Biological activity of Cymbopogon schoenanthus essential oil

IntroductionA number of plant species, including Cymbopogon schoenanthus, are traditionally used for the treatment of various diseases. C. schoenanthus is currently, traded in the Saudi markets, and thought to have medicinal value. This study aimed at investigating the biological activities of C. schoenanthus against both Gram-positive and Gram-negative bacteria and to identify its chemical ingredients.Materials and methodsThe inhibitory effects of water extracts of C. schoenanthus essential oils were evaluated against ten isolates of both Gram-positive and Gram-negative bacteria using the agar well diffusion and dilution methods. The minimum inhibitory concentration (MIC) was assayed using the Broth microdilution test on five of the ten isolates. The death rates were determined by the time kill assay, done according to the Clinical Laboratory Standards Institute (CLSI) guidelines. The chemical composition of the essential oils of the plant was performed using GC/MS.ResultsThe C. schoenanthus essential oil was effective against Escherichia coli, Staphylococcus aureus, methicillin-sensitive (MSSA) S. aureus (MRSA) and Klebsiella pneumoniae. The essential oil was not effective against Staphylococcus saprophyticus at the highest concentration applied of >150 μg/ml. The MIC values were as follows: 9.37 μg/ml for E. coli 4.69 μg/ml for S. aureus (MRSA), 2.34 mg/ml for MSSA and 2.34 μg/ml for K. pneumoniae. The time-kill assay indicated that there was a sharp time dependent decline in K. pneumoniae counts in the presence of the oil. This is in contrast to a gradual decline in the case of S. aureus under the same conditions. The eight major components of the essential oil were: piperitone (14.6%), cyclohexanemethanol (11.6%), β-elemene (11.6%), α-eudesmol (11.5%), elemol (10.8%), β-eudesmol (8.5%), 2-naphthalenemethanol (7.1%) and γ-eudesmol (4.2%).ConclusionThe results of the present study provide a scientific validation for the traditional use of C. schoenanthus as an antibacterial agent. Future work is needed to investigate and explore its application in the environmental and medical fields. In addition, to evaluating the efficacy of the individual ingredients separately to better understand the underlying mechanism.     

Oral toxicity of symbiotic bacteria Photorhabdus spp. against immature stages of insects

The oral toxicity of 5 Photorhabdus spp. strains collected in different regions of Korea was determined in the larvae of Plodia interpunctella, Galleria mellonella, Lucilia caesar, and Culex pipiens pallens. When diet or water containing culture media containing 1 of the 5 different strains was ingested by immature insects, the first instar larvae of both G. mellonella and L. caesar and young larvae of C. pipiens pallens died within 3–5 days after treatment. However, mortality of P. interpunctella neonate larvae was slightly slower and reached 94.4%–100% within 7 days after treatment. The mortality rate of a control group given a diet containing water, the medium without cultured bacteria, or Escherichia coli culture medium was not affected. The mortality rates were 100%, 45.3%, 2.8%, and 0% for Galleria, Lucilia, Plodia, and Culex, respectively, in another control group given a culture medium of Photorhabdus luminescens ssp. laumondii (TT01). In addition, culture media containing Photorhabdus strains significantly inhibited molting of third instar Plodia larvae by as much as 88% 7 days after treatment, whereas molting inhibition was reduced by 0%, 4%, and 20% following treatments with water, E. coli, or TT01 culture media, respectively. Our results suggest that the oral administration of Photorhabdus bacterial medium was highly effective for controlling various immature insects.     

