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.     

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.     

Fumigant and repellent properties of essential oils and component compounds against permethrin-resistant Pediculus humanus capitis (Anoplura: Pediculidae) from Argentina

The repeated use of permethrin and other insecticides for the control of head lice, Pediculus humanus capitis De Geer (Anoplura: Pediculidae), during past decades has resulted in the development of marked levels of resistance. Thus, new alternative insecticides are needed for the control of head lice. We studied the fumigant and repellent properties of essential oils from 16 native and exotic plants in Argentina, and 21 chemical components against permethrin-resistant head lice from Argentina. With a direct vapor-exposure bioassay, the most effective oil was from the native Myrcianthes cisplatensis Cambess (Myrtaceae) with a time to 50% knockdown (KT50) of 1.3 min, followed by exotic species, Eucalyptus cinerea F.V. Muell., Eucalyptus viminalis Labill., and Eucalyptus saligna Smith. with KT50 values of 12.0, 14.9, and 17.4 min, respectively. The most effective components were 1,8-cineole and anisole, with KT50 values of 11.1 and 12.7 min, respectively. Regression analysis of KT50 values and vapor pressures and water-partition coefficients for the essential oil components revealed that the most effective fumigants were among the more volatile components. Repellency assays indicated that the essential oil from Mentha pulegium L. and its benzyl alcohol component were the most effective repellents, having repellency indices of 75.5 and 57.8%, respectively. Thus, some Argentinean plants contain essential oils and components that function as fumigants or as repellents and thereby show potential for development of new control products for head lice.     

A new shampoo based on neem (Azadirachta indica) is highly effective against head lice in vitro

Because topical compounds based on insecticidal chemicals are the mainstay of head lice treatment, but resistance is increasing, alternatives, such as herbs and oils are being sold to treat head lice. To test a commercial shampoo based on seed extract of Azadirachta indica (neem tree) for its in vitro effect, head lice (n=17) were collected from school children in Australia and immersed in Wash-Away Louse™ shampoo (Alpha-Biocare GmbH, Germany). Vitality was evaluated for more than 3 h by examination under a dissecting microscope. Positive and negative controls were a commercially available head lice treatment containing permethrin 1% (n=19) and no treatment (n=14). All lice treated with the neem shampoo did not show any vital signs from the initial examination after immersion at 5–30 min; after 3 h, only a single louse showed minor signs of life, indicated by gut movements, a mortality of 94%. In the permethrin group, mortality was 20% at 5 min, 50% at 15 min, and 74% after 3 h. All 14 head lice of the negative control group survived during the observation period. Our data show that Wash-Away Louse™ is highly effective in vitro against head lice. The neem shampoo was more effective than the permethrin-based product. We speculate that complex plant-based compounds will replace the well-defined chemical pediculicides if resistance to the commonly used products further increases.     

Effect of oregano (<Emphasis Type="Italic">Origanum vulgare</Emphasis> L.) and thyme (<Emphasis Type="Italic">Thymus vulgaris</Emphasis> L.) essential oils on <Emphasis Type="Italic">Trypanosoma cruzi</Emphasis> (Protozoa: Kinetoplastida) growth and ultrastructure

In the present work, we have investigated the effect of essential oils obtained from Origanum vulgare L. (oregano) and Thymus vulgaris L. (thyme) on growth and ultrastructure of diverse evolutive forms of Trypanosoma cruzi. Culture epimastigotes and bloodstream trypomastigotes were incubated for 24 h with different concentrations of oregano or thyme essential oils and with thymol (the main constituent of thyme), and the inhibitory concentration (IC)₅₀ was determined by cell counting. Crude extract of oregano essential oil inhibited epimastigote growth (IC₅₀/24 h = 175 μg/ml) and also induced trypomastigote lysis (IC₅₀/24 h = 115 μg/ml). Thyme essential oil presented IC₅₀/24 h values of 77 μg/ml for epimastigotes and 38 μg/ml for trypomastigotes, while treatment with thymol resulted in an IC₅₀/24 h of 62 μg/ml for epimastigotes and 53 μg/ml for trypomastigotes. Scanning electron microscopy of treated cells showed few morphological alterations at the plasma membrane. Observation by transmission electron microscopy showed cytoplasmic swelling with occasional morphological alterations in plasma and flagellar membrane. Our data indicate that oregano and thyme essential oils are effective against T. cruzi, with higher activity of thyme, and that thymol may be the main component responsible for the trypanocidal activity.     

