Citrus essential oils and four enantiomeric pinenes against Culex pipiens (Diptera: Culicidae)

The aim of this study was to evaluate the toxicity of pinenes (entantiomers of α- and β-) and essential oils from Greek plants of the Rutaceae family against the mosquito larvae of Culex pipiens (Diptera: Culicidae). Essential oils were isolated by hydrodistillation from fruit peel of orange (Citrus sinensis L.), lemon (Citrus limon L.), and bitter orange (Citrus aurantium L.). The chemical composition was determined by gas chromatography/mass spectrometry (GC/MS) analysis. Citrus essential oils contained in high proportion limonene and in lower quantities p-menthane molecules and pinenes. The insecticidal action of these essential oils and entantiomers of their pinenes on mosquito larvae was evaluated. Plant essential oils exhibited strong toxicity against larvae with the LC₅₀ values ranging from 30.1 (lemon) to 51.5 mg/L (orange) depending on Citrus species and their composition. Finally, the LC₅₀ value of pinenes ranging from 36.53 to 66.52 mg/L indicated an enantioselective toxicity only for the β-pinene entantiomer.     

Chemical composition,Aedes mosquito larvicidal activity,and repellent activity against Triatoma rubrofasciata of Severinia monophylla leaf essential oil

Aedes aegypti and Ae. albopictus are key vectors in the spread of arboviruses such as dengue, chikungunya, yellow fever, and Zika. Triatoma rubrofasciata is an “assassin bug” whose populations and association with humans have dramatically increased and may represent a serious health concern. Control of insect vectors is a logical course of action to prevent the spread of these insect-borne infections. This work presents the leaf essential oil composition, mosquito larvicidal activities, and insect-repellent activity of Severinia monophylla. The essential oil of S. monophylla from Vietnam was obtained by hydrodistillation and analyzed by gas chromatography and mass spectrometry. The major components were sabinene, β-caryophyllene, bicyclogermacrene, germacrene D, (E)-nerolidol, globulol, and linalool. The leaf essential oil showed remarkable larvicidal activity against Ae. aegypti with LC₅₀ (48 h) of 7.1 μg/mL and Ae. albopictus with LC₅₀ (48 h) of 36 μg/mL. The essential oil also showed repellent activity on T. rubrofasciata at a concentration of 0.5%.

     

Composition of the essential oil constituents from leaves and stems of Korean Coriandrum sativum and their immunotoxicity activity on the Aedes aegypti L.

The leaves and stems of Coriandrum sativum were extracted and the essential oil composition and immunotoxicity effects were studied. The analyses were conducted by gas chromatography–mass spectroscopy (GC-MS), which revealed the essential oils of C. sativum leaves and stems. Thirty-nine components representing 99.62% of the total oil were identified from the leaves. The major components are cyclododecanol (23.11%), tetradecanal (17.86%), 2-dodecenal (9.93%), 1-decanol (7.24%), 13-tetradecenal (6.85%), 1-dodecanol (6.54%), dodecanal (5.16%), 1-undecanol (2.28%), and decanal (2.33%). Thirty-eight components representing 98.46% of the total oil were identified from the stems of the coriander. The major components are phytol (61.86%), 15-methyltricyclo[6.5.2(13,14),0(7,15)]-pentadeca-1,3,5,7,9,11,13-heptene (7.01%), dodecanal (3.18%), and 1-dodecanol (2.47%). The leaf oil had significant toxic effects against the larvae of Aedes aegypti with an LC₅₀ value of 26.93?ppm and an LC₉₀ value of 37.69?ppm and the stem oil has toxic effects against the larvae of A. aegypti with an LC₅₀ value of 29.39?ppm and an LC₉₀ value of 39.95?ppm. Also, the above data indicate that the major compounds may play an important role in the toxicity of essential oils.     

