Comparative larvicidal activity of essential oils from three medicinal plants against Aedes aegypti L

This work aimed at comparing larvicidal activity of essential oils extracted from the dried leaves of Alpinia speciosa, Cymbopogon citratus, and Rosmarinus officinalis against Ae. aegypti larvae. The larvae were observed for 4 h and at 24 h according to a completely randomized design with three replications and the following concentrations [μl/ml]: 0.25, 0.5, 1.0, 1.5, 2.0, 2.5, and controls were distilled water, and commercial standard citral, camphor, eucalyptol, α‐pinene, and β‐myrcene. The essential oil of C. citratus had the lowest LC₅₀ (0.28) and LC₉₀ (0.56) values, followed by that of A. speciosa (0.94 and 1.2, resp.) and of R. officinalis (1.18 and 1.67, resp.), and only the commercial standards citral and α‐pinene were larvicidal.     

Larvicidal effects of some essential oils against Aedes aegypti (L.), the vector of dengue fever in Saudi Arabia

Essential oils are very popular among organic growers because they are ecologically safe, do not have mammalian toxicity, and cannot be resistant to a variety of contaminants. Four essential oils, Lemon, Lavender, Peppermint, and Neem, were tested for larvicide efficacy against the dengue fever vector Aedes aegypti larvae under laboratory conditions using dipping bioassay techniques. Among the essential oils tested, lemon, peppermint, and lavender oils showed high larvicidal activity against larvae of Ae. aegypti. Lemon oil showed the highest effects (LC₅₀ 10.676 ppm), while Peppermint, Lavender and Neem oil showed the lowest effects (LC₅₀ 21.380, 29.818 and 38.058 ppm, respectively). As a result, the mixture of lemon oil (LC₅₀) with Peppermint oil (LC₂₅) showed the highest co-toxicity factor, whereas the mixture of Lemon oil (LC₅₀) with Diesel oil (LC₂₅) showed the lowest co-toxicity factor. Based on the results of this study, it appears that essential oils may be useful as larvicides against Ae. aegypti larvae. In search of new natural larvicides, these compounds may provide an alternative to Synthetic insecticides as these are environmentally safe insecticides.     

Larvicidal effects of fungal Meroterpenoids in the control of Aedes aegypti L., the main vector of dengue and Yellow fever

The mosquito Aedes aegypti is an increasing problem of public health, being the vector responsible for dengue and Yellow Fever in tropical and subtropical regions. The aim of this work was to determine the potential larvicidal activity of a series of meroterpenoids, compounds 1-7, previously obtained fungal secondary metabolites from Penicillium sp., against the third-instar larvae of A. aegypti. The lethal concentrations (LC(50) and LC(90)) of 1-7 were evaluated 24 h after exposure. Dehydroaustin (4) was the most active meroterpenoid in the series, with an LC(50) value of 2.9 ppm, making it an attractive natural insecticide.     

Chicory (Cichorium intybus) and wormwood (Artemisia absinthium) extracts exhibit strong larvicidal activity against mosquito vectors of malaria,dengue fever,and filariasis

Vector-borne diseases transmitted by mosquitoes cause globally important diseases such as malaria, dengue fever, and filariasis. The incidence of these diseases can be reduced through mosquito control programs but these control programs currently rely on synthetic insecticides that can impact the environment, and has selected widespread mosquito resistance. Environment friendly and biodegradable natural insecticides discovered in plants offer an alternative approach to mosquito control. Here, we investigated extracts from root or aerial parts of Chicory (Cichorium intybus) and wormwood (Artemisia absinthium) against the early 4th instar larvae of Anopheles stephensi (malaria vector), Aedes aegypti (dengue fever vector), and Culex quinquefasciatus (filariasis vector). The root and aerial parts extracts of A. absinthium and C. intybus at 200, 100, 50, 25 and 12.5?ppm caused significant mortality of the tested mosquito species. Root extracts exhibited higher larvicidal activity that aerial part extracts. The highest larvicidal activity was recorded in methanol extract of roots of C. intybus with LC50?=?66.16, 18.88 and LC¬90?=?197.56, 107.16?ppm for An. stephensi; LC50?=?78.51, 40.15 and LC90?=?277.31, 231.28?ppm for Ae. aegypti and LC50?=?103.99, 64.56 and LC¬90?=?314.04, 247.54?ppm for Cx. quinquefasciatus. These results reveal potent mosquito larvicidal activity against vectors of malaria, dengue fever, and filariasis is present in extracts of chicory and wormwood.     

