Human-bait Technique Research Articles

Essential oils extracted from Citrus macroptera and Homalomena aromatica (Spreng.) Schott. exhibit repellent activities against Aedes aegypti (Diptera: Culicidae)

Background & objectives: Mosquitoes alone transmit diseases to around 700 million individuals annually, killing approximately 0.7 million people every year worldwide. Considering the potential health risks linked with synthetic repellents, it has become vital to identify eco-friendly, natural repellents for mosquito control as well as to understand the underlying mechanism for mosquito repellent activity. To address this, objectives were set to extract essential oils from Citrus macroptera peel and Homalomena aromatica (Spreng.) Schott. rhizomes, evaluate their mosquito repellent activity against Aedes aegypti, and further explore their mosquito odorant receptor inhibition potential. Methods: The oils were extracted using Clevenger’s apparatus, and properties like specific gravity, refractive index, and boiling point were evaluated and characterised using Fourier transform infrared spectroscopy (FTIR) and gas chromatography-mass spectroscopy (GC-MS). Aedes aegypti mosquito eggs collected from the Indian Council of Medical Research (ICMR), Dibrugarh, were reared in the Department of Pharmaceutical Sciences, Research Laboratory, to obtain adult Aedes aegypti mosquitoes for the mosquito repellent activity evaluation of the essential oils using the Human Bait technique’. Molecular docking studies were performed for the oil components against mosquito odorant binding proteins. Further, toxicity studies of these two oils were evaluated against human dermal fibroblast adult (HDFa) cells. Results: The results revealed the presence of limonene (86.76%) and linalool (52.35%), respectively, in Citrus macroptera and Homalomena aromatica oils. It was found that the combination of the oils in a ratio of 1:1 showed mosquito repellent activity for up to 6.33 ± 0.23 h. Molecular docking studies showed the presence of major oil components having mosquito odorant receptor blocking potential comparable to N, N-diethyl-meta-toluamide (DEET), indicating a rationale for extended mosquito repellent action. Further, both of these oils were found to be non-cytotoxic against HDFa cells after 24 h. Interpretation & conclusion: The encouraging mosquito repellent activity of these two oils as compared to synthetic mosquito repellent DEET might pave the way for the development of novel herbal mosquito repellent formulations containing these essential oils.

Repellent effect of local indigenous knowledge-based repellent in Nakhon Si Thammarat, Thailand, against Aedes aegypti mosquito

Dengue fever has been a significant disease in Thailand for a long time, ranking it as one of the major health problems in the country. Management of the adult stage of mosquito vectors is approached by applying various synthetic chemicals such as adulticides, attractants, deterrents, and repellents. In Thailand, mosquito control and personal protection from mosquito bites are currently the most important measures for preventing and controlling mosquito-borne diseases. Although there are various control strategies for dengue disease, participation from the local community plays a vital role in the success of disease control. At present, a lot of local people have seen the value of local indigenous knowledge and used this to improve their life. The local community in the southern part of Thailand has used mosquito repellent from local knowledge for a long time. The problem regarding mosquito repellent made from local indigenous knowledge is that it has not yet been tested to determine its effectiveness. Therefore, this research aims to assess the effectiveness of mosquito repellent from local learning from Nakhon Si Thammarat provinces in Thailand. From the survey, out of 23 districts, six mosquito repellents were found in 3 communities, including Nabon, Muang, and Thasala. The repellent efficacy against the laboratory strain of Aedes aegypti by using the human-bait technique of the WHO (1996) standard method, with slight modifications. Approximately 0.1 ml of each test sample was applied evenly onto a 30 cm2 test site on one forearm of each human volunteer. Exposure experiments continued at 30 min intervals until at least two bites occurred in a 3-min period, or when a first bite was followed by a confirming bite (second bite) in the subsequent observation period. Each test was duplicated on different days for the two human volunteers. The result shows that three mosquito repellents made from local indigenous knowledge that have protection that lasts for more than 2 h are Ban Ko Sa Child Development Center's citronella spray (Nabon district, Kaew Saen subdistrict), Khun Lang's citronella spray, and Khun Lang's citronella ointment (Muang district, Pak Phun subdistrict). The result of this research was reported back to the local community to re-evaluate their self-reliance on their protection against mosquito biting.