In vitro antiplasmodial activity and cytotoxicity of crude extracts and compounds from the stem bark of <Emphasis Type="Italic">Kigelia africana</Emphasis> (Lam.) Benth (Bignoniaceae)

In order to assess the potential of the stem bark of Kigelia africana (Lam.) Benth as source of new anti-malarial leads, n-hexane and ethyl acetate (EtOAc) extracts and four compounds isolated from the stem bark were screened in vitro against the chloroquine-resistant W-2 and two field isolates of Plasmodium falciparum using lactate dehydrogenase assay. The products were also tested for their cytotoxicity on LLC/MK2 monkey kidney cells. The EtOAc extract exhibited a significant antiplasmodial activity (IC₅₀ = 11.15 μg/mL on W-2; 3.91 and 4.74 μg/mL on field CAM10 and SHF4 isolates, respectively), whereas the n-hexane fraction showed a weak activity (IC₅₀ = 73.78 μg/mL on W-2 and 21.85 μg/mL on SHF4). Three out of the four compounds showed good activity against all the three different parasite strains (IC₅₀ < 5 μM). Specicoside exhibited the highest activity on W-2 (IC₅₀ = 1.54 μM) followed by 2β, 3β, 19α-trihydroxy-urs-12-en-28-oic acid (IC₅₀ = 1.60 μM) and atranorin (IC₅₀ = 4.41 μM), while p-hydroxycinnamic acid was the least active (IC₅₀ = 53.84 μM). The EtOAc extract and its isolated compounds (specicoside and p-hydroxycinnamic acid) were non-cytotoxic (CC₅₀ > 30 μg/mL), whereas the n-hexane extract and two of its products, atranorin and 2β, 3β, 19α-trihydroxy-urs-12-en-28-oic acid showed cytotoxicity at high concentrations, with the last one being the most toxic (CC₅₀ = 9.37 μg/mL). These findings justify the use of K. africana stem bark as antimalaria by traditional healers of Western Cameroon, and could constitute a good basis for further studies towards development of new leads or natural drugs for malaria.     

Antimalarial drug interactions of compounds isolated from Kigelia africana (Bignoniaceae) and their synergism with artemether, against the multidrug-resistant W2mef Plasmodium falciparum strain

For decades, drug resistance has been the major obstacle in the fight against malaria, and the search for new drugs together with the combination therapy constitutes the major approach in responding to this situation. The present study aims at assessing the in vitro antimalarial activity of four compounds isolated from Kigelia africana stem bark (atranorin - KAE1, specicoside - KAE7, 2β,3β,19α-trihydroxy-urs-12-20-en-28-oic acid – KAE3, and p-hydroxy-cinnamic acid – KAE10) and their drug interactions among themselves and their combination effects with quinine and artemether. The antiplasmodial activity and drug interactions were evaluated against the multidrug-resistant W2mef strain of Plasmodium falciparum using the parasite lactate dehydrogenase assay. Three of the four compounds tested were significantly active against W2mef: specicoside (IC₅₀ = 1.02 ± 0.17 μM), 2β,3β,19α-trihydroxy-urs-12-en-28-oic acid (IC₅₀ = 1.86 ± 0.15 μM) and atranorin (IC₅₀ = 1.78 ± 0.18 μM), whereas p-hydroxy-cinnamic acid showed a weak activity (IC₅₀ = 12.89 ± 0.87 μM). A slight synergistic effect was observed between atranorin and 2β,3β,19α-trihydroxy-urs-12-en-28-oic acid (Combination index, CI = 0.82) whereas the interaction between specicoside and p-hydroxy-cinnamic acid were instead antagonistic (CI = 2.67). All the three compounds showed synergistic effects with artemether, unlike the slight antagonistic interactions of atranorin and 2β,3β,19α-trihydroxy-urs-12-en-28-oic acid in combination with quinine. K. africana compounds are therefore likely to serve as leads in the development of new partner drugs in artemether-based combination therapy.     