Toxicity of Thiophenes from Echinops transiliensis (Asteraceae) against Aedes aegypti (Diptera: Culicidae) Larvae

Structure? activity relationships of nine thiophenes, 2,2′: 5′,2″‐terthiophene ( 1 ), 2‐chloro‐4‐[5‐(penta‐1,3‐diyn‐1‐yl)thiophen‐2‐yl]but‐3‐yn‐1‐yl acetate ( 2 ), 4‐(2,2′‐bithiophen‐5‐yl)but‐3‐yne‐1,2‐diyl diacetate ( 3 ), 4‐[5‐(penta‐1,3‐diyn‐1‐yl)thiophen‐2‐yl]but‐3‐yne‐1,2‐diyl diacetate ( 4 ), 4‐(2,2′‐bithiophen‐5‐yl)‐2‐hydroxybut‐3‐yn‐1‐yl acetate ( 5 ), 2‐hydroxy‐4‐[5‐(penta‐1,3‐diyn‐1‐yl)thiophen‐2‐yl]but‐3‐yn‐1‐yl acetate ( 6 ), 1‐hydroxy‐4‐[5‐(penta‐1,3‐diyn‐1‐yl)thiophen‐2‐yl]but‐3‐yn‐2‐yl acetate ( 7 ), 4‐(2,2′‐bithiophen‐5‐yl)but‐3‐yne‐1,2‐diol ( 8 ), and 4‐[5‐(penta‐1,3‐diyn‐1‐yl)thiophen‐2‐yl]but‐3‐yne‐1,2‐diol ( 9 ), isolated from the roots of Echinops transiliensis, were studied as larvicides against Aedes aegypti. Structural differences among compounds 3, 5 , and 8 consisted in differing AcO and OH groups attached to C(3″) and C(4″), and resulted in variations in efficacy. Terthiophene 1 showed the highest activity (LC₅₀, 0.16 μg/ml) among compounds 1 – 9 , followed by bithiophene compounds 3 (LC₅₀, 4.22 μg/ml), 5 (LC₅₀, 7.45 μg/ml), and 8 (LC₅₀, 9.89 μg/ml), and monothiophene compounds 9 (LC₅₀, 12.45 μg/ml), 2 (LC₅₀, 14.71 μg/ml), 4 (LC₅₀, 17.95 μg/ml), 6 (LC₅₀, 18.55 μg/ml), and 7 (LC₅₀, 19.97 μg/ml). These data indicated that A. aegypti larvicidal activities of thiophenes increase with increasing number of thiophene rings, and the most important active site in the structure of thiophenes could be the tetrahydro‐thiophene moiety. In bithiophenes, 3, 5 , and 8 , A. aegypti larvicidal activity increased with increasing number of AcO groups attached to C(3″) or C(4″), indicating that AcO groups may play an important role in the larvicidal activity.     

Geographic and ecological distribution of the dengue and chikungunya virus vectors Aedes aegypti and Aedes albopictus in three major Cameroonian towns

Aedes albopictus (Diptera: Culicidae) was first reported in Central Africa in 2000, together with the indigenous mosquito species Aedes aegypti (Diptera: Culicidae). Because Ae. albopictus can also transmit arboviruses, its introduction is a public health concern. We undertook a comparative study in three Cameroonian towns (Sahelian domain: Garoua; equatorial domain: Douala and Yaoundé) in order to document infestation by the two species and their ecological preferences. High and variable levels of pre‐imaginal Ae. aegypti and Ae. albopictus infestation were detected. Only Ae. aegypti was encountered in Garoua, whereas both species were found in Douala and Yaoundé, albeit with significant differences in their relative prevalence. Peridomestic water containers were the most strongly colonized and productive larval habitats for both species. No major differences in types of larval habitat were found, but Ae. albopictus preferentially bred in containers containing plant debris or surrounded by vegetation, whereas Ae. aegypti tended to breed in containers located in environments with a high density of buildings. These findings may have important implications for vector control strategies.     