Efficacy of bioactive compounds from Curcuma longa L. against mosquito larvae

To identify larvicidal compounds from the ethanolic extracts of Curcuma longa root, the active compounds were isolated using activity‐guided fractionation with column chromatography and identified based on nuclear magnetic resonance (NMR) and mass spectrometry (MS) data. The dipping method was used to determine the larvicidal activities of each compound against 4th‐instar larvae of Culex pipiens pallens. Two compounds were isolated and identified, ar‐turmerone and 8‐hydroxyl‐ar‐turmerone. The two compounds exhibited larvicidal activities against the 4th‐instar larvae of C. pipiens pallens after 24 hr of treatment with LC₅₀ values of 138.86 and 257.68 ppm, respectively. The larvicidal activities of ar‐turmerone and 8‐hydroxyl‐ar‐turmerone against C. pipiens pallens are reported herein for the first time. The elucidation of the structure of these phytochemicals and their insecticidal activities are important for assessing the potential of this plant as a botanical insecticide.     

Synthesis of some novel phosphorylated and thiophosphorylated benzimidazoles and benzothiazoles and their evaluation for larvicidal potential to Aedes albopictus and Culex quinquefasciatus

Series of benzimidazole and benzothiazole linked phosphoramidates and phosphoramidothioates (5a–j) and benzimidazole linked phenylphosphoramidates and phenylphosphoramidothioates (10a–e) were synthesized. The title compounds were preliminary screened for mosquito larvicidal properties against Aedes albopictus and Culex quinquefasciatus at different concentration from 40 to 5 mg/L. Among the screened compounds three compounds revealed potential larvicidal effects with 100% mortality in the order of 10e > 5j > 5e. Compound 10e was found to be the most toxic compound to Ae. albopictus and Cx. quinquefasciatus. The LC₅₀ of 10e against Ae. albopictus was found to be 6.42 and 5.25 mg/L at 24 and 48 h, respectively, whereas it was 7.01 and 3.88 mg/L, respectively in Cx. quinquefasciatus. Temephos was used as positive control.     

Comparative determination of the essential oil composition in Bulgarian endemic plant Achillea thracica Velen. during the process of ex situ conservation

Ex situ conservation of Bulgarian endemic plant Achillea thracica Velen. was achieved by successful in vitro cultivation of mono-nodal segments on MS-B5 medium supplemented with 1.0 mg/L BA for 20 days and subsequent transferring of regenerated plants on hormone free basal MS-B5 medium for root development and accumulation of leaf biomass. In vitro multiplicated plants were successfully acclimated in a growth chamber with 100% survival. GC–MS analysis of the essential oils resulted in the identification of 30, 10 and 28 compounds in in situ grown, in vitro cultivated and ex vitro adapted plants, respectively, constituting 77.7%, 99.9% and 84.1% of the total oils. The wider variety of compounds was found in the essential oils of in situ and ex vitro adapted plants where santolina alcohol, β-eudesmol, 1,8-cineole, germacrene D, α-cadinol and artemisia alcohol were the principal components comprising 68.7% and 69.3 of the oil, respectively. In vitro cultivated plants consist of mainly 1,8-cineole, germacrene D and artemisia alcohol representing 87% of the oil. Different growth conditions affect the composition of essential oils, suggesting their possible involvement in the process of adaptation and surviving in changing environmental conditions.     

Chemical composition,angiotensin I-converting enzyme (ACE) inhibitory,antioxidant and antimicrobial activities of the essential oil from south Tunisian Ajuga pseudoiva Rob. Lamiaceae

The essential oil of Ajuga pseudoiva, collected from Tunisia, was analyzed using gas chromatography–mass spectroscopy. Thirty-two compounds accounting for 95.76% of the total oil were identified. Sesquiterpenes were found to be the most abundant components of A. pseudoiva oil. And they were mainly represented by viridiflorol (30.17%), germacrene B (9.26%) (α, β and γ)-eudesmol (8.11%) and aromadendrene (7.45%). The essential oil of A. pseudoiva showed radical scavengers activity (IC₅₀ = 0.72 mg/mL) and displayed lipid peroxidation inhibitory activity (IC₅₀ = 0.6 mg/mL). A. pseudoiva essential oil was also found to exhibit a dose-dependent ACE inhibitory activity with an IC₅₀ value of 65.5 μg/mL. Moreover, the antimicrobial activity of the essential oil was tested against 17 species of microorganisms, and the results obtained showed significant antibacterial activity against the Gram-positive and Gram-negative bacteria, with inhibition zones and minimal inhibitory concentration values of 14–32 mm and 84–137 μg/mL and 6–21 mm and 105–336 μg/mL, respectively. Higher activity was also found against several fungal strains.     