In vitro comparison of four treatments which discourage infestation by head lice

Products which discourage the transmission of head lice are appealing; however, few studies have tested this concept. This study aims to test the efficacy of four commercial products which claim to discourage infestation by head lice; MOOV Head Lice Defence Spray (MOOV), Wild Child Quit Nits Head Lice Defence Spray (Wild Child), 100% Natural Head Lice Beater (Lice Beater) or Lysout Natural Anti-Lice Spray (Lysout). An in vitro challenge test was used. Briefly, one half of a filter paper lining the base of a petri dish was treated with the test product. Lice were then introduced to the centre of the dish, which was covered and placed in the dark at 20°C for 30 min. The number of lice on the treated and untreated sides of the filter paper was then counted after 2, 4 and 8 h post-application. MOOV was significantly more effective at discouraging the transmission of lice than the water control (p < 0.01), while Wild Child and Lysout were not at all time points. Lice Beater was significantly worse than the water control after 2 h (p < 0.01), while there was no difference after 4 and 8 h. MOOV was found to perform significantly better than Wild Child (p < 0.05) and Lice Beater (p < 0.05) at all time points. It also performed significantly better than Lysout at 2 (p < 0.05) and 8 h (p < 0.05), but not 4 h. MOOV offers the best efficacy and consistency of performance of the four products tested to discourage the transmission of head lice.     

Effects of essential oils from Cymbopogon citratus (DC) Stapf., Lippia sidoides Cham., and Ocimum gratissimum L. on growth and ultrastructure of Leishmania chagasi promastigotes

The current therapy for leishmaniasis, which affects annually about 2 million people, is far from satisfactory. All available drugs require parenteral administration and are potentially toxic. Plant essential oils have been traditionally used in folk medicine and appear as valuable alternative source for chemotherapeutic compounds. In this study, we demonstrated the effect of essential oils from Cymbopogon citratus, Lippia sidoides, and Ocimum gratissimum on growth and ultrastructure of Leishmania chagasi promastigote forms. Steam distillation was used to isolate the essential oils, and their constituents were characterized by gas chromatography coupled to mass spectrometry and nuclear magnetic resonance. All essential oils showed in vitro inhibitory action on L. chagasi promastigotes growth in a dose-dependent way, with IC₅₀/72 h of 45, 89, and 75 μg/mL for C. citratus, L. sidoides, and O. gratissimum, respectively. Drastic morphological alterations were observed in all essential oil-treated parasites, including cell swelling, accumulation of lipid droplets in the cytoplasm, and increase of acidocalcisome volume. Furthermore, aberrant-shaped cells with multi-septate body were observed by scanning electron microscopy, suggesting an additional effect on cytokinesis. Taken together, our data show that these essential oils affect the parasite viability being the C. citratus essential oil the most effective against L. chagasi.     

Ovicidal effects of a neem seed extract preparation on eggs of body and head lice

The eggs (nits) of head and body lice (Pediculus humanus capitis, Pediculus humanus corporis) were incubated for 5, 10, 15, 20, 30 or 45 min into a neem seed extract contained in a fine shampoo formulation (e.g. Wash Away? Louse), which is known for its significant killing effects of larvae and adults of head lice. The aim of the study was to test whether the developmental stages inside the eggs are also killed after the incubation into the shampoo. It was found that an incubation time of only 5 min was sufficient to prohibit any hatching of larvae, whilst 93 ± 4% of the larvae in the untreated controls of body lice hatched respectively about 76% of the controls in the case of head lice. Apparently, the neem-based shampoo blocked the aeropyles of the eggs, thus preventing the embryos of both races of lice from accessing oxygen and from releasing carbon dioxide. Thus, this product offers a complete cure from head lice upon a single treatment, if the lice (motile stages, eggs) are fully covered for about 10 min.     