Chemical composition and larvicidal activity of the essential oil of Plectranthus amboinicus (Lour.) Spreng against Anopheles stephensi: a malarial vector mosquito

Essential oil of Plectranthus amboinicus was studied for its chemical composition and larvicidal potential against the malarial vector mosquito Anopheles stephensi. Totally 26 compounds were identified by GC and GC-MS. The major chemical compounds were carvacrol (28.65%) followed by thymol (21.66%), α-humulene (9.67%), undecanal (8.29%), γ-terpinene (7.76%), ρ-cymene (6.46%), caryophyllene oxide (5.85%), α-terpineol (3.28%) and β-selinene (2.01%). The larvicidal assay was conducted to record the LC₅₀ and LC₉₀ values and the larval mortality was observed after 12 and 24 h of exposure period. The LC₅₀ values of the oil were 33.54 (after 12 h) and 28.37 ppm (after 24 h). The LC₉₀ values of the oil were 70.27 (after 12 h) and 59.38 ppm (after 24 h). The results of the present study showed that the essential oil of P. amboinicus is one of the inexpensive and eco-friendly sources of natural mosquito larvicidal agent to control/reduce the population of malarial vector mosquito.     

Acaricidal and insecticidal activity of essential oils on <Emphasis Type="Italic">Varroa destructor</Emphasis> (Acari: Varroidae) and <Emphasis Type="Italic">Apis mellifera</Emphasis> (Hymenoptera: Apidae)

Varroa destructor is an external parasitic mite that is a serious pest of honeybees and has caused severe losses of colonies worldwide. One of the feasible alternative treatments being used for their control is essential oils. The aim of this work was to evaluate the bioactivity of some essential oils on V. destructor and Apis mellifera in relation with their chemical composition and physicochemical properties. Lavender, lavendin and laurel essential oils showed linalool as main compound in their composition. 1,8-Cineole was also present as a predominant component in the laurel essential oil. However, thyme oil was characterized by a high concentration of thymol. Mites and bees toxicity was tested by means of complete exposure method. For mites, LC₅₀ values for laurel, lavender and lavendin essential oil did not show significant variation throughout all observation times. However, the LC₅₀ values for thyme oil at 48 and 72 h were lower than at 24 h. Bee mortality was evident only in treatment with thyme oil. At 48 and 72 h, lavender essential oil presented better selectivity indexes. In this research, all essential oils caused mite mortality without severe harmful effects on adult bees. The simultaneous evaluation of the physicochemical analysis of the essential oils, the characterization of the dosage response relationships among them, and the mortality effects on mite and bees, give us the possibility to obtain comparative results for future research in Varroa control.     

Essential oils of indigenous in Greece six <Emphasis Type="BoldItalic">Juniperus</Emphasis> taxa

The chemical composition of 14 essential oils (EOs), obtained from various parts (leaves, fruits, wood) of the six indigenous in Greece Juniperus family taxa, was determined by GC and GC/MS analysis. The insecticidal properties of these EOs were evaluated against Culex pipiens L. larvae of 3rd and early 4th instars, in order to delineate the relationship between the phytochemical content of the EOs and their larvicidal activities. The analytical data indicated that the EOs mainly consisted of monoterpenes, mostly cyclic and only occasionally aliphatic, and to a lesser percent, of diterpenes. The larvicidal bioassays against C. pipiens larvae revealed that the most active EO was derived from the wood of Juniperus drupacea and contains mainly non-oxygenated monoterpenes and a significant amount of diterpenes, displaying the highest chemodiversity. Its initial LC₅₀ value was 26.47 mg L⁻¹. On the contrary, the EO isolated from J. phoenicea berries, which consisted of monoterpenes (non-oxygenated, cyclic), was the less active displaying an LC₅₀ value of 96.69 mg L⁻¹. In respect to the contained phytochemicals, myrcene was assayed as the most toxic, displaying an LC₅₀ value of 33.83 mg L⁻¹, while the four isomers of pinene abundant in all EOs were less active exhibiting LC₅₀ values ranging from 70.40 to 94.88 mg L⁻¹. Results herein reveal that the EOs isolated from the studied Juniperus family taxa represent an inexpensive source of natural mosquito control mixtures.     