Essential oils of four wild plants inhibit the blood seeking behaviour of female Aedes aegytpi

Aedes aegypti (Diptera: Culicidae) mosquito is an important vector of many disease-causing pathogens. An effective way to escape from these mosquito-borne diseases is to prevent mosquito bites. In the current study, essential oils of Lepidium pinnatifidum, Mentha longifolia, Origanum vulgare, and Agrimonia eupatoria were evaluated for their repellent potential against Ae. aegypti females. Essential oils were extracted using steam distillation from freshly collected aerial parts of the plants and tested against 4–5 day old females of Ae. aegypti through the human bait technique for repellency and repellent longevity assays. The chemical composition of extracted essential oils was explored by gas chromatography coupled with mass spectrometry (GC-MS). The essential oils of L. pinnatifidum, M. longifolia, O. vulgare, and A. eupatoria at a dose of 33 μg/cm2 showed 100%, 94%, 87%, and 83% mosquito repellent activity, respectively. Furthermore, M. longifolia and O. vulgare essential oils exhibited 100% repellency at a dose of 165 μg/cm2, whereas A. eupatoria essential oil showed 100% repellency only at 330 μg/cm2. In the time-span bioassay, M. longifolia and O. vulgare essential oils showed protection against Ae. aegypti bites for 90 and 75 min, respectively whereas both A. eupatoria and L. pinnatifidum were found active for 45 min. Phenylacetonitrile (94%), piperitone oxide (34%), carvacrol (20%) and α-pinene (62%) were the most abundant compounds in L. pinnatifidum, M. longifolia, O. vulgare and A. eupatoria essential oils, respectively. The current study demonstrates that M. longifolia and O. vulgare essential oils possess the potential to be used as an alternative to synthetic chemicals to protect humans from mosquito bites.

Transmission potentials status of simulium damnosum and willingness to comply with Ivermectin Treatment in Imo River Basin, Nigeria

Entomological, quantitative and qualitative data collection on willingness to comply with ivermectin treatment was conducted between May 2019 and March 2020 in Imo River Basin Nigeria. Simulium damnosum collected at Rivers Lolo and Ibii breeding sites by human-bait technique was assessed for transmission indices by standard methods. Structured questionnaires were used to ascertain compliance levels by communities (Umulolo and Amuro) and willingness to sustain the long-term ivermectin treatment. Entomologic indices (overall and specific for both sites) showed that infection, infective and parous rates were 0.7% (0.6% versus 0.7%), 0.0% (0.0% versus 0.0%), and 21.0% (22.3% versus 19.9%) respectively. Monthly biting rate (MBR) and monthly parous biting rate (MPBR) were 6,779.25 (3,291.75 versus 3,507.75) and 1,427.25 (770.0 versus 657.25) bites/person/month. Monthly transmission potentials (MTP) were zero indicative of no transmission. Of the 458 interviewed, 31.6% and 68.3% were males and females respectively. Among them, 66.8% were males and 67.4% were females treated before and 21 (14.5%) and 38 (121.1%) were high compliers. Sex did not affect the rate of compliance (p>0.05). Age group 25 years and above (74.3%) had been treated before with 21.3% high compliers among age groups. Analysis of data revealed that age significantly affected the intake of drug (p0.05). Suggested ways to improve compliance were documented and findings discussed in the context of possible onchocerciasis elimination.

Mosquito Repellent Potential of Carpesium abrotanoides Essential Oil and Its Main Components Against a Dengue Vector, Aedes aegypti (Diptera: Culicidae).

