Larvicidal and adulticidal effects of essential oils of Corymbia citriodora (Myrtaceae) and Xylopia aetiopica (Annonaceae) on Anopheles gambiae sensu stricto Giles 1902

The present study was carried out for the first time in Morocco to valorise plant species of the Artemisia genus. Its aim was to evaluate the larvicidal activity of essential oils from six Artemisia plants (A. herba alba, A. absinthium, A. campestris L., A. negrei, A. pontica, and A. arborescens) against Culex pipiens mosquitoes, which are recognised as potential vectors of West Nile virus. Bioinsecticides derived from EOs have shown promise as effective mosquito control agents. The EOs were analysed using GC–MS and GC‐FID and were obtained by hydrodistillation from the aerial parts of the plants. Besides, the experiment was carried out according to the standard WHO protocol. Thujone and camphor were identified as the predominant compounds in all six Artemisia plants. A. herba alba demonstrated the highest larvicidal activity with LC50 and LC90 values of 4.85 and 15.39 μg/mL, respectively. Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA) were employed to explore the correlation between major EO compounds and larvicidal efficacy. The results suggest that these findings could pave the way for the development of tailored biocides that specifically target important disease vectors.

The Asteraceae family is well known for its toxic and repellent activity against mosquitoes. In this study, essential oils (EOs) extracted from the aerial parts of both wild and cultivated Artemisia campestris L. plants were tested for larvicidal activity against Culex pipiens (Diptera: Culicidae), a pest mosquito widely suspected to be the vector responsible for West Nile virus transmission. The research aims at comparing the chemical composition and insecticidal activity of cultivated and wild A. campestris EOs. The EOs were obtained by hydrodistillation from the plant's aerial parts and were analyzed using GC-MS. Furthermore, the larviciding experiment was carried out following the standard WHO protocol. The result showed that wild and cultivated plant EOs differed only quantitatively, while the qualitative profile revealed a nearly identical chemical composition. Camphor (18.98%), car-3-en-5-one (11.25%), thujone (6.36%), chrysanthenone (6.24%), filifolone (4.56%), and borneol (3.56%) dominate the wild plant EO. Camphor (21.01%), car-3-en-5-one (17%), chrysanthenone (10.15%), filifolone (7.90%), borneol (3.38%), and thujone (3.08%) are the major compounds of the cultivated plant. Cultivation did not affect the EO production since the yield of the cultivated plant was 0.5 ± 0.1% and 0.6 ± 0.2% for the wild plant. The cultivated A. campestris EO had the highest insecticidal activity (LC50 = 9.79 µg/ml), and no significant difference was noticed between wild and cultivated A. campestris EO in terms of LC90. These findings could pave the way for a new method of producing biocides to control major disease vectors and offer a potential alternative for pest control.

Carlina oxide from Carlina acaulis root essential oil acts as a potent mosquito larvicide

To evaluate the pyrrole insecticide chlorfenapyr, which has a novel non-neurotoxic mode of action and is a promising alternative to conventional adulticides, against Anopheles funestus. The toxicity of a range of concentrations of chlorfenapyr against pyrethroid resistant and susceptible laboratory reared southern African An. funestus was assessed using standard WHO protocols and analysed using probit analysis. The pyrethroid resistant strain showed consistently higher LD50 and LD95 values compared to the susceptible strain, but these differences were not statistically significant and the magnitude was twofold at most. The LD50 values recorded for An. funestus are approximately three-fold higher than those reported elsewhere for other species of anopheline. Monooxygenase based pyrethroid resistance in An. funestus does not influence the toxic effect of chlorfenapyr. It is unlikely that such a small decrease in susceptibility of An. funestus to chlorfenapyr relative to other anophelines would have any operational implications. Chlorfenapyr is an important addition to insecticides available for malaria vector control, and could be used as a resistance management tool to either circumvent or slow the development of resistance.