Housefly (Musca domestica L.) control potential of Cymbopogon citratus Stapf. (Poales: Poaceae) essential oil and monoterpenes (citral and 1,8-cineole)

In spite of being a major vector for several domestic, medical, and veterinary pests, the control aspect of the common housefly, Musca domestica L. (Diptera: Muscidae) is often neglected. In the present study, the essential oil of Cymbopogon citratus and its major components were evaluated for control of housefly. The chemical composition analysis of C. citratus oil by gas chromatographic mass spectrometry (GC–MS) revealed citral (47 %) and 1,8-cineole (7.5 %) as principal components. The analysis of oil vapor by solid phase microextraction (SPME/GC–MS) showed increase in citral (74.9 %) and 1,8-cineole (8.6 %) content. Assay of oil against housefly larvae and pupae through contact toxicity assay showed lethal concentration (LC)₅₀ value of 0.41 μl/cm² and of percentage inhibition rate (PIR) of 77.3 %, respectively. Fumigation assay was comparatively more effective with LC₅₀ of 48.6 μl/L against housefly larvae, and a PIR value of 100 % against housefly pupae. The monoterpenes, citral, and 1,8-cineole, when assessed for their insecticidal activity against housefly larvae, showed LC₅₀ of 0.002 and 0.01 μl/cm² (contact toxicity assay) and LC₅₀ of 3.3 and 2.4 μl/L (fumigation assay). For pupicidal assay, both citral and 1,8-cineole had a PIR value of 100 %. High efficacy of citral and 1,8-cineole against housefly, established them to be an active insecticidal agent of C. citratus oil. The study demonstrates potentiality of C. citratus oil as an excellent insecticide for housefly control, and the results open up the opportunity of oil/monoterpenes being developed into an eco-friendly, economical, and acceptable product.     

Larvicidal potential of ethanolic extracts of dried fruits of three species of peppercorns against different instars of an indian strain of dengue fever mosquito, Aedes aegypti L. (Diptera: Culicidae)

Larvicidal bioassay was carried out in the laboratory to assess the potential of ethanolic extracts of dried fruits of three species of peppercorns: Long pepper, Piper longum L., Black pepper, Piper nigrum, and White pepper, Piper nigrum against the different instars of field-collected Indian strain of dengue fever mosquito (Aedes aegypti L.). The investigations established the larvicidal potential of all the varieties of pepper fruits against Ae. aegypti. Against early fourth instar, the ethanolic extracts of Black and White P. nigrum proved to be 30–40% less toxic than the extracts of P. longum, whereas against third instars, white pepper extracts exhibited 7% more efficacy than that of black pepper and 47% more toxicity than that of long pepper. The results also revealed that the extracts of all the three pepper species were 11–25 times more toxic against the third instar larvae as compared to the early fourth instars. The lethal concentration, 50% (LC₅₀) values obtained with ethanolic extracts of P. longum, White P. nigrum and Black P. nigrum against early fourth instar larvae were 0.248, 0.356, and 0.405 ppm, respectively, and the lethal concentration, 90% (LC₉₀) values were 0.605, 0.758, and 0.801 ppm, respectively. Whereas against third instar larvae, the LC₅₀ values recorded with three extracts were 0.022, 0.015, and 0.016 ppm and the LC₉₀ values recorded were 0.054, 0.034, and 0.046 ppm, respectively. The larvae treated with all the pepper species showed initial abnormal behavior in their motion followed by excitation, convulsions, and paralysis, leading to 100% kill indicating delayed larval toxicity and effects of the extracts on the neuromuscular system. Observations of morphological alterations on treated larvae under light microscopy revealed that most organs, except anal papillae, had a normal structural appearance as that of controls. The structural deformation in the form of shrinkage in the internal membrane exhibited by anal papillae suggests the anal papillae as the probable action sites of the pepper extracts. The potential of peppercorns as new types of larvicides for the control of mosquitoes are explored.     