Chemical composition,oviposition deterrent and larvicidal activities against Aedes aegypti of essential oils from Piper marginatum Jacq. (Piperaceae)

The essential oils of leaves, stems and inflorescences of Piper marginatum, harvested in the Atlantic forest in the State of Pernambuco, Brazil, were obtained by hydrodistillation. GC and GC–MS analyses revealed the presence of 40 components accounting, respectively, for 99.6%, 99.7% and 99.1% of the leaf, stem and inflorescence oil, the most abundant being (Z)- or (E)-asarone and patchouli alcohol. The essential oil of the inflorescences exhibited potent activity against the 4th instar of Aedes aegypti with LC₁₀ and LC₅₀ values of 13.8 and 20.0 ppm, respectively. Furthermore, the inflorescence oil did not interfere in the oviposition of A. aegypti females when assayed at 50 ppm. These properties suggest that P. marginatum oil is a potential source of valuable larvicidal compounds for direct use or in conjunction with baits in traps constructed to capture eggs and larvae.     

Chemical composition and larvicidal activity of Piper capense essential oil against the malaria vector,Anopheles gambiae

Hydro-distilled essential oil from Kenyan Piper capense (Piperaceae) was analysed by gas chromatography mass spectrometry (GC–MS) and evaluated for larvicidal activity against the malaria vector, Anopheles gambiae. The oil consisted mainly of sesquiterpene hydrocarbons which accounted for 43.9% of the oil. The major sesquiterpenes were δ-cadinene (16.82%), β-bisabolene (5.65%), and bicyclogermacrene (3.30%). The oil also had appreciable amounts of monoterpene hydrocarbons (30.64%), including β-pinene (7.24%) and α-phellandrene (4.76%), and arylpropanoids (8.64%), including myristicin (4.26%). The oil showed larvicidal activity against third instar larvae of A. gambiae, with LC₅₀ and LC₉₀ values of 34.9 and 85.0 ppm, respectively. Most of the larvae died within the first few hours. The high larvicidal activity of this oil was indicated by the fact that over 80% mortality was observed at a concentration of 100 ppm after 24 h. These results compared favourably with the commercial larvicide pylarvex® which had LC₅₀ and LC₉₀ values of 3.7 and 7.8 ppm, respectively. Application of this oil or of products derived from it to larval habitats may lead to promising results in malaria and mosquito management programmes.     

Efficient phototrophic production of a high-value sesquiterpenoid from the eukaryotic microalga Chlamydomonas reinhardtii

The heterologous expression of terpene synthases in microbial hosts has opened numerous possibilities for bioproduction of desirable metabolites. Photosynthetic microbial hosts present a sustainable alternative to traditional fermentative systems, using freely available (sun)light and carbon dioxide as inputs for bio-production. Here, we report the expression of a patchoulol synthase from Pogostemon cablin Benth in the model green microalga Chlamydomonas reinhardtii. The sesquiterpenoid patchoulol was produced from the alga and was used as a marker of sesquiterpenoid production capacity. A novel strategy for gene loading was employed and patchoulol was produced up to 922±242 µg g⁻¹ CDW in six days. We additionally investigated the effect of carbon source on sesquiterpenoid productivity from C. reinhardtii in scale-up batch cultivations. It was determined that up to 1.03 mg L⁻¹ sesquiterpenoid products could be produced in completely photoautotrophic conditions and that the alga exhibited altered sesquiterpenoid production metabolism related to carbon source.     

