Larvicidal activity against Aedes aegypti of some plants native to the West-Central region of Brazil

Use of essential oils from plants of Araripe National Forest against Aedes aegypti (Diptera: Culicidae)

Aedes aegypti control is achieved with chemical insecticides that can promote insecticide resistance. In the search for new forms of control, the use of botanical products is currently growing and many tests with oils have already been performed. The plant diversity of Araripe National Forest enables the study of several species against this vector. To evaluate the larvicidal effect of essential oils from plants of this forest, we used field rosemary, copaiba, bay leaf, cashew and pequi. The work was divided into three stages: all oils with the same dosage; the best oil at dosages of 0, 5, 10, 20, 50 and 75 µg/mL; and the best dosage at temperatures of 15, 20, 25, 30 and 35 °C. The oils of field rosemary, copaiba, bay leaf, cashew and pequi were good insecticides when used at dosages above 5 μg/mL. The bay leaf oil showed high larvicidal activity at all dosages tested, showing the highest efficiency at 75 μg/mL. Temperatures of 15 and 35 °C increased the susceptibility of the insect to the effect of the bay leaf oil. The essential oils of field rosemary, copaiba, bay leaf, cashew and pequi, from Araripe National Forest, applied at a dosage of 5μg/mL, showed insecticidal action, although with low efficiency.

Exploring Natural Alkaloids from Brazilian Biodiversity as Potential Inhibitors of the Aedes aegypti Juvenile Hormone Enzyme: A Computational Approach for Vector Mosquito Control

This study explores the potential inhibitory activity of alkaloids, a class of natural compounds isolated from Brazilian biodiversity, against the mJHBP enzyme of the Aedes aegypti mosquito. This mosquito is a significant vector of diseases such as dengue, zika, and chikungunya. The interactions between the ligands and the enzyme at the molecular level were evaluated using computational techniques such as molecular docking, molecular dynamics (MD), and molecular mechanics with generalized Born surface area (MMGBSA) free energy calculation. The findings suggest that these compounds exhibit a high binding affinity with the enzyme, as confirmed by the binding free energies obtained in the simulation. Furthermore, the specific enzyme residues that contribute the most to the stability of the complex with the compounds were identified: specifically, Tyr33, Trp53, Tyr64, and Tyr129. Notably, Tyr129 residues were previously identified as crucial in the enzyme inhibition process. This observation underscores the significance of the research findings and the potential of the evaluated compounds as natural insecticides against Aedes aegypti mosquitoes. These results could stimulate the development of new vector control agents that are more efficient and environmentally friendly.

Plant-derived alkaloids acting on dengue virus and their vectors: from chemistry to pharmacology

Dengue is a mosquito-borne viral infection, with its prevention and control depending on effective vector control measures. At present, dengue virus (DENV) is an epidemic in more than 100 countries of Southeast Asia, Africa, Eastern Mediterranean, the Americas and the Western Pacific. Several alkaloids isolated from natural herbs can serve as a reservoir for antiDENV drug development. Traditionally, plant extracts rich in alkaloids are used for the treatment of fever and have also revealed antimicrobial activity against various pathogenic bacteria, fungi and virus. The present narrative review collates the literature-based scenario of alkaloids and derivatives acting on DENV. The mechanism of action of such alkaloids with antiDENV and vector activity is also discussed.

A Review on Classification and Biological Activities of Alkaloids from the Genus Zanthoxylum Species

Many plants in the genus Zanthoxylum, belonging to the Rutaceae family, are used as folk medicines for the treatment of various diseases, which have gained much attention for their phytochemical and pharmacological activity investigations. Alkaloids are the largest secondary metabolites with structurally diverse types found in this genus and they demonstrate a wide range of biological activities. The aim of this review is to provide a summary on the isolation, classification, and biological properties of alkaloids from Zanthoxylum species, which also will bring more attention to other researchers for further biological study on alkaloids for the new drug development.

Preliminary evaluation of the larvicidal activity of extracts and fractions from Ocotea nutans (Nees) Mez against Aedes aegypti

INTRODUCTION:

Aedes aegypti is the main vector of dengue and yellow fever. Recently, the use of plant-sourced larvicides has gained momentum.

METHODS:

The hydroethanolic extracts and fractions ofOcotea nutansleaves and stems were bioassayed to determine the larvicidal efficacy of these samples.