Disease vectoring mosquitoes are a serious threat to humans. However, till today only few mosquito repellents have been identified. The current study was conducted to evaluate the repellent potential of Carpesium abrotanoides essential oil against Aedes aegypti females by human bait technique. Essential oil was extracted by steam distillation process while the identification of chemical constituents was carried out by gas chromatography-mass spectrometry. Time span repellent bioassays of C. abrotanoides essential oil in comparison to DEET were performed at three different doses (33 μg/cm2, 165 μg/cm2, and 330 μg/cm2) under laboratory conditions. Highest repellency periods for essential oil and DEET were observed at the tested dose of 330 μg/cm2 with 315 min and 720 min, respectively. Lowest repellency period of 45 min for essential oil and 105 min for DEET was recorded at the tested dose of 33 μg/cm2. Major constituents caryophyllene (24.3%) and trans-nerolidol (12.0%) of C. abrotanoides essential oil were also evaluated as repellents at three different doses (330 μg/cm2, 165 μg/cm2, and 33 μg/cm2) against Ae. aegypti. Surprisingly, trans-nerolidol completely inhibited Ae. aegypti landings for 45 min when tested at 330 μg/cm2. However, caryophyllene did not completely inhibit Ae. aegypti landing even after immediate application at the tested dose of 330 μg/cm2. At the tested dose of 330 μg/cm2, the mixture (trans-nerolidol + caryophyllene) completely inhibited Ae. aegypti landing for 60 min indicating the synergistic effect of caryophyllene. Hence, C. abrotanoides as well as its major constituent, especially trans-nerolidol, have potential to formulate as mosquito repellent comparable of DEET.

Chemical composition and repellent activity of native plants essential oils against dengue mosquito, Aedes aegypti

Aedes aegypti L. (Diptera: Culicidae) mosquito is an important vector of chikungunya, dengue and yellow fever. Plant based essential oils may serve as good alternatives to commercially available mosquito repellent, DEET. Steam distillation was used for the extraction of essential oils from fresh collected aerial parts of plants viz Chenopodium ambrosioides, Conyza sumatrensis, Erigeron canadensis, Eucalyptus camaldulensis, Mentha spicata, Parthenium hysterophorus, and Tagetes minuta. The essential oils were tested for mosquito repellent activity against laboratory reared female Ae. aegypti by human bait technique. Identification of chemical constituents of essential oils was carried out by gas chromatography-mass spectrometry (GC–MS). The essential oil of M. spicata, E. canadensis, P. hysterophorus, C. sumatrensis, T. minuta, C. ambrosioides, and E. camaldulensis exhibited 100%, 80%, 63.9%, 51.4%, 50.2%, 39.7%, and 13.7% mosquito repellent activity respectively, at the tested dose of 30 μg/cm2. The most abundant constituents of M. spicata, E. canadensis, P. hysterophorus, C. sumatrensis and T. minuta essential oils were piperitenone oxide (47.1%), limonene (41.3%), germacrene D (36.6%), cis-lachnophyllum ester (33.3%) and dihydrotagetone (20.9%) respectively. M. spicata essential oil completely inhibited the attractiveness of human hands toward female mosquitoes for more than 45 min thus showed bioactivity comparable to that of commercially used mosquito repellent, DEET. This study suggests that the dilute solution of M. spicata essential oil could be used as potent mosquito repellent against Ae. aegypti alternative to commercially available synthetic mosquito repellents.

Surveillance of Mosquitoes (Diptera, Culicidae) in a Northern Central Region of Spain: Implications for the Medical Community.

