Larvicidal activity of neem oil (Azadirachta indica) formulation against mosquitoes

Assessment of biorational larvicides and botanical oils against Culex quinquefasciatus Say (Diptera: Culicidae) larvae in laboratory conditions

Mosquitoes are known vectors that transmit deadly diseases to millions of people across the globe. The reliance on synthetic insecticides has been the sole way to combat mosquito vectors for decades. In recent years, the extensive use of conventional insecticides in mosquito suppression has led to significant pesticide resistance and serious human health hazards. In this light, investigating the potential application of biorational compounds for vector management has drawn significant attention. We, hereby, evaluated the efficacy of three microbial derivative biorational insecticides, abamectin, spinosad, and buprofezin, and two botanical oils, neem (Azadirachta indica A. Juss) and karanja oil (Pongamia pinnata Linn.) against the Culex quinquefasciatus under laboratory conditions. The fourth-instar C. quinquefasciatus larvae were exposed to different concentrations of the selected larvicides and lethality was estimated based on LC50 and LT50 with Probit analysis. All larvicides showed concentration-dependent significant effects on survival and demonstrated larvicidal activity against C. quinquefasciatus larvae. However, abamectin exerted the highest toxicity (LC50 = 10.36 ppm), exhibited statistically significant effects on C. quinquefasciatus larval mortality, followed by spinosad (LC50 = 21.32 ppm) and buprofezin (LC50 = 56.34 ppm). Abamectin caused larval mortality ranged from 30.00 to 53.33 % and 53.00-70.00 % at 06 and 07 h after treatment (HAT), respectively. In the case of botanicals, karanja oil (LC50 = 216.61 ppm) was more lethal (more than 1.5 times) and had a shorter lethal time than neem oil (LC50 = 330.93 ppm) and showed a classic pattern of relationship between concentrations and mortality over time. Overall, the present study highlighted the potential of deploying new generation biorational pesticides and botanicals in mosquito vector control programs.

Effect of Mosquitocidal, histopathological alteration and non target effects of Sigesbeckia orientalis L. on Anopheles stephensi Liston, Culex quinquefasciatus say and Aedes aegypti L

Diseases transmitted by vectors have a significant collision on society and community health, particularly in tropical and subtropical regions, where they can cause large-scale outbreaks shortly after initial transmission. The intent of this investigation was to study the plant extract derived from Sigesbeckia orientalis L. in controlling the immature stages of Anopheles, Culex and Aedes mosquitoes, while also considering its potential toxicity to ecosystems. The immature stages were exposed to different extracts (62.5-500 ppm), and the mortality of larvae and pupae, as well as ovicidal activity, were noted after 24 and 120 h of the experiment. The hexane and ethyl aceate extract of S. orientalis presented 100% ovicidal activity against the eggs of Anopheles, Aedes and Culex at 500 ppm concentration after 5 days of treatment. The hexane and ethylacetate extracts presented strong larvicidal activity with LC50 values of 215.7, 332.0, 197.4 and 212.6, 694.9 and 201.7 ppm against treated mosquitoes at 24 h, respectively. The same extract also presented promising pupicidal activity. The LC50 values of hexane extract were 219.6, 353.6, 194.2 and LC50 values of ethyl acetate were 257.6, 387.8 and 259.07 ppm against early stage pupae of three vector mosquitoes, respectively. The extracts from S. orientalis had strong inhibitory activity against growth and development of mosquitoes. SI/PSF values showed that the extracts of S. orientalis did not harm Poecilia reticulata, Diplonychus indicus (Water bug), Gambusia affinis and dragon fly nymph at tested concentrations. Furthermore, examinations of histopathology and growth disruption revealed significant damage to the midgut cells in the treated larvae. The formulations utilizing hexane and ethyl acetate extracts exhibited potent activity without posing any toxicity towards non-target organisms. This study clearly indicated that hexane and ethylacetate extracts showed promising results against treated mosquitoes. The present study documents the first report of the extracts from S. orientalis and they can be further assessed to identify compounds for application purposes.

Mitigating the Public Health Issues Caused by the Filarial Vector, Culex quinquefasciatus (Diptera: Culicidae) Through Phytocontrol and Larval Source Marker Management

Failure of conventional mosquito control strategies to curb the population of vectors have made the humans vulnerable to serious medical problems transmitted by them. This effect has been compounded by global climate change enabling the mosquitoes to cross geographical boundaries and cause trouble in regions where they were initially not found. As such, the scientific community has been compelled to devise alternative and innovative strategies of mosquito control that can be integrated with the conventional practices to implement multi-phasic approach of vector management. Culex quinquefasciatus is one such mosquito species that is reported to be one of the primary vectors of lymphatic filariasis and many other diseases of global health concern. However, not much is known about its breeding habitat ecology and microbial properties that have enabled the species to achieve reproductive success in urbanized habitats. The current investigation was carried out at Digha, West Bengal, India. The region, despite being endemic for lymphatic filariasis, has rarely been explored for its mosquito diversity and/or their breeding habitat characteristics. Therefore, these were attempted. For survey and sampling, seven villages were chosen, namely, Duttapur, Jatimati, Champabani, Padima, Gobindabasan, Bhagibaharampur and Palsandapur. The study showed that Cx. quinquefasciatus is the dominant mosquito species at the sampling sites with the highest density of their larvae being recorded from man-made structures like drains and pools close to human habitations and livestock. The study was, therefore, restricted to Cx. quinquefasciatus. Seasonal abundance showed that they were most prevalent in the monsoon followed by summer. The physicochemical characterization showed their larvae to prefer almost neutral pH (6.9 to 7.3), low chloride concentration (98 to 258 ppm) and turbidity. As far as other parameters are concerned, they were tolerant towards a wide range allowing them to adapt varied habitats in the study areas. The bacterial profiling of their natural habitat waters revealed the presence of Paenibacillus nanensis DGX1(OQ690670), Bacillus cereus DGX2(OQ690675), Bacillus sp. DGX3(OQ690700) and Escherichia coli DGX4(OQ690701). Bacillus cereus was found to have high oviposition attractant properties in oviposition assays. Bacillus cereus was also obtained from the midgut of third instar larvae indicating that they had entered from the surrounding medium and colonized the larval gut. Subsequent tests exhibited the roles of B. cereus in larval development. Numerous plant products have been reported either as insecticides for killing larvae or adult mosquitoes or as repellents for mosquito biting and the best alternatives for mosquito control. Larvicidal potential of emulsified neem oil formulation against the field collected 3rd instar larvae of Culex quinquefasciatus mosquito under laboratory conditions was also evaluated. The information thus obtained can be pooled to generate larval source markers and larval source management practices by altering their habitats that cannot be removed. Furthermore, the time of implementation of these strategies can also be planned.

Chemical compositions, antioxidant, antimicrobial, and mosquito larvicidal activity of Ocimum americanum L. and Ocimum basilicum L. leaf essential oils

BACKGROUND

Ocimum americanum L. (O. americanum) and Ocimum basilicum L. (O. basilicum) are highly valued aromatic medicinal plants. Their leaves are widely used as spices in traditional cuisine. Their essential oils (EOs) are extensively used in food, cosmetic, and pharmaceutical industries. This study aimed to investigate the main chemical profiles of O. americanum and O. basilicum leaf EOs and assess their effects on antibacterial, antioxidant, and larvicidal properties.

METHODS

EOs were extracted from the leaves of O. basilicum and O. americanum using steam distillation in a Clevenger-type apparatus. The chemical constituents of the EOs were analyzed using gas chromatography-mass spectrometry. 2,2-Diphenyl-1-picrylhydrazyl (DPPH), ferric reducing antioxidant power (FRAP), and metal-chelating techniques were used to assess the free-radical scavenging capability of the oils. The extracted oils were also tested for their antibacterial activities via a disk-diffusion test and the broth microdilution method. Furthermore, the mosquito larvicidal (Aedes aegypti) activity was tested using standard protocols.

