Baccharis dracunculifolia (Asteraceae) essential oil toxicity to Culex quinquefasciatus (Culicidae)

Larvicidal potential, antimicrobial properties and molecular docking analysis of Egyptian Mint (Mentha rotundifolia) against Culex pipiens L. (Diptera: Culicidae) and Midgut-borne Staphylococcus aureus

Mosquitoes prefer stagnant areas near hospitals to live and easily spread pathogenic bacteria. Our current study aims to isolate multidrug-resistant (MDR) Staphylococcus aureus isolates from midguts of Mosquito Culex pipiens and study the potential of mint as a biocontrol strategy against C. pipiens larvae and their midgut-borne S. aureus. Samples of the third and fourth larval instars of C. pipiens were collected from water ponds around three Cairo hospitals. Ciprofloxacin, gentamycin and tetracycline, as well as various concentrations of mint leaf extract (MLE) were tested for antibiotic susceptibility. Sixty-five isolates were obtained and showed antibiotic resistance to tetracycline, gentamycin, ciprofloxacin, and undiluted MLE with resistant percentages (%) of 27.69, 30.76, 17.46, and 23.08%, respectively. Undiluted MLE inhibited 61.53% of the multidrug S. aureus isolates, whereas it couldn't inhibit any of these isolates at dilutions less than 50 μg/mL. The MIC of MLE was ≤ 700 µg/mL, while the MIC of the antibiotics ranged from 0.25 to 5.0 µg/mL for the three antibiotics. The most inhibited S. aureus isolate was identified by 16SrRNA sequencing approach and registered in GenBank as S. aureus MICBURN with gene accession number OQ766965. MLE killed all larval stages after 72 h of exposure, with mortality (%) reaching 93.33 and 100% causing external hair loss, breakage of the outer cuticle epithelial layer of the abdomen, and larvae shrinkage. Histopathology of treated larvae showed destruction of all midgut cells and organelles. Gas chromatography (GC) of MLE revealed that menthol extract (35.92%) was the largest active ingredient, followed by menthone (19.85%), D-Carvone (15.46%), Pulegone (5.0579%). Docking analysis confirmed that alpha guanine and cadinol had the highest binding affinity to both predicted active sites of Culex pipiens acetylcholinesterase. As a result, alpha-guanine and cadinol might have a role as acetylcholinesterase inhibitors.

Cellulose microcrystalline: A promising ecofriendly approach to control Culex quinquefasciatus larvae

The growing use of synthetic chemical compounds/substances in vector control of mosquitoes, associated with their adverse effects on the environment and non-target organisms, has demanded the development of eco-friendly alternatives. In this context, this study aimed to evaluate the larvicidal action of different cellulose microcrystalline (CMs) concentrations and investigate their toxicity mechanisms in Culex quinquefasciatus fourth instar larvae as a model species. Probit analysis revealed that the median lethal concentrations (LC50) for 24 h and 36 h exposure were 100 and 58.29 mg/L, respectively. We also showed that such concentrations induced a redox imbalance in the larvae, marked by an increase in the production of reactive oxygen species (ROS) and thiobarbituric acid reactive substances (TBARS), as well as a reduction in the activity of superoxide dismutase (SOD) and catalase (CAT). Furthermore, different alterations in the external morphology of the larvae were associated with the ingestion of CMs. On the other hand, exposure of adult zebrafish (Danio rerio) to LC5024h and LC5036h for seven days did not induce any behavioral changes or alterations mutagenic, genotoxic, biochemical, or in the production of cytokines IFN-γ and IL-10. Thus, taken together, our study demonstrates for the first time that the use of CMs can constitute a promising strategy in the control of C. quinquefasciatus larvae, combining insecticidal efficiency with an "eco-friendly" approach in the fight against an important mosquito vector of several human diseases.

