Ethnobotanical knowledge on botanical repellents employed in the African region against mosquito vectors – A review

Chemical composition and toxicity of commercial Mentha spicata and Eucalyptus citriodora essential oils on Culex quinquefasciatus and non-target insects

Current vector control strategies based on synthetic chemicals are not eco-friendly against non-target organisms; hence, alternative approaches are highly required. Commercially purchased oil of Mentha spicata (Spearmint) and Eucalyptus citriodora (Citriodora) were examined against the medical pest Cx. quinquefasciatus (Say) and their non-toxicity on the aquatic species was evaluated. Chemical screening with gas chromatography coupled with mass spectrometry (GC-MS) analysis revealed a total of 14 and 11 compounds in Citriodora and Spearmint oils, respectively, with the highest peak (%) at carvone (70.44%) and isopulegol (30.4%). The larvicidal activity on the fourth instar larvae of Cx. quinquefasciatus showed dose-dependent mortality and significance at a 100 ppm concentration 48 h post-treatment with Citriodora (76.4%, P ≤ 0.001) and Spearmint (100%, P ≤ 0.001). Additionally, the photomicrograph of the fourth instar larvae revealed significant physical abnormalities in the head and midgut tissues post-exposure to Spearmint and Citriodora oils. Moreover, the histological assay revealed severe damage in the epithelial cells and gut lumen 2 to 24 h post-treatment. The repellency percentage of adult Culex mosquitoes was prominent across both oils at 150 ppm 210 min post-exposure. Non-target toxicity on the aquatic predator showed both essential oils (Spearmint oil (17.2%) and Citriodora oil (15.2%)) are safer at the maximum treatment (200 ppm) compared to temephos (75.4% at 1 ppm). The in silico screening of phyto-compounds derived by both essential oils with BeeTox (online server) showed no contact toxicity to the honey bee Apis mellifera. Overall, the present research revealed that Spearmint and Citriodora essential oils and their active phyto-compounds were toxic to Cx. quinquefasciatus and harmless to the aquatic predator and honey bee.

Phytochemical characterisation and toxicity effect of Tithonia diversifolia (Hemls.) A. Gray leaf extract on fall army worm Spodoptera frugiperda (JE Smith) larvae

OBJECTIVES

To mitigate the losses due to fall armyworm (FAW) infestation in maize, chemical pesticides had been the first choice and widely used as an emergency response. However, it comes with attendant health effect. This necessitates the development of plant based effective and safer pesticides. This research investigate response of fall armyworm larvae when they are exposed to crude and partially purified Tithonia diversifolia leaf extract.

METHODS

Chemical constituent of the extract was identified using NIST08.LIB library spectra provided by the software on a GC-MS system and FTIR analysis was done using KBr pellet technique with a resolution and scanning speed of 4 cm-1 and 2 mm/s. Dose dependent toxicity assay of T. diversifolia extracts on FAW at different growth stages under controlled environment in laboratory, followed by its effect under phytotron were examined against control and azadirachtin from neem.

RESULTS

The GC-MS of the butanol eluent revealed 20 compounds out of which the major ones being beta-d-glucopyranoside, methyl (15.225 %) palmitic acid, TMS derivative (10.98 %) and hexadecanoic acid, 2-[(trimethylsily)oxy]-, methyl ester (8.75 %). The FT-IR spectroscopic analysis of the butanol eluent of T. diversifolia leaf extract revealed the presence of alcohols, phenols, aldehydes, ketones, alkanes and primary amines. The butanol eluent and crude extract caused 96 % mortality at neonate and first instar FAW larvae.

CONCLUSIONS

The toxic and repellant effects revealed by diet bioassay and phytotron experiment respectively suggest that butanol eluent of T. diversifolia leaf extract could be a good and effective target for biopesticide production against FAW.

Essential oils extracted from Citrus macroptera and Homalomena aromatica (Spreng.) Schott. exhibit repellent activities against Aedes aegypti (Diptera: Culicidae)

BACKGROUND OBJECTIVES

Mosquitoes alone transmit diseases to around 700 million individuals annually, killing approximately 0.7 million people every year worldwide. Considering the potential health risks linked with synthetic repellents, it has become vital to identify eco-friendly, natural repellents for mosquito control as well as to understand the underlying mechanism for mosquito repellent activity. To address this, objectives were set to extract essential oils from Citrus macroptera peel and Homalomena aromatica (Spreng.) Schott. rhizomes, evaluate their mosquito repellent activity against Aedes aegypti, and further explore their mosquito odorant receptor inhibition potential.