RESULTS

Camphor (33.869%), limonene (7.215%), longifolene (6.727%), caryophyllene (5.500%), and isoledene (5.472%) were the major compounds in O. americanum leaf EO. The EO yield was 0.4%, and citral (19.557%), estragole (18.582%) camphor (9.224%) and caryophyllene (3.009%) were the major compounds found among the 37 chemical constituents identified in O. basilicum oil. O. basilicum exhibited a more potent antioxidant activity in DPPH, FRAP, and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid tests than O. americanum. The zones of inhibition and minimum inhibitory concentration of the oils in the microdilution and disk diffusion methods were 8.00 ± 0.19 mm to 26.43 ± 2.19 mm and 3.12-100 µg/mL, respectively. At 400 ppm, O. basilicum and O. americanum EOs demonstrated larvicidal activity, with mortality ratios of 73.60% ± 0.89% and 78.00% ± 1.00%, respectively. Furthermore, after 30 min of exposure to O. americanum and O. basilicum EOs, the larval death rates were 73.60% ± 0.89% and 78.00% ± 1.00%, respectively.

CONCLUSIONS

The findings revealed that the EOs extracted from the leaves of O. basilicum and O. americanum exhibited reasonable antioxidant, antibacterial, and mosquito larvicidal potentials, and can be used as alternative medicine for the treatment of human health and larvicidal mosquito control.

Oviposition Preferences of Aedes aegypti in Msambweni, Kwale County, Kenya

Aedes aegypti is the primary vector of dengue fever virus (DENV) worldwide. Infusions made from organic materials have been shown to act as oviposition attractants for Ae. aegypti; however, studies on locally suitable infusion materials are lacking. The current study assessed the suitability of 4 locally available materials as oviposition infusions for use in surveillance and control of Ae. aegypti in Kwale County, Kenya. Oviposition infusion preferences were assessed in laboratory, semifield, and field conditions, using 4 infusions made from banana, grass, neem, and coconut. In addition, ovitrapping in wall, grass, bush, and banana microhabitats was done in 10 houses each in urban and rural coastal households to determine suitable oviposition microhabitats. Overall, the highest oviposition responses were observed for banana infusion, followed by neem and grass infusions, which were comparable. Coconut infusion resulted in the lowest oviposition response. Although female Ae. aegypti did not show preference for any microhabitat, the oviposition activity across all the microhabitats was highly enhanced by use of the organic infusions. Banana, neem, and grass infusions could be used to attract gravid mosquitoes to oviposition sites laced with insecticide to kill eggs. Additionally, banana plantings could be important targets for integrated vector control programs.

Larvicidal Activities of Allium sativum L. and Zingiber officinale Rosc. Extracts against Filariasis Vectors in Hadiya Zone, Ethiopia

Mosquitoes present an immense threat to millions of people worldwide and act as vectors for filariasis disease. The objective of the study was to determine the effect of Allium sativum and Zingiber officinale extracts against filariasis vectors. The larvae were collected from the breeding site by using standard procedures for identification and larvicidal activities. Twenty grams (20 g) from each (Allium sativum and Zingiber officinale) were extracted separately by aqueous, ethanol, and methanol solvents. The phytochemical analysis was determined in the crude sample by using standard methods. Then, larvicidal effects were determined by introducing 10 larvae of the vectors to the concentrations of 250 ppm, 500 ppm, and 750 ppm of the crude sample, and data were subjected to probit analysis to determine the LC50 and Chi-squared test to check the significance of the mortality by R software. Anopheles funestus, Anopheles gambiae s.l., Anopheles pharoensis, Culex antennatus, and Culex quinquefasciatus were the filariasis vectors identified during the study period. The presence of phytochemical tests such as anthraquinones, flavonoids, glycosides, phenol, saponin, steroids, tannin, and terpenes was obtained. The larvicidal effects of the selected plant extracts ranged from 0%-100%. The lowest LC50 (53 ppm) was observed for A. sativum methanol test extract against Cx. quinquefasciatus. Ethanol extracts of A. sativum have a significant effect on An. funestus (X2 = 7.5, p = 0.02352) and Cx. quinquefasciatus (X2 = 10.833, p = 0.0.0044), whereas aqueous extracts have a significant effect only on An. gambiae s.l. (X2 = 7.0807, p = 0.029. Ethanol extracts of Z. officinale have a significant effect only on the mortality of An. pharoensis (X2 = 7.0807, p = 0.029), but methanol and aqueous extracts have no significant effect against filariasis vectors. In conclusion, A. sativum have a high toxic effect than Z. officinale extract against filariasis vectors in all type of solvents. So using those plant extracts is the best to reduce the risk of the synthetic chemical on nontarget organisms and the environment, in addition to the control of mosquito-borne diseases, but further studies will be conducted to evaluate the toxicity at different stages of the vectors.

Neem-based products as potential eco-friendly mosquito control agents over conventional eco-toxic chemical pesticides-A review

Mosquitoes cause serious health hazards for millions of people across the globe by acting as vectors of deadly communicable diseases like malaria, filariasis, dengue and yellow fever. Use of conventional chemical insecticides to control mosquito vectors has led to the development of biological resistance in them along with adverse environmental consequences. In this light, the recent years have witnessed enormous efforts of researchers to develop eco-friendly and cost-effective alternatives with special emphasis on plant-derived mosquitocidal compounds. Neem oil, derived from neem seeds (Azadirachta indica A. Juss, Meliaceae), has been proved to be an excellent candidate against a wide range of vectors of medical and veterinary importance including mosquitoes. It is environment-friendly, and target-specific at the same time. The active ingredients of neem oil include limonoids like azadirachtin A, nimbin, salannin and numerous other substances that are still waiting to be discovered. Of these, azadirachtin has been shown to be very effective and is mainly responsible for its toxic effects. The quality of the neem oil depends on its azadirachtin content which, in turn, depends on its manufacturing process. Neem oil can be used directly or as nanoemulsions or nanoparticles or even in the form of effervescent tablets. When added to natural breeding habitat waters they exert their mosquitocidal effects by acting as ovicides, larvicides, pupicides and/or oviposition repellents. The effects are generated by impairing the physiological pathways of the immature stages of mosquitoes or directly by causing physical deformities that impede their development. Neem oil when used directly has certain disadvantages mainly related to its disintegration under atmospheric conditions rendering it ineffective. However, many of its formulations have been reported to remain stable under environmental conditions retaining its efficiency for a long time. Similarly, neem seed cake has also been found to be effective against the mosquito vectors. The greatest advantage is that the target species do not develop resistance against neem-based products mainly because of the innumerable number of chemicals present in neem and their combinations. This makes neem-based products highly potential yet unexplored candidates of mosquito control agents. The current review helps to elucidate the roles of neem oil and its various derivatives on mosquito vectors of public health concern.

LC-MS Analysis, Computational Investigation, and Antimalarial Studies of Azadirachta indica Fruit

Malaria is a deadly disease that continues to pose a threat to children and maternal well-being. This study was designed to identify the chemical constituents in the ethanolic fruit extract of Azadirachta indica, elucidate the pharmacological potentials of identified phytochemicals through the density functional theory method and carry out the antimalarial activity of extract using chemosuppression and curative models. The liquid chromatography-mass spectrometry (LC-MS) analysis of the ethanolic extract was carried out, followed by the density functional theory studies of the identified phytochemicals using B3LYP and 6-31G (d, p) basis set. The antimalarial assays were performed using the chemosuppression (4 days) and curative models. The LC-MS fingerprint of the extract led to the identification of desacetylnimbinolide, nimbidiol, O-methylazadironolide, nimbidic acid, and desfurano-6α-hydroxyazadiradione. Also, the frontier molecular orbital properties, molecular electrostatic potential, and dipole moment studies revealed the identified phytochemicals as possible antimalarial agents. The ethanolic extract of A indica fruit gave 83% suppression at 800 mg/kg, while 84% parasitaemia clearance was obtained in the curative study. The study provided information about the phytochemicals and background pharmacological evidences of the antimalarial ethnomedicinal claim of A indica fruit. Thus, isolation and structure elucidation of the identified phytochemicals from the active ethanolic extract and extensive antimalarial studies towards the discovery of new therapeutic agents is recommended for further studies.