RESULTS:

S-HEX (hexane fraction from the crude stem extract) demonstrated high potential for controlling third-stage larvae, with an LC₅₀ of 14.14 µg.mL^-1 (concentration required to inhibit 50% of the treated larvae).

CONCLUSIONS

Extracts from O. nutans were effective against third-stage larvae ofA. aegyptiafter 24 h of exposure.

The Potential of Biologically Active Brazilian Plant Species as a Strategy to Search for Molecular Models for Mosquito Control

Natural products are a valuable source of biologically active compounds and continue to play an important role in modern drug discovery due to their great structural diversity and unique biological properties. Brazilian biodiversity is one of the most extensive in the world and could be an effective source of new chemical entities for drug discovery. Mosquitoes are vectors for the transmission of dengue, Zika, chikungunya, yellow fever, and many other diseases of public health importance. These diseases have a major impact on tropical and subtropical countries, and their incidence has increased dramatically in recent decades, reaching billions of people at risk worldwide. The prevention of these diseases is mainly through vector control, which is becoming more difficult because of the emergence of resistant mosquito populations to the chemical insecticides. Strategies to provide efficient and safe vector control are needed, and secondary metabolites from plant species from the Brazilian biodiversity, especially Cerrado, that are biologically active for mosquito control are herein highlighted. Also, this is a literature revision of targets as insights to promote advances in the task of developing active compounds for vector control. In view of the expansion and occurrence of arboviruses diseases worldwide, scientific reviews on bioactive natural products are important to provide molecular models for vector control and contribute with effective measures to reduce their incidence.

Larvicidal Activity of Ketapang Leaf Fraction (Terminalia catappa L) on Aedes aegypti Instar III

BACKGROUND:

Mosquito control is essential in preventing mosquito-borne diseases. Natural substances originated from plants possessed the great potential of insecticidal properties, the resistance occurs at a slower rate compared to the synthetics, with less toxicity to other living creatures.

AIM:

This study aimed to identify the fraction of ketapang leaf (Terminalia catappa L) with larvicidal activity on Aedes aegypti instar III larvae, the concentration of ketapang active leaf fraction comparable to temephos, and Lethal Concentration 50 (LC50).

METHODS:

This study was experimental in vitro. The experiment was performed with five different concentrations of ketapang leaf water-ethanol fraction, i.e. 1200 ppm, 1400 ppm, 1600 ppm, 1800 ppm, 2000 ppm. Observation of morphological damage of mosquito larvae was conducted with the microscope and ImageJ application. Data analysis was performed using One Way ANOVA. LC50 was determined with probit analysis.

RESULTS:

Phytochemical screening revealed a water-ethanol fraction of ketapang leaf contained tannin, saponin, and flavonoid compounds. The water-ethanol fraction with 1800 ppm concentration possessed significant larvicidal effect comparable to temephos. Probit test revealed an LC50 value of 1563.082 μg/ml.

CONCLUSION:

Water-ethanol fraction of ketapang leaf possessed high biolarvicidal activity against Ae. aegypti larvae instar III comparable to temephos.

Plant extracts for developing mosquito larvicides: From laboratory to the field, with insights on the modes of action

In the last decades, major research efforts have been done to investigate the insecticidal activity of plant-based products against mosquitoes. This is a modern and timely challenge in parasitology, aimed to reduce the frequent overuse of synthetic pesticides boosting resistance development in mosquitoes and causing serious threats to human health and environment. This review covers the huge amount of literature available on plant extracts tested as mosquito larvicides, particularly aqueous and alcoholic ones, due to their easy formulation in water without using surfactants. We analysed results obtained on more than 400 plant species, outlining that 29 of them have outstanding larvicidal activity (i.e., LC₅₀ values below 10 ppm) against major vectors belonging to the genera Anopheles, Aedes and Culex, among others. Furthermore, synergistic and antagonistic effects between plant extracts and conventional pesticides, as well as among selected plant extracts are discussed. The efficacy of pure compounds isolated from the most effective plant extracts and - when available - their mechanism of action, as well as the impact on non-target species, is also covered. These belong to the following class of secondary metabolites: alkaloids, alkamides, sesquiterpenes, triterpenes, sterols, flavonoids, coumarins, anthraquinones, xanthones, acetogenonins and aliphatics. Their mode of action on mosquito larvae ranges from neurotoxic effects to inhibition of detoxificant enzymes and larval development and/or midugut damages. In the final section, current drawbacks as well as key challenges for future research, including technologies to synergize efficacy and improve stability - thus field performances - of the selected plant extracts, are outlined. Unfortunately, despite the huge amount of laboratory evidences about their efficacy, only a limited number of studies was aimed to validate their efficacy in the field, nor the epidemiological impact potentially arising from these vector control operations has been assessed. This strongly limits the development of commercial mosquito larvicides of botanical origin, at variance with plant-borne products developed in the latest decades to kill or repel other key arthropod species of medical and veterinary importance (e.g., ticks and lice), as well as mosquito adults. Further research on these issues is urgently needed.

