Towards the optimization of botanical insecticides research: Aedes aegypti larvicidal natural products in French Guiana

Comparing the sensitivity of aquatic organisms relative to Daphnia sp. toward essential oils and crude extracts: A meta-analysis

Interest on aromatic and medicinal plants (AMP)-based products, especially crude extracts (CE) and essential oils (EO), has increased over recent years due to their bioactive and biopesticide properties, though a variety of these compounds is environmentally damaging. Aquatic organisms can easily be exposed to the toxicological risks of AMP-based products, but research exploring existing ecotoxicity data to non-target organisms is limited. The present study aimed to, for the first time, systematically review published evidence on the acute/short-term toxicity (LC50, EC50 or IC50) of CE and EO from AMP, comparing sensitivity of aquatic organisms. Eleven studies that reported the sensitivity of aquatic taxa and Daphnia sp. to CE and/or EO, were included in the review, contributing with 27 effect sizes, calculated as the response ratio R (EcotoxicityAquatTaxa/EcotoxicityDaphnia). Meta-analytic technics were used to estimate the overall sensitivity of aquatic taxa relative to Daphnia sp. while identifying moderators [plant preparation (CE or EO), extraction type, plant part, plant family, and aquatic taxa identity] potentially affecting relative sensitivities. The overall effect size R was 1.51 (95 % CI = 0.97 to 2.34, N = 27), indicating a non-significant difference in the toxicity of CE and EO to aquatic taxa relative to Daphnia sp. However, the high heterogeneity among individual effect sizes (I2 = 99 %) suggested opposing responses of aquatic taxa relative to Daphnia sp. The magnitude of effects (R) was strongly influenced only by plant family. Daphnia sp. arose as a potential model organism for assessing the ecotoxicity of CE and EO, along with the fish Danio rerio and the crustacean Thamnocephalus platyurus, while Artemia sp. seems a relevant alternative for a preliminary screening. Likewise, the current study sheds light on the (underestimated) toxicity of CE and EO to aquatic ecosystems and that much remains to be uncovered, providing insights and recommendations for future research.

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.

Discovery of novel natural products for mosquito control

Vector control plays a key role in reducing the public health burden of mosquito-borne diseases. Today's vector control strategies largely rely on synthetic insecticides that can have a negative environmental impact when applied outdoors and often become inefficient because of the mosquitoes' ability to develop resistance. An alternative and promising approach to circumvent these challenges involves the implementation of insecticides derived from nature (biopesticides) for vector control. Biopesticides can constitute naturally occurring organisms or substances derived from them that have lifespan-shortening effects on disease vectors such as mosquitoes. Here we present the discovery and evaluation of natural product-based biological control agents that can potentially be developed into biopesticides for mosquito control. We screened a natural product collection comprising 390 compounds and initially identified 26 molecules with potential ability to kill the larval stages of the yellow fever mosquito Aedes aegypti, which is responsible for transmitting viruses such as dengue, Zika, chikungunya and yellow fever. Natural products identified as hits in the screen were further evaluated for their suitability for biopesticide development. We show that a selection of the natural product top hits, bactobolin, maytansine and ossamycin, also killed the larval stages of the malaria-transmitting mosquito Anopheles gambiae as well as the adult form of both species. We have further explored the usefulness of crude extracts and preparations from two of the best candidates' sources (organisms of origin) for mosquitocidal activity, that is extracts from the two bacteria Burkholderia thailandensis and Streptomyces hygroscopicus var. ossamyceticus.

Bioprospection for new larvicides against Aedes aegypti based on ethnoknowledge from the Amazonian São Sebastião de Marinaú riverside community

ETHNOPHARMACOLOGICAL RELEVANCE

Vector-borne diseases represent a huge global burden impacting health systems. Aedes aegypti is the main vector of arboviral diseases including dengue, Zika, chikungunya and urban yellow fever in both tropical and subtropical areas. Ethnopharmacological investigations provide potential avenues for developing new vector control strategies.

AIM OF THE STUDY

The objective of this study is to document the São Sebastião de Marinaú riverside community's ethnoknowledge of local plants used to control mosquitoes and perform bioguided fractionation to isolate the compounds active against the arboviral disease vector Ae. aegypti.

MATERIALS AND METHODS

Semi-structured interviews were conducted with residents of the Marinaú community located in the Caxiuanã National Forest, in the Amazon biome, Pará, Brazil. The plants used to control mosquitoes were subjected to phytochemical studies guided by Ae. aegypti assays. Extracts were obtained from seven species using distinct organic solvents. Active extracts and fractions were separated by chromatographic techniques. Isolated compounds were characterized by NMR, LC/MS and GC/MS. Sample activity against Ae. aegypti larvae and pupae was evaluated after 24, 48 and 72 h exposure. The extracts were also investigated against adult female mosquitoes. The LC₅₀ values were determined by diluting each sample to obtain different concentrations in the respective activity range.