Combination of GC-MS Molecular Networking and Larvicidal Effect against Aedes aegypti for the Discovery of Bioactive Substances in Commercial Essential Oils

Dengue is a neglected disease, present mainly in tropical countries, with more than 5.2 million cases reported in 2019. Vector control remains the most effective protective measure against dengue and other arboviruses. Synthetic insecticides based on organophosphates, pyrethroids, carbamates, neonicotinoids and oxadiazines are unattractive due to their high degree of toxicity to humans, animals and the environment. Conversely, natural-product-based larvicides/insecticides, such as essential oils, present high efficiency, low environmental toxicity and can be easily scaled up for industrial processes. However, essential oils are highly complex and require modern analytical and computational approaches to streamline the identification of bioactive substances. This study combined the GC-MS spectral similarity network approach with larvicidal assays as a new strategy for the discovery of potential bioactive substances in complex biological samples, enabling the systematic and simultaneous annotation of substances in 20 essential oils through LC50 larvicidal assays. This strategy allowed rapid intuitive discovery of distribution patterns between families and metabolic classes in clusters, and the prediction of larvicidal properties of acyclic monoterpene derivatives, including citral, neral, citronellal and citronellol, and their acetate forms (LC50 < 50 µg/mL).

Mosquitoes Larvicidal Activity of Ocimum kilimandscharicum Oil Formulation under Laboratory and Field-Simulated Conditions

Simple Summary

Mosquitoes are vectors of many severe diseases, notably malaria, yellow as well as dengue fever, and lymphatic filariasis. Vector control with synthetic chemical insecticides has been associated with resistance development and undesirable human and ecological effects. Ocimum kilimandscharicum oil formulation was evaluated for larvicidal activity against third instar mosquito larvae in the laboratory. The formulation was then compared with Bacillus thuringiensis subsp. israelensis (Bti) granules on An. gambiae larvae under field-simulated field trials. The LC₅₀ for O. kilimandscharicum oil after 24 h against third instar larvae of An. gambiae was 0.74 ppm while for the emulsified O. kilimandscharicum oil formulation against third instar larvae of An. gambiae and An. arabiensis was 0.07 and 0.31 ppm, respectively. The high bioactivity and sublethal toxic effects to offspring of treated mosquito larvae in terms of the disruption of larval morphological aspects suggest its high potential as a botanical larvicide for the control of disease vectors. The bioactive formulation had the advantage of high solubility in aqueous media; it is also easily produced, ecofriendly, and low-cost. Moreover, because O. kilimandscharicum can easily be widely cultivated and has high EO yields, it may provide a valuable alternative for the effective and eco-friendly control of disease vectors among developing and developed communities.

Abstract

Mosquitoes are vectors of many severe diseases, including malaria, yellow as well as dengue fever, and lymphatic filariasis. The use of synthetic chemical insecticides for mosquito control has been associated with resistance development and detrimental human, and ecological effects. For a safer alternative, the emulsified Ocimum kilimandscharicum oil formulation was evaluated for its larvicidal activity. The oil was analyzed by GC and GC/MS. The formulations were evaluated against third instar mosquito larvae in the laboratory and later compared with Bacillus thuringiensis subsp. israelensis against An. gambiae under field-simulated conditions. Thirty-nine compounds were identified in the oil, the main ones being D-camphor (36.6%) and limonene (18.6%). The formulation showed significant larval mortalities against An. gambiae and An. arabiensis larvae with LC₅₀ of 0.07 and 0.31 ppm, respectively, at 24 h. Under the field-simulated trial, within 24 h, the formulation showed 98% mortality while Bti had achieved 54%. On day three, it caused 100% mortality while Bti achieved 76.5%. The high bioactivity and sublethal toxic effects to offspring of treated mosquito larvae, in terms of disruption of larval morphological aspects, suggest the high potential of the formulation as a botanical larvicide. The formulation, thus, may provide a valuable alternative for the effective and eco-friendly control of disease vectors.

Plant-Based Bioinsecticides for Mosquito Control: Impact on Insecticide Resistance and Disease Transmission

Simple Summary

Mosquito-borne diseases cause millions of deaths each year. There has been an increase in the use of insecticides to combat disease transmission caused by mosquitoes. Synthetic insecticides have been effectively used to protect humans from mosquito bites through insecticide-treated mosquito nets, fabrics, and indoor sprays. Despite the considerable progress made in reducing mosquito borne diseases, extensive usage of insecticides has caused serious health problems to humans and animals, insecticide resistance or insensitivity in mosquitoes, and environmental damage. A success in the fight with mosquito disease transmission can only be accomplished by adequate and effective implementation of insecticide resistance monitoring and management programs globally. For this purpose, extensive research focuses on exploring insecticide resistance mechanisms in mosquitoes and how they get resistant to chemical applications over time. The search also focuses on novel compounds that are more effective, safer, and eco-friendly for improved management of mosquito vectors. In this review, we provide the current literature on the synthetic insecticides and how mosquitoes develop resistance to them, with further emphasis on bioinsecticides that could replace conventional synthetic insecticides. In this context, plant-based compounds are explained in detail with their potential applications to control mosquitoes.

Abstract

The use of synthetic insecticides has been a solution to reduce mosquito-borne disease transmission for decades. Currently, no single intervention is sufficient to reduce the global disease burden caused by mosquitoes. Problems associated with extensive usage of synthetic compounds have increased substantially which makes mosquito-borne disease elimination and prevention more difficult over the years. Thus, it is crucial that much safer and effective mosquito control strategies are developed. Natural compounds from plants have been efficiently used to fight insect pests for a long time. Plant-based bioinsecticides are now considered a much safer and less toxic alternative to synthetic compounds. Here, we discuss candidate plant-based compounds that show larvicidal, adulticidal, and repellent properties. Our discussion also includes their mode of action and potential impact in mosquito disease transmission and circumvention of resistance. This review improves our knowledge on plant-based bioinsecticides and the potential for the development of state-of-the-art mosquito control strategies.

Screening and testing potential inhibitors of sulphide gas production by sulphate-reducing bacteria

Sulphate-reducing bacteria are commonly associated with biological causes of oil well souring. Biosulphetogenesis can directly affect oil quality and storage due to the accumulation of sulphides. In addition, these microorganisms can create bio-incrustation that can clog pipes. Sulphite reductase (SIR) is the enzyme responsible for converting ion sulphite into sulphide and several substances may interfere or control such activity. This interference can hinder growth of the sulphate-reducing bacteria and, consequently, it reduces sulphide accumulation in situ. This work focuses on molecular modelling techniques along with in vitro experiments in order to investigate the potential of two essential oils and one vegetable oil as main inhibitors of sulphite reductase activity. Docking simulation identified several substances present in Rosmarinus officinalis, Tea tree and Neem extractable oils as potential inhibitors of SIR. Substances present in Neem vegetable oil are the most potent inhibitors, followed by Rosmarinus officinalis and Tea tree essential oils. The Neem oil mixture showed a superior effectiveness in intracellular SIR inhibitory effects.

Harnessing the Phytotherapeutic Treasure Troves of the Ancient Medicinal Plant Azadirachta indica (Neem) and Associated Endophytic Microorganisms

Azadirachta indica, commonly known as neem, is an evergreen tree of the tropics and sub-tropics native to the Indian subcontinent with demonstrated ethnomedicinal value and importance in agriculture as well as in the pharmaceutical industry. This ancient medicinal tree, often called the "wonder tree", is regarded as a chemical factory of diverse and complex compounds with a plethora of structural scaffolds that is very difficult to mimic by chemical synthesis. Such multifaceted chemical diversity leads to a fantastic repertoire of functional traits, encompassing a wide variety of biological activity and unique modes of action against specific and generalist pathogens and pests. Until now, more than 400 compounds have been isolated from different parts of neem including important bioactive secondary metabolites such as azadirachtin, nimbidin, nimbin, nimbolide, gedunin, and many more. In addition to its insecticidal property, the plant is also known for antimicrobial, antimalarial, antiviral, anti-inflammatory, analgesic, antipyretic, hypoglycaemic, antiulcer, antifertility, anticarcinogenic, hepatoprotective, antioxidant, anxiolytic, molluscicidal, acaricidal, and antifilarial properties. Notwithstanding the chemical and biological virtuosity of neem, it has also been extensively explored for associated microorganisms, especially a class of mutualists called endophytic microorganisms (or endophytes). More than 30 compounds, including neem "mimetic" compounds, have been reported from endophytes harbored in the neem trees in different ecological niches. In this review, we provide an informative and in-depth overview of the topic that can serve as a point of reference for an understanding of the functions and applications of a medicinal plant such as neem, including associated endophytes, within the overall theme of phytopathology. Our review further exemplifies the already-noted current surge of interest in plant and microbial natural products for implications both within the ecological and clinical settings, for a more secure and sustainable future.