Sesquiterpenes from essential oil of Amyris balsamifera

Six sesquiterpenes were isolated and identified from the essential oil of the wood of Amyris balsamifera (Rutaceae): 10-epi-γ-eudesmol, α-agarofuran, 4-hydroxydihydroagarofuran, valerianol, β-eudesmol, elemol.     

Larvicidal activities of the stem bark extract and rotenoids of Millettia usaramensis subspecies usaramensis on Aedes aegypti L. (Diptera: Culicidae)

The dichloromethane/methanol (1:1) extract of the stem bark of Millettia usaramensis subspecies usaramensis was tested for its larvicidal activity against the 4th instar Aedes aegypti larvae and demonstrated activity with LC₅₀ value of 50.8 ± 0.06 μg/mL at 48 h. Compounds isolated from the extract were also tested for their larvicidal activities, and the rotenoid usararotenoid-A (LC₅₀ 4.3 ± 0.8 μg/mL at 48 h) was identified as the most active principle. This compound appears to be the first rotenoid having a trans-B/C ring junction and methylenedioxy group at C-2/C-3 with high larvicidal activity. Related rotenoids with the same configuration at the B/C-ring junction did not show significant activity at 100 μg/mL.     

Acetylenic 2-phenylethylamides and new isobutylamides from Acmella oleracea (L.) R. K. Jansen,a Brazilian spice with larvicidal activity on Aedes aegypti

Ethanol extract obtained from dried leaves of Acmella oleracea afforded after a liquid/liquid partition procedure a larvicidal hexane fraction (LC₅₀ = 145.6 ppm) and a non larvicidal dichloromethane one. From the inactive fraction, three amides were identified, two new structures, named deca-6,9-dihydroxy-(2E,7E)-dienoic acid isobutylamide (1), deca-8,9-dihydroxy-(2E,6Z)-dienoic acid isobutylamide (2) and the known nona-2,3-dihydroxy-6,8-diynoic acid 2-phenylethylamide (3). Bioassay-guided chromatographic fractionation of the hexane partition led to the identification of an amide mixture, nona-(2Z)-en-6,8-diynoic acid 2-phenylethylamide (4) and deca-(2Z)-en-6,8-diynoic acid 2-phenylethlylamide (5). This mixture was active against Aedes aegypti larvae at LC₅₀ = 7.6 ppm. Low toxicity of crude extracts and derived fractions on Artemia salina nauplies showed the possibility of using them to control the A. aegypti mosquito larvae. This is the first report on larvicidal activity of acetylenic 2-phenylethylamides and their identification in A. oleracea leaves.     

Effect of enzymatic and hydrothermal treatments of rapeseeds on quality of the pressed rapeseed oils: Part I: Antioxidant capacity and antioxidant content

Response surface methodology was used to evaluate the quantitative effects of three independent variables: rapeseed moisture content, concentration of the added enzymes and conditioning temperature, on the antioxidant capacity and total phenolic, tocopherol, and phospholipid contents in the enzyme-treated rapeseed oils. The highest antioxidant capacity (1220.0, 964.8 μmol TE/100 g) total phenolic (83.3, 74.0 mg SA/100 g) and phospholipid (12,532, 12,376 mg/kg) contents reveal two rapeseed oils extruded from seeds contained 11% moisture, treated with cellulolytic and pectolytic enzymes (0.05%), respectively, and heated at 120 °C. However, the highest content of total tocopherols was determined in rapeseed oils pressed from seeds with 7% moisture, after addition of cellulolytic (0.05%) and pectolytic (0.1%) enzymes, heated at 90 and 105 °C, respectively. Total phenolic and phospholipid contents in the enzyme-treated rapeseed oils correlated significantly (p < 0.0000001) with antioxidant capacities of oils (R² = 0.8710 and 0.6581, respectively). Experimental results of the antioxidant capacity, total phenolic, tocopherol and phospholipid contents were close to the predicted values calculated from the polynomial response surface models equations (R² = 0.9727, 0.9870, 0.8390 and 0.9706 for the cellulolytic enzyme-assisted rapeseed oils and R² = 0.9148, 0.9489, 0.9426 and 0.9479 for the pectolytic enzyme-assisted rapeseed oils). The optimum rapeseed moisture content, enzyme concentration and conditioning temperature for the cellulolytic and pectolytic enzyme-treated rapeseed oils were 11% and 9.7%, 0.08% and 0.1%, and 120 °C, respectively.     