Mosquitoes are important to public and animal health due to their capacity to transmit diseases. Since the Zika virus was declared a pandemic by the WHO in 2016, and it has been recorded in different regions of Mediterranean Area (included Spain), the Government of La Rioja (Northern Spain) through the Center of Rickettsiosis and Arthropod-Borne Diseases, implemented an entomological surveillance programme of mosquitoes in La Rioja and in a close area of Navarra. This surveillance extended to some of the pathogens that they can transmit. Here we describe the framework of the initial surveillance programme for the detection of mosquitoes and associated human pathogens. We outline the benefits and the limitation of the programme to date, and explore how greater benefits can be achieved, for example using a One Health approach. Entomological surveillance has been carried out with BG-Sentinel traps, human bait technique and other methods such as collecting adults in resting places or immature stages by dipping in several wetlands. Since Aedes albopictus, vector of arbovirus such as Dengue, Chikungunya, and Zika, has not been detected yet in the region, the entomological programme included the surveillance of this exotic species using ovitraps in the most important cities. Morphological identification was supported using the mitochondrial cytochrome C oxidase subunit I and the internal transcribed spacer 2 genes analysis. In 2016 and 2017, more than 6,000 mosquitoes were collected. The mosquito's community included 21 species associated with six genera: Anopheles (n = 4), Aedes (n = 5), Culex (n = 6), Culiseta (n = 4), Uranotaenia (n = 1) and Coquillettidia (n = 1). Eleven species represent new records for La Rioja and Navarra regions. Several species were collected biting humans and a great proportion of the sampled mosquito population are competent vectors of several pathogens, such as West Nile virus. Sequences closely related to mosquito–only flavivirus have been detected in 0.34% of analysed pools. At the same time, the epidemiological surveillance emphasis is placed in the early detection of mosquito-borne diseases in primary health and emergency services. The surveillance programme represents a relevant and necessary assessment of the risk of pathogen transmission in a region, and it allows for the establishment of the appropriate preventive measures.

Impact of Ocimum Basilicum Leaf Essential Oil on The Survival and Behaviour of An Indian Strain of Dengue Vector, Aedes aegypti (L.)

Objective: Aedes aegypti (L.) is a well-known widely spread disease vector transmitting several diseases of concern. Current investigations were undertaken to discover the larvicidal and repellent potential of essential oil from the basil plant, Ocimum basilicum leaves against Ae. aegypti as a suitable and eco-safe alternate to chemical insecticides. Methods: The larvicidal potential of basil oil was evaluated against Ae. aegypti early fourth instars using WHO protocol and LC50 and LC90 values were calculated. The efficacy of basil oil as mosquito repellent was assessed using the human-bait technique for 3 hours and the percent protection was calculated. Results: Exposure of early fourth instars of Ae. aegypti with various concentrations of O. basilicum essential oil for 24 h revealed a moderate LC50 and LC90 value of 141.95 ppm and 100.82 ppm, respectively. The investigations also showed that oil did not have any hormono-mimetic effects as it did not result in the formation of any larval-pupal intermediates. However, the basil essential oil exhibited significant effective repellency against adult Ae. aegypti. Introduction of the arms of human volunteers applied with basil oil in the cages of dengue vector resulted in 100% protection till 120 min as compared to control arm which experienced 3 to 8 bites. Remarkably, the experimental arm was bitten just once in every 15 minutes in next 45 minutes after which only 2 bites were recorded until 180 min of exposure. Conclusion: Our results recommended the efficient use of basil leaf essential oil as an efficient repellent and as a moderate larvicide agent against Ae. aegypti. Identification of bioactive components in the oil, their individual mode of action and synergistic effects, along with investigations on their impact on the environment and nontarget organisms would help in formulating strategies for mosquito management.

Impact of vegetable crop agriculture on anopheline agressivity and malaria transmission in urban and less urbanized settings of the South region of Cameroon.

BackgroundThe use of inland valley swamps for vegetable crop agriculture contributes to food security in urban and less urbanized settings in Africa. The impact of this agriculture on aggressive mosquitoes’ diversity and malaria transmission in central Africa is poorly documented. This study is aimed at assessing the impact of vegetable crop agriculture on these entomological parameters in urban and less urbanized settings of the forest area, south of Cameroon.MethodsThe human bait technique was used for the capture of aggressive mosquitoes from January to December 2012. For three consecutive days each month, captures were performed on volunteers in hydro-agricultural and river bank sites of Akonolinga and Yaoundé. Physico-chemical characteristics of mosquito breeding sites were recorded. Molecular alongside morpho-taxonomic techniques were used for the identification of mosquito species; ELISA test was used to reveal Plasmodium falciparum infected mosquitoes through the detection of CSP. Mosquito diversity, aggressivity and malaria transmission in sites and settings were determined and compared.ResultsBiting rates were higher in hydro-agricultural sites of less urbanized and urban settings (31.8 b/p/n and 28.6 b/p/n respectively) than in river banks sites (6.83 b/p/n and 3.64 b/p/n respectively; p < 0.0001). Physico-chemical parameters of breeding sites were not fundamentally different. Five anopheline species were identified; An. gambiae, An. funestus s.s., An. moucheti s.s., An. hancocki and An. nili s.s. In hydro-agricultural sites 2 species were captured in the urban setting versus 4 in the less urbanized setting, meanwhile in river bank sites, 3 species were captured in the urban setting versus 4 species in the less urbanized setting. An. nili s.s. was found in river banks only. An. hancocki was not found to insure Plasmodium falciparum Welch transmission. EIR in hydro-agricultural sites varied from 1.86 ib/p/n (urban area) to 2.13 ib/p/n (less urbanized area) with higher rates in April/May and August. Overall, EIR was higher in less urbanized areas (p < 0.0001) but the difference was nullified with the practice of vegetable crop agriculture (p = 0.2).ConclusionThese results highlight the need for specific preventive measures that take into account the ecological peculiarities related to vegetable crop agriculture on hydro-agricultural lands, in order to protect inhabitants from malaria.