Repellency and larvicidal activities of Azadirachta indica seed oil on Anopheles gambiae in Nigeria

Despite the recent decline in the global prevalence of malaria, the disease continues to be one of the major causes of morbidity and mortality among pregnant women and under-five children in Nigeria. The adoption of an integrated approach to malaria control including the use of bio-insecticide will further reduce the burden of malaria. This study determined the repellency and bio-insecticidal effects of Azadirachta indica oil on Anopheles gambiae in Ibadan, Nigeria. The study was experimental in design. Oil was extracted from the ground seed kernel of Azadirachta indica plants using N-hexane as a solvent. Larvicidal tests were carried out on 600 third and fourth instar stages of Anopheles gambiae using an aliquot of extracted oil emulsified with a surfactant (Tween 80) at concentrations ranging from 100 to 500 ppm. Mortality was recorded every 24 h for five days. Repellency tests were carried out by exposing Guinea pigs that were previously treated with the oil mixed with paraffin at 10–40%v/v concentrations, to 70 adult female Anopheles gambiae in netted cages. Data were analysed using descriptive statistics and ANOVA. The oil yield accounted for 40.0% weight of the ground seed kernel. The larvicidal effect was significant across the concentration of the emulsified Azadirachta oil ranging from 91.6-100.0%, compared to the control experiment ranging from 5-15% (LC50 and LC90: -1666.86 ppm and -2880.94 ppm respectively). A 100.0% larval mortality of Anopheles gambiae was recorded within three days at 500 ppm. All the concentrations of the oil solution also caused 100% inhibition of pupae formation. The repellent effect of adult Anopheles was significant (p < 0.05) across the concentrations but with varying degrees of protection. The highest repellent effect was observed at 40.0% (v/v). The possibility of using Azadirachta indica as bio-insecticide against Anopheles gambiae was established in this study.

The Mosquito Larvicidal Activity of Essential Oils from Cymbopogon and Eucalyptus Species in Vietnam

The larvicidal activity of essential oils (EOs) extracted from Cymbopogon citratus, Cymbopogon winterianus, Eucalyptus citriodora, and Eucalyptus camaldulensis aromatic plants grown in Vietnam was evaluated on Aedes aegypti larvae. The EOs were hydro-distilled in a Clevenger-type apparatus. The EOs were analyzed by gas chromatography–mass spectrometry (GC–MS). The mortality rates obtained from the bioassays were used to calculate the lethal concentrations (LC₅₀) of the EOs by the probit analysis method. These essential oils exhibited toxicity to the larvae of Aedes aegypti. Results were obtained for Cymbopogon citratus (LC₅₀ = 120.6 ppm), Cymbopogon winterianus (LC₅₀ = 38.8 ppm), Eucalyptus citriodora (LC₅₀ = 104.4 ppm), and Eucalyptus camaldulensis (LC₅₀ = 33.7 ppm). The essential oils of Eucalyptus camaldulensis and Cymbopogon winterianus were found to be the most efficient, and their respective values of LC₅₀ were 33.7 ppm, 38.8 ppm. In conclusion, this research adds to the growing body of literature on natural larvicides from essential oils against Aedes aegypti mosquitoes.

Neem oil increases the persistence of the entomopathogenic fungus Metarhizium anisopliae for the control of Aedes aegypti (Diptera: Culicidae) larvae

Background

The entomopathogenic fungus Metarhizium anisopliae is a candidate for the integrated management of the disease vector mosquito Aedes aegypti. Metarhizium anisopliae is pathogenic and virulent against Ae. aegypti larvae; however, its half-life is short without employing adjuvants. Here, we investigated the use of neem oil to increase virulence and persistence of the fungus under laboratory and simulated field conditions.

Methods

Neem was mixed with M. anisopliae and added to recipients. Larvae were then placed in recipients at 5-day intervals for up to 50 days. Survival rates were evaluated 7 days after exposing larvae to each treatment. The effect of neem on conidial germination following exposure to ultraviolet radiation was evaluated under laboratory conditions. Statistical tests were carried out using ANOVA and regression analysis.

Results

Laboratory bioassays showed that the fungus alone reduced survival to 30% when larvae were exposed to the treatment as soon as the suspension had been prepared (time zero). A mixture of fungus + neem resulted in 11% survival at time zero. The combination of fungus + neem significantly reduced larval survival rates even when suspensions had been maintained for up to 45 days before adding larvae. For simulated-field experiments 1% neem was used, even though this concentration is insecticidal, resulting in 20% survival at time zero. However, this toxic effect was reduced over time. When used alone under simulated-field conditions the fungus rapidly lost virulence. The formulation fungus + neem effectively maintained fungal virulence, with larval survival rates significantly reduced for up to 45 days after preparation of the suspensions. The effective half-life of the fungus or neem when used separately was 6 and 13 days, respectively. The half-life of fungus formulated in 1% neem was 34 days. Conidia suspended in neem maintained high levels of germination even following a 2-h exposure to ultraviolet radiation.

Conclusions

A combination of the entomopathogenic fungus M. anisopliae with neem oil effectively increases the half-life and virulence of the fungus when tested against Ae. aegypti larvae, even under simulated field conditions. Neem oil also protected the fungus from the damaging effects of ultraviolet radiation.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3415-x) contains supplementary material, which is available to authorized users.

Adenosine Triphosphate-Binding Cassette Transporters Are Not Involved In the Detoxification of Azadirachta indica Extracts In Anopheles stephensi Larvae

Detoxifying pathways of mosquitoes against the neem (Azadirachta indica) extracts are still unclear. The aim of the present study was to investigate the role of adenosine triphosphate-binding cassette (ABC) transporters in this process in Anopheles stephensi, one of the main malaria vectors in southern Asia. Third-stage larvae of An. stephensi were fed with fish food alone or in combination with neem extract at 0.5%, 1%, 5%, and 10%. Six ABC-transporter genes from 3 different subfamilies (B, C, and G) were analyzed to assess their relative expression compared with controls. A bioassay was also performed to assess larval mortality rate at different concentrations and in combination with verapamil, an ABC-transporter inhibitor. No significant variation in the expression levels of any transporter belonging to the B, C, and G subfamilies was detected. Furthermore, the use of verapamil did not induce an increase in mortality at any of the tested neem extract concentrations, indicating that ABC transporters are not involved in the detoxification of neem extracts in An. stephensi larvae.

The prevalence of Gasterophilus intestinalis (Diptera: Oestridae) in donkeys (Equus asinus) in Egypt with special reference to larvicidal effects of neem seed oil extract (Azadirachta indica) on third stage larvae

Gasterophiline larvae are of veterinary and medical importance caused specific equine intestinal myiasis. Gasterophilus intestinalis (Botfly larvae) had a wide geographical distribution. The present study explores the prevalence rate of G. intestinalis 3^rd stage larvae in Egypt from January- December 2017; besides, in vitro trials to control of this larvae and evaluation of this trial using Scanning Electron Microscope (SEM) and histopathology of treated larvae. In the present study, the 3^rd larval stage of G. intestinalis was found in clusters in the epithelium of the investigated stomach and infested with prevalence rate 97.2%. The highest collected numbers of larvae were found in two months; March and August (570 & 520 larvae) and lowest numbers (200 larvae) were collected in October, November, and December. The calculated LC₅₀ and LC₉₀ values of neem seed extract were 707.9 ppm and 1090.7 ppm. The different alteration was recorded after exposure to oil extract which showed some destruction on cuticle surface as folded and corrugated cuticle, destruction of maxillae with pits on its surface, disfigure and irregularity of cephalic spines. Histopathology of exposed G. intestinalis larvae showed different changes as thinning of cuticle at the different level (exocuticle, endocuticle, cell layers), degeneration of epithelial cells of the gut and different degree of necrosis was described. Life cycle of G.intestinalis was followed up after treatment with neem seed extract.