Baccharis Species Essential Oils: Repellency and Toxicity against Yellow Fever Mosquitoes and Imported Fire Ants

Essential oils from five Baccharis species were screened for their toxicity and biting deterrence/repellency against yellow fever mosquito, Aedes aegypti (L.), and imported fire ants, including Solenopsis invicta Buren (RIFA), Solenopsis richteri Forel (BIFA) and their hybrids (HIFA). Baccharis microdonta DC. and B. punctulata DC. at 10 µg/cm2 showed biting deterrence similar to DEET, N, N-diethyl-meta-toluamide at 25 nmol/cm2, whereas the repellency of B. pauciflosculosa DC., B. sphenophylla Dusén ex Malme and B. reticularioides Deble & A.S. Oliveira essential oils was significantly lower than DEET against mosquitoes. Two major compounds from the active essential oils, kongol and spathulenol, also exhibited biting deterrence similar to DEET against mosquitoes. The highest toxicity exhibited against mosquitoes was by Baccharis punctulata essential oil (LC50 = 20.4 ppm), followed by B. pauciflosculosa (LC50 = 31.9 ppm), B. sphenophylla (LC50 = 30.8 ppm), B. microdonta (LC50 = 28.6 ppm), kongol (LC50 = 32.3 ppm), spathulenol (LC50 = 48.7 ppm) and B. reticularioides essential oil (LC50 = 84.4 ppm). Baccharis microdonta essential oil showed repellency against RIFA, BIFA and HIFA at 4.9, 4.9 and 39 µg/g, respectively. Baccharis microdonta essential oil also showed toxicity with LC50 of 78.9, 97.5 and 136.5 µg/g against RIFA, BIFA and HIFA, respectively, at 24 h post treatment.

Larvicidal potential, toxicological assessment, and molecular docking studies of four Egyptian bacterial strains against Culex pipiens L. (Diptera: Culicidae)

Mosquito control in Egypt depends on applying chemical synthetic pesticides that impact negatively on human health and the environment as well as the development of antibiotic and chemical resistance. This study aims to control the 3rd and 4th instars of Culex pipiens larvae using four bacterial strains. According to Phenotypic and molecular identification, the four isolates were identified as Bacillus subtilis MICUL D2023, Serratia marcescens MICUL A2023, Streptomyces albus LARVICID, and Pseudomonas fluorescens MICUL B2023. All strains were deposited in GenBank under accession numbers OQ764791, OQ729954, OQ726575, and OQ891356, respectively. Larvicidal activity of all microbial strain metabolites against a field strain of C. pipiens explored low LC50 results and reached its lowest values on the 3rd day with values of 6.40%, 38.4%, and 46.33% for P. fluorescens, S. albus, and S. marcescens, respectively. In addition, metabolites of P. fluorescence were more toxic than those of S. albus, followed by S. marcescens. B. subtilis shows no larvicidal effect on both field and lab mosquito strains. Microscopic alterations of 3rd and 4th instars showed toxic effects on different body parts (thorax, midgut, and anal gills), including losing external hairs, abdominal breakage, and larvae shrinkage, as well as different histological malformations in the digestive tract, midgut, and cortex. GC-MS analysis detected 51, 30, and 32 different active compounds from S. albus, S. marcescens, and P. fluorescens, respectively. GC detected 1, 2-BENZEA2:A52NEDICARBOXYLIC ACID, 2-Cyclohexene-1-carboxylic-acid-5-2-butenyl-methyl ester, and 3 octadecahydro2R3S4Z9Z-11R-12S from S. albus, S. marcesens, and P. fluorescens, respectively. Total protein, Total carbohydrate, and Acetylcholine esterase activity indicated significantly low levels on the 3rd day. All strain metabolites were safe against HSF cell lines. The docking results confirmed the role of the produced metabolites as larvicidal agents and Acetylcholine esterase inhibition. Such a problem need more studies on applying more and more natural pesticides.

Ethnomedicinal, phytochemical and pharmacological investigations of Baccharis dracunculifolia DC. (ASTERACEAE)