Mosquito larvicidal activity of citrus limonoids against Aedes albopictus

Citrus limonoids, nomilin and limonin, were used for larvicidal assay against Aedes albopictus utilizing WHO methodology. LC_50s were 305.83, 176.08, and 136.07 μM for nomilin and 850.09, 600.72, and 407.09 μM for limonin after 24, 48, and 72 h, respectively. LT₅₀ assays exhibited that Savage citrange oil was the best at all concentrations (400, 500, 600, and 700 ppm) while Fairchild and Cassa grande were the weakest oils at 400 ppm, but at 500, 600, and 700 ppm, Carrizo citrange remained at the bottom with highest LT₅₀ values. Results exhibited that nomilin was more toxic than limonin and therefore provided a clear indication that limonoids in sample oils influenced the potential of respective oil. Out of the 10 tested citrus seed oils, Savage citrange (Citrus sinensis) comprised the maximum amount of limonin (2823.59 μg/ml) followed by grapefruit, Sacaton citrumelo, and Jaffa. When this oil (Savage citrange) was evaluated for bioassay against larvae of Ae. albopictus, it reflected complete dominance (LC₅₀ and LT₅₀) as compared to rest of the oils. Although Jaffa (Citrus paradisi) was found to contain nomilin and limonin, it was found less effective as compared to Savage citrange. The oils from Minneola and Chinese lime did not contain limonin and nomilin, and were therefore weak in terms of LC₅₀ values. Presence of limonin and nomilin in plant products is therefore a significant indicator of the pest control that needs to be exploited in other plants as well.     

Insecticidal Evaluation of essential oils of <Emphasis Type="BoldItalic">Citrus sinensis</Emphasis> L. (Myrtales: Myrtaceae) against housefly, <Emphasis Type="BoldItalic">Musca domestica</Emphasis> L. (Diptera: Muscidae)

The housefly, Musca domestica L., is one of the most common insects, associated with vectoring of various etiological agents. In order to search for effective control agent, the essential oil of sweet orange [Citrus sinensis (L.) Osbeck] was evaluated for its insecticidal activity against the larvae and pupae of housefly using contact toxicity and fumigation bioassays. In the contact toxicity assay, lethal concentration, LC₅₀ of C. sinensis essential oil against housefly larvae, varied between 3.93 and 0.71 μl/cm² for different observation days, while lethal time, LT₅₀, varied between 5.8 to 2.3 days. Mortality of larvae were significant with different concentrations (F = 2.79, df = 4, P < 0.05) and time (F = 6.69, df = 3, P < 0.01). In fumigant assay for housefly larvae, LC₅₀ of 71.2 and 52.6 μl/l was obtained in 24 and 48 h, respectively. Scanning electron microscopy of oil treated larvae revealed extreme dehydration and surface distortion while control larvae were free from any of the above symptoms and presented smooth surface, conforming effect of essential oil on housefly larvae. Percentage inhibition rate of oil against housefly pupae was 27.3–72.7% for contact toxicity and 46.4–100% for fumigation assay. Compositional analysis of C. sinensis essential oil using gas chromatography/mass spectrometry (GC-MS) revealed d-limonene (73.24%), α-pinene (5.86%) and myrcene (4.45%) as major components whereas its vapour profile (solid-phase micro extraction-GC/MS) was dominated by d-limonene at 92.57%. Significant activity of C. sinensis essential oil against larvae and pupae of housefly, pave the way for its use as eco-friendly housefly control measure.     