Insecticidal Effect of Solenostemma argel Extracts Against Culex pipiens

Of the various plant extracts from 10 plant species tested against larvae of Culex pipiens in the laboratory, only extracts from Solenostemma argel exhibited larvicidal activity. A chloroform leaf extract of S. argel exhibited relatively high activity with a lethal concentration causing 50% mortality (LC₅₀) of 15.89 ppm, while chloroform and ethyl acetate extracts of S. argel fruits were 19.70 and 19.52 ppm, respectively. The chloroform fruit extract at 10 ppm reduced the hatchability of Cx. pipiens eggs by 20%, whereas the chloroform leaf extract was found to be less effective (5% reduction). At 10 ppm, adult emergence was reduced by 84% and 75% for chloroform and ethyl acetate extracts of fruits, respectively. Metamorphosis of larvae exposed to chloroform fruit extract (10 ppm) was extended to 15 days, as compared to 10 days for control larvae. It took 12 days at 1 ppm, and 15 days at 6 and 10 ppm for chloroform fruit extract-treated embryos to develop into adult mosquito while it took 10 days in the control treatment. However, 100% toxicity was observed in the embryos of zebrafish, Danio rerio, treated with the ethyl acetate fruit extracts (LC₅₀ of 20 ppm and LC₁₀₀ of 40 ppm) and chloroform leaf extract (LC₅₀ of 30 ppm and LC₁₀₀ of 60 ppm). These findings emphasize the need to further isolate the bioactive molecules in S. argel crude extracts that may still be mosquitocidal but produce no, or minimal, adverse effects on nontarget organisms such as zebrafish.

A Small-Scale Investigation Into the Effect of A Larvicidal Oil On Oviposition Site Preference By Aedes aegypti

Larvicidal oils can be used to control immature Aedes aegypti and other pestiferous mosquitoes. To test whether oil-based larvicides also act as oviposition deterrents, indoor and semi-field trials were conducted at the Navy Entomology Center of Excellence in Jacksonville, FL. In both studies, treatment cages consisted of oviposition cups lined with seed germination paper as an oviposition substrate and filled with 1-wk-old southern live oak ( Quercus virginiana) leaf litter-infused water. Treatment cages consisted of 2 cups treated with CocoBear™ Mosquito Larvicidal Oil, while 2 cups were untreated. Control cages contained oviposition cups with only oak leaf litter-infused water. Gravid Ae. aegypti were released into cages and allowed to oviposit for 24 h, after which eggs were counted. The number of eggs deposited in treatment and control cages was not significantly different (indoor P = 0.0865; outdoor P = 0.9765). However, the number of eggs deposited in untreated cups was significantly greater than that deposited in treated cups within treatment cages (indoor P < 0.0001; outdoor P = 0.0050). These results suggest that the presence of the larvicidal oil CocoBear may cause gravid female Ae. aegypti to seek alternative oviposition sites.

Mosquito larvicidal activity of Cassia tora seed extract and its key anthraquinones aurantio-obtusin and obtusin

Background

The edible and medicinal leguminous plant Cassia tora L. (Fabaceae) is known to possess insecticidal properties against a wide range of plant-feeding insects. However, the bioactivity of extracts of this plant and their constituents against vectors of medical importance has been largely unexplored. We investigated the mosquito larvicidal activity of the seed extract and its major anthraquinones against larvae of the African malaria vector Anopheles gambiae (s.s.).

Methods

Third-fourth instar larval mortality was observed after 24, 48, 72 and 96 h of exposure to varying doses of the extracts, and two anthraquinones isolates identified using liquid chromatography- quadrupole time of flight mass spectrometry (LC-QtoF-MS). The mosquito larval mortality was evaluated relative to the natural insecticide azadirachtin.

Results

Fractionation of the crude extract decreased mosquito larvicidal activity, however, larvicidal activity increased with increasing dose of the treatment and exposure time. The known anthraquinones aurantio-obtusin and obtusin were identified as key larvicidal compounds. Aurantio-obtusin and obtusin, exhibited similar toxicity to larvae of A. gambiae (s.s.) with LD₅₀ values of 10 and 10.2 ppm, respectively. However, the two anthraquinones were four- and ~ six-fold less potent than that of the crude seed extract and azadirachtin, which had comparable LD₅₀ values of 2.5 and 1.7 ppm, respectively.

Conclusion

Both aurantio-obtusin and obtusin showed mosquito larvicidal activity which were comparable to their respective fractions although they were less potent relative to the crude extract and azadirachtin. Further studies need to be conducted on C. tora for its exploitation as a potential eco-friendly tool in mosquito larval source reduction.

Evaluation of Larvicidal Activity of Essential Oil from Leaves of Coccinia grandis against Three Mosquito Species

BACKGROUND

To study the chemical constituents and larvicidal activity of essential oil extracted from the leaves of Coccinia grandis against three mosquito species.

METHODS

Essential oil was extracted by hydro distillation using clevenger apparatus and was analyzed for chemical constituents by gas chromatography-mass spectrophotometry (GC-MS). Larvicidal activity was recorded after 12 and 24h of post-exposure against three mosquito species, Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus. Dead larvae were identified when they failed to move after probing with a needle in the siphon or cervical region. The LC₅₀ and LC₉₀ values for three mosquito larvae were calculated by Probit analysis.

RESULTS

The GC-MS analysis revealed that essential oil contains 23 different constituents. Out of these 23 constituents, major constituents identified were n-tetracosane (39.18%), n-eicosane (30.04%), tetratriacotane (2.97%), 7-octadecanal (2.81%), and tricosane (2.31%). Essential oil from leaves of Coccinia grandis exhibited significant larvicidal activity against An. stephensi with LC₅₀ and LC₉₀ values 39.41ppm and 123.24ppm, respectively. This was followed by Ae. aegypti and Cx. quinquefasciatus with LC₅₀ and LC₉₀ values of 48.20ppm, 131.84ppm and 52.80ppm, 135.48ppm, respectively after 24h of exposure.

CONCLUSION

The results could be useful in developing a cost effective, ecofriendly, region specific and practical strategy for the control of mosquito vectors.

Bluetongue outbreaks: Looking for effective control strategies against Culicoides vectors

Several arthropod-borne diseases are now rising with increasing impact and risks for public health, due to environmental changes and resistance to pesticides currently marketed. In addition to community surveillance programs and a careful management of herds, a next-generation of effective products is urgently needed to control the spread of these diseases, with special reference to arboviral ones. Natural product research can afford alternative solutions. Recently, a re-emerging of bluetongue disease is ongoing in Italy. Bluetongue is a viral disease that affects ruminants and is spread through the bite of bloodsucking insects, especially Culicoides species. In this review, we focused on the importance of vector control programs for prevention or bluetongue outbreaks, outlining the lack of effective tools in the fight against Culicoides vectors. Then, we analyzed a field case study in Sardinia (Italy) concerning the utilization of the neem cake (Azadirachta indica), to control young instar populations of Culicoides biting midges, the vectors of bluetongue virus. Neem cake is a cheap and eco-friendly by-product obtained from the extraction of neem oil. Overall, we propose that the employ of neem extraction by-products as aqueous formulations in muddy sites close to livestock grazing areas may represent an effective tool in the fight against the spread of bluetongue virus in the Mediterranean areas.

Progress on Azadirachta indica Based Biopesticides in Replacing Synthetic Toxic Pesticides

Over the years, extensive use of commercially available synthetic pesticides against phytophagous insects has led to their bioaccumulation in the environment causing increased resistance and reduction in soil biodiversity. Further, 90% of the applied pesticides enter the various environmental resources as a result of run-off, exposing the farmers as well as consumers of the agricultural produce to severe health issues. Therefore, growing attention has been given toward the development of alternate environmentally friendly pesticides/insecticides that would aid an efficient pest management system and also prevent chronic exposures leading to diseases. One such strategy is, the use of neem plant's (Binomial name: Azadirachta indica) active ingredients which exhibit agro-medicinal properties conferring insecticidal as well as immunomodulatory and anti-cancer properties. The most prominent constituent of neem is azadirachtin, which has been established as a pivotal insecticidal ingredient. It acts as an antifeedant, repellent, and repugnant agent and induces sterility in insects by preventing oviposition and interrupting sperm production in males. This review discusses, key neem pesticidal components, their active functional ingredients along with recent strategies on employing nanocarriers, to provide controlled release of the active ingredients and to improve their stability and sustainability.