Baccharis dracunculifolia DC (Lamiaceae) (Asteraceae) is found in South America, mainly in Argentina, Brazil, Bolivia, Paraguay and Uruguay. Folk medicine is used as a sedative, hypotensive, bronchodilator, cardiovascular disorders, anti-flu, and also in skin wounds. Considered the main source of green propolis, which increases the pharmacological interest in this species. It is also known as a "benefactor" plant facilitating the development of other plant species around it, being indicated for the recovery of degraded areas. This species has been studied for decades in order to isolate and identify the active principles present in the aerial parts (leaves and flowers) and roots. The present study consists of a review of the scientific literature addressing the ethnobotanical, ethnomedicinal, phytochemical, pharmacological and potential cytotoxic effects of the B. dracunculifolia species. In this survey, we sought to investigate issues related to the botanical and geographic description of the species, the ethnobotanical uses, as well as the phytochemical studies of the essential oil, extracts and green propolis obtained from the aerial parts and roots of B. dracunculifolia. Using high precision analytical tools, numerous compounds have already been isolated and identified from leaves and flowers such as the flavonoids: naringenin, acacetin, dihydrokaempferol, isosakuranetin and kaempferide; phenolic acids: p-coumaric, dihydrocoumaric, ferulic (E)-cinnamic, hydroxycinnamic, gallic, caffeic, and several caffeoylquinic acids derivatives; phenolic acids prenylated: artepillin C, baccharin, drupanin; the glycosides dracuculifosides and the pentacyclic triterpenoids: Baccharis oxide and friedelanol. The predominant class in the essential oil of leaves and flowers are terpenoids comprising oxygenated monoterpenes and sesquiterpenes, highlighting the compounds nerolidol, spathulenol, germacrene D and bicyclogermacrene. These compounds give the species high antimicrobial, antioxidant, antitumor, analgesic, immunomodulatory and antiparasitic potential, making this species a promising herbal medicine. In vitro toxicity assays with B. dracunculifolia extract showed low or no cytotoxicity. However, in vivo analyses with high doses of the aqueous extract resulted in genotoxic effects, which leads us to conclude that the toxicity of this plant is dose-dependent.

Eugenia uniflora, Melaleuca armillaris, and Schinus molle essential oils to manage larvae of the filarial vector Culex quinquefasciatus (Diptera: Culicidae)

Populations of Culex quinquefasciatus Say, 1823 (Diptera: Culicidae) have shown resistance to insecticides of the carbamate and organophosphate classes. The objective of this study was to assess the susceptibility of C. quinquefasciatus larvae to essential oils from leaves of Eugenia uniflora L., Melaleuca armillaris (Sol. ex Gaertn.) Sm., and Schinus molle L and C. quinquefasciatus larvae's biochemical responses after their exposure to these leaves. The essential oils were chemically analyzed by GC and GC/MS. First, the lethal concentration for 50% (LC₅₀) values was estimated using different concentrations of essential oils and probit analysis. The larvae were exposed for 1 h at the LC₅₀ estimated for each essential oil. The susceptibility of the larvae to essential oils was evaluated using the following biochemical parameters: concentrations of total protein and reduced glutathione; levels of production of hydrogen peroxide and lipid peroxidation; and the activity of the enzyme acetylcholinesterase (AChE). The main chemical constituents in E. uniflora were E-β-ocimene, curzerene, germacrene B, and germacrone; in M. armillaris were 1,8-cineole and terpinolene; and in S. molle were sabinene, myrcene, and sylvestrene. The essential oils had LC₅₀ values between 31.52 and 60.08 mg/L, all of which were considered effective. All of them also promoted changes in biochemical parameters when compared to the control treatment. The essential oils of S. molle and E. uniflora inhibited the activity of the AChE enzyme, and the essential oil of M. armillaris increased it. All essential oils had larvicidal activity against C. quinquefasciatus, but the essential oil of E. uniflora was the most efficient. Thus, the findings of the present study suggest that the essential oil of E. uniflora can be considered promising for the development of botanical larvicides.

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.

Shedding light on toxicity of SARS-CoV-2 peptides in aquatic biota: A study involving neotropical mosquito larvae (Diptera: Culicidae)

Knowledge about how the COVID-19 pandemic can affect aquatic wildlife is still extremely limited, and no effect of SARS-CoV-2 or its structural constituents on invertebrate models has been reported so far. Thus, we investigated the presence of the 2019-new coronavirus in different urban wastewater samples and, later, evaluated the behavioral and biochemical effects of the exposure of Culex quinquefasciatus larvae to two SARS-CoV-2 spike protein peptides (PSPD-2002 and PSPD-2003) synthesized in our laboratory. Initially, our results show the contamination of wastewater by the new coronavirus, via RT-qPCR on the viral N1 gene. On the other hand, our study shows that short-term exposure (48 h) to a low concentration (40 μg/L) of the synthesized peptides induced changes in the locomotor and the olfactory-driven behavior of the C. quinquefascitus larvae, which were associated with increased production of ROS and AChE activity (cholinesterase effect). To our knowledge, this is the first study that reports the indirect effects of the COVID-19 pandemic on the larval phase of a freshwater invertebrate species. The results raise concerns at the ecological level where the observed biological effects may lead to drastic consequences.