Comparative delta-endotoxins of Bacillus thuringiensis against mosquito vectors (Aedes aegypti and Culex pipiens)

Pure crystals of seven Bacillus thuringiensis field isolates from the Lower Silesia region (Poland) were tested against larvae of Aedes aegypti L. and Culex pipiens L. (Culicidae, Diptera). The crystals of OpQ3 phylloplane isolate (belonging to the first biochemical type of B. thuringiensis subsp. japonensis, yoso, jinghongiensis) killed from 68 +/- 7% to 84 +/- 7% of the fourth instar larvae of A. aegypti. The crystals of two other strains (KpF3 and KpC1) of this group caused mortality between 3 +/- 2% and 70 +/- 7%. The LC50 ranged from 3.2 +/- 0.4 to 34.1 +/- 4.8 microg/ml. The effect of B. thulringiensis wratislaviensis H-47 crystals was the lowest with larval mortality from 0% to 17 +/- 3%. No significant (0%-37 +/- 6%) effect of B. thuringiensis crystals on the larvae of C. pipiens was observed. Our results show that the delta-endotoxins of B. thuringiensis act very specifically.     

Larvicidal effects of some natural products on the Aedes aegypti mosquito,a vector of dengue fever and Zika virus

Natural products are considered a good choice in the biological control of mosquitoes because they are an effective way to eliminate larvae and prevent an increase in mosquito numbers, while simultaneously not polluting the environment or damaging health. This investigation was designed to study the potential toxicity of three species of algae, Caulerpa racemosa (Weber-van Bosse, 1909), Padina boryana (Thivy, 1966), and Turbinaria ornata (Turner J. Agardh, 1848), on the larvae of Aedes aegypti mosquito, the vector of dengue and Zika viruses. Among the studied species, Caulerpa racemosa showed the greatest effectiveness in eradicating A. aegypti larvae with an LC₅₀ = 43.5 ppm, followed by Padina boryana with an LC₅₀ = 51.93 ppm. Both species proved to be excellent candidates as a source of larvicidal agents and could be used commercially in mosquito control programs as eco-friendly biopesticides. The combined activity of different mixtures against mosquito larvae was expressed as the coeffective factor (C.F.). C.F. values showed that the joint activity of insect growth regulator Dudim in combination with Caulerpa racemosa and Padina boryana extracts produced degrees of potentiation effects and degrees of additive effects were obtained with Dudim in combination with Turbinaria ornata extract.     

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.     

Evaluation of larvicidal efficacy of Ricinus communis (Castor) and synthesized green silver nanoparticles against Aedes aegypti L.

Aedes mosquitoes are the most important group of vectors that transmit pathogens, including arboviruses, and cause human diseases such as dengue fever, yellow fever, Zika virus, and Chikungunya. Biosynthesis and the use of green silver nanoparticles (AgNPs) is a vital step to identify reliable and eco-friendly controls for these vectors. In this study, Aedes (Ae.) aegypti larvae (2nd and 3rd instar) were exposed to leaf extracts of Ricinus communis (Castor) and AgNPs synthesized from the extract to evaluate their larvicidal potential. Synthesized AgNPs were characterized by UV–Vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), and energy-dispersive X-ray spectroscopy (XRD). Ae. aegypti larvae were treated with different concentrations (50–250 ppm) of the leaf extract and synthesized AgNPs. There were five replicates per treatment, in addition to a positive (temephos) and negative control (dechlorinated water). Mortality was recorded after 12, 24, 36, and 48 h and the data were subjected to Probit analysis. The nanoparticles were more toxic (LC₅₀ = 46.22 ppm and LC₉₀ = 85.30 ppm) than the plant extract (106.24 and 175.73 ppm, respectively). The leaf extracts of Ricinus communis were subjected to HPLC analysis to identify their chemical constituents. This study suggests that plant extracts and synthesized nanoparticles are excellent alternatives to hazardous chemical pesticides used to control vector mosquitoes. This is a potentially useful technique that can reduce aquatic toxicity from insecticide use.     

