Validation of models to estimate the fumigant and larvicidal activity of Eucalyptus essential oils against Aedes aegypti (Diptera: Culicidae)

The aim of this work is to validate the pre-existing models that relate the larvicidal and adulticidal activities of the Eucalyptus essential oils on Aedes aegypti. Previous works at our laboratory described that the larvicidal activity of Eucalyptus essential oils can be estimated from the relative concentration of two main components (p-cymene and 1,8-cineole) and that the adulticidal effectiveness can be explained, to a great extent, by the presence of large amounts of the component 1,8-cineole in it. In general, the results show that the higher adulticidal effect of essential oils the lower their larvicidal activity. Fresh leaves was harvested and distilled. Once the essential oil was obtained, the chemical composition was analysed, evaluating the biological activity of 15 species of the genus Eucalyptus (Eucalyptus badjensis Beuzev and Welch, Eucalyptus badjensis × nitens, Eucalyptus benthamii var Benthamii Maiden and Cambage, Eucalyptus benthamii var dorrigoensis Maiden and Cambage, Eucalyptus botryoides Smith, Eucalyptus dalrympleana Maiden, Eucalyptus fastigata Deane and Maiden, Eucalyptus nobilis L.A.S. Johnson and K.D.Hill, Eucalyptus polybractea R. Baker, Eucalyptus radiata ssp radiata Sieber ex Spreng, Eucalyptus resinifera Smith, Eucalyptus robertsonii Blakely, Eucalyptus robusta Smith, Eucalyptus rubida Deane and Maiden, Eucalyptus smithii R. Baker). Essential oils of these plant species were used for the validation of equations from preexistent models, in which observed and estimated values of the biological activity were compared. The regression analysis showed a strong validation of the models, re-stating the trends previously observed. The models were expressed as follows: A, fumigant activity [KT_50(min) = 10.65–0.076 × 1,8-cineole (%)](p < 0.01; F, 397; R ², 0.79); B, larval mortality (%)_(40 ppm) = 103.85 + 0.482 × p-cymene (%) − 0.363 × α-pinene (%) − 1.07 × 1,8-cineole (%) (p < 0.01; F, 300; R ², 0.90). These results confirmed the importance of the mayor components in the biological activity of Eucalyptus essential oils on A. aegypti. However, it is worth mentioning that two or three species differ in the data estimated by the models, and these biological activity results coincide with the presence of minor differential components in the essential oils. According to what was previously mentioned, it can be inferred that the model is able to estimate very closely the biological activity of essential oils of Eucalyptus on A. aegypti.     

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.     

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.     

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.     

Adulticidal and larvicidal activity of Beauveria bassiana and Metarhizium anisopliae against housefly, Musca domestica (Diptera: Muscidae), in laboratory and simulated field bioassays

The susceptibility of the adult and larval stage of housefly, Musca domestica L. (Diptera: Muscidae), to two entomopathogenic fungi, Metarhizium anisopliae (Metsch.) Sor. and Beauveria bassiana (Bals.) Vuill., was evaluated under laboratory and simulated field bioassays. Bioassays on adult houseflies were carried out at different conidial concentrations ranging from 10³ to 10⁹ conidia/ml in petri plate and minichamber assays. Absolute mortality was observed within 4–5 days at all the concentrations tested. M. anisopliae was found to be more effective with LC₅₀ of 6.75 × 10⁷ conidia/ml compared with 1.21 × 10⁸ conidia/ml of B. bassiana in petri plate bioassay. Similar trend was observed in minichamber bioassay. Larvicidal activity evaluated through petri plate bioassay also indicated that M. anisopliae was more effective larvicide with LC₅₀ of 4.1 × 10⁸ conidia/ml as against 3.31 × 10⁹ conidia/ml of B. bassiana. Larvicidal activity was further evaluated in simulated field condition of decaying waste matrix using dry conidial formulations (10⁸ conidia/g) of both the fungi. Larval mortality obtained in this assay was 43% (B. bassiana) and 63% (M. anisopliae). Remarkably better performance of M. anisopliae as an adulticidal and larvicidal agent over B. bassiana in laboratory bioassays as well as simulated field conditions suggests that it may have good potential to become part of an integrated housefly control program.     