Angelica sinensis (Umbelliferae) with proven repellent properties against Aedes aegypti, the primary dengue fever vector in Thailand

Botanical resources with great diversity in medicinal and aromatic plants are a rich and reliable source for finding insect repellents of plant origin, which are widely popular among today's consumers. Although some herbal-based repellents have been proven comparable to or even better than synthetics, commercially available natural repellents generally tend to be expensive, with short-lived effectiveness. This critical flaw leads to ongoing research for new and effective repellents, which provide longer protection against vector and nuisance-biting insects, while remaining safe, user friendly, and reasonably priced. This study aimed to evaluate the repellent activity of plant-derived products against the primary dengue vector, Aedes aegypti, by following the human bait technique of World Health Organization guidelines. Preliminary laboratory screening tests for repellency of 33 plant species clearly demonstrated Angelica sinensis as the most effective repellent from each kind of extracted product, with its essential oil and ethanolic extract having median complete protection times of 7.0 h (6.0-7.5) and 2.5 h (2.0-2.5), respectively. Due to its low yield (0.02 %), pungent smell, and little cause of irritation, A. sinensis essential oil did not qualify as a candidate for further repellent assessment. However, subsequent extractions of A. sinensis with different organic solvents of increasing polarity provided four extractants with varying degrees of repellency against A. aegypti. The hexane extract of A. sinensis provided excellent repellency, with a median complete protection time of 7.5 h (6.5-8.5), which was longer than that of ethanol (2.5, 2.0-2.5 h), acetone (1.75, 0.5-2.5 h), and methanol extracts (0.5, 0-1.0 h). By being the most effective product, A. sinensis hexane extract gave significant protection comparable to that of its essential oil and the standard synthetic repellent, N,N-diethyl-3-methylbenzamide (DEET: 6.25, 5.0-6.5 h). Qualitative gas chromatography/mass spectrometry analysis demonstrated the presence of phthalides and phthalates, including 3-N-butylphthalide, butylidenephthalide, ligustilide, and di-iso-octyl phthalate, as the principal constituents in A. sinensis products. The success of A. sinensis products, particularly that of hexane extract, has proved their potential as bioactive candidates in the next step for developing and producing alternative natural repellents with commercial aspirations.

Repellent effect of the leaf extracts of &lt;i&gt;Euphorbia Balsamifera&lt;/i&gt; (AIT) against &lt;i&gt;Anopheles gambiae&lt;/i&gt;

The ethanol extract of the leaves of Euphorbia balsamifera (commonly known as Gwadayi in Hausa) was sequentially extracted with petroleum ether, chloroform, ethyl acetate and methanol. The resulting extracts were designated EB1, EB2, EB3, and EB4 respectively. The ethanol extract designated EB. These extracts were tested for repellence against Anopheles gambiae using the human-bait technique under laboratory conditions, where five volunteers participated in the tests, one each for the extracts. The chloroform extract labelled EB1-02 was found to be the most active with 100% repellence at 25% (w/v) concentration, and 97.2% at 12.5% (w/v) concentration, while the ethyl acetate extract (EB1-03) recorded the least repellence activity of 32.4% at 25% (w/v) concentration, and 21.6% at 12.5% (w/v) concentration. It can thus be concluded that the phytochemicals present in the chloroform extract were responsible for repellent activity of E. balsamifera , and there is a need for further studies in order to ascertain the active compound in the plant. Keywords: Repellence, Anopheles gambiae, human-bait technique, Euphorbia balsamifera extracts.