Anti-Giardia activity of phenolic-rich essential oils: effects of Thymbra capitata, Origanum virens, Thymus zygis subsp. sylvestris, and Lippia graveolens on trophozoites growth, viability, adherence, and ultrastructure

The present work evaluates the anti-Giardia activity of phenolic-rich essential oils obtained from Thymbra capitata, Origanum virens, Thymus zygis subsp. sylvestris chemotype thymol, and Lippia graveolens aromatic plants. The effects were evaluated on parasite growth, cell viability adherence, and morphology. The tested essential oils inhibited the growth of Giardia lamblia. T. capitata essential oil is the most active followed by O. virens, T. zygis subsp. sylvestris, and L. graveolens oils. The tested essential oils at IC50 (71–257) μg/ml inhibited parasite adherence (p < 0.001) since the first hour of incubation and were able to kill almost 50% of the parasites population in a time-dependent manner. The main ultrastructural alterations promoted by essential oils were deformations in typical trophozoite appearance, often roundly shape, irregular dorsal and ventral surface, presence of membrane blebs, electrodense precipitates in cytoplasm and nuclei, and internalization of flagella and ventral disc. Our data suggest that essential oils induced cell death probably by processes associated to the loss of osmoregulation caused by plasmatic membrane alterations. Experiments revealed that the essential oils did not present cytotoxic effects in mammalian cells. In conclusion, T. capitata, O. virens, T. zygis subsp. sylvestris chemotype thymol, and L. graveolens essential oils have antigiardial activity in vitro and seem to have potential for the treatment of the parasitic disease caused by the protozoan G. lamblia.     

In vitro anthelmintic activity of the essential oils of <Emphasis Type="BoldItalic">Zanthoxylum zanthoxyloides</Emphasis> and <Emphasis Type="BoldItalic">Newbouldia laevis</Emphasis> against <Emphasis Type="BoldItalic">Strongyloides ratti</Emphasis>

The need for new anthelmintic with no chemical residues is becoming urgent. In a program aiming at the evaluation of plant as sources of new active molecules, the anthelmintic activities of the essential oils (EOs) obtained from either Zanthoxylum zanthoxyloides seeds or Newbouldia laevis leaves were evaluated against Strongyloides ratti by analyzing the results of two in vitro bioassays. These two plants and their tested parts were retained after an ethnopharmacology survey that confirmed their use by small-scale farmers for treatment of small ruminants affected by digestive helminths. The plants were harvested in Benin, and their EO were obtained by hydrodistillation. The EO yield of extraction was 0.65% (w/w) of for Z. zanthoxyloides seeds and 0.05% (w/w) for N. laevis. The chemical compositions of the two EOs were analyzed by gas chromatography coupled with mass spectrometry. The major constituents of the EO from Z. zanthoxyloides consisted of the following compounds: γ-terpinene (18 %), undecane (15 %), valencene (8.3 %), decanal (8.3 %), and 3-carene (6.7 %). In contrast, the major constituents of the EO from N. laevis leaves consisted of the following compounds: β-caryophyllene (36 %) and eugenol (5.8 %). An egg-hatching inhibition (EHI) assay was developed and a larval migration inhibition assay was used on S. ratti to examine the effects of the EOs and to evidence their inhibitory concentrations (IC₅₀ and IC₉₀) values on this nematode. Furthermore, the toxicity of the two EOs on Vero cell line was evaluated. When tested on S. ratti egg hatching, the two EOs resulted in similar IC₅₀ values (19.5 and 18.2 μg/ml for Z. zanthoxyloides and N. laevis, respectively), which were about sevenfold higher than that of the control (thiabendazole, IC₅₀ = 2.5 μg/ml). Larval migration was inhibited at similar concentrations for: Z. zanthoxyloides (IC₅₀ = 46 μg/ml), N. laevis (IC₅₀ = 51 μg/ml), and the control [levamisole (IC₅₀ = 36 μg/ml)]. No cytotoxicity was found on Vero cells because both EOs had IC₅₀ values higher than 50 μg/ml. Therefore, we have concluded that the EOs from two plants, used in folk medicine, may contain compounds with anthelmintic activity and could be used as improved traditional medicines or, at least, as food additives in a combined treatment for the control of helminth infections.     