Neemazal ® as a possible alternative control tool for malaria and African trypanosomiasis?

BACKGROUND

Research efforts to identify possible alternative control tools for malaria and African trypanosomiasis are needed. One promising approach relies on the use of traditional plant remedies with insecticidal activities.

METHODS

In this study, we assessed the effect of blood treated with different doses of NeemAzal ® (NA, neem seed extract) on mosquitoes (Anopheles coluzzii) and tsetse flies (Glossina palpalis gambiensis) (i) avidity to feed on the treated blood, (ii) longevity, and (iii) behavioural responses to human and calf odours in dual-choice tests. We also gauged NeemAzal ® toxicity in mice.

RESULTS

In An. coluzzii, the ingestion of NA in bloodmeals offered by membrane feeding resulted in (i) primary antifeedancy; (ii) decreased longevity; and (iii) reduced response to host odours. In G. palpalis gambiensis, NA caused (i) a knock-down effect; (ii) decreased or increased longevity depending on the dose; and (iii) reduced response to host stimuli. In both cases, NA did not affect the anthropophilic rate of activated insects. Overall, the most significant effects were observed with NA treated bloodmeals at a dose of 2000 μg/ml for mosquitoes and 50 μg/ml for tsetse flies. Although no mortality in mice was observed after 14 days of follow-up at oral doses of 3.8, 5.6, 8.4 and 12.7 g/kg, behavioural alterations were noticed at doses above 8 g/kg.

CONCLUSION

This study revealed promising activity of NA on A. coluzzii and G. palpalis gambiensis but additional research is needed to assess field efficacy of neem products to be possibly integrated in vector control programmes.

In vivo and in vitro effectiveness of Azadirachta indica-synthesized silver nanocrystals against Plasmodium berghei and Plasmodium falciparum, and their potential against malaria mosquitoes

Malaria transmission is a serious emergence in urban and semiurban areas worldwide, becoming a major international public health concern. Malaria is transmitted through the bites of Anopheles mosquitoes. The extensive employ of synthetic pesticides leads to negative effects on human health and the environment. Recently, plant-synthesized nanoparticles have been proposed as highly effective mosquitocides. In this research, we synthesized silver nanoparticles (AgNP) using the Azadirachta indica seed kernel extract as reducing and stabilizing agent. AgNP were characterized by UV-vis spectrophotometry, SEM, EDX, XRD and FTIR spectroscopy. The A. indica seed kernel extract was toxic against Anopheles stephensi larvae and pupae, LC50 were 232.8ppm (larva I), 260.6ppm (II), 290.3ppm (III), 323.4ppm (IV), and 348.4ppm (pupa). AgNP LC50 were 3.9ppm (I), 4.9ppm (II), 5.6ppm (III), 6.5ppm (IV), and 8.2ppm (pupa). The antiplasmodial activity of A. indica seed kernel extract and AgNP was evaluated against CQ-resistant (CQ-r) and CQ-sensitive (CQ-s) strains of Plasmodium falciparum. IC50 of A. indica seed kernel extract were 63.18μg/ml (CQ-s) and 69.24μg/ml (CQ-r). A. indica seed kernel-synthesized AgNP achieved IC50, of 82.41μg/ml (CQ-s) and 86.12μg/ml (CQ-r). However, in vivo anti-plasmodial experiments conducted on Plasmodium berghei infecting albino mice showed moderate activity of the A. indica extract and AgNP. Overall, this study showed that the A. indica-mediated fabrication of AgNP is of interest for a wide array of purposes, ranging from IPM of mosquito vectors to the development of novel and cheap antimalarial drugs.

Screening of Methanolic Plant Extracts against Larvae of Aedes aegypti and Anopheles stephensi in Mysore

BACKGROUND

Mosquitoes transmit serious human diseases, causing millions of death every year. Vector control is facing a threat due to the emergence of resistance to synthetic insecticides. Insecticides of botanical origin may serve as suitable alternative biocontrol techniques in the future. Nine different locally available medicinally important plants suspected to posse larvicidal property were screened against fourth instar larvae of Aedes aegypti and Anopheles stephensi to a series of concentrations of the methanolic extracts.

METHODS

Susceptibility tests on Ae. aegypti and An. stephensi were conducted using standard WHO methods. The larvae of two mosquito species were exposed to methanolic extracts and mortality counts were made after 24 hours of exposure as per WHO method. Larvae of Ae. aegypti were more susceptible than that of An. stephensi.

RESULTS

Among the nine plant species tested, Annona reticulata leaf extract was more effective against Ae. aegypti larvae with LC50 and LC90 values of 95.24 and 262.64 ppm respectively and against An. stephensi larvae 262.71 and 636.94 ppm respectively. The least efficacy was in Cosmos bipinnatus with LC50 and LC90 values of 442.6 and 1225.93 ppm against Ae. aegypti and LC50 and LC90 values of 840.69 and 1334.01 ppm of Thespesia populnea against An. stephensi.

CONCLUSION

The crude methanolic extract of the An. reticulata with good larvicidal efficacy could be considered for further characterization to control mosquito vectors instead of chemical insecticides. High efficacy found in An. reticulata extract will be considered for further studies to isolate the bioactive compound.

Neem oil increases the efficiency of the entomopathogenic fungus Metarhizium anisopliae for the control of Aedes aegypti (Diptera: Culicidae) larvae

Background

Entomopathogenic fungi are potential candidates for use in integrated vector management and many isolates are compatible with synthetic and natural insecticides. Neem oil was tested separately and in combination with the entomopathogenic fungus Metarhizium anisopliae against larvae of the dengue vector Aedes aegypti. Our aim was to increase the effectiveness of the fungus for the control of larval mosquito populations.

Methods

Commercially available neem oil was used at concentrations ranging from 0.0001 to 1 %. Larval survival rates were monitored over a 7 day period following exposure to neem. The virulence of the fungus M. anisopliae was confirmed using five conidial concentrations (1 × 10⁵ to 1 × 10⁹ conidia mL⁻¹) and survival monitored over 7 days. Two concentrations of fungal conidia were then tested together with neem (0.001 %). Survival curve comparisons were carried out using the Log-rank test and end-point survival rates were compared using one-way ANOVA.

Results

1 % neem was toxic to A. aegypti larvae reducing survival to 18 % with S₅₀ of 2 days. Neem had no effect on conidial germination or fungal vegetative growth in vitro. Larval survival rates were reduced to 24 % (S₅₀ = 3 days) when using 1 × 10⁹ conidia mL⁻¹. Using 1 × 10⁸ conidia mL⁻¹, 30 % survival (S₅₀ = 3 days) was observed. We tested a “sub-lethal” neem concentration (0.001 %) together with these concentrations of conidia. For combinations of neem + fungus, the survival rates were significantly lower than the survival rates seen for fungus alone or for neem alone. Using a combination of 1 × 10⁷ conidia mL⁻¹ + neem (0.001 %), the survival rates were 36 %, whereas exposure to the fungus alone resulted in 74 % survival and exposure to neem alone resulted in 78 % survival. When using 1 × 10⁸ conidia mL⁻¹, the survival curves were modified, with a combination of the fungus + neem resulting in 12 % survival, whilst the fungus alone at this concentration also significantly reduced survival rates (28 %).

Conclusions

The use of adjuvants is an important strategy for maintaining/increasing fungal virulence and/or shelf-life. The addition of neem to conidial suspensions improved virulence, significantly reducing larval survival times and percentages.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-015-1280-9) contains supplementary material, which is available to authorized users.

Tagetes erecta Linn. and its mosquitocidal potency against Culex quinquefasciatus

OBJECTIVE

To investigate mosquitocidal effects of ethanolic extract of flowers of Tagetes erecta (T. erecta) and its chloroform and petroleum ether soluble fractions against the larvae of Culex quinquefasciatus (Cx. quinquefasciatus).