Evaluation of larvicidal activity of Acalypha alnifolia Klein ex Willd. (Euphorbiaceae) leaf extract against the malarial vector, Anopheles stephensi, dengue vector, Aedes aegypti and Bancroftian filariasis vector, Culex quinquefasciatus (Diptera: Culicidae)

The leaf extract of Acalypha alnifolia with different solvents — hexane, chloroform, ethyl acetate, acetone and methanol — were tested for larvicidal activity against three important mosquitoes such as malarial vector, Anopheles stephensi, dengue vector, Aedes aegypti and Bancroftian filariasis vector, Culex quinquefasciatus. The medicinal plants were collected from the area around Kallar Hills near the Western Ghats, Coimbatore, India. A. alnifolia plant was washed with tap water and shade dried at room temperature. The dried leaves were powdered mechanically using commercial electrical stainless steel blender. The powder 800 g of the leaf material was extract with 2.5 litre of various each organic solvents such as hexane, chloroform, ethyl acetate, acetone, methanol for 8 h using Soxhlet apparatus, and filtered. The crude plant extracts were evaporated to dryness in a rotary vacuum evaporator. The yield of extracts was hexane (8.64 g), chloroform (10.74 g), ethyl acetate (9.14 g), acetone (10.02 g), and methanol (11.43 g). One gram of the each plant residue was dissolved separately in 100 ml of acetone (stock solution) from which different concentrations, i.e., 50, 150, 250, 350 and 450 ppm, was prepared. The hexane, chloroform, ethyl acetate, acetone was moderate considerable mortality; however, the highest larval mortality was methanolic extract observed in three mosquito vectors. The larval mortality was observed after 24 h exposure. No mortality was observed in the control. The early fourth-instar larvae of A. stephensi had values of LC₅₀ = 197.37, 178.75, 164.34, 149.90 and 125.73 ppm and LC₉₀ = 477.60, 459.21, 435.07, 416.20 and 395.50 ppm, respectively. The A. aegypti had values of LC₅₀ = 202.15, 182.58, 160.35, 146.07 and 128.55 ppm and LC₉₀ = 476.57, 460.83, 440.78, 415.38 and 381.67 ppm, respectively. The C. quinquefasciatus had values of LC₅₀ = 198.79, 172.48, 151.06, 140.69 and 127.98 ppm and LC₉₀ = 458.73, 430.66, 418.78, 408.83 and 386.26 ppm, respectively. The results of the leaf extract of A. alnifloia are promising as good larvicidal activity against the mosquito vector, A. stephensi, A. aegypti, C. quinquefasciatus. Therefore, this study provides first report on the larvicidal activities against three species of mosquito vectors of this plant extracts from Southern India.     

Insecticidal activity of essential oils from native medicinal plants of Central Argentina against the house fly, <Emphasis Type="Italic">Musca domestica</Emphasis> (L.)

The insecticidal activity of nine essential oils (EOs) against the house fly (Musca domestica) was evaluated by placing flies in a screw-cap glass jar holding a piece of EO-treated cotton yarn. The dose necessary to kill 50% of flies (LC₅₀) in 30 min was determined at 26?±?1°C. The EOs showed LC₅₀ values ranging from 0.5 to 46.9 mg/dm³. The EO from Minthostachys verticillata was the most potent insecticide (LC₅₀?=?0.5 mg/dm³) followed by EOs from Hedeoma multiflora (LC₅₀?=?1.3 mg/dm³) and Artemisia annua (LC₅₀?=?6.5 mg/dm³). The compositions of the nine EOs, obtained by hydrodistillation of medicinal herbs, were analyzed by gas chromatography/mass spectroscopy. These analyses showed that (4R)(+)-pulegone (69.70%), menthone (12.17%), and limonene (2.75%) were the principal components of M. verticillata EO. (4R)(+)-pulegone was also the main constituent (52.80%) of H. multiflora, while artemisia ketone (22.36%) and 1,8-cineole (16.67%) were the major constituents of A. annua EO. The terpene (4R)(+)-pulegone showed a lower toxicity (LC₅₀?=?1.7 mg/dm³) than M. verticillata or H. multiflora EOs. Dimethyl 2,2-dichlorovinyl phosphate, selected as a positive control, showed an LC₅₀ of 0.5 mg/dm³. EOs from M. verticillata and H. multiflora show promise as natural insecticides against houseflies.     