Acaricidal activity and chemical composition of the essential oil from three Piper species

The chemical composition of the essential oil obtained by hydrodistillation of the aerial parts of Piper amalago, Piper mikanianum, and Piper xylosteoides was elucidated by gas chromatography (GC) and GC/mass spectrometry analyses. P. mikanianum and P. xylosteoides essential oils presented phenylpropanoids as their main compounds (67.89% and 48.53%, respectively) whereas P. amalago was rich in monoterpene and sesquiterpene hydrocarbons (84.95%). The essential oils obtained were investigated for their effect on newly hatched larvae of the cattle tick, Rhipicephalus (Boophilus) microplus. The essential oil of P. mikanianum (LC₅₀ 2.33 μL/mL) was more active than that of P. xylosteoides (LC₅₀ 6.15 μL/mL) against the larvae, while the oil of P. amalago was inactive. These results suggest that phenylpropanoids, mainly apiol and safrole, are responsible for the acaricidal activity.     

Evaluation of mosquitocidal activity of essential oil and sesquiterpenes from leaves of <Emphasis Type="Italic">Chloroxylon swietenia</Emphasis> DC.

Growing awareness in using ecofriendly and biologically compatible phytoconstituents as natural insecticides and repellents for the safety of life and ecological balance led to conscientious efforts by scientists all over the world to search for alternative sources of plant derivatives for effective use as mosquitocides. Encouraged by this, the essential oil and the sesquiterpenes isolated from the leaves of Chloroxylon swietenia DC. were screened for mosquitocidal activity by fumigant toxicity against three mosquito species, Anopheles gambiae, Culex quinquefasciatus and Aedes aegypti. The essential oil had pronounced mosquitocidal activity with LD₅₀ of 1.0, 1.2 and 1.7 × 10⁻³ mg/cm⁻³, respectively, for the three vector species. Furthermore, the major sesquiterpenes were tested at different doses, which again showed varying levels of toxicity. However, germacrene D performed better and proved to be the potential candidate with LD₅₀ values of 1.8–2.8 × 10⁻³ mg/cm⁻³ followed by pregeijerene and geijerene. Nevertheless, the oil and the isolated compounds were particularly active against A. gambiae. The essential oil from the leaves was obtained by hydrodistillation, and the chemical composition was determined by GC and GC–MS. The main compounds identified were limonene, germacrene D, geijerene, pregeijerene, trans-β-ocimene and methyl eugenol. The present study indicates that the oil and the isolated compounds of C. swietenia displayed remarkable mosquitocidal activity suggesting that the method could be extended for future field trials in various mosquito control programmes, and the results are compared with synthetic insecticides.     

Acaricidal activity of the essential oils from Eucalyptus citriodora and Cymbopogon nardus on larvae of Amblyomma cajennense (Acari: Ixodidae) and Anocentor nitens (Acari: Ixodidae)

The present study evaluated the acaricidal activity of essential oils from Eucalyptus citriodora and Cymbopogon nardus on non-engorged larvae of Amblyomma cajennense and Anocentor nitens. In order to carry out the study, six groups were formed, each concentration being a treatment (6.25%, 12.5%, 25%, and 50%, respectively) and also with the creation of a control group (distilled water) and a positive control (Deltametrine). For each treatment, approximately 100 larvae of these ticks were placed onto filter papers (2 × 2 cm) impregnated with the concentrations used to test. Next, the envelopes were closed bearing inside the filter paper with measurements of 6 × 6 cm. For each group, six repetitions were performed, and after 24 h live and dead larvae were counted. This procedure was carried out for two essential oils on the two species of ticks. For A. cajennense, the acaricide efficacy of E. citriodora oil was of 10.8%, 35.3%, 34.5%, and 53.1%, whereas the efficacy of C. nardus was of 0.0%, 0.0%, 0.0%, and 61.1% at concentrations of 6.25%, 12.5%, 25.0%, and 50.0%, respectively. In relation to A. nitens, the acaricide efficacy of E. citriodora oil was of 20.1%, 84.5%, 89.2%, and 100.0%, whereas the efficacy of C. nardus was of 0.0%, 90.8%, 100.0%, and 100.0% at concentrations of 6.25%, 12.5%, 25.0%, and 50.0%, respectively. The results indicate that the essential oils tested showed a promising acaricidal activity mainly on A. nitens larvae.     