Prevalence and resting behaviour of dengue vectors,Aedes aegypti and Aedes albopictus in dengue high risk urban settings in Colombo,Sri Lanka

Understanding local geographical variation in vector density and bionomics related to virus transmission are critical for planning effective vector control programs to control dengue virus transmission. This study investigated the prevalence and resting behaviour of Aedes aegypti and Ae. albopictus in three dengue high-risk areas in the Colombo District, Sri Lanka. Monthly sampling of resting adult mosquitoes was conducted from August 2019 to February 2020. Thirty-seven percent of the households (289/776) harboured Aedes mosquitoes, and 603 Aedes mosquitoes were collected. The proportion of Ae. aegypti was higher in the overall collection during the collection period (94% [569/603]), and 62% (352/569) were females. Significant monthly variations in Ae. aegypti were observed with respect to the indices: number of females per surveyed house (F/SH; p = 0.001), number of females per Aedes positive house (F/PH; p = 0.029), adult house index (AHI; p = 0.001), adult density (AD; p = 0.005) and resting ratio (RR; p = 0.001). AHI, AD, and RR had statistically significant positive correlations with monthly rainfall (p = 0.001, p = 0.011, and p = 0.002 respectively) and one-month lagged dengue cases (p = 0.002, p = 0.005, and p < 0.001 respectively). A statistically significantly higher proportion of Ae. aegypti females were caught resting indoors (N = 309, 88%) than outdoors (N = 43, 12%; p < 0.001). The most common resting areas were bedrooms (51%) & living/dining rooms (37%), and places were under or on furniture (47%) & hangings (34%) for Ae. aegypti. Conversely, 74% of female Ae. albopictus were collected outdoors. Results of this study could have strong implications to improve vector surveillance and control by early detection of dengue to detect outbreaks and minimization of disease transmission.     

Knockdown and lethal effects of three mosquito coil formulations against Aedes aegypti and Culex quinquefasciatus under different nutritional conditions

Three mosquito coil formulations, each containing either metofluthrin 0.025% w/w, d-allethrin 0.225% w/w, or esbiothrin 0.10% w/w were evaluated for knockdown and killing properties against laboratory populations of female Aedes aegypti (L.) and Culex quinquefasciatus Say under different nutritional-energy sources of blood, sucrose, and water. The tests were conducted in a 70 cm × 70 cm × 70 cm glass chamber. Mosquito responses were measured by knockdown times during the 20-min exposure period and mortality at 24 h post-exposure. The results showed the metofluthrin coil provided the most rapid knockdown for both test species and regardless of nutritional condition compared with the other two coils. Metofluthrin and d-allethrin were highly effective in killing Ae. aegypti (95–100% mortality), whereas esbiothrin produced 100% mortality to water-fed mosquitoes and 78.3 and 80% mortality for blood- and sucrose-fed specimens, respectively. >85% mortality was observed in sucrose- and water-fed Cx. quinquefasciatus against metofluthrin, while 78.3% blood-fed females survived exposure. This species showed very low mortality with d-allethrin (3.3% to 28.3%), with the highest mortality recorded (71.7%) for water-fed with esbiothrin. Overall, Ae. aegypti was more sensitive to all three coil products than Cx. quinquefasciatus. The mortality between species and nutritional conditions showed significant differences for all comparisons except for sucrose-fed mosquitoes exposed to metofluthrin.     