Acaricidal, pediculocidal and larvicidal activity of synthesized ZnO nanoparticles using wet chemical route against blood feeding parasites

The present study was based on assessments of the anti-parasitic activities to determine the efficacies of synthesized zinc oxide nanoparticles (ZnO NPs) prepared by wet chemical method using zinc nitrate and sodium hydroxide as precursors and soluble starch as stabilizing agent against the larvae of cattle tick Rhipicephalus (Boophilus) microplus, Canestrini (Acari: Ixodidae); head louse Pediculus humanus capitis, De Geer (Phthiraptera: Pediculidae); larvae of malaria vector, Anopheles subpictus, Grassi; and filariasis vector, Culex quinquefasciatus, Say (Diptera: Culicidae). R. microplus larvae were exposed to filter paper envelopes impregnated with different ZnO NP concentrations. Direct contact method was conducted to determine the potential of pediculocidal activity. Parasite larvae were exposed to varying concentrations of synthesized ZnO NPs for 24 h. The results suggested that the mortality effects of synthesized ZnO NPs were 43% at 1 h, 64% at 3 h, 78% at 6 h, and 100% after 12 h against R. microplus activity. In pediculocidal activity, the results showed that the optimal times for measuring mortality effects of synthesized ZnO NPs were 38% at 10 min, 71% at 30 min, 83% at 1 h, and 100% after 6 h against P. humanus capitis. One hundred percent lice mortality was observed at 10 mg/L treated for 6 h. The mortality was confirmed after 24 h of observation period. The larval mortality effects of synthesized ZnO NPs were 37%, 72%, 100% and 43%, 78% and 100% at 6, 12, and 24 h against A. subpictus and C. quinquefasciatus, respectively. It is apparent that the small size and corresponding large specific surface area of small nanometer-scale ZnO particles impose several effects that govern its parasitic action, which are size dependent. ZnO NPs were synthesized by wet chemical process, and it was characterized with the UV showing peak at 361 nm. X-ray diffraction (XRD) spectra clearly shows that the diffraction peaks in the pattern indexed as the zinc oxide with lattice constants a = 3.249 and c = 5.206 ?. The FTIR spectrum showed the range of 400–4,000 cm⁻¹. The band at 899.56 cm⁻¹; 1,151.87 cm⁻¹; 1,396 cm⁻¹; and these bands showed the complete composition of ZnO NPs. SEM micrograph showed 60–120-nm size and aggregates of spherical shape nanoparticles. EDX showed the complete chemical composition of the synthesized nanoparticles of zinc oxide. The maximum efficacy was observed in zinc oxide against the R. microplus, P. humanus capitis, and the larvae of A. subpictus, C. quinquefasciatus with LC₅₀ values of 29.14, 11.80, 11.14, and 12.39 mg/L; r ² = 0.805, 0.876, 0.894, and 0.904, respectively. The synthesized ZnO NPs showed the LC₅₀ and r ² values against the R. microplus (13.41 mg/L; 0.982), P. humanus capitis (11.80 mg/L; 0.966), and the larvae of A. subpictus (3.19; 0.945 mg/L), against C. quinquefasciatus (4.87 mg/L; 0.970), respectively. The control (distilled water) showed nil mortality in the concurrent assay. This is the first report on anti-parasitic activity of the synthesized ZnO NPs.     

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.     

Effect of Chrysosporium keratinophilum metabolites against Culex quinquefasciatus after chromatographic purification

