative variation of this composition. All oils showed promising results against Ae. aegypti larvae with LC50 between 41.7 and 275.8 µg/mL. They were efficient against Ae. aegypti but showed high toxicity to non-target organisms, requiring additional safety studies. Despite these results showing that those essential oils are not ideal larvicides because they presented toxicity to non-target organisms, bioprospection is a promising tool to help reduce the dissemination of arboviruses, and they can use in artificial breeders of Ae. aegypti larvae, where water will not be reused for human consumption or have other cohabiting organisms.

Molluscicidal activity of monoterpenes and their effects on inhibition of acetylcholinesterase activity on Biomphalaria glabrata, an intermediate host of Schistosoma mansoni.

The molluscicidal action of essential oils have been attributed to the most prevalent terpene compounds. However, molluscicidal properties, mode of action, and toxicity to non-target organisms remain unclear. In this study, the molluscicidal potential of four monoterpenes (camphor, thymol, α-pinene, and 1,8-cineole) against the snail Biomphalaria glabrata, an intermediate host of Schistosoma mansoni, was analyzed. The molluscicide activity of each monoterpene was assessed by the standardized test of the World Health Organization (WHO) and the monoterpenes considered active against B. glabrata were analyzed as inhibitors of the enzymatic activity of acetylcholinesterase (AChE) extracted from snails. In addition, acute toxicity to non-target organisms was assessed against Danio rerio fish. The results show that camphor and 1,8-cineole monoterpenes did not induce snail mortality. Thymol and α-pinene were active against B. glabrata, inducing mortality in concentration-dependent patterns and showing a lethal effect in concentrations compatible with that recommended by the WHO (LC90 of 7.11 and LC90 10.34 µg ∙ mL-1, respectively). The toxic action of thymol and α-pinene on snails indicates that these monoterpenes may account for or largely contribute to the molluscicidal activity of essential oils that contain them as major compounds. Thymol and α-pinene inhibit the AChE of B. glabrata at concentrations higher than those used in the molluscicide test. These monoterpenes show low toxicity to non-target organisms compared to the commercial molluscicide niclosamide. Knowledge about monoterpene toxicity against B. glabrata contributes to its potential use in molluscicidal formulations and in alternatives to the control of snails that host intermediate S. mansoni, a crucial action in the prevention and transmission of schistosomiasis, a neglected tropical disease.

Assessment of the biological potential of diaryltriazene-derived triazene compounds.

In the present study, novel, 1,3-diaryltriazene-derived triazene compounds were synthesized and tested. Triazenes are versatile and belong to a group of alkylating agents with interesting physicochemical properties and proven biological activities. This study describes the synthesis, molecular and crystalline structure, biological activity evaluation, and antifungal and antimicrobial potentials of 1,3-bis(X-methoxy-Y-nitrophenyl)triazenes [X = 2 and 5; Y = 4 and 5]. The antimicrobial and antifungal activities of the compounds were tested by evaluating the sensitivity of bacteria (American Type Culture Collection, ATCC) and clinical isolates to their solutions using standardized microbiological assays, cytotoxicity evaluation, and ecotoxicity tests. The antimicrobial potentials of triazenes were determined according to their minimum inhibitory concentrations (MICs); these compounds were active against gram-positive and gram-negative bacteria, with low MIC values. The most surprising result was obtained for T3 having the effective MIC of 9.937 µg/mL and antifungal activity against Candida albicans ATCC 90028, C. parapsilosis ATCC 22019, and C. tropicallis IC. To the best of our knowledge, this study is the first to report promising activities of triazene compounds against yeast and filamentous fungi. The results showed the potential utility of triazenes as agents affecting selected resistant bacterial and fungal strains.

Essential oils and their chemical constituents against Aedes aegypti L. (Diptera: Culicidae) larvae.