METHODS

The oils were extracted using Clevenger's apparatus, and properties like specific gravity, refractive index, and boiling point were evaluated and characterised using Fourier transform infrared spectroscopy (FTIR) and gas chromatography-mass spectroscopy (GC-MS). Aedes aegypti mosquito eggs collected from the Indian Council of Medical Research (ICMR), Dibrugarh, were reared in the Department of Pharmaceutical Sciences, Research Laboratory, to obtain adult Aedes aegypti mosquitoes for the mosquito repellent activity evaluation of the essential oils using the Human Bait technique'. Molecular docking studies were performed for the oil components against mosquito odorant binding proteins. Further, toxicity studies of these two oils were evaluated against human dermal fibroblast adult (HDFa) cells.

RESULTS

The results revealed the presence of limonene (86.76%) and linalool (52.35%), respectively, in Citrus macroptera and Homalomena aromatica oils. It was found that the combination of the oils in a ratio of 1:1 showed mosquito repellent activity for up to 6.33 ± 0.23 h. Molecular docking studies showed the presence of major oil components having mosquito odorant receptor blocking potential comparable to N, N-diethyl-meta-toluamide (DEET), indicating a rationale for extended mosquito repellent action. Further, both of these oils were found to be non-cytotoxic against HDFa cells after 24 h.

INTERPRETATION CONCLUSION

The encouraging mosquito repellent activity of these two oils as compared to synthetic mosquito repellent DEET might pave the way for the development of novel herbal mosquito repellent formulations containing these essential oils.

Larvicidal, pupalicidal and adulticidal effects of Artemisia absinthium L. against dengue vector Aedes aegypti (Diptera: Culicidae) in Jazan region, K.S.A

In the current study, the biological effects of various solvents concentrations of Artemisia absinthium were assayed on different stages (larva, pupa and adult) of Aedes aegypti under controlled laboratory conditions. The life initiation and mortality for each insect stage were evaluated. Different lethal concentrations were measured. Aedes aegypti L. was susceptible to all plant extract solvents in different conc. ANOVA test, correlation analysis and simple linear regression were used to evaluate the significance. The results correlated with other comparative studies with different Artemisia sp. to put the studied species in the proper way in Asteraceae family. The study gave A. absinthium L. its bright position as a perfect natural insecticide especially as larvicidal due to the low Lc50 degree. Scientists welcome to use natural insecticide at initial stages of insect not in later ones.

Evaluation of the mosquito larvicidal potential and comparative assessment of the juice of Lantana camara Linn and Ocimum gratissimum Linn

In the present study, the larvicidal efficacy of the juices of the weeds Lantana camara Linn (L. camara) and Ocimum gratissimum Linn (O. gratissimum) was evaluated against the larvae of the malaria vectors Aedes aegypti, Anopheles subpictus and Culex quinquefasciatus. The freshly prepared juices of leaves were prepared by grinding them and diluting them at concentrations of 25, 50, 75, and 100 ppm. Twenty larvae of each species were introduced in different sterile Petri dishes in aqueous media under a controlled environment for the assessment of biological activity. The larvicidal activity of both juices was evaluated at 6, 12 and 24 hr post-exposure time points by observing the movement of each larva. The obtained data were subjected to probit analysis to determine the lethal concentrations that kill 50% and 90% (LC50 and LC90) of the treated larvae. The results revealed a noticeable larvicidal activity following 24 h of exposure. The juice of L. camara leaves exhibited an LC50 range of 47.47-52.06 ppm and an LC90 range of 104.33-106.70 ppm. Moreover, for the juice of O. gratissimum leaves, the LC50 range was 42.94-44.91 ppm and the LC90 range was 105.11-108.66 ppm. Taken together, the results indicate that the juices of L. camara and O. gratissimum leaves may be useful as effective, economical and eco-friendly larvicidal agents. However, additional studies are needed to explore the bioactive components of the weeds that exhibit larvicidal activity along with their mode of action.

The biological and therapeutic potentials of Cyclotrichium genus: a systematic review

The genus Cyclotrichium includes nine species that are mainly distributed in Turkey, Lebanon, Iraq, and Iran, and are used in the kitchen, and also in complementary medicine to treat various diseases. During recent years, considerable progress has been made in analyzing their phytochemical composition in parallel with their antimicrobial properties and their therapeutic potentials. This study reviews the present knowledge about investigations on antimicrobial, insecticidal, and anticancer properties of the essential oils and any other purified chemical compounds of the Cyclotrichium species. Various phytochemicals have been isolated from the extracts of the plants of this genus having significant biological and therapeutic potentials. In conclusion, these gathered data strongly support the viewpoint that the species belonging to the genus Cyclotrichium have various biological and pharmaceutical activities to treat various diseases including cancer in addition to the remarkable antimicrobial and insecticidal potential with no or minimal health and environmental hazards.