New spot-on formulation containing chlorpyrifos for controlling horn flies on cattle: laboratory model of insecticide release and field trial

A highly viscous formulation containing chlorpyrifos (RET) was evaluated under laboratory, pre-field, and field conditions, and compared against ear tags with organophosphorus insecticides. Laboratory bioassays were performed using Musca domestica L. and a thin layer chromatography (TLC) plate of reversed phase silica gel modeling a lipophilic surface. Insects were exposed to the insecticide vapors of both formulations, directly and indirectly to test for lateral diffusion. Knockdown time 50% (KT₅₀) values were determined as toxicological indicators of insecticide release. Minimum KT₅₀ values of the direct effect of both formulations on horn flies were reached 4 weeks after being applied. The KT₅₀ effect of migrated insecticides showed that RET formulation had a maximal effectiveness between the fourth and tenth last week. The KT₅₀ effect of the insecticide migrating from ear tags decreased during the last 2 weeks of the experiment, and the KT₅₀ effect of the laterally migrated insecticide was significantly higher for the RET formulation during this period. A pre-field bioassay was performed by exposing pieces of rabbit leather with both formulations and recording the KT₅₀. At the end of the experiment, the KT₅₀ effect of laterally migrated insecticide was significantly higher for the RET formulation. Regarding vapor emission, as a general trend the KT₅₀ effect of ear tags was greater than for the RET formulation. To evaluate the horn fly infestation in the field bioassays, photographs of the animal were taken. The results shows that RET provided significant control for 11 weeks while the ear tags provided protection until the 12th week.     

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

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

In vitro pediculicidal activity of herbal shampoo base on Thai local plants against head louse (Pediculus humanus capitis De Geer)

Head lice infestation, a worldwide head infestation caused Pediculus humanus capitis De Geer, is an important public health problem in Thailand. Several chemical pediculicides have lost in efficacy due to increasing resistance of lice against insecticide. Therefore, non-toxic alternative products, such as natural products from plants, e.g. plant extract pediculicides, are needed for head lice control. The aims of this study were to evaluate the potential of pediculicidal activity of herbal shampoo base on three species of Thai local plants (Accacia concinna (Willd.) DC, Averrhoa bilimbi Linn. and Tamarindus indica Linn.) against head lice and to compare them with carbaryl shampoo (Hafif shampoo®; 0.6 % w/v carbaryl) and non-treatment control in order to assess their in vitro. Doses of 0.12 and 0.25 ml/cm² of each herbal shampoo were applied to filter paper, and ten head lice were place on the filter paper. The mortalities of head lice on the filter paper were recorded at 1, 5, 10, 30 and 60 min by sterio-microscope. All herbal shampoos at 0.25 ml/cm² were more effective pediculicide than carbaryl shampoo with 100 % mortality at 5 min. The median lethal time (LT₅₀) of all herbal shampoos at 0.25 ml/cm² showed no significant differences over at 0.12 ml/cm² (P?<?0.01). The most effective pediculicide was T. indica extract shampoo, followed by Av. bilimbi extract shampoo and Ac. concinna extract shampoo, with LT₅₀ values <1.0 min. Our data showed that all herbal shampoos have high potential of pediculicide to head lice treatments for schoolchildren.     