Chrysosporium keratinophilum is known to be a keratinophilic fungus and an effective mosquito control agent. This fungus was grown on Sabauraud dextrose broth in the laboratory at 25°C, while the relative humidity was maintained at 75 ± 5% for 15 days. Filtration process of metabolites was done using whatman-1 filter paper, column chromatography and flash, chromatography. Larvicidal efficacy was performed against all instars of Culex quinquefasciatus. Larvicidal efficacy was performed at six different concentrations with different effective ratios (ethanol/metabolites: 9:1, 8:2, 7:3, 6:4, 5:5, 4:6, 3:7, 2:8, and 1:9). The mortality values were then subjected by the probit analysis. The larval mortalities were observed for a period of 24, 48, and 72 h, respectively. The first and second instars were highly susceptible to 2:8 ratio. In the first instar after column chromatography, LC₅₀ = 26.66 ppm, LC₉₀ = 121.96 ppm, LC₉₉ = 231.86 ppm were observed after 72 h, while after flash chromatography the LC₅₀ = 20 ppm, LC₉₀ = 123.02 ppm, LC₉₉ = 281.83 ppm were observed after 48 h. In the second instar after column chromatography, LC₅₀ = 18.19 ppm, LC₉₀ = 102.32 ppm, LC₉₉ = 162.18 ppm were observed after 72 h, while doing flash chromatography 100% mortality could be recorded after 24 h. In the third instar after column chromatography, the LC₅₀ = 38.01 ppm, LC₉₀ = 131.82 ppm, LC₉₉ = 245.47 ppm were observed after 72 h, while after flash chromatography the LC₅₀ = 17.78 ppm, LC₉₀ = 100 ppm, LC₉₉ = 151.35 ppm. In the fourth instar, LC₅₀ = 61.65 ppm, LC₉₀ = 181.97 ppm, LC₉₉ = 436.51 ppm, while after flash chromatography LC₅₀ = 40 ppm, LC₉₀ = 120 ppm, and LC₉₉ = 223.87 ppm were observed after 72 h. The extracellular metabolites of C. keratinophilum could be a fungal based larvicides resource for the control of C. quinquefasciatus larvae. This could be another agent for biotechnological exploitation, if found suitable in field trials.     

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.     

Evaluation of larvicidal nature of fleshy fruit wall of Momordica charantia Linn. (family: cucurbitaceae) in the management of mosquitoes

In view of the recently increased interest in developing plant-based insecticides as an alternative to chemical insecticides, this study was undertaken to assess the larvicidal potential of the various fruit wall extracts of Momordica charantia (cucurbitaceae) against two species of mosquito vectors, Anophels stephensi and Culex quinquefasciatus. Among the extracts tested, petroleum ether (LC₅₀ = 27.60; 17.22 ppm and 41.36; 15.62 ppm) extract was found more effective than carbon tetrachloride (LC₅₀ = 49.58; 16.15 ppm and 80.61; 27.64 ppm) and methanol (LC₅₀ = 142.82; 95.98 ppm and 1,057.49; 579.93 ppm) extracts towards anopheline and culicine larvae after 24 and 48 h of exposure respectively. Thus, all fruit wall extracts of M. charantia are toxic to both the larval species. M. charantia may, therefore, act as an effective biolarvicide against mosquitoes in the future.     

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.     

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.     

Larvicidal, repellent, and ovicidal activity of marine actinobacteria extracts against Culex tritaeniorhynchus and Culex gelidus

The purpose of the present study was to assess the effect of crude extracts of marine actinobacteria on larvicidal, repellent, and ovicidal activities against Culex tritaeniorhynchus and Culex gelidus (Diptera: Culicidae). The early fourth instar larvae of C. tritaeniorhynchus and C. gelidus, reared in the laboratory, were used for larvicidal, ovicidal, and repellent assay with crude extracts of actinobacteria. Saccharomonospora spp. (LK-1), Streptomyces roseiscleroticus (LK-2), and Streptomyces gedanensis (LK-3) were identified as potential biocide producers. Based on the antimicrobial activity, three strains were chosen for larvicidal activity. The marine actinobacterial extracts showed moderate to high larvicidal effects after 24 h of exposure at 1,000 ppm and the highest larval mortality was found in extract of LK-3 (LC₅₀ = 108.08 ppm and LC₉₀ = 609.15 ppm) against the larvae of C. gelidus and (LC₅₀ = 146.24 ppm and LC₉₀ = 762.69 ppm) against the larvae of C. tritaeniorhynchus. Complete protections for 240 min were found in crude extract of LK-2 and LK-3 at 1,000 ppm, against mosquito bites of C. tritaeniorhynchus and C. gelidus, respectively. After 24-h treatment, mean percent hatchability of the ovicidal activity was observed. The percent hatchability was inversely proportional to the concentration of extract and directly proportional to the eggs. Crude extracts of LK-1 and LK-3 showed no hatchability at 1,000 ppm against C. tritaeniorhynchus and C. gelidus, respectively. This is an ideal ecofriendly approach for the control of Japanese encephalitis vectors, C. tritaeniorhynchus and C. gelidus.     