Mosquito larvicidal activity of Aloe vera (Family: Liliaceae) leaf extract and Bacillus sphaericus,against Chikungunya vector,Aedes aegypti

The bio-efficacy of Aloe vera leaf extract and bacterial insecticide, Bacillus sphaericus larvicidal activity was assessed against the first to fourth instars larvae of Aedes aegypti, under the laboratory conditions. The plant material was shade dried at room temperature and powdered coarsely. A. vera and B. sphaericus show varied degrees of larvicidal activity against various instars larvae of A. aegypti. The LC₅₀ of A. vera against the first to fourth instars larvae were 162.74, 201.43, 253.30 and 300.05 ppm and the LC₉₀ 442.98, 518.86, 563.18 and 612.96 ppm, respectively. B. sphaericus against the first to fourth instars larvae the LC₅₀ values were 68.21, 79.13, 93.48, and 107.05 ppm and the LC₉₀ values 149.15, 164.67, 183.84, and 201.09 ppm, respectively. However, the combined treatment of A. vera + B. sphaericus (1:2) material shows highest larvicidal activity of the LC₅₀ values 54.80, 63.11, 74.66 and 95.10 ppm; The LC₉₀ values of 145.29, 160.14, 179.74 and 209.98 ppm, against A. aegypti in all the tested concentrations than the individuals and clearly established that there is a substantial amount of synergist act. The present investigation clearly exhibits that both A. vera and B. sphaericus materials could serve as a potential larvicidal agent. Since, A. aegypti is a container breeder vector mosquito this user and eco-friendly and low-cost vector control strategy could be a viable solution to the existing dengue disease burden. Therefore, this study provides first report on the mosquito larvicidal activity the combined effect of A. vera leaf extract and B. sphaericus against as target species of A. aegypti.     

Toxicity of basil and orange essential oils and their components against two coleopteran stored products insect pests

Two commercialized essential oils and their constituent compounds were investigated for fumigant and contact activities against two grain storage insects, adults of the maize weevil (Sitophilus zeamais) and the red flour beetle (Tribolium castaneum). The two commercialized basil and orange oils showed strong fumigant and contact activities against S. zeamais and T. castaneum. The constituents of the basil oil were linalool (21.83%), estragole (74.29%), and α-humulene (2.17%), and those of the orange oil were α-pinene (0.54%), sabinene (0.38%), β-myrcene (1.98%), limonene (96.5%), and linalool (0.6%). As a toxic fumigant, the basil oil was more effective (24-h LC₅₀ = 0.014 and 0.020 mg cm^− 3) than the orange oil (24-h LC₅₀ = 0.106 and 0.130 mg cm^− 3) against S. zeamais and T. castaneum adults, respectively. Among the constituents of the two essential oils, the toxicity of estragole was the highest (0.004 and 0.013), followed by linalool (0.016 and 0.023), limonene (0.122 and 0.171), α-pinene (0.264 and 0.273), and β-myrcene (0.274 and 0.275) based on 24-h LC₅₀ values (mg cm^− 3). Similar results were obtained in a contact toxicity test. The contact activity of basil oil was more toxic than orange oil, and estragole and linalool showed pronounced contact toxicity against S. zeamais and T. castaneum adults. Alpha-humulene had no activity as a fumigant at the tested doses, but it did have an effect as a contact poison, having 24-h LD₅₀ values of 0.040 and 0.045 mg adult^− 1 to S. zeamais and T. castaneum, respectively. Although basil oil, orange oil, and their components displayed both contact and fumigant toxicities, their effects were mainly exerted by fumigant action via the vapor phase. Thus, basil oil, orange oil, and their components could be potential candidates as new fumigants for the control of S. zeamais and T. castaneum adults.     