Mosquito repellent activity of the leaf extracts of &lt;i&gt;Lawsonia inermis (l)&lt;/i&gt;

The ethanolic extract of the leaves of Lawsonia inermis (commonly known as lalle in Hausa) was sequentially extracted with petroleum ether, chloroform, ethyl acetate and methanol. The extracts were respectively labeled LI1, LI2, LI3, and LI4, with the ethanolic extract labeled LI, and 12.5% and 25% of the test extracts were tested for repellency against Anopheles gambiae, and the repellent activity was assessed using the human-bait technique. Five volunteers participated in the laboratory tests, one each for the extracts. The chloroform extract labeled LI1-02 was found to be the most active, (100% repellency), while the extract labeled LI1-03 (25%) recorded the least activity (15.4%). It can be concluded that the chloroform extract labeled LI1-02 is responsible for repellent activity of Lawsonia inermis.Keywords: Repellency, Anopheles gambiae, human-bait technique, Lawsonia inermis extracts.

Chemical Composition and Mosquito Repellency of Essential Oil of Tagetes minuta from the Southern Slopes of Mount Elgon in Western Kenya

Ethnopharmacologically, Tagetes minuta has a lot of applications in the history of human life. The study aimed at characterizing the essential oil from fresh aerial parts of T. minuta and evaluating its repellent effect on the host-seeking female Anopheles arabiensis mosquitoes, the vector of African malaria. The oil was obtained by hydrodistillation and analyzed by gas chromatography (GC) and gas chromatographymass spectrometry (GC-MS). Compounds were identified by comparison of their mass spectra with those in Wiley NBS and NIST databases and GC retention times to those of authentic samples. The repellent effect of the essential oil was evaluated using a human-bait technique to simulate field situation. The percentage yield of the essential oil of T. minuta was 0.00029 % w/w with a specific gravity of 0.8953 mg/ml. The oil showed a complex composition of about 119 hydrocarbon compounds and may be richer in monoterpenes (47.90 %) than in any other type of compounds. The main principal constituents of the essential oil of T. minuta included: ocimene, dihydrotagetone, tagetones, ocimenones, piperitenone, 3,9-epoxy-p-metha-1,8(10) diene, βcaryophyllene, bicyclogermacrene and AR-turmerone. Some of these constituents reported in literature have shown insecticidal, acaricidal, pesticidal and/or repellent properties. Although not manifesting a clear general trend, the essential oil however showed a significant dose-response effect of repellency (p < 0.05). More mosquitoes significantly landed and bit the control arm treated with vaseline pure petroleum jelly than the arm treated with the essential oil of T. minuta (p < 0.05), thus showing repellency properties of the oil against An. Arabiensis mosquitoes. Nevertheless, the underlying mechanism of repellency remains unknown. However, the oil may represent a potentially new, most practical and economic way and readily available and applicable malaria vector control tool for incorporation into integrated vector management strategies and contribute to the provision of prophylactic measures, particularly at an individual level.

Effects of Glucam P-20, Vanillin, and Fixolide on Mosquito Repellency of Citronella Oil Lotions

The objective of this study was to investigate the effects of three fragrance fixatives, Glucam P-20, Vanillin, and Fixolide, on the mosquito repellent property of citronella oil lotions. In the current study, two formulae (A and B) of oil-in-water citronella oil lotions were formulated using different ingredients (emulsifiers [Cremophors or Emulwax], stiffening agents, and emollients). Citronella oil was used at 10% wt:wt. The weight ratios tested between citronella oil and each fixative were 1:0.25, 1:0.5, and 1:1. Overall, 20 formulations, including one with no fixatives for both A and B, were produced, A1-A10 and B1-B10. The repellent activities of these 20 lotions against Aedes aegypti (L.) were tested using a human-bait technique. The types and concentrations of fixatives as well as the compositions of the formulations did affect the protection time of the citronella oil lotions. The lotion containing Emulwax and 5% vanillin (B6) was the most effective repellent. It provided the longest protection time of 4.8 h, which exceeded the minimum requirement of 2 h set by the National Institute of Health, Thailand. The shortest protection time (1 h) was observed in the lotion containing Emulwax and 2.5% Glucam P-20 (B2). It could be concluded that the tested fixatives affected the repellent activity of the citronella oil lotions.