Effectiveness of Metarhizium anisopliae formulations against dengue vectors under laboratory and field conditions

The oviposition behaviour of Aedes aegypti and the effectiveness of Metarhizium anisopliae conidia formulated in water or oil-in-water against A. aegypti adults and eggs were tested in multi-choice and no-choice tests in oviposition devices under laboratory conditions. Both females and males rested in the devices, regardless of the formulation, and were not repelled by the presence of conidia (up to 10⁶?conidia/cm²) without oil or formulated with oil on treated filter paper arranged in the device. However, at higher oil concentrations (≥0.1?μl/cm²), regardless of the presence of conidia, the number of eggs laid by gravid females on the filter paper dropped. The susceptibility of adults, especially of males, to fungal infection increased up to a 15-day incubation. An elevated number of larvae (≥41%) eclosed from eggs laid on the moistened filter paper in the device even without submersion of eggs in water, and these larvae subsequently died. In the laboratory, 1?μl/cm² oil combined with 10⁶?conidia/cm² clearly reduced eclosion to 1.8% after submersion of eggs in water compared to ≥13% eclosion in the control. In field tests in Goiânia, Brazil, eclosion of aedine larvae from eggs laid on filter paper previously treated with oil-in-water formulated conidia dropped to between 0% and 36% compared to 22–50% in the control. Promising results of laboratory and field tests with M. anisopliae formulated in water or oil-in-water and tested in a device emphasised the effectiveness of a fungus-based formulation for aedine mosquitoes in peridomestic areas.     

Essential oils enhance the toxicity of permethrin against Aedes aegypti and Anopheles gambiae

Insecticide resistance and growing public concern over the safety and environmental impacts of some conventional insecticides have resulted in the need to discover alternative control tools. Naturally occurring botanically‐based compounds are of increased interest to aid in the management of mosquitoes. Susceptible strains of Aedes aegypti (Linnaeus) (Diptera: Culicidae) and Anopheles gambiae (Meigen) (Diptera: Culicidae) were treated with permethrin, a common type‐I synthetic pyrethroid, using a discriminate dose that resulted in less than 50% mortality. Piperonyl butoxide (PBO) and 35 essential oils were co‐delivered with permethrin at two doses (2 and 10 µg) to determine if they could enhance the 1‐h knockdown and the 24‐h mortality of permethrin. Several of the tested essential oils enhanced the efficacy of permethrin equally and more effectively than piperonyl butoxide PBO, which is the commercial standard to synergize chemical insecticide like pyrethroids. PBO had a strikingly negative effect on the 1‐h knockdown of permethrin against Ae. aegypti, which was not observed in An. gambiae. Botanical essential oils have the capability of increasing the efficacy of permethrin allowing for a natural alternative to classic chemical synergists, like PBO.     

Mark-release-recapture study to measure dispersal of the mosquito Aedes aegypti in Cairns, Queensland, Australia

In Queensland, Australia, in response to isolated cases of dengue infection, larval control of the vector Aedes aegypti (L.) (Diptera: Culicidae) is targeted at breeding sites within 200 m of a case and interior spraying with a pyrethroid adulticide is targeted at premises within 100 m. To ascertain whether these limits are appropriate, we conducted a mark-release-recapture study to measure the dispersal of female Ae. aegypti in the city of Cairns where transmission occurs. Female mosquitoes reared from wild collected eggs were differentially marked with fluorescent dust depending on whether they were to be released blood-fed or non-blood-fed, and a total of 1,948 females was released. A total of 132 sticky ovitraps was set at 64 premises within a 200 m radius and collections of trapped adults were made at 5-15 days post-release. Sixty-seven females (3.4%) were recaptured, with the furthest being caught 200 m from the release point, and the mean distance travelled was 78 m. Overall, 23.1% of the recaptures outside the release site were taken beyond 100 m by day 15. Dispersal was comparable for both blood-fed and non-blood-fed releases. There was a significant tendency for dispersal to be in a north-westerly direction, probably because of the presence of numerous containers and heavy shading by trees in this direction and a busy road to the south of the release point that appeared to inhibit dispersal. The results suggest that adulticiding may have to be extended beyond 100 m if more than 8 days have elapsed since female Ae. aegypti could have fed upon a viraemic dengue case. The study also shows that dispersal is not random, and that it may be possible to maximize vector control by taking into account environmental factors that affect the direction of female mosquito flight.     