Chemical composition and larvicidal activity of leaf essential oil from Clausena dentata (Willd) M. Roam. (Rutaceae) against the chikungunya vector,Aedes aegypti Linn. (Diptera: Culicidae)

Larvicidal activity of essential oil and isolated compounds from Clausena dentata leaves were tested against early fourth instar Aedes aegypti larvae. GC–MS analysis of essential oil revealed the presence of fourteen compounds of which the major compounds were sabinene (21.27%), biofloratriene (19.61%), borneol (18.34%) and β-bisabolol (17.68%). The essential oil of C. dentata exhibited significant larvicidal activity, with 24 h LC₅₀ and LC₉₀ values of 140.2 and 341.6 mg/l, respectively. Larvicidal activities of the four major compounds of essential oil were also tested. The LC₅₀ values of sabinene, biofloratriene, borneol and β-bisabolol were 27.3, 47.4, 43.5 and 33.2 mg/l, respectively. Results of this study show that the leaf essential oil of C. dentata and its four major compounds may be a potent source of natural larvicides.     

Bioactivity of powders and essential oils of three Asteraceae plants as post-harvest grain protectants against three major coleopteran pests

Powders and essential oils were obtained from Achillea biebersteinii, A. fragrantissima and Ageratum conyzoides and tested for their insecticidal activity against Sitophilus oryzae, Rhyzopertha dominica and Tribolium castaneum. Composition of the oils was identified by gas chromatography (GC) and GC/mass spectrometry (MS). The tested plants showed adulticidal activity, where toxicity varied with dosage of the plant product, the insect tested and the exposure period. When mixed with grains as ground powders, a dosage of 20 g/kg grains killed 88.2, 73.6 and 64.4% of S. oryzae after 12 days of exposure with 79.6, 63.3 and 48% reduction in progeny for powders of A. biebersteinii, A. conyzoides and A. fragrantissima, respectively. Under the same assay conditions, A. biebersteinii and A. conyzoides powders killed 100% of R. dominica. T. castaneum was less susceptible to the plant powders. The LC₅₀ values for powders were 22.8, 31.6 and 39.7 mg/g grains for A. biebersteinii, 27.1, 35.4 and 47.8 mg/g grains for A. conyzoides and 36.9, 48.3 and 78.6 mg/g grains for A. fragrantissima against R. dominica, S. oryzae and T. castaneum, respectively. Upon fumigation, a dose of 60 μl/L air of A. biebersteinii and A. conyzoides oils was sufficient to kill 100% of R. dominica after 12 days of adult exposure, while 91.3% adult mortality was recorded in the case of A. fragrantissima oil. S. oryzae and T. castaneum showed a great susceptibility to the plant oils. Powders exhibited a moderate to strong residual activity where A. conyzoides showed the greatest grain protecting activity.     

Effect of enzymatic and hydrothermal treatments of rapeseeds on quality of the pressed rapeseed oils: part II. Oil yield and oxidative stability