Acaricidal activity of essential oils from five endemic conifers of New Caledonia on the cattle tick Rhipicephalus (Boophilus) microplus

The aim of the present study was to demonstrate acaricidal activity on the cattle tick Rhipicephalus (Boophilus) microplus of essential oils from endemic conifers of New Caledonia in the context of the development of natural alternatives. Acaricidal activity of essential oils extracted from resin and heartwood of five endemic conifers of New Caledonia (Araucaria columnaris, Agathis moorei, Agathis ovata, Callitris sulcata, and Neocallitropsis pancheri) was evaluated on 14- to 21-day-old Rhipicephalus microplus tick larvae using the Larval Packal Test bioassay. A first screening with 5 % dilute solution was carried out and the oils with 100 % of mortality at this rate were diluted until no activity was shown. The heartwood oils of the two Cupressaceae were the most active with LC₅₀ value of 0.65 % for C. sulcata and 0.55 % for N. pancheri while resin oil of A. columnaris (LC₅₀?=?1.62 %) was the most active of the Araucariaceae family. Negative control (ethanol) was not toxic to the larvae. The chemical composition of essential oil from resin of A. columnaris was analyzed by gas chromatography–mass spectrometry. The essential oil was characterized by high level of sesquiterpene hydrocarbons and oxygenated sesquiterpenes and was composed mainly of aromadendrene (23.1 %) and bicyclogermacrene (16.0 %). In order to compare different plant resources in a sustainable program of natural acaricide, an “essential oil efficiency EOE” can be measured as the ratio between the yield of extraction and LC₅₀ value. This study shows that A. columnaris (EOE?=?2.36) and N. pancheri (EOE?=?3.51) could provide valuable and effective natural acaricides for control of the cattle tick R. microplus.     

Larvicidal activity of selected plant hydrodistillate extracts against the house mosquito, Culex pipiens, a West Nile virus vector

The larvicidal activity of hydrodistillate extracts from Chrysanthemum coronarium L., Hypericum scabrum L., Pistacia terebinthus L. subsp. palaestina (Boiss.) Engler, and Vitex agnus castus L. was investigated against the West Nile vector, Culex pipiens L. (Diptera: Culicidae). Yield and identification of the major essential oils from each distillation was determined by GC-MS analyses. The major essential oil component for each plant species was as follows: α-pinene for P. terebinthus palaestina, and H. scabrum (45.3% and 42.3%, respectively), trans-β-caryophyllene for V. agnus castus (22.1%), and borneol for C. coronarium (20.9%). A series of distillate concentrations from these plants (that ranged from 1 ppm to 500 ppm, depending on plant species) were assessed against late third to early fourth C. pipiens larvae at 1, 6, and 24 h posttreatment. In general, larval mortality to water treated with a distillate increased as concentration and exposure time increased. H. scabrum and P. terebinthus palaestina were most effective against the mosquito larvae and both produced 100% mortality at 250 ppm at 24-h continuous exposure compared with the other plant species. Larval toxicity of the distillates at 24 h (LC₅₀ from most toxic to less toxic) was as follows: P. terebinthus palaestina (59.2 ppm) > H. scabrum (82.2 ppm) > V. agnus castus (83.3 ppm) > C. coronarium (311.2 ppm). But when LC₉₀ values were compared, relative toxicity ranking changed as follows: H. scabrum (185.9 ppm) > V. agnus castus (220.7 ppm) > P. terebinthus palaestina (260.7 ppm) > C. coronarium (496.3 ppm). Extracts of native Turkish plants continue to provide a wealth of potential sources for biologically active agents that may be applied against arthropod pests of man and animals.     

In vitro efficacy of plant extracts and synthesized substances on <Emphasis Type="Italic">Rhipicephalus</Emphasis> (<Emphasis Type="Italic">Boophilus</Emphasis>) <Emphasis Type="Italic">Microplus</Emphasis> (Acari: Ixodidae)