Energy cost and efficiency of Venetian rowing on a traditional,flat hull boat (<Emphasis Type="Italic">Bissa</Emphasis>)

The total net metabolic power output (, kW) required to scull a traditional, flat hull boat—the “Bissa”, 9.02 m long and weighting about 500 kg including the crew—was assessed at different constant speeds (ν) ranging from 2.44 to 3.75 m s⁻¹. increased with the speed:  = 0.417 × e ^0.664v ; r ² = 0.931. The amount of metabolic energy spent per unit distance (C, J m⁻¹) to move the “Bissa”, calculated by dividing by the corresponding ν, was a linear function of ν: C = 0.369 ν –0.063; r ² = 0.821. The hydrodynamic resistance met by the boat in the water—drag (D, N)—was estimated by analysing the decay of the reciprocal of ν as a function of time measured during several spontaneous deceleration tests carried out in still water and by knowing the total mass of the watercraft plus crew. D increased as a square function of speed: D = 12.76 v ². This allowed us to calculate the drag efficiency (η_d), as the ratio of D to C: η_d increased from 8.9 to 13.7% in the range of the speeds tested. The “Bissa” turned out to be as economical as other flat hull, traditional watercrafts, such as the bigger Venetian gondola, and her η_d was similar to that of other modern and traditional watercrafts.     

Bioactivity of essential oils of <Emphasis Type="BoldItalic">Zingiber officinalis</Emphasis> and <Emphasis Type="BoldItalic">Achyranthes aspera</Emphasis> against mosquitoes

Due to the global health problems associated with mosquito-borne diseases, over two million people primarily in the tropical countries are at risk. The widely and commonly used chemical method though effective, has some major disadvantages making insect control practically difficult. In view of the above, it is unavoidable to search for new molecules, which are eco-friendly, cheaper, and safer. The present study deals with evaluation of bioactive potential of two commonly occurring plants against mosquitoes presenting an alternative to the conventional chemical methods. Essential oils extracted by steam distillation from rhizome of Zingiber officinalis and leaf and stem of Achyranthes aspera were evaluated for larvicidal, attractant/repellent, and oviposition attractant/deterrent activity against two mosquito species viz. Aedes aegypti and Culex quinquefasciatus. The highest larvicidal activity, i.e., LC₅₀ = 154 ppm and LC₅₀ = 197 ppm for A. aegypti and C. quinquefasciatus, respectively was shown by Z. officinalis. This oil also offers 5-h protection at the concentration of 0.5 mg/cm2 from both mosquito species. The highest oviposition deterrence activity was exhibited by A. aspera stem oil, i.e., 100% and 85.71%, in case of A. aegypti and C. quinquefasciatus, respectively, at the concentration of 0.1%. These results reveal that both these oils have control potential against A. aegypti and C. quinquefasciatus.     

Synthesis of pediculocidal and larvicidal silver nanoparticles by leaf extract from heartleaf moonseed plant, Tinospora cordifolia Miers

Insecticide resistance and inadequate attention to the application instructions of topical pediculicides are common reasons for treatment failure. Essential oils or plant extracts are good and safe alternatives due to their low toxicity to mammals and easy biodegradability. The present study was carried out to establish the pediculocidal and larvicidal activity of synthesized silver nanoparticles (AgNPs) using leaf aqueous extract of Tinospora cordifolia Miers (Menispermaceae) against the head louse Pediculus humanus capitis De Geer (Phthiraptera: Pediculidae) and fourth instar larvae of malaria vector, Anopheles subpictus Grassi and filariasis vector, Culex quinquefasciatus Say (Diptera: Culicidae). We reported the aqueous plant extract and synthesized AgNPs against head lice and vectors. Direct contact method was conducted to determine the potential of pediculocidal activity. The synthesized AgNPs characterized by UV–vis spectrum, scanning electron microscopy, Fourier transform infrared, and X-ray diffraction. Head lice and mosquito larvae were exposed to varying concentrations of aqueous extracts and synthesized AgNPs for 24 h. The results suggest that the optimal times for measuring mortality effects of synthesized AgNPs were 33% at 5 min, 67% at 15 min, and 100% after 1 h. The maximum activity was observed in the synthesized AgNPs against lice, A. subpictus and C. quinquefasciatus (LC₅₀ = 12.46, 6.43 and 6.96 mg/L; r ² = 0.978, 0.773 and 0.828), respectively. The findings revealed that synthesized AgNPs possess excellent anti-lice and mosquito larvicidal activity. These results suggest that the green synthesis of AgNPs have the potential to be used as an ideal ecofriendly approach for the control of head lice and vectors.     