Sustainable development through the bio-fabrication of ecofriendly ZnO nanoparticles and its approaches to toxicology and environmental protection

Mosquito control is becoming more difficult as a result of the rise in resistance to toxic chemical insecticides. The insecticides of bio-fabrication sources may serve as a convenient alternative to environmentally acceptable methods in the future. The larvicidal and pupicidal activities of bio-fabricated zinc oxide nanoparticles (ZnO NPs) on the different instar larvae and pupae of Anopheles subpictus Grassi (Malaria vector) and Culex quinquefasciatus Say (lymphatic filariasis) were investigated in this study. The results recorded from XRD, FTIR, SEM-EDX, and TEM analyses confirmed the bio-fabrication of ZnO NPs. Such nanoparticles were nearly spherical and agglomerated with a size of 34.21 nm. GC-MS analysis of methanol extract revealed the compound, stigmasterol (C29H48O) as major one. Mosquito larvae and pupae of targeted mosquito were tested against varied concentrations of the bio-fabricated ZnO NPs and methanol extract of Vitex negundo for 24 h. The maximum activity was recorded from ZnO NPs against the larvae and pupae of A. subpictus LC50 which were 1.70 (I), 1.66 (II), 1.93 (III), 2.48 (IV), and 3.63 mg/L (pupa) and C. quinquefasciatus LC50 were 1.95 (I), 2.63 (II), 2.90 (III), 4.32 (IV), and 4.61 mg/L (pupa) respectively. ZnO NPs exhibited strong DPPH radical and FRAP scavengers compared to the aqueous extract of V. negundo. Also, V. negundo leaf methanol extract (VNLME) and ZnO NPs were evaluated for their cytotoxicity on HeLa cells, which exhibited the IC50 values of 72.35 and 43.70μg/mL, respectively. The methylene blue (MB) dye, which is harmful to both aquatic and terrestrial life, was degraded using the biosynthesized ZnO nanoparticles. At 664 nm, 81.2% of the MB dye had degraded after 120 min of exposure to sunlight. Overall, our results revealed that ZnO NPs are the perfect biological agent and economical for the control of malaria, filariasis vectors, antioxidant, HeLa cells, and MB blue dye degradation under sunlight irradiation.

Graphical abstract

Insecticidal effects of some selected plant extracts against Anopheles stephensi (Culicidae: Diptera)

BACKGROUND

The use of synthetic insecticides against mosquitoes may lead to resistance development and potential health hazards in humans and the environment. Consequently, a paradigm needs to shift towards the alternative use of botanical insecticides that could strengthen an insecticide resistance management programme. This study aimed to assess the insecticidal effects aqueous, hexane, and methanol crude leaf extracts of Calpurnia aurea, Momordica foetida, and Zehneria scabra on an insectary colony of Anopheles stephensi larvae and adults.

METHODS

Fresh leaves of C. aurea, M. foetida and Z. scabra were collected and dried, then separately ground to powder. Powdered leaves of test plants were extracted using sonication with aqueous, hexane, and methanol solvents. The extracts were concentrated, and a stock solution was prepared. For comparison, Temephos (Abate®) and control solutions (a mixture of water and emulsifier) were used as the positive and negative controls, respectively. Different test concentrations for the larvae and the adults were prepared and tested according to WHO (2005) and CDC (2010) guidelines to determine lethal concentration (LC) values. Mortality was observed after 24 h exposure. The statistical analyses were performed using Statistical Package for the Social Sciences (SPSS) software (Kruskal-Wallis test) and R software (a generalized linear model was used to determine LC₅₀ and LC₉₀ values of the extracts).

RESULTS

The lowest LC₅₀ values were observed in aqueous extracts of M. foetida followed by Z. scabra extract and C. aurea leaves at 34.61, 35.85, and 38.69 ppm, respectively, against the larvae. Larval mortality was not observed from the hexane extracts and negative control, while the standard larvicide (temephos) achieved 100% mortality. Further, the adulticidal efficacy was greatest for aqueous extract of Z. scabra with LC₅₀ = 176.20 ppm followed by aqueous extract of C. aurea (LC₅₀ = 297.75 ppm).

CONCLUSION

The results suggest that the leaf extracts of the three test plants have the potential of being used for the control of vector An. stephensi larvae and adult instead of synthetic mosquitocides. Further studies need to be conducted to identify the active ingredients and their mode of action.

Larvicidal Activity of Methyl Benzoate, a Volatile Organic Compound, Against the Mosquitoes Aedes albopictus and Culex pipiens (Diptera: Culicidae)

Methyl benzoate (MBe) is a volatile organic molecule found in various plants; it is used as an insect semiochemical. MBe also has a biorational insecticidal effect against various agricultural and urban arthropod pests. The present study was the first to assess the larvicidal potential of MBe against fourth-instar larvae of the mosquitoes Aedes albopictus (Skuse) and Culex pipiens (L.). A positive association was observed between MBe concentrations and larval mortality in both the species. The highest mortality recorded was 100% for Ae. albopictus and 56% for Cx. pipiens after 24 h of exposure to 200 ppm MBe. The lethal median concentration (LC50) values of MBe against fourth-instar larvae of Ae. albopictus and Cx. pipiens were 61 ppm and 185 ppm, respectively. These results suggest that MBe has great potential for use as an environmentally friendly larvicidal agent for mosquito control.