Repellent effect of Salvia dorisiana, S. longifolia, and S. sclarea (Lamiaceae) essential oils against the mosquito Aedes albopictus Skuse (Diptera: Culicidae)

Aedes albopictus (Diptera: Culicidae) has been one of the fastest spreading insects over the past 20 years. Its medical importance is due to the aggressive daytime human-biting behavior and the ability to vector many viruses, including dengue, LaCrosse, Eastern Equine encephalitis and West Nile viruses. In this research, the essential oils (EOs) extracted from fresh air dried leaves of Salvia dorisiana, S. longifolia, and S. sclarea (Lamiaceae) were evaluated for their repellent activity against A. albopictus by using the human-bait technique. The EOs chemical composition was also investigated, and EOs were divided in three different profiles on the basis of their chemical composition: EO with large amount of monoterpenes from S. sclarea, EO rich in oxygenated sesquiterpenes from S. dorisiana, and S. longifolia EO characterized by similar percentages of monoterpenes and sesquiterpenes. The efficacy protection from S. dorisiana, S. longifolia, and S. sclarea EOs, at dosages ranging from 0.004 to 0.4 μL cm(-2) of skin, was evaluated during 120 min of observation. Results indicated that S. dorisiana, S. longifolia, and S. sclarea EOs had a significant repellent activity (RD(50) =0.00035, 0.00049, and 0.00101 μL cm(-2), respectively), with differences in repellency rates, as a function of oil, dosage, and observation time. S. dorisiana was the most effective oil: at the two higher dosages, it gave almost complete protection (with a protective efficacy of 90.99% and 95.62%, respectively) for 90 min. The best protection time was achieved with S. dorisiana essential oil. It ranged from 9.2 to 92.4 min. Protection times of S. longifolia and S. sclarea oils ranged from 3.2 to 60 min, and from 3.6 to 64.2 min, respectively. Our findings clearly reveal that these EOs have a good repellent activity against A. albopictus, therefore they can be proposed to improve the efficacy of repellent formulations against the Asian tiger mosquito.

Investigation of inclusion complexes of citronella oil, citronellal and citronellol with β-cyclodextrin for mosquito repellent

The aim of this study was to prepare the inclusion complexes of citronella oil, citronellal or citronellol with β-cyclodextrin and evaluate their physicochemical properties using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). A kneading method was employed to prepare the inclusion complexes and weight ratios of each of the active substance to β-cyclodextrin were 1:1 (1:1 CPX) and 1:2 (1:2 CPX). For comparison purposes, physical mixtures of these active compounds and β-cyclodextrin were also prepared and investigated. Unlike the physical mixtures, the SEM technique revealed drastic changes in the shapes and morphologies of the particles for the inclusion complexes. Furthermore, the FTIR and DSC results seemed to reveal some interactions between the active substance and β-cyclodextrin. The o/w lotions, which contained 10% w/w citronella oil (normal citronella oil; 1:1 CPX or 1:2 CPX), were formulated using Cremophors as emulsifiers. With modified Franz diffusion cell and synthetic membrane, the release rates of citronella oil from the lotions containing the inclusion complexes were significantly lower than that from the prepared lotion containing normal citronella oil. The mosquito (Aedes aegypti) repellent efficacy of the lotions containing citronella oil, citronellal or citronellol (both normal and inclusion complexes) was further evaluated by human-bait technique. The highest mosquito repellent activity was observed in the formulation which contained citronella oil–β-cyclodextrin inclusion complex at weight ratio of 1:1.