Response surface methodology was used to evaluate the quantitative effects of three independent variables: rapeseed moisture content (MC), enzymes dosage (ED) and conditioning temperature (T) on rapeseed oil yield (OY), efficiency of pressing (EP), and oxidative stability (OS). The highest OY (16.4%) and EP (42.8%) were obtained from pectolytic enzyme (0.1%) treated seeds (MC = 9%, T = 90 °C). The highest OS (12.6 h) was found for oil pressed from rapeseeds heated at 120 °C (MC = 11%), after the cellulolytic enzyme treatment. Results of OY, EP and OS determinations correlate with the predicted values calculated from the partial cubic models (PCMs) equations (R² = 0.9995, 0.9994, 0.9974 for the cellulolytic enzyme-treated oils and 0.9900, 0.9900, 0.9990 for the pectolytic enzyme-treated oils). The predicted optimum MC = 9.5% and 8.6%, ED = 0.06% and 0.1%, T = 91.2 °C and 90.1 °C resulted in OY = 15.5% and 16.5%, EP = 40.4% and 43.0% for rapeseed oils from seeds treated with cellulolytic and pectolytic enzymes. OS values (12.6 h and 11.8 h) at the optimum conditions of MC = 11.0% and 10.1%, ED = 0.04% and 0.08%, T = 120.0 °C and 119.9 °C for the cellulolytic and pectolytic enzyme-treated oils were also calculated using PCM. Moreover, scanning electron microscopy revealed structural changes in the rapeseed after enzymatic treatment.     

Toxicity of Acalypha indica (Euphorbiaceae) and Achyranthes aspera (Amaranthaceae) leaf extracts to Aedes aegypti (Diptera: Culicidae)

Alternative control strategies for the dengue vector Aedes aegypti L. (Diptera: Culicidae) include botanical insecticides. They are believed to pose little threat to the environment or to human health and may provide practical substitutes for synthetic insecticides. In this study, we determined the biological activities of methanol extracts of Acalypha indica L. (Euphorbiaceae) and Achyranthes aspera L (Amaranthaceae) leaves individually and in combination as botanical insecticides against Ae. aegypti. Based on LC₅₀ values for 4th instar Ae. aegypti, the combined extracts showed the strongest larvicidal activity (277 ppm). A. aspera and A. indica extracts individually gave similar results (409 and 420 ppm, respectively). Respective LC₅₀ values for pupae were 326 ppm, 456 ppm, and 467 ppm. In studies of smoke toxicity, 64% of females exposed to negative control smoke (no extract) blood fed on chicken, whereas 17% blood fed when exposed to smoke containing A. aspera extract and to positive control smoke (0.2% d-allethrin). In the field, treatment of water storage tanks (≈ 0.5 m³) with combined plant extract reduced larval and pupal populations by 97% and 81%, respectively, after 5 days. Given the results of this study, further evaluation of the combined (A. indica + A. aspera) extract as a mosquito larvicide is warranted. Mosquito coils with A. aspera extract also show promise as a practical and potentially economical means for mitigating mosquito blood feeding.     

Synergistic effects of essential oil-based cream formulations against Culex quinquefasciatus Say and Aedes aegypti L. (Diptera: Culicidae)

Mosquitoes are major arthropod vectors responsible for several pathogenic diseases. In recent years, repellents of botanical origin, particularly essential oils, have been used against mosquitoes and have been found effective and safe. In this study, five different repellent cream formulations (CF1–5) were prepared using combinations of essential oils, including camphor, cinnamon, citronella, lemongrass, lime, orange, neem, basil, Vitex, Lantana, eucalyptus, and clove, and their repellency was tested using Culex quinquefasciatus Say and Aedes aegypti L. under laboratory conditions and compared to the standard synthetic repellent N,N-diethyl-meta-toluamide (DEET-12%, w/w). Among the five cream formulations, CF2 at a dose of 5 mg/cm² showed the longest protection time of 4.18 h and 3.31 h against C. quinquefasciatus and A. aegypti, respectively, under laboratory conditions. CF3 at a dose of 5 mg/cm² was moderately effective, with protection times of 3.42 h and 2.58 h against C. quinquefasciatus and A. aegypti, respectively, under laboratory conditions. CF2 at a dose of 5 mg/cm² was also tested in the field against wild mosquitoes for 3 h, and 100% protection was observed for the entire study period. Thus, CF2 could be used in developing an effective natural repellent as an alternative to the existing synthetic repellents to C. quinquefasciatus and A. aegypti.