RESULTS

The Marinaú community uses more than ten plants as a repellent, most of which are trees native to the region. The primary applications of these plants to protect against insect bites were: burning plants (fumigation), application of body oils and bathing in macerated plants. Carapa guianensis is the predominant species used as a repellent. Extracts from Diospyros guianensis fruits, Carapa guianensis seed shells and Aspidosperma nitidum wood demonstrated Ae. aegypti larvicidal activity. The C. guianensis seed shell extract demonstrated a residual larvicidal effect. Plumbagin, stigmasterol, β-sitosterol, betulinic, ursolic and oleanolic acids, and betulin were identified in the D. guianensis extract. The plumbagin, ursolic and oleanolic acids displayed larvicidal activity. Oleanolic, ursolic and betulinic acids, and betulin were considered pupicidal. Aricine, the major alkaloid isolated from A. nitidum wood, also presented larvicidal activity.

CONCLUSIONS

Ten plant species traditionally used by the Marinaú community to afford protection against mosquitoes were reported. C. guianensis, D. guianensis and A. nitidum extracts were considered larvicidal against Ae. aegypti. Four triterpenes stood out as very active compounds against pupae. Aricine, an indole alkaloid, displayed larvicidal activity. Therefore, traditional knowledge of Amazonian plants combined with bioguided fractionation constitutes a strategy for the development of eco-friendly insecticides to control Ae. aegypti, an arbovirus vector.

Ecotoxicity of plant extracts and essential oils: A review

Plant-based products such as essential oils and other extracts have been used for centuries due to their beneficial properties. Currently, their use is widely disseminated through a variety of industries and new applications are continuously emerging. For these reasons, they are produced industrially in large quantities and consequently they have the potential to reach the environment. However, the potential effects that these products have on the ecosystems' health are mostly unknown. In recent years, the scientific community started to focus on the possible toxic effects of essential oils and plant extracts towards non-target organisms. As a result, an increasing body of knowledge has emerged. This review describes the current state of the art on the toxic effects that essential oils and plant extracts have towards organisms from different trophic levels, including producers, primary consumers, and secondary consumers. The majority of the studies (76.5%) focuses on the aquatic environment, particularly in aquatic invertebrates (45.1%) with only 23.5% of the studies focusing on the potential toxicity of plant-derived products on terrestrial ecosystems. While some essential oils and extracts have been described to have no toxic effects to the selected organisms or the toxic effects were only observable at high concentrations, others were reported to be toxic at concentrations below the limit set by international regulations, some of them at very low concentrations. In fact, L(E)C₅₀ values as low as 0.0336 mg.L^-1, 0.0005 mg.L^-1 and 0.0053 mg.L^-1 were described for microalgae, crustaceans and fish, respectively. Generally, essential oils exhibit higher toxicity than extracts. However, when the extracts are obtained from plants that are known to produce toxic metabolites, the extracts can be more toxic than essential oils. Overall, and despite being generally considered "eco-friendly" products and safer than they synthetic counterparts, some essential oils and plant extracts are toxic towards non-target organisms. Given the increasing interest from industry on these plant-based products further research using international standardized protocols is mandatory.

Challenges, Advances and Opportunities in Exploring Natural Products to Control Arboviral Disease Vectors

Natural products constitute an important source of molecules for product development. However, despite numerous reports of compounds and active extracts from biodiversity, poor and developing countries continue to suffer with endemic diseases caused by arboviral vectors, including dengue, Zika, chikungunya and urban yellow fever. Vector control remains the most efficient disease prevention strategy. Wide and prolonged use of insecticides has resulted in vector resistance, making the search for new chemical prototypes imperative. Considering the potential of natural products chemistry for developing natural products-based products, including insecticides, this contribution discusses the general aspects and specific characteristics involved in the development of drug leads for vector control. Throughout this work, we highlight the obstacles that need to be overcome in order for natural products compounds to be considered promising prototypes. Moreover, we analyze the bottlenecks that should be addressed, together with potential strategies, to rationalize and improve the efficiency of the drug discovery process.

Ecology, evolution, and epidemiology of zoonotic and vector-borne infectious diseases in French Guiana: Transdisciplinarity does matter to tackle new emerging threats

French Guiana is a European ultraperipheric region located on the northern Atlantic coast of South America. It constitutes an important forested region for biological conservation in the Neotropics. Although very sparsely populated, with its inhabitants mainly concentrated on the Atlantic coastal strip and along the two main rivers, it is marked by the presence and development of old and new epidemic disease outbreaks, both research and health priorities. In this review paper, we synthetize 15 years of multidisciplinary and integrative research at the interface between wildlife, ecosystem modification, human activities and sociodemographic development, and human health. This study reveals a complex epidemiological landscape marked by important transitional changes, facilitated by increased interconnections between wildlife, land-use change and human occupation and activity, human and trade transportation, demography with substantial immigration, and identified vector and parasite pharmacological resistance. Among other French Guianese characteristics, we demonstrate herein the existence of more complex multi-host disease life cycles than previously described for several disease systems in Central and South America, which clearly indicates that today the greater promiscuity between wildlife and humans due to demographic and economic pressures may offer novel settings for microbes and their hosts to circulate and spread. French Guiana is a microcosm that crystallizes all the current global environmental, demographic and socioeconomic change conditions, which may favor the development of ancient and future infectious diseases.