Mosquitoes are significant public health pests and act as a vector of several diseases viz ., malaria, filariasis, Japanese encephalitis, dengue fever and chikungunya, which are transmitted by the three genera of mosquitoes, viz ., Anopheles, Culex and Aedes . Mosquito control strategies have depended primarily on the use of synthetic chemical insecticides but resulted in rebounding vectorial capacity, environmental and human health concerns. Plants may be a source of alternative agents to replace the synthetic insecticides for mosquito control. In the present study, the isolated fractions of Murraya koenigii hexane leaf extracts were evaluated for larvicidal activity against vector mosquitoes viz., Aedes aegypti , Anopheles stephensi and Culex quinquefasciatus . Six fractions viz., A, B, C, D, E and F were obtained from the residue of hexane extract by column chromatography. Standard WHO protocol with minor modifications was adopted for the larvicidal bioassay. Larvicidal activity was evaluated against the isolated fractions at concentrations of 25, 50, 75 and 100 ppm. Larval mortality was observed 24 hours post exposure. Amongst the isolated fractions tested, fraction ‘D’ showed 100.0, 97.6 and 99.2% mortality against third instar larvae of Aedes aegypti , Culex quinquefasciatus and Anopheles stephensi at 100 ppm, respectively and LC50 values were 35.06, 27.20 and 42.51 ppm respectively. Further investigations are needed to explore the larvicidal activity of the isolated fraction ‘D’ of hexane leaf extract of this plant and also the active principle(s) responsible for larvicidal activity.

Microcos paniculata traditionally known as 'Kathgua or Fattashi' in Bangladesh is widely used for the treatment of various ailments including colds ,diarrhea, hepatitis, heat stroke, dyspepsia, wound healing, fever and as an insecticide. Hence, the present study was designed to investigate the antibacterial, toxicity & 4 th instar Culex quinquefasciatus mosquito larvicidal activities of fruit extracts of M. paniculata using a range of organic & inorganic solvents (methanol, chloroform and water). Antibacterial, toxicity & larvicidal effects were studied by means of agar disc diffusion, brine shrimp lethality bioassay (BSLB) & standard WHO protocol with slight modification. The susceptibility of the microorganisms to the plant extracts was compared with standard antibiotic flucloxacilin. Fruit methanol extract (FME) revealed a broad spectrum of antibacterial activity in contrast to other extracts (Fruit chloroform extract-FCE & Fruit water extract-FWE) , particularly significant against gram negative bacteria, Proteus mirabilis being the most (zone of inhibition 28 mm). Moreover, the FME was found to be the most toxic to brine shrimp nauplii, with LC50 of 52.7 μg/ml, indicating the possibility of finding potential toxic compounds in this plant. 4 th instar Culex quinquefasciatus larval mortality was observed and recorded after 24 h exposure period. Both FME & FCE exhibited considerable larvicidal effects with LC50 of 342.1 μg/ml &441.7 μg/ml respectively. Altogether, these results propose that the organic fractions, FME & FCE could be used as a potential sources of antibacterial agents along with their toxic & larvicidal potentiality.

Insecticide resistance molecular markers can provide sensitive indicators of resistance development in Anopheles vector populations. Assaying these makers is of paramount importance in the resistance monitoring programme. We investigated the presence and distribution of knock-down resistance (kdr) mutations in Anopheles gambiae s.l. in Tanzania. Indoor-resting Anopheles mosquitoes were collected from 10 sites and tested for insecticide resistance using the standard WHO protocol. Polymerase chain reaction-based molecular diagnostics were used to genotype mosquitoes and detect kdr mutations. The An. gambiae tested were resistance to lambdacyhalothrin in Muheza, Arumeru and Muleba. Out of 350 An. gambiae s.l. genotyped, 35% were An. gambiae s.s. and 65% An. arabiensis. L1014S and L1014F mutations were detected in both An. gambiae s.s. and An. arabiensis. L1014S point mutation was found at the allelic frequency of 4-33%, while L1014F was at the allelic frequency 6-41%. The L1014S mutation was much associated with An. gambiae s.s. (χ(2) = 23.41; P < 0.0001) and L1014F associated with An. arabiensis (χ(2) = 11.21; P = 0.0008). The occurrence of the L1014S allele was significantly associated with lambdacyhalothrin resistance mosquitoes (Fisher exact P < 0.001). The observed co-occurrence of L1014S and L1014F mutations coupled with reports of insecticide resistance in the country suggest that pyrethroid resistance is becoming a widespread phenomenon among our malaria vector populations. The presence of L1014F mutation in this East African mosquito population indicates the spreading of this gene across Africa. The potential operational implications of these findings on malaria control need further exploration.