Pathogenicity of entomopathogenic fungus,Metarhizium anisopliae MET-GRA4 isolate on dengue vectors,Aedes albopictus and Aedes aegypti mosquito larvae (Diptera: Culicidae)

Considering the rapid transmission of the dengue virus, substantial efforts need to be conducted to ward-off the epidemics of dengue viruses. The control effort is depending on chemical insecticides and had aroused undesirable conflicts of insecticide resistance. Here, we study the entomopathogenic fungus, Metarhizium anisopliae as a promising new biological control agent for vector control. The pathogenicity effects of Metarhizium anisopliae against field and laboratory strains of Aedes albopictus and Aedes aegypti larvae were tested using the larvicidal bioassay technique. The results demonstrate that the treatments using M. anisopliae isolate MET-GRA4 were highly effective and able to kill 100% of both Ae. albopictus and Ae. aegypti mosquito larvae at a conidia concentration of 1 × 10?/ml within 7 days of the treatment period. The fungus displayed high larvicidal activity against laboratory and field strain of Ae. aegypti larvae with LC₅₀ values (9.6 × 10³/ml, 1.3 × 10³/ml) and LC₉₅ values (1.2 × 10?/ml, 5.5 × 10⁵/ml) respectively. For Ae. albopictus, LC₅₀ values for laboratory and field strains were (1.7 × 10⁴/ml, 2.7 × 10⁴/ml) and the LC₉₅ values were (2.1 × 10?/ml, 7.0 × 10⁵/ml) respectively. Interestingly, the susceptibility of field strain towards M. anisopliae was higher as compared to the laboratory strain Aedes larvae. In which, the causative agents of all the dead larvae were verified by the virulence of M. anisopliae and caused morphological deformities on larval body. The findings from this study identify this isolate could be an effective potential biocontrol agent for vector mosquitoes in Malaysia.     

Repellent,larvicidal and adulticidal activities of essential oil from Dai medicinal plant Zingiber cassumunar against Aedes albopictus

Zingiber cassumunar is an important plant used in traditional medicine and as a natural mosquito repellent. However, the compounds responsible for the repellent activity of the plant are still unknown. The aim of the study is to identify the components of Z. cassumunar essential oil that show repellent activity against Aedes albopictus. We also evaluated the larvicidal and adulticidal activities of Z. cassumunar essential oil against Ae. albopictus. In-cage mosquito repellent experiments showed that Z. cassumunar essential oil possessed moderate repellent activity with a minimum effective dose (MED) of 0.16 ± 0.01 mg/cm², compared to reference standard N,N-diethyl-3-methylbenzamide (DEET, 0.03 ± 0.01 mg/cm²). Bioassay-guided fractionation identified the major active compound of Z. cassumunar essential oil as (−)-terpinen-4-ol (1) (MED: 0.19 ± 0 mg/cm²). We also found that Z. cassumunar essential oil showed moderate larvicidal activity against first instar larvae of Ae. albopictus with a LC₅₀ (50% lethal concentration) of 44.9 μg/L after 24 h. Fumigation bioassays showed that Z. cassumunar essential oil exhibits moderate adulticidal activity against Ae. albopictus with a LC₅₀ of 5.44%, while (−)-terpinen-4-ol showed significant adulticidal activity with a LC₅₀ of 2.10% after 24 h. This study verifies that the Z. cassumunar essential oil has mosquito repellent activity, and that (−)-terpinen-4-ol is mainly responsible for this activity. Furthermore, this study provides scientific support for the folk usage of Z. cassumunar essential oil as mosquito repellent and indicates that Z. cassumunar essential oil and (−)-terpinen-4-ol can be used as plant-derived repellents and insecticides for mosquito control.     