Evaluation of medicinal plant extracts against blood-sucking parasites

The present study was based on assessments of the antiparasitic activities to determine the efficacies of acetone, chloroform, ethyl acetate, hexane, and methanol dried leaf, flower, and seed extracts of Cassia auriculata L., Rhinacanthus nasutus KURZ., Solanum torvum Swartz, Terminalia chebula Retz., and Vitex negundo Linn. were tested against larvae of cattle tick Rhipicephalus (Boophilus) microplus Canestrini, 1887 (Acari: Ixodidae), adult of Haemaphysalis bispinosa Neumann, 1897 (Acarina: Ixodidae), hematophagous fly Hippobosca maculata Leach (Diptera: Hippoboscidae), nymph of goat-lice Damalinia caprae Gurlt (Trichodectidae), and adult sheep parasite Paramphistomum cervi Zeder, 1790 (Digenea: Paramphistomatidae). All plant extracts showed moderate parasitic effects after 24 h of exposure at 3,000 ppm; however, the highest parasite mortality was found in leaf ethyl acetate, flower methanol of C. auriculata, leaf and seed methanol of S. torvum, seed acetone of T. chebula, and leaf hexane extracts of V. negundo against the larvae of R. microplus (LC₅₀ = 335.48, 309.21, 297.43, 414.99, 167.20, and 611.67 ppm; LC₉₀ = 1571.58, 1111.82, 950.98, 1243.64, 595.31, and 1875.50 ppm), the leaf and flower methanol of R. nasutus, leaf and seed methanol of S. torvum, and seed methanol extracts of T. chebula against the nymph of D. caprae (LC₅₀ = 119.26,143.10,164.93,140.47, and 155.98 ppm; LC₉₀ = 356.77, 224.08, 546.20, 479.72, and 496.06 ppm), the leaf methanol of R. nasutus, leaf and seed methanol of S.torvum, and seed acetone of T. chebula against the adult of H. bispinosa (LC₅₀ = 333.15, 328.98, 312.28, and 186.46 ppm; LC₉₀ = 1056.07, 955.39, 946.63, and 590.76 ppm), the leaf methanol of C. auriculata, the leaf and flower methanol of R. nasutus, the leaf ethyl acetate of S. torvum against the H. maculata (LC₅₀ = 303.36, 177.21, 204.58, and 211.41 ppm; LC₉₀ = 939.90, 539.39, 599.43, and 651.90 ppm), and the leaf acetone of C. auriculata, the flower methanol of R. nasutus, the seed methanol of S. torvum, and the seed acetone of T. chebula were tested against the adult of P. cervi (LC₅₀ = 180.54, 168.59, 200.89, and 87.08 ppm; LC₉₀ = 597.51, 558.65, 690.37, and 433.85 ppm), respectively. Therefore, this study provides first report on the veterinary parasitic activity of plant extracts from Southern India.     

<Emphasis Type="Italic">Pediculus humanus capitis</Emphasis> (head lice) and <Emphasis Type="Italic">Pediculus humanus humanus</Emphasis> (body lice): response to laboratory temperature and humidity and susceptibility to monoterpenoids

Human pediculosis is produced by Pediculus humanus humanus (Linnaeus 1758) and Pediculus humanus capitis (De Geer 1767). Laboratory-reared body lice, susceptible to insecticides, were used as reference in toxicological studies on head lice. In this work, we evaluated the survival of both subspecies at different temperatures and relative humidities and we propose the optimal conditions for comparative bioassays. Moreover, we used these conditions to test the activity of three monoterpenoids against both lice. The results showed differential response to changes in temperature and humidity between both organisms. The survival of body lice ranged between 83% and 100% and was not affected for the tested conditions. The survival of head lice depended on temperature, humidity, and exposure time. The optimal conditions for head lice were 18oC and 97% relative humidity at 18 h of exposition. The insecticidal activity of three monoterpenoids (pulegone, linalool, and 1,8-cineole), evaluated according the selected conditions by topical application, showed no significant differences between males of body and head lice. To conclude, as head lice required more special laboratory conditions than body lice, the optimal head lice conditions should be used in both organisms in comparative bioassays. Body louse is an appropriate organism for testing products against of head louse.