Bioefficacy of Mentha piperita essential oil against dengue fever mosquito Aedes aegypti L

Objective To assess the larvicidal and repellent potential of the essential oil extracted from the leaves of peppermint plant, Mentha piperita ( M. piperita) against the larval and adult stages of Aedes aegypti ( Ae. Aegypti). Methods The larvicidal potential of peppermint oil was evaluated against early fourth instar larvae of Ae. aegypti using WHO protocol. The mortality counts were made after 24 and 48 h, and LC 50 and LC 90 values were calculated. The efficacy of peppermint oil as mosquito repellent was assessed using the human-bait technique. The measured area of one arm of a human volunteer was applied with the oil and the other arm was applied with ethanol. The mosquito bites on both the arms were recorded for 3 min after every 15 min. The experiment continued for 3 h and the percent protection was calculated. Results The essential oil extracted from M. piperita possessed excellent larvicidal efficiency against dengue vector. The bioassays showed an LC 50 and LC 90 value of 111.9 and 295.18 ppm, respectively after 24 h of exposure. The toxicity of the oil increased 11.8% when the larvae were exposed to the oil for 48 h. The remarkable repellent properties of M. piperita essential oil were established against adults Ae. aegypti. The application of oil resulted in 100% protection till 150 min. After next 30 min, only 1-2 bites were recorded as compared with 8-9 bites on the control arm. Conclusions The peppermint essential oil is proved to be efficient larvicide and repellent against dengue vector. Further studies are needed to identify the possible role of oil as adulticide, oviposition deterrent and ovicidal agent. The isolation of active ingredient from the oil could help in formulating strategies for mosquito control.

Characterization and Evaluation of Repellent Effect of Essential Oil of Mangifera indica L. from Kenya

Ethnopharmacologically, the mango has a lot of applications in life in human health and ethnoveterinary medicines since ancient times. The study aimed at characterizing the essential oil of Mangifera indica L. leaves and evaluating its repellent effect on the host-seeking female Anopheles gambiae, the vector of African malaria. The essential oil was obtained by hydrodistillation and analyzed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). The repellent effect of the essential oil was evaluated using the human-bait technique to simulate field situation. Of the 26 major hydrocarbon compounds identified, α-pinene occurred in the largest amount (33.3 %), followed by α-phellandrene (22.6 %), Limonene (13.2 %), p-cymene (6.1 %), Heptane (3.8 %), β-pinene (2.6 %), Ledene (1.3 %), (-)-α-gurjunene (1.2 %), β-myrcene (1.1 %), γ-terpinene (1.0 %), (+)-2-carene (0.9 %) and trans (β)-caryophyllene (0.9 %) in that order. The oil showed a significant dose-dependent repellent effect on host-seeking female Anopheles gambiae s.s. The oil showed a complex composition of hydrocarbon compounds and may be richer in monoterpenes than in any other type of compounds. It showed the potential to repel mosquitoes.

Flebotomíneos da floresta de terra firme da Amazônia Peruana (Diptera: Psychodidae)

Um total de 1030 flebotomíneos, pertencentes a 14 espécies, foram coletados com armadilha tipo Shannon e isca humana, nos meses de Julho e Agosto de 1991, nos horários das 18:00 h. às 21:00 h., nas localidades de San Juan, San Pedro e 25 de Diciembre localizadas na Amazônia Peruana. As fêmeas foram mais abundantes do que os machos (96,98% e 3,02% respectivamente). Os subgêneros Psychodopygus (49,27% e 7 spp. coletadas) e Nyssomyia (48,79% e 4 spp. coletadas) comportaram o maior número de espécies e indivíduos. As espécies Lutzomyia richardwardi (48,4%) e L. carrerai (29,2%) foram as mais abundantes. Na localidade de San Juan foi coletado o maior número de indivíduos (55,2%), porém o maior número de espécies foi obtido na localidade de 25 de Diciembre. Quanto a estratégia de coleta, o mesmo número de espécies (12 spp.) foram obtidos com ambas as armadilhas, porém um maior número de indivíduos foi capturado com a técnica de isca humana.