The present study was carried out to investigate the phytochemical, antioxidant and larvicidal property of different solvent extracts of leaves of Clerodendrum infortunatum and fruit peel of Citrus grandis. The antioxidant property was studied by ferric reducing antioxidant power (FRAP), total antioxidant capacity (TAC), 1,1‑diphenyl‑2‑picrylhydrazyl (DPPH), 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonate) (ABTS) and thiobarbituric acid reactive species (TBARS) assays. The total phenolic and flavonoid contents of the extracts were estimated following standard protocols. Larvicidal activity of the plant extracts were evaluated following standard WHO protocol. In a series of test doses (100 to 2000 μg/mL), 20 numbers of Aedes aegypti larvae were exposed and the mortality was recorded after 24 h and LC50 were calculated. The study showed that the C. grandis extracts have better phytochemical, antioxidant and larvicidal activity compared to C. infortunatum. Among the four solvent fractions, diethyl ether extract showed higher activity in both the plants. The present study thus showed potential larvicidal property of the plants against A. aegypti. However, further characterization and identification of active compound (s) need to be carried out to study the exact mode of action.

The present investigation highlights the antimicrobial, toxic & larvicidal activities of the root extracts of Microcos paniculata using various organic & inorganic solvents (methanol, chloroform and water). Antimicrobial, toxicity & larvicidal outcomes were studied by means of agar disc diffusion, brine shrimp lethality bioassay (BSLB) & standard WHO protocol with slight modification. The susceptibility of the microorganisms to the plant extracts was compared with standard antibiotic ciprofloxacin. Root chloroform extract (RCE) revealed a broad spectrum of antimicrobial activity in contrast to other extracts, particularly significant against gram negative bacteria, Vibrio cholerae being the most (zone of inhibition 27 mm).Moreover, the RCE was found to be the most toxic to brine shrimp nauplii, with LC50 of 19.4 μg/ml, whereas anticancer drug vincristine sulphate (VS) proved LC50 value 1.7 μg/ml indicating that there is a possibility of finding potent toxic compounds in this plant have affinity relatively for non- polar solvents. 4 th instar Culex quinquefasciatus larval mortality was observed and recorded after 24 h exposure period. Both the root methanolic extract (RME) & RCE exhibited larvicidal effects with LC50 of 257.3 μg/ml & 267.6 μg/ml respectively. Taken together, these results suggest that the organic fractions, RME & RCE could be potential sources of natural antimicrobial, toxic & larvicidal agents.

BackgroundThe current study was undertaken to determine the optimal wash-drying regimen and the effects of different washing procedures on the efficacy, and durability of four brands of newly introduced long-lasting insecticide-treated nets (LLINs) under tropical conditions.MethodsIn the current study, the following four LLINs were tested: Olyset®, PermaNet ®2.0, BASF® and TNT®. Nets were divided into three sets; one set was washed by hand rubbing and air-dried either hanging or spread on the ground in direct sunlight or hanging or spread on the ground under the shade. A second set was washed using the WHO protocol (machine) and the third set was washed by beating the nets on rocks. The biological activities of the nets were assessed by a three-minute bioassay cone test and the residual insecticide contents were determined using high performance liquid chromatography (HPLC) procedure.ResultsNets that were dried hanging under the shade retained more insecticide, 62.5% and recorded higher mortality compared to nets which were dried lying on the ground in direct sunlight 58.8%, nets dried under the shade spread on the ground 56.3%, and 57.8% for nets dried hanging in direct sunlight. It was also observed that nets washed by the standard WHO protocol, retained more insecticide and were more effective in killing mosquitoes compared to nets washed by local methods of hand rubbing and beating on rocks. There were significant differences between drying regimens (p < 0.0001) and between washing procedures (p < 0.001) respectively. However, the effect of net type was statistically insignificant. The statistical differences on individual nets were also compared, for PermaNet® and TNT there were no significant differences observed between the four drying regimens (p = 0.7944 and 0.4703) respectively). For BASF and Olyset, the differences were significant (p < 0.001 and p > 0.0001).ConclusionThe results of this study suggest that washing and drying regimen influence the insecticidal activity of LLINs. The standard WHOPES washing protocol underestimates the amount of insecticide washed from LLINs compared to the abrasive washing procedures that are used in the field. This suggests that there is need to educate net users to adopt a more gentle washing procedure while handling LLINs. The education should accompany net distribution campaigns.