Herbal drugs have been widely evaluated as an alternative method of parasite control, aiming to slow development of resistance and obtain low-cost biodegradable parasiticides. This study evaluated the in vitro efficacy on Rhipicephalus (Boophilus) microplus of extracts from Carapa guianensis seed oil, Cymbopogon martinii and Cymbopogon schoenanthus leaf essential oil, and Piper tuberculatum leaf crude extract and similar synthesized substances. In the immersion test, engorged females were evaluated in five dilutions ranging from 10% to 0.030625% concentration. In the larval test on impregnated filter paper, the concentration ranged from 10% to 0.02%. The treatments and controls were done in three replicates. Chemical analysis of the oils was performed by gas chromatography. The main compounds were oleic acid (46.8%) for C. guianensis and geraniol for C. martinii (81.4%), and C. schoenanthus (62.5%). The isolated and synthesized substances showed no significant effect on larvae and adult. C. martinii and P. tuberculatum showed the best efficacy on the engorged females. The LC₅₀ and LC₉₀ were 2.93% and 6.66% and 3.76% and 25.03%, respectively. In the larval test, the LC₅₀ and LC₉₀ obtained for C. martinii, P. tuberculatum, and C. schoenanthus were 0.47% and 0.63%, 0.41% and 0.79%, 0.57% and 0.96%, respectively. The fact that geraniol is present in greater quantities in C. martinii explains its higher activity in relation to C. shoenanthus. It is necessary to validate the in vivo use of safe and effective phytoparasiticidal substances. Efforts should be focused on developing formulations that enhance the efficacy in vivo and lengthen the residual period.     

Evaluation of bioefficacy of three Citrus essential oils against the dengue vector Aedes albopictus (Diptera: Culicidae) in correlation to their components enantiomeric distribution

Laboratory experiments were conducted to study the bioefficacy against Ae. albopictus of three Citrus essential oils, derived from peels of Citrus sinensis, Citrus limon, and Citrus paradise and of their components. Chiral gas chromatography analysis revealed the dominant occurrence of R-(+)-limonene and (?)-??-pinene in all three essential oils while in the case of lemon oil ??-terpinene, neral, and geranial detected also among other components. The tested Citrus essential oils were toxic against mosquito larvae with LC₅₀ values ranging from 25.03 to 37.03?mg?l^?1. Among citrus essential oils components tested, ??-terpinene was the most toxic (LC₅₀?=?20.21?mg?l^?1) followed by both enantiomeric forms of limonene (LC₅₀?=?35.99 and 34.89?mg?l^?1, for R-(+)-limonene and S-(?)-limonene, respectively). The delayed toxic effects after exposure of larvae to sublethal (LC₅₀) doses were also investigated for citrus essential oils and their major component R-(+)-limonene, indicating a significant reduction of pupal survival. In repellent bioassays, lemon essential oil, S-(?)-limonene, citral (mixture of neral\geranial) and (+)-??-pinene were the most effective compared with other citrus essential oils and components against adult mosquitoes. Repellent bioassays also revealed that limonenes and ??-pinenes showed an isomer dependence repellent activity. Finally, according to enantiomeric distribution of limonene and ??- and ??-pinene, the repellency of lemon essential oil is possibly attributed to the presence of citral.     

Acaricide activity of different extracts from Piper tuberculatum fruits against Rhipicephalus microplus

Rhipicephalus microplus is the main tick that affects cattle. Plant bioactive molecules can be used to control this ectoparasite. The aim of this study was to evaluate the in vitro efficacy of Piper tuberculatum fruit extracts obtained with different solvents on R. microplus larvae and engorged females. Hexane, ethyl ether, ethanolic, and methanolic extracts of P. tuberculatum fruits were evaluated. After extraction, all of the extracts were dried. Adult immersion tests and larval packet tests were performed with five different concentrations of each of the extracts. The hexane extracts of P. tuberculatum showed the highest larvicidal activity against R. microplus (lethal concentration (LC₅₀?=?0.04 mg/mL), followed by the ethyl ether (LC₅₀?=?0.08 mg/mL), ethanolic (LC₅₀?=?2.73 mg/mL), and methanolic (LC₅₀?=?4.49 mg/mL) extracts. The P. tuberculatum fruit extracts were also effective against R. microplus-engorged females. Ethyl acetate extracts showed the highest efficiency (LC₅₀?=?18.4 mg/mL), followed by the methanolic (LC₅₀?=?105.6 mg/mL), ethanolic (LC₅₀?=?140.0 mg/mL), and hexane (LC₅₀?=?297.4 mg/mL) extracts. All of the extracts showed similar chromatographic profiles containing 24 % piperine. The P. tuberculatum fruit extracts contain bioactive compounds with great potential to improve the standard formulations of acaricides for the control of R. microplus.     