Plant-based larvicidal agents: An overview from 2000 to 2018

Current review aims to systematically segregate, analyze and arrange the key findings of the scientific reports published on larvicidal plants including larvicidal formulations. The investigation was carried out by analyzing the published literature in various scientific databases, subsequently, the key findings of the selective scientific reports having larvicidal potency (LC₅₀) of extract or isolated oil<100 μg/mL were tabulated to provide the concise and crucial information. Special emphasis was given on reports in which LC₅₀ of extract or isolated oil was reported to be < 10 μg/mL, genus or species documented in multiple independent studies, advancement in larvicidal formulations and activity of isolated phytoconstituents. Extensive analysis of published literature revealed that the larvicidal potency of herbal resources varied from sub-microgram/ml to practically insignificant. Overall, this unprecedented summarized and arranged information can be utilized for design, development and optimization of herbal based formulation having potential larvicidal activity.

Larvicidal Activity against Aedes aegypti and Chemical Characterization of the Inflorescences of Tagetes patula

The crude acetone extract (CAE) of defatted inflorescences of Tagetes patula was partitioned into five semipurified fractions: n-hexane (HF), dichloromethane (DF), ethyl acetate (EAF), n-butanol (BF), and aqueous (AQF). BF was fractionated by reversed-phase polyamide column chromatography, obtaining 34 subfractions, which were subjected to HSCCC, where patuletin and patulitrin were isolated. CAE and the fractions BF, EAF, DF, and AQF were analyzed by LC-DAD-MS, and patuletin and patulitrin were determined as the major substances in EAF and BF, respectively. BF was also analyzed by HPLC and capillary electrophoresis (CE), and patulitrin was again determined to be the main substance in this fraction. CAE and the semipurified fractions (750, 500, 300, 100, and 50 mg/L) were assayed for larvicidal activity against Aedes aegypti, with mortality rate expressed as percentage. All fractions except AQF showed insecticidal activity after 24 h exposure of larvae to the highest concentration. However, EAF showed the highest activity with more than 50% reduction in larval population at 50 mg/L. The insecticidal activity observed with EAF might have been due to the higher concentration of patuletin present in this fraction.

Larvicidal efficacies of plants from Midwestern Brazil: melianodiol from Guarea kunthiana as a potential biopesticide against Aedes aegypti

A total of 36 ethanol extracts from different anatomical parts of 27 plant species (18 families), native to the Pantanal and Cerrado biomes in Midwest Brazil, was assessed for their effect against Aedes aegypti larvae, the vector of dengue, hemorrhagic dengue, Zika and chikungunya fevers. Only the extract obtained from seeds of Guarea kunthiana (Meliaceae) proved active (LC50 = 169.93 μg/mL). A bioassay-guided investigation of this extract led to the isolation and identification of melianodiol, a protolimonoid, as the active constituent (LC50 = 14.44 mg/mL). Meliantriol, which was also obtained from the bioactive fraction, was nevertheless devoid of any larval toxicity, even at the highest concentration tested (LC50 > 100.0 mg/mL). These results indicate that the larvicidal activity of melianodiol stems from the presence of the carbonyl moiety at C-3 in the 21,23-epoxy-21,24,25-trihydroxy-tirucall-7-ene-type skeleton. The structures of both protolimonoids were established on the basis of spectral methods (1H and 13C NMR and MS). This is the first report on the toxicity of melianodiol against Ae. aegypti larvae. Based on the results, melianodiol can be regarded as a potential candidate for use as an ecologically sound biocontrol agent for reducing the larval population of this vector.