Early supplementation with high-dose vitamin A in The Gambia

Effectiveness of an early supplementation scheme of high-dose vitamin A versus standard WHO protocol in Gambian mothers and infants: a randomised controlled trial

Larvicidal potential of selected indigenous lichens against three mosquito species–Culex quinquefasciatus, Aedes aegypti and Anopheles stephensi

Mosquitoes are the most important group of insects in terms of public health importance, which transmit serious human diseases. The continuous application of synthetic insecticides to control these mosquitoes causes development of resistance in vector species, and an adverse effect on environmental quality and non-target organisms including human health. Therefore, the use of active toxic agents from plant extracts as alternative mosquito control strategy cannot be over emphasized, as these are non-toxic, easily available at affordable prices, biodegradable and show target - specific activities against different species of vector mosquitoes. The aim of the present study was to evaluate the larvicidal efficacy of the aqueous and methanol leaf extracts of H. suaveolens against the fourth instars larvae of Anopheles species. Standard WHO protocols was adopted for the larvicidal bioassay. Larvicidal activity was evaluated at concentrations of 200, 400, 600, 800 and 1000 mg/L. The larval mortality was observed after 24 and 48hours bioassay. The results are mean of three replicates and the mortalities recorded were subjected to chi-square test and probit analysis to determine median lethal concentrations (LC50). TheGC-MS analysis ofthe methanolic leaf extract of the plantrevealed the presence of twelve compounds on the chromatogram. Among the major compounds areOleic Acid (33.33%), Octadecanoic acid (13.52%), 1,3-Cyclohexadiene-1-methanol,alpha.,2,6,6-(10.42%), 1,3-Cyclopentanediol, trans (9.60%), n-Hexadecanoic acid (9.01%) and 4-Hepten-3-one, 4-methyl (7.0%).The phytochemical screening of the aqueous and methanol leaf extracts of the plant revealed the presence of Tannins, Terpenoids, Flavonoids, Steroids, Carbohydrates, Cardiac glycoside and resins. The LC50 values estimated were 316.22mg/Lfor methanol extract and 323.59 mg/L for aqueous extract. The differences between the two extracts were however not significantly different at P&gt;0.05. The findings also revealed that mortality was concentration dependent and both extracts showed promising larvicidal activity against Anopheles species larvae. Therefore, the crude leaf extract of the plant is recommended to be used as alternative to synthetic larvicides and further research is needed to test the activity of the plant on non-target organisms.

BackgroundAedes aegypti (Diptera: Culicidae) is the main vector of the dengue virus globally. Dengue vector control is mainly based on reducing the vector population through interventions, which target potential breeding sites. However, in Tanzania, little is known about this vector’s habitat productivity and insecticide susceptibility status to support evidence-based implementation of control measures. The present study aimed at assessing the productivity and susceptibility status of A. aegypti mosquitoes to pyrethroid-based insecticides in Dar es Salaam, Tanzania.MethodsAn entomological assessment was conducted between January and July 2015 in six randomly selected wards in Dar es Salaam, Tanzania. Habitat productivity was determined by the number of female adult A. aegypti mosquitoes emerged per square metre. The susceptibility status of adult A. aegypti females after exposure to 0.05% deltamethrin, 0.75% permethrin and 0.05% lambda-cyhalothrin was evaluated using the standard WHO protocols. Mortality rates were recorded after 24 h exposure and the knockdown effect was recorded at the time points of 10, 15, 20, 30, 40, 50 and 60 min to calculate the median knockdown times (KDT50 and KDT95).ResultsThe results suggest that disposed tyres had the highest productivity, while water storage tanks had the lowest productivity among the breeding habitats Of A. aegypti mosquitoes. All sites demonstrated reduced susceptibility to deltamethrin (0.05%) within 24 h post exposure, with mortalities ranging from 86.3 ± 1.9 (mean ± SD) to 96.8 ± 0.9 (mean ± SD). The lowest and highest susceptibilities were recorded in Mikocheni and Sinza wards, respectively. Similarly, all sites demonstrated reduced susceptibility permethrin (0.75%) ranging from 83.1 ± 2.1% (mean ± SD) to 96.2 ± 0.9% (mean ± SD), in Kipawa and Sinza, respectively. Relatively low mortality rates were observed in relation to lambda-cyhalothrin (0.05%) at all sites, ranging from 83.1 ± 0.7 (mean ± SD) to 86.3 ± 1.4 (mean ± SD). The median KDT50 for deltamethrin, permethrin and lambda-cyhalothrin were 24.9–30.3 min, 24.3–34.4 min and 26.7–32.8 min, respectively. The KDT95 were 55.2–90.9 min for deltamethrin, 54.3–94.6 min for permethrin and 64.5–69.2 min for lambda-cyhalothrin.ConclusionsThe productive habitats for A. aegypti mosquitoes found in Dar es Salaam were water storage containers, discarded tins and tyres. There was a reduced susceptibility of A. aegypti to and emergence of resistance against pyrethroid-based insecticides. The documented differences in the resistance profiles of A. aegypti mosquitoes warrants regular monitoring the pattern concerning resistance against pyrethroid-based insecticides and define dengue vector control strategies.