METHODS

The fresh flowers of T. erecta were extracted in cold with ethanol (5.0 L) and after concentration, the ethanol extract was fractionated with chloroform and petroleum ether to afford a brownish syrupy suspension of ethanol extract (50.0 g), petroleum ether soluble fraction (18.6 g) and chloroform soluble fraction (23.8 g). The larvicidal effect of ethanol extract and their solvent fractions were determined by the standard procedure of WHO against different instars of Cx. quinquefasciatus.

RESULTS

Among the tested samples the chloroform soluble fractions showed the highest toxicity and consequently, the lowest LC50 values (14.14 µg/mL, 17.06 µg/mL, 36.88 µg/mL and 75.48 µg/mL) for all the instars larvae of Cx. quinquefasciatus. The larvae showed comparative tolerance in the course of increasing age and time.

CONCLUSIONS

It can be concluded that the flowers of T. erecta are very effective natural larvicide and could be useful against Cx. quinquefasciatus.

Efficacy of neem chippings for mosquito larval control under field conditions

BACKGROUND

An in depth understanding of mosquito breeding biology and factors regulating population sizes is fundamental for vector population control. This paper presents results from a survey of mosquito breeding habitats and the efficacy of neem chippings as a potential larvicide that can be integrated in mosquito control on Nyabondo Plateau in western Kenya.

RESULTS

Six main mosquito habitat types namely artificial ponds, abandoned fish ponds, active fish ponds, open drains, temporary pools and swamps were found in Nyabondo. Early anopheline instars were mainly recovered from temporary pools, artificial ponds and abandoned fish ponds. The mosquitoes collected were Anopheles gambiae sensu lato (35%), An. coustani (46%) and Culex spp (19%). Both early and late instar larvae of anopheline and culicine mosquitoes were more abundant in the controls than in the Bti and neem treated habitats. Within treated habitats, early instar anopheline mosquitoes were recovered more from habitats provided with neem and fish compared to Bti treated habitats. All treated habitats recorded higher numbers of early instar larvae than late instars or pupae, indicating that gravid female mosquitoes still oviposited within treated habitats.

CONCLUSIONS

Neem chippings are a good tool for mosquito larval source management under field conditions. However, more research needs to be done to quantify the contribution of this tool to the overall mosquito borne disease transmission.

Old ingredients for a new recipe? Neem cake, a low-cost botanical by-product in the fight against mosquito-borne diseases

Mosquitoes (Diptera: Culicidae) represent an important threat to millions of people worldwide, since they act as vectors for important pathogens, such as malaria, yellow fever, dengue and West Nile. Control programmes mainly rely on chemical treatments against larvae, indoor residual spraying and insecticide-treated bed nets. In recent years, huge efforts have been carried out to propose new eco-friendly alternatives, with a special focus on the evaluation of plant-borne mosquitocidal compounds. Major examples are neem-based products (Azadirachta indica A. Juss, Meliaceae) that have been proven as really effective against a huge range of pests of medical and veterinary importance, including mosquitoes. Recent research highlighted that neem cake, a cheap by-product from neem oil extraction, is an important source of mosquitocidal metabolites. In this review, we examined (i) the latest achievements about neem cake metabolomics with special reference to nor-terpenoid and related content; (ii) the neem cake ovicidal, larvicidal and pupicidal toxicity against Aedes, Anopheles and Culex mosquito vectors; (iii) its non-target effects against vertebrates; and (iv) its oviposition deterrence effects on mosquito females. Overall, neem cake can be proposed as an eco-friendly and low-cost source of chemicals to build newer and safer control tools against mosquito vectors.

Content of trace elements and chromium speciation in Neem powder and tea infusions

Total concentrations of selected trace elements in Neem powder and in Neem tea were determined by inductively coupled plasma mass spectrometry (ICP-MS). The data revealed that despite high total concentrations of the potentially toxic elements Al and Ni in Neem powder, their amounts dissolved in Neem tea were low. Total concentrations of the other toxic elements Pb, As and Cd were also very low and do not represent a health hazard. In contrast, total concentrations of the essential elements Fe, Cu, Zn, Se Mo and Cr in Neem powder were high and also considerable in Neem tea. Consuming one cup of Neem tea (2g per 200 mL of water) covers the recommended daily intakes for Cr and Se and represents an important source of Mo and Cu. Speciation analysis of Cr by high performance liquid chromatography (HPLC) coupled to ICP-MS with the use of enriched Cr isotopic tracers to follow species interconversions during the analytical procedure demonstrated that toxic Cr(VI) was not present either in Neem powder or in Neem tea. Its concentrations were below the limits of detection of the HPLC-ICP-MS procedure applied. The speciation analysis data confirmed that even Cr(VI) was added, it was rapidly reduced by the presence of antioxidants in Neem leaves. By the use of enriched Cr isotopic spike solutions it was also demonstrated that for obtaining reliable analytical data it is essential to apply the extraction procedures which prevent Cr species interconversions, or to correct for species transformation.

Larvicidal and ovideterrent properties of neem oil and fractions against the filariasis vector Aedes albopictus (Diptera: Culicidae): a bioactivity survey across production sites

Neem seed oil (NSO) of Azadirachta indica (Meliaceae) contains more than 100 determined biologically active compounds, and many formulations deriving from them showed toxicity, antifeedancy and repellence against a number of arthropod pests. However, it is widely known that botanical products can differ in their chemical composition and bioactivity, as function of the production site and production process. We used high-performance thin layer chromatography (HPTLC) to investigate differences in chemical constituents of NSOs from three production sites. HPTLC analyses showed several differences in chemical abundance and diversity among NSOs, with special reference to limonoids. Furthermore, the three NSOs and their fractions of increasing polarities [i.e. ethyl acetate (EA) fraction and butanol (BU) fraction] were evaluated for larvicidal toxicity and field oviposition deterrence against the Asian tiger mosquito, Aedes albopictus, currently the most invasive mosquito worldwide. Results from bioactivity experiments showed good toxicity of NSOs and EA fractions against A. albopictus fourth instar larvae (with LC50 values ranging from 142.28 to 209.73 ppm), while little toxicity was exerted by BU fractions. A significant effect of the production site and dosage was also found and is probably linked to differences in abundance of constituents among samples, as highlighted by HPTLC analyses. NSOs and EAs were also able to deter A. albopictus oviposition in the field (effective repellence values ranging from 98.55 to 70.10%), while little effectiveness of BU fractions was found. Concerning ovideterrent activity, no difference due to the production site was found. This is the first report concerning larvicidal toxicity of NSO against A. albopictus and ovideterrence against Culicidae in the field. The chance to use chemicals from the NSO EA fraction seems promising, since they are effective at lower doses, if compared to synthetic products currently marketed, and could be an advantageous alternative to build newer and safer mosquito control tools.

Cumulative mortality of Aedes aegypti larvae treated with compounds

OBJECTIVE

To evaluate the larvicidal activity of Azadirachta indica, Melaleuca alternifolia, carapa guianensis essential oils and fermented extract of Carica papaya against Aedes aegypti (Linnaeus, 1762) (Diptera: Culicidae).

METHODS

The larvicide test was performed in triplicate with 300 larvae for each experimental group using the third larval stage, which were exposed for 24h. The groups were: positive control with industrial larvicide (BTI) in concentrations of 0.37 ppm (PC1) and 0.06 ppm (PC2); treated with compounds of essential oils and fermented extract, 50.0% concentration (G1); treated with compounds of essential oils and fermented extract, 25.0% concentration (G2); treated with compounds of essential oils and fermented extract, 12.5% concentration (G3); and negative control group using water (NC1) and using dimethyl (NC2). The larvae were monitored every 60 min using direct visualization.

RESULTS

No mortality occurred in experimental groups NC1 and NC2 in the 24h exposure period, whereas there was 100% mortality in the PC1 and PC2 groups compared to NC1 and NC2. Mortality rates of 65.0%, 50.0% and 78.0% were observed in the groups G1, G2 and G3 respectively, compared with NC1 and NC2.

CONCLUSIONS

The association between three essential oils from Azadirachta indica, Melaleuca alternifolia, Carapa guianensis and fermented extract of Carica papaya was efficient at all concentrations. Therefore, it can be used in Aedes aegypti Liverpool third larvae stage control programs.