This review focused on the toxicity of essential oils and their constituents against Aedes aegypti L. (Diptera, Culicidae) larvae, a key vector of important arboviral diseases, such as dengue, chikungunya, zika, and yellow fever. This review is based on original articles obtained by searching major databases in the last six years. Our literature review shows that 337 essential oils from 225 plant species have been tested for larvicidal bioactivity. More than 60% of these essential oils were considered active (LC50<100 µg/mL). Most species belong to the families Lamiaceae (19.3%), Lauraceae (9.9%), and Myrtaceae (9.4%). The plants studied for their larvicidal activity against A. aegypti were mainly collected in India and Brazil (30 and 20%, respectively) and the parts of the plants most used were the leaves. Less than 10% of essential oils were evaluated for toxicity against non-target organisms and with the aim to demonstrate safe use. The most used plant parts are leaves and the main compounds of essential oils were described. The most active essential oils are rich in sesquiterpene hydrocarbons, oxygenated sesquiterpenes, and monoterpene hydrocarbons. Here, factors affecting bioactivity (chemical composition, plant parts, and harvesting site) of essential oils and their constituents, as well as safety to non-target organisms are discussed. Essential oils have considerable potential against A. aegypti. This review shows that essential oils might be used to control arboviruses, and further studies on safety and formulations for application in the field should be performed.

Hydroalcoholic extract of Caryocar brasiliense Cambess. leaves affect the development of Aedes aegypti mosquitoes.

INTRODUCTION: Curtailing the development of the aquatic immature stages of Aedes aegypti is one of the main measures to limit their spread and the diseases transmitted by them. The use of plant extracts is a promising approach in the development of natural insecticides. Thus, this research aimed to characterize the inhibitory effect of the hydroalcoholic extract of Caryocar brasiliense leaves on the emergence of adult A. aegypti and the main substances that constitute this extract. METHODS: C. brasiliense leaf extract was prepared by ethanol (70%) extraction. Bioassays using L3 larvae were performed at concentrations of 200, 300, 400, and 500 ppm. We identified the major secondary metabolites present in this extract, and performed toxicity tests on an off-target organism, Danio rerio. RESULTS: We observed a significant delay in the development of A. aegypti larvae mainly at a concentration of 500 ppm, and estimated an emergence inhibition for 50% of the population of 150 ppm. Moreover, the C. brasiliense leaf extracts exhibited low toxicity in D. rerio. The main compounds found in the extract were quercetin, violaxanthin, myricetin3-O-hexoside, methyl-elagic-3-arabinose acid, and isoquercitrin. CONCLUSIONS: Herein, we demonstrate the inhibition of mosquito development by the hydroalcoholic extract of C. brasiliense and suggest substances that may act as active principles.

Hydroalcoholic extract of Caryocar brasiliense Cambess. leaves affect the development of Aedes aegypti mosquitoes

Abstract INTRODUCTION: Curtailing the development of the aquatic immature stages of Aedes aegypti is one of the main measures to limit their spread and the diseases transmitted by them. The use of plant extracts is a promising approach in the development of natural insecticides. Thus, this research aimed to characterize the inhibitory effect of the hydroalcoholic extract of Caryocar brasiliense leaves on the emergence of adult A. aegypti and the main substances that constitute this extract. METHODS: C. brasiliense leaf extract was prepared by ethanol (70%) extraction. Bioassays using L3 larvae were performed at concentrations of 200, 300, 400, and 500 ppm. We identified the major secondary metabolites present in this extract, and performed toxicity tests on an off-target organism, Danio rerio. RESULTS: We observed a significant delay in the development of A. aegypti larvae mainly at a concentration of 500 ppm, and estimated an emergence inhibition for 50% of the population of 150 ppm. Moreover, the C. brasiliense leaf extracts exhibited low toxicity in D. rerio. The main compounds found in the extract were quercetin, violaxanthin, myricetin3-O-hexoside, methyl-elagic-3-arabinose acid, and isoquercitrin. CONCLUSIONS: Herein, we demonstrate the inhibition of mosquito development by the hydroalcoholic extract of C. brasiliense and suggest substances that may act as active principles.