Green synthesis of nano-liposomes containing Bunium persicum and Trachyspermum ammi essential oils against Trichomonas vaginalis

BackgroundTrichomonas vaginalis, a parasitic flagellated protozoan, is one of the main non-viral sexually transmitted diseases worldwide. Treatment options for trichomoniasis are limited to nitroimidazole compounds. However, resistance to these drugs has been reported, which requires the development of new anti-Trichomonas agents that confer suitable efficacy and less toxicity.MethodsIn the present work, we assessed the effectiveness of the liposomal system containing essential oils of Bunium persicum and Trachyspermum ammi against T. vaginalis in vitro. The chemical composition of B. persicum and T. ammi were analyzed using gas chromatography-mass spectrometry (GC–MS). Liposomal vesicles were prepared with phosphatidylcholine) 70%) and cholesterol)30%) using the thin-film method. The essential oils of B. persicum and T. ammi were loaded into the liposomes using the inactive loading method. Liposomal vesicles were made for two plants separately. Their physicochemical features were tested using Zeta-Sizer, AFM and SEM. The anti-Trichomonas activity was determined after 12 and 24 h of parasite cultures in TYI-S-33 medium.ResultsAfter 12 and 24 h of administration, the IC₅₀ of the B. persicum essential oil nano-liposomes induced 14.41 μg/mL and 45.19 μg/mL, respectively. The IC₅₀ of T. ammi essential oil nano-liposomes induced 8.08 μg/mL and 25.81 μg/mL, respectively.ConclusionsThese data suggested that nano-liposomes of the essential oils of B. persicum and T. ammi may be a promising alternative to current treatments for Trichomonas infection.     

Antiplasmodial volatile extracts from Cleistopholis patens Engler & Diels and Uvariastrum pierreanum Engl. (Engl. & Diels) (Annonaceae) growing in Cameroon

In a search for alternative treatment for malaria, plant-derived essential oils extracted from the stem barks and leaves of Cleistopholis patens and Uvariastrum pierreanum (Annonaceae) were evaluated in vitro for antiplasmodial activity against the W2 strain of Plasmodium falciparum. The oils were obtained from 500 g each of stem barks and leaves, respectively, by hydrodistillation, using a Clevenger-type apparatus with the following yields: 0.23% and 0.19% for C. patens and 0.1% and 0.3% for U. pierreanum (w/w relative to dried material weight). Analysis of 10% (v/v) oil in hexane by gas chromatography and mass spectrometry identified only terpenoids in the oils, with over 81% sesquiterpene hydrocarbons in C. patens extracts and U. pierreanum stem bark oil, while the leaf oil from the latter species was found to contain a majority of monoterpenes. For C. patens, the major components were α-copaene, δ-cadinene, and germacrene D for the stem bark oil and β-caryophyllene, germacrene D, and germacrene B for the leaf oil. The stem bark oil of U. pierreanum was found to contain mainly β-bisabolene and α-bisabolol, while α- and β-pinenes were more abundant in the leaf extract. Concentrations of oils obtained by diluting 1-mg/mL stock solutions were tested against P. falciparum in culture. The oils were active, with IC₅₀ values of 9.19 and 15.19 μg/mL for the stem bark and leaf oils, respectively, of C. patens and 6.08 and 13.96 μg/mL, respectively, for those from U. pierreanum. These results indicate that essential oils may offer a promising alternative for the development of new antimalarials.     