Larvicidal efficacy of Catharanthus roseus Linn. (Family: Apocynaceae) leaf extract and bacterial insecticide Bacillus thuringiensis against Anopheles stephensi Liston

OBJECTIVE

To explore the larvicidal activity of Catharanthus roseus (C. roseus) leaf extract and Bacillus thuringiensis (B. thuringiensis) against the malarial vector Anopheles stephensi (An. stephensi), when being used alone or together.

METHODS

The larvicidal activity was assayed at various concentrations under the laboratory and field conditions. The LC50 and LC90 values of the C. roseus leaf extract were determined by probit analysis.

RESULTS

The plant extract showed larvicidal effects after 24 h of exposure; however, the highest larval mortality was found in the petroleum ether extract of C. roseus against the first to fourth instars larvae with LC50=3.34, 4.48, 5.90 and 8.17 g/L, respectively; B. thuringiensis against the first to fourth instars larvae with LC50=1.72, 1.93, 2.17 and 2.42 g/L, respectively; and the combined treatment with LC50=2.18, 2.41, 2.76 and 3.22 g/L, respectively. No mortality was observed in the control.

CONCLUSIONS

The petroleum ether extract of C. roseus extract and B. thuringiensis have potential to be used as ideal eco-friendly agents for the control of An. stephensi in vector control programs. The combined treatment with this plant crude extract and bacterial toxin has better larvicidal efficacy against An. stephensi.

Survival and swimming behavior of insecticide-exposed larvae and pupae of the yellow fever mosquito Aedes aegypti

BACKGROUND

The yellow fever mosquito Aedes aegypti is essentially a container-inhabiting species that is closely associated with urban areas. This species is a vector of human pathogens, including dengue and yellow fever viruses, and its control is of paramount importance for disease prevention. Insecticide use against mosquito juvenile stages (i.e. larvae and pupae) is growing in importance, particularly due to the ever-growing problems of resistance to adult-targeted insecticides and human safety concerns regarding such use in human dwellings. However, insecticide effects on insects in general and mosquitoes in particular primarily focus on their lethal effects. Thus, sublethal effects of such compounds in mosquito juveniles may have important effects on their environmental prevalence. In this study, we assessed the survival and swimming behavior of A. aegypti 4th instar larvae (L4) and pupae exposed to increasing concentrations of insecticides. We also assessed cell death in the neuromuscular system of juveniles.

METHODS

Third instar larvae of A. aegypti were exposed to different concentrations of azadirachtin, deltamethrin, imidacloprid and spinosad. Insect survival was assessed for 10 days. The distance swam, the resting time and the time spent in slow swimming were assessed in 4th instar larvae (L4) and pupae. Muscular and nervous cells of L4 and pupae exposed to insecticides were marked with the TUNEL reaction. The results from the survival bioassays were subjected to survival analysis while the swimming behavioral data were subjected to analyses of covariance, complemented with a regression analysis.

RESULTS

All insecticides exhibited concentration-dependent effects on survival of larvae and pupae of the yellow fever mosquito. The pyrethroid deltamethrin was the most toxic insecticide followed by spinosad, imidacloprid, and azadirachtin, which exhibited low potency against the juveniles. All insecticides except azadirachtin reduced L4 swimming speed and wriggling movements. A similar trend was also observed for swimming pupa, except for imidacloprid, which increased the swimming activity of pupa. Curiously, the insecticides did not affect cell damage in the neuromuscular system of larvae and pupae.

CONCLUSIONS

Deltamethrin and spinosad were the main compounds to exhibit lethal effects, which allowed the control of A. aegypti larvae and pupae, and impair their swimming potentially compromising foraging and predation likelihood.

Shedding light on bioactivity of botanical by-products: neem cake compounds deter oviposition of the arbovirus vector Aedes albopictus (Diptera: Culicidae) in the field

Industrial plant-borne by-products can be sources of low-cost chemicals, potentially useful to build eco-friendly control strategies against mosquitoes. Neem cake is a cheap by-product of neem oil extraction obtained by pressing the seeds of Azadirachta indica. Neem products are widely used as insecticides since rarely induce resistance because their multiple mode of action against insect pests and low-toxicity rates have been detected against vertebrates. In this research, we used field bioassays to assess the effective oviposition repellence of neem cake fractions of increasing polarity [n-hexane (A), methanol (B), ethyl acetate (C), n-butanol (D), and aqueous (E) fraction] against Aedes albopictus, currently the most invasive mosquito worldwide. These fractions, already characterized for low nortriterpenoids contents by HPLC analyses, were analyzed for their total content by HPTLC, highlighting striking differences in their chemical composition. Field results showed that B, A, and C tested at 100 ppm exerted higher effective repellence over the control (71.33, 88.59, and 73.49% of ER, respectively), while E and D did not significantly deter A. albopictus oviposition (17.06 and 22.72% of ER, respectively). The highest oviposition activity index was achieved by A (-0.82), followed by C (-0.63), and B (-0.62). Lower OAIs were achieved by D (-0.14) and E (-0.09). On the basis of our results, we believe that A, B, and C are very promising as oviposition deterrents against the arbovirus vector A. albopictus since they are proved as rich in active metabolites, cheap, and really effective at low doses.

Homeostatic imbalance and colon cancer: the dynamic epigenetic interplay of inflammation, environmental toxins, and chemopreventive plant compounds

The advent of modern medicine has allowed for significant advances within the fields of emergency care, surgery, and infectious disease control. Health threats that were historically responsible for immeasurable tolls on human life are now all but eradicated within certain populations, specifically those that enjoy higher degrees of socio-economic status and access to healthcare. However, modernization and its resulting lifestyle trends have ushered in a new era of chronic illness; one in which an unprecedented number of people are estimated to contract cancer and other inflammatory diseases. Here, we explore the idea that homeostasis has been redefined within just a few generations, and that diseases such as colorectal cancer are the result of fluctuating physiological and molecular imbalances. Phytochemical-deprived, pro-inflammatory diets combined with low-dose exposures to environmental toxins, including bisphenol-A (BPA) and other endocrine disruptors, are now linked to increasing incidences of cancer in westernized societies and developing countries. There is recent evidence that disease determinants are likely set in utero and further perpetuated into adulthood dependent upon the innate and environmentally-acquired phenotype unique to each individual. In order to address a disease as multi-factorial, case-specific, and remarkably adaptive as cancer, research must focus on its root causes in order to elucidate the molecular mechanisms by which they can be prevented or counteracted via plant-derived compounds such as epigallocatechin-3-gallate (EGCG) and resveratrol. The significant role of epigenetics in the regulation of these complex processes is emphasized here to form a comprehensive view of the dynamic interactions that influence modern-day carcinogenesis, and how sensibly restoring homeostatic balance may be the key to the cancer riddle.

Neem oil (Azadirachta indica) nanoemulsion--a potent larvicidal agent against Culex quinquefasciatus

BACKGROUND

Nanoemulsion composed of neem oil and non-ionic surfactant Tween 20, with a mean droplet size ranging from 31.03 to 251.43 nm, was formulated for various concentrations of the oil and surfactant. The larvicidal effect of the formulated neem oil nanoemulsion was checked against Culex quinquefasciatus.

RESULTS

O/W emulsion was prepared using neem oil, Tween 20 and water. Nanoemulsion of 31.03 nm size was obtained at a 1:3 ratio of oil and surfactant, and it was found to be stable. The larger droplet size (251.43 nm) shifted to a smaller size of 31.03 nm with increase in the concentration of Tween 20. The viscosity of the nanoemulsion increased with increasing concentration of Tween 20. The lethal concentration (LC50) of the nanoemulsion against Cx. quinquefasciatus was checked for 1:0.30, 1:1.5 and 1:3 ratios of oil and surfactant respectively. The LC50 decreased with droplet size. The LC50 for the ratio 1:3 nanoemulsions was 11.75 mg L(-1).

CONCLUSION

The formulated nanoemulsion of 31.03 nm size was found to be an effective larvicidal agent. This is the first time that a neem oil nanoemulsion of this droplet size has been reported. It may be a good choice as a potent and selective larvicide for Cx. quinquefasciatus.