Relationship between Baccharis dracunculifolia DC. and B. microdonta DC. (Asteraceae) by Their Different Seasonal Volatile Expression

Baccharis dracunculifolia DC. and Baccharis microdonta DC. (Asteraceae) are woody species morphologically similar growing in Uruguay, where not taxonomists people often confuse them in field conditions. As the essential oil of B. dracunculifolia ('vassoura' oil) is highly prized by the flavor and fragrance industry, the correct differentiation of the two species is a key factor in exploiting them profitably and reasonably. To differentiate both Baccharis species, in this work their volatile expression profiles were studied as an alternative tool to determine authenticity and quality. Volatile organic compounds (VOCs) were monthly extracted during an entire year from aerial parts of wild populations by simultaneous distillation extraction (SDE), and studied by gas chromatography/mass spectrometry (GC/MS; identification) and conventional gas chromatography (GC-FID; component abundances determination). Enantioselective gas chromatography/mass spectrometry (Es-GC/MS) was applied in the search of parameters able to ensure genuineness of each species extract. Qualitative VOCs profiles were found to be similar for both species, being β-pinene, limonene, spathulenol, caryophyllene oxide, and viridiflorol the main components. However, the abundance of those VOCs were two to ten times higher in B. dracunculifolia than in B. microdonta during the year of study. These Baccharis spp. showed species-specific patterns of VOCs expression according to the seasonality, and interestingly, oxygenated compounds (trans-pinocarveol and myrtenal) increased their abundances at full-flowering stages. The enantiomeric distribution of selected monoterpenes (α- and β-pinenes, limonene, linalool, terpinen-4-ol, and α-terpineol) presented differential values for both Baccharis spp., meaning that Es-GC might be a useful tool for differentiating chemically both species in Uruguay for genuineness determination purposes.

Insecticidal and oviposition deterrent effects of essential oils of Baccharis spp. and histological assessment against Drosophila suzukii (Diptera: Drosophilidae)

The diverse flora of the Atlantic Forest is fertile ground for discovering new chemical structures with insecticidal activity. The presence of species belonging to the genus Baccharis is of particular interest, as these species have shown promise in pest management applications. The objective of this study is to chemically identify the constituents expressed in the leaves of seven species of Baccharis (B. anomala DC., B. calvescens DC., B. mesoneura DC., B. milleflora DC., B. oblongifolia Pers., B. trimera (Less) DC. and B. uncinella DC.) and to evaluate the toxicological and morphological effects caused by essential oils (EOs) on the larvae and adults of Drosophila suzukii (Diptera: Drosophilidae). Chemical analysis using gas chromatography-mass spectrometry (GC-MS) indicated that limonene was the main common constituent in all Baccharis species. This constituent in isolation, as well as the EOs of B. calvescens, B. mesoneura, and B. oblongifolia, caused mortality in over 80% of adults of D. suzukii at a discriminatory concentration of 80 mg L^-1 in bioassays of ingestion and topical application. These results are similar to the effect of spinosyn-based synthetic insecticides (spinetoram 75 mg L^-1) 120 h after exposure. Limonene and EOs from all species had the lowest LC₅₀ and LC₉₀ values relative to spinosyn and azadirachtin (12 g L^-1) in both bioassays. However, they showed the same time toxicity over time as spinetoram when applied to adults of D. suzukii (LT₅₀ ranging from 4.6 to 8.7 h) in a topical application bioassay. In olfactometry tests, 92% of D. suzukii females showed repellent behavior when exposed to the EOs and limonene. Likewise, the EOs of B. calvescens, B. mesoneura, and B. oblongifolia significantly reduced the number of eggs in artificial fruits (≅ 7.6 eggs fruit^-1), differing from the control treatment with water (17.2 eggs fruit^-1) and acetone (17.6 eggs fruit^-1). According to histological analyses, the L3 larvae of D. suzukii had morphological and physiological alterations and deformations after exposure to treatments containing EOs and limonene, which resulted in high larval, pupal, and adult mortality. In view of the results, Baccharis EOs and their isolated constituent, limonene, proved to be promising alternatives for developing bioinsecticides to manage of D. suzukii.