Larvicidal and repellent activity of essential oils from wild and cultivated Ruta chalepensis L. (Rutaceae) against Aedes albopictus Skuse (Diptera: Culicidae), an arbovirus vector

Rutaceae are widely recognized for their toxic and repellent activity exerted against mosquitoes. In our research, the essential oils extracted from fresh leaves of wild and cultivated plants of Ruta chalepensis L. (Rutaceae) were evaluated for larvicidal and repellent activity against the Asian tiger mosquito, Aedes albopictus Skuse (Diptera: Culicidae), currently the most invasive mosquito worldwide. In this research, gas chromatography and gas chromatography–mass spectrometry analyses of the essential oils from wild and cultivated plants showed only quantitative differences, in particular relatively to the amounts of ketone derivatives, while the qualitative profile evidenced a similar chemical composition. Both essential oils from wild and cultivated R. chalepensis plants were able to exert a very good toxic activity against A. albopictus larvae (wild plants, LC₅₀?=?35.66 ppm; cultivated plants, LC₅₀?=?33.18 ppm), and mortality was dosage dependent. These data are the first evidence of the toxicity of R. chalepensis against mosquitoes. Furthermore, the R. chalepensis essential oil from wild plants was an effective repellent against A. albopictus, also at lower dosages: RD₅₀ was 0.000215 μL/cm² of skin, while RD₉₀ was 0.007613 μL/cm². Our results clearly evidenced that the larvicidal and repellent activity of R. chalepensis essential oil could be used for the development of new and safer products against the Asian tiger mosquito.     

Insecticidal and repellent activities of thymol from the essential oil of Trachyspermum ammi (Linn) Sprague seeds against Anopheles stephensi

Essential oil of seeds of Trachyspermum ammi (Linn.) Sprauge and its pure constituent thymol showed promising results when evaluated for larvicidal, oviposition-deterrent, vapor toxicity, and repellent activity against malarial vector, Anopheles stephensi. Thymol was 1.6-fold more toxic than the oil toward fourth-instar larvae of A. stephensi with LD₅₀ values of 48.88 and 80.77 μg/ml, respectively. Egg laying by female adults of A. stephensi was much significantly reduced when exposed to vapors of thymol compared to the oil of T. ammi seeds, and similar effects were recorded for subsequent egg hatching and larval survival. Vapor toxicity assay showed LC₅₀ value of 79.5 mg/mat for thymol against adults of A. stephensi, whereas the crude oil exhibited the LC₅₀ value of 185.4 mg/mat. Thymol provided complete repellency toward A. stephensi adults at the dose of 25.0 mg/mat after 1 h duration, whereas same degree of repellency was obtained by the oil at the dose of 55.0 mg/mat, indicating its double-fold activity than the oil.     

Essential oil composition, adult repellency and larvicidal activity of eight Cupressaceae species from Greece against Aedes albopictus (Diptera: Culicidae)

The present study evaluated leaf essential oils from eight Cupresaceae species; Cupressus arizonica, Cupressus benthamii, Cupressus macrocarpa, Cupressus sempervirens, Cupressus torulosa, Chamaecyparis lawsoniana, Juniperus phoenicea, and Tetraclinis articulata for their larvicidal and repellent properties against Aedes albopictus, a mosquito of great ecological and medical importance. Based on the LC₅₀ values, C. benthamii essential oil was the most active (LC₅₀?=?37.5 mg/L) while the other tested Cupressaceae essential oils provided rather moderate toxicity against larvae (LC₅₀?=?47.9 to 70.6 mg/L). Under the used laboratory conditions, three of the essential oils (C. benthamii, C. lawsoniana, and C. macrocarpa) provided sufficient protection against mosquito adults, equivalent to the standard repellent “Deet” in the 0.2 mg/cm² dose, while C. macrocarpa assigned as the superior repellent oil in the 0.08 mg/cm² dose. Chemical analysis of the essential oils using gas chromatography and gas chromatography–mass spectrometry revealed the presence of 125 components.