Insecticidal activities of bark, leaf and seed extracts of Zanthoxylum heitzii against the African malaria vector Anopheles gambiae

The olon tree, Zanthoxylum heitzii (syn. Fagara heitzii) is commonly found in the central-west African forests. In the Republic of Congo (Congo-Brazzaville) its bark is anecdotally reported to provide human protection against fleas. Here we assess the insecticidal activities of Z. heitzii stem bark, seed and leaf extracts against Anopheles gambiae s.s, the main malaria vector in Africa. Extracts were obtained by Accelerated Solvent Extraction (ASE) using solvents of different polarity and by classical Soxhlet extraction using hexane as solvent. The insecticidal effects of the crude extracts were evaluated using topical applications of insecticides on mosquitoes of a susceptible reference strain (Kisumu [Kis]), a strain homozygous for the L1014F kdr mutation (kdrKis), and a strain homozygous for the G119S Ace1R allele (AcerKis). The insecticidal activities were measured using LD₅₀ and LD₉₅ and active extracts were characterized by NMR spectroscopy and HPLC chromatography. Results show that the ASE hexane stem bark extract was the most effective compound against An. gambiae (LD₅₀ = 102 ng/mg female), but was not as effective as common synthetic insecticides. Overall, there was no significant difference between the responses of the three mosquito strains to Z. heitzii extracts, indicating no cross resistance with conventional pesticides.

The component of Carica papaya seed toxic to A. aegypti and the identification of tegupain, the enzyme that generates it

As Aedes aegypti transmits the etiologic agents of both yellow and dengue fever; vector control is considered essential to minimise their incidence. The aim of this work was to identify the component of Carica papaya seed toxic to A. aegypti, and the identification of tegupain, the enzyme that generates it. Aqueous extracts (1%, w/v) of the seed tegument and cotyledon of C. papaya are not larvicidal isolately. However, a mixture of 17μgmL(-1) tegument extract and 27μgmL(-1) cotyledon extract caused 100% larval mortality in a bioassay. The mixture was no longer larvicidal after the tegument extract was pre-treated at 100°C for 10min. The enzyme tegupain efficiently hydrolysed the substrate Z-Phe-Arg-pNan (Km 58.8μM, Kcat 28020s(-1), Kcat/Km 5×10(8)M(-1) s(-1)), and its activity increased with 2mM dithiothreitol (DTT), at 37°C, pH 5.0. The chelating agent EDTA did not modify the enzyme activity. Inhibition of tegupain by cystatin (Kiapp 2.43nM), E64 (3.64nM, 83% inhibition), and the propeptide N-terminal sequence indicate that the toxic activity is due to a novel cysteine proteinase-like enzyme, rendered active upon the hydrolysis of a cotyledon component of C. papaya seeds.

In vitro activities of plant extracts from the Brazilian Cerrado and Pantanal against Rhipicephalus (Boophilus) microplus (Acari: Ixodidae)

A total of 73 ethanol extracts from different anatomical parts of 44 plant species belonging to 24 families, native to the Mid-Western region of Brazil, were assessed in vitro for their effect on the reproductive cycle of engorged females of the cattle tick Rhipicephalus (Boophilus) microplus, using the adult immersion test. All extracts were evaluated at the concentration of 0.2 % and, among the extracts tested, the one obtained from the fruits of Guarea kunthiana (Meliaceae) proved to be highly efficacious, showing 99.1 % of product effectiveness. Extracts from other three species were shown to be moderately active, namely Nymphaea amazonum trunk (Nymphaeaceae) [51.7 %], Strychnos pseudoquina trunk (Loganiaceae) [48 %] [corrected] and Ocotea lancifolia leaves (Lauraceae) [34.5 %], while the remaining extracts were shown to be weakly active or inactive. This is the first report on the bioactivity of these species on egg production by engorged females of R. microplus.

Zanthoxoaporphines A-C: Three new larvicidal dibenzo[de,g]quinolin-7-one alkaloids from Zanthoxylum paracanthum (Rutaceae)

The bioassay-guided purification of Zanthoxylum paracanthum (Rutaceae) extracts led to the isolation of three new alkaloids, namely 1-hydroxy-10-methoxy-7H-dibenzo[de,g]quinolin-7-one (zanthoxoaporphine A, 2), 1-hydroxy-7H-dibenzo[de,g]quinolin-7-one (zanthoxoaporphine B, 3) and 1,8-dihydroxy-9-methoxy-7H-dibenzo[de,g]quinolin-7-one (zanthoxaporphine C, 4), and a known lignan identified as sesamin (1). Isolation and purification of the constituent compounds was achieved through conventional chromatographic methods. The chemical structures of the isolated compounds were determined on the basis of UV, IR, NMR and MS data, and confirmed by comparison with those reported in the literature. The larvicidal activity of some of the isolated compounds was investigated by using third-instar Anopheles gambiae larvae.