Effect of sanguinarine from the leaves of Macleaya cordata against Ichthyophthirius multifiliis in grass carp (Ctenopharyngodon idella)

The ciliate Ichthyophthirius multifiliis is one of the most pathogenic parasites of fish maintained in captivity. In this study, effects of crude extracts, fractions, and compounds from the leaves of Macleaya cordata against I. multifiliis were investigated under in vitro conditions by bioactivity-guided isolation method. The dried ethanol extract of M. cordata was extracted successively in a separating funnel with petroleum ether, ethyl acetate, chloroform and n-butanol. Among them, only the chloroform extract showed promising activity and therefore, was subjected to further separation and purification using various chromatographic techniques. Four compounds were isolated from chloroform extract, but only one compound showed potent activity. The structure of the active compound was elucidated as sanguinarine by hydrogen, carbon-13 nuclear magnetic resonance spectrum and electron ionization mass spectrometry. In vitro antiparasitic efficacy tests exhibited that sanguinarine was 100% effective against I. multifiliis at a concentration of 0.7 mg l⁻¹, with LC₅₀ and LC₉₀ values of 0.437 and 0.853 mg l⁻¹ after 4 h of exposure. In vivo antiparasitic efficacy tests showed that the number of I. multifiliis on the gills in the treatment group (in 0.9 mg l⁻¹ sanguinarine) was reduced by 96.8%, in comparison to untreated group at 25°C for 48 h. Mortality of fish did not occur in the treatment group during the trail, although 40% of untreated fish died. Our results indicate that the studied plant extracts, as well as sanguinarine might be potential sources of new antiparasitic drug for the control of I. multifiliis.     

Larvicidal activity of Copaifera sp. (Leguminosae) oleoresin microcapsules against Aedes aegypti (Diptera: Culicidae) larvae

Studies have demonstrated the potential of Copaifera sp. oleoresin to control Aedes aegypti proliferation. However, the low water solubility is a factor that limits its applicability. Thus, the micro- or nanoencapsulation could be an alternative to allow its use in larval breeding places. The purpose of this study was to evaluate if achievable lethal concentrations could be obtained from Copaifera sp. oleoresin incorporated into polymers (synthetic or natural) and, mainly, if it can be sustained in the residual activity compared to the pure oil when tested against the A. aegypti larvae. Microcapsules were prepared by the process of emulsification/precipitation using the polymers of cellulose acetate (CA) and poly(ethylene-co-methyl acrylate) (PEMA), yielding four types of microcapsules: MicPEMA₁ and MicPEMA₂, and MicCA₁ and MicCA₂. When using only Copaifera sp. oleoresin, the larvicidal activity was observed at concentrations of LC₅₀ = 48 mg/L and LC₉₉ = 149 mg/L. For MicPEMA₁, the LC₅₀ and LC₉₉ were 78 and 389 mg/L, respectively. Using MicPEMA₂, the LC₅₀ was 120 mg/L and LC₉₉ >500 mg/L. For microcapsules MicCA₁ and MicCA₂, the LC₅₀ and LC₉₉ were 42, 164, 140, and 398 mg/L, respectively. For a dose of 150 mg/L of pure oleoresin, the residual activity remained above 20% for 10 days, while the dose of 400 mg/L remained above 40% for 21 days. The MicPEMA₁ microcapsules showed a loss in residual activity up to the first day; however, it remained in activity above 40% for 17 days. The microcapsules of MicCA₁ showed similar LC₅₀ of pure oil with 150 mg/L.