Identification of Bioactive Compounds against Aedes aegypti (Diptera: Culicidae) by Bioassays and in Silico Assays

Most of the hematophagous insects act as disease vectors, including Aedes aegypti, responsible for transmitting some of the most critical arboviruses globally, such as Dengue. The use of repellents based on natural products is a promising alternative for personal protection compared to industrial chemical repellents. In this study, the repellent effect of essential oils extracted from Lippia thymoides, Lippia alba, Cymbopogon winterianus, and Eucalyptus globulus leaves was evaluated. Essential oils used showed repellent activity against Ae. aegypti in laboratory bioassays, obtaining protection rates above 70 % from 3.75 mg/mL and higher concentration for all analyzed oils. GC/MS identified 57 constituents, which were used in the ligand-based pharmacophore model to expose compounds with requirements for repellents that modulate mosquitoes behavior through odorant-binding protein 1 Ae. aegypti. Ligand-based pharmacophore model approach results suggested that repellent activity from C. winterianus, L. alba, and L. thymoides essential oils’ metabolites is related to Citronelal (QFIT=26.77), Citronelol (QFIT=11.29), Citronelol acetate (QFIT=52.22) and Geranil acetate (QFIT=10.28) with synergistic or individual activity. E. globulus essential oil's repellent activity is associated with Ledol (0.94 %; QFIT=41.95). Molecular docking was applied to understand the binding mode and affinity of the essential oils’ data set at the protein binding site. According to molecular docking, Citronelol (ChemPLP=60.98) and geranyl acetate (ChemPLP=60.55) were the best-classified compounds compared to the others and they can be explored to develop new repellents.     

Development of robust in vitro RNA-dependent RNA polymerase assay as a possible platform for antiviral drug testing against dengue

NS5 is the largest and most conserved protein among the four dengue virus (DENV) serotypes. It has been the target of interest for antiviral drug development due to its major role in replication. NS5 consists of two domains, the N-terminal methyltransferase domain and C-terminal catalytic RNA-dependent RNA polymerase (RdRp) domain. It is an unstable protein and is prone to inactivation upon prolonged incubation at room temperature, thus affecting the inhibitor screening assays. In the current study, we expressed and purified DENV RdRp alone in Esherichia coli (E. coli) cells. The N-terminally His-tagged construct of DENV RdRp was transformed into E. coli expression strain BL-21 (DE3) pLysS cells. Protein expression was induced with isopropyl-β-D-thiogalactopyranoside (IPTG) at a final concentration of 0.4 mM. The induced cultures were then grown for 20 h at 18 °C and cells were harvested by centrifugation at 6000 x g for 15 min at 4 °C. The recombinant protein was purified using HisTrap affinity column (Ni-NTA) and then the sample was subjected to size exclusion chromatography, which successfully removed the degradation product obtained during the previous purification step. The in vitro polymerase activity of RdRp was successfully demonstrated using homopolymeric polycytidylic acid (poly(rC)) RNA template. This study describes the high level production of enzymatically active DENV RdRp protein which can be used to develop assays for testing large number of compounds in a high-throughput manner. RdRp has the de novo initiation activity and the in vitro polymerase assays for the protein provide a platform for highly robust and efficient antiviral compound screening systems.     

Comparative repellency of commercial formulations of deet, permethrin and citronellal against the mosquito Aedes aegypti, using a collagen membrane technique compared with human arm tests

A collagen membrane technique, based on the membrane blood-feeding system of Cosgrove et al . (1994) , was used to compare repellents against Aedes aegypti mosquitoes. Repellency was defined in terms of inhibition of probing (ED₅₀ and ED₉₀) after 5 min exposure. A direct comparison was made with repellency from probing after 5 min on five male volunteers.
Four repellent products were compared with technical DEET as the standard. The liquid formulations tested were: Autan^® (20% deet; Bayer); Repel Plus^® (20% deet plus 0.05% permethrin; Boots); permethrin (Zeneca) and citronellal (Sigma) .
Membrane and arm tests gave similar results. Deet formulations required less active compound than citronellal for the same degree of repellency. Pure deet and Autan gave similar results, dose for dose. Permethrin was highly repellent at very low doses, but Repel Plus did not enhance the immediate repellency of deet. A technique using the same membrane system was developed to evaluate persistence of Autan, which declined to 75% after 1 h against Ae. aegypti , and to about 50% after 2–4 h.