Larvicidal and repellent activity of N-methyl-1-adamantylamine and oleic acid a major derivative of bael tree ethanol leaf extracts against dengue mosquito vector and their biosafety on natural predator

Aegle marmelos (L.) Correa belongs to the family Rutaceae is generally known as "bael fruit tree" occuring across the south Asian countries. The current investigation screened the main derivatives from crude ethanolic extracts of the Bael tree leaf and evaluated activity effects on the larvae and adults of Aedes aegypti (L.) Dengue vector mosquito and a non-target aquatic predator. The GC-MS results showed that the peak area was found to be profound in N-methyl-1-adamantaneacetamide (N-M 1a) followed by oleic acid (OA) with 63.08 and 11.43% respectively. The larvicidal activity against the fourth instar larvae and the crude Ex-Am showed prominent mortality rate (93.60%) at the maximum dosage of 100 ppm. The mortality rate of N-M 1a and OA was occurred at 10 ppm (97.73%) and 12 ppm (95.4%). The repellent activity was found to be prominent at crude Ex-Am (50 ppm) as compared to the pure compounds (N-m 1a and OA) with maximum protection time up to 210 min. The non-target screening of Ex-Am, N-M 1a, and OA on mosquito predator Tx. splendens showed that they are scarcely toxic even at the maximum dosage of 1000 ppm (34.13%), 100 ppm (27.3%), and 120 ppm (31.3%) respectively. Thus, the present investigation clearly proved that the crude Ex-Am and their major derivatives Nm 1-a and OA showed their acute larval toxicity as well as potential mosquito repellent against the dengue mosquito and eco-safety against the mosquito predator.

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.

Essential Oils from Artemisia herba alba Asso., Maticaria Recutita L., and Dittrichia Viscosa L. (Asteraceae): A Promising Source of Eco-Friendly Agents to Control Callosobruchus maculatus Fab. Warehouse Pest

Callosobruchus maculatus (Fab.) (C. maculatus) is one of the major pests of legume seeds in storage causing significant damage, leading to food insecurity and low income for farmers. This work was planned to develop eco-friendly agents from essential oils of Artemisia herba alba Asso. (AEO), Maticaria Recutita L. (MEO), and Dittrichia Viscosa L. (DEO) to control C. maculatus. To achieve this goal, essential oils (EOs) were extracted by hydro-distillation using Clevenger apparatus before being characterized by GC-MS. EOs were used for testing purposes using three different tests, namely, inhalation toxicity, contact toxicity, and repellency tests. GC-MS analysis of EOs showed the presence of 16 potentially active compounds in AEO and 38 in MEO, whilst 15 compounds were identified in DEO. AEO was higher in thujone (57.6%) and chrysanthenone (11.8%). Santolina alcohol (40.7%) and germacrene D (8.9%) were the major compounds identified in MEO, whereas isocostic acid (72.3%) was the chief compound of DEO. The obtained findings showed that the studied EOs showed considerable insecticidal activity against C. maculatus with a lethal dose (LC50) of 3.78, 8.86, and 14.34 μL/1 liter of air by AEO, MEO, and DEO, respectively. At 1 μL/1 liter of air, the oviposition reduction rate was 90.02%, 70.65%, and 48.23% by AEO, MEO, and DEO, respectively, whereas the emergence reduction rate was 87.32%, 60.08%, and 32.24% by AEO, MEO, and DEO, respectively. With increasing doses up to 20 μL/L, the reduction of individual emergence reached 98.8% by AEO of 24 h after treatment. AEO, MEO, and DEO showed significant repellent effects against adults of C. maculatus with repulsion percentages of 60.83%, 50.83%, and 72.5%, respectively. The outcome of this work suggests that the essential oils of the studied plants, particularly Artemisia herba alba Asso. oils, can constitute a natural and environmentally friendly alternative to develop new bioinsecticides for the control of C. maculatus.

Prototyping a Knowledge-Based System to Identify Botanical Extracts for Plant Health in Sub-Saharan Africa

Replacing synthetic pesticides and antimicrobials with plant-based extracts is a current alternative adopted by traditional and family farmers and many organic farming pioneers. A range of natural extracts are already being marketed for agricultural use, but many other plants are prepared and used empirically. A further range of plant species that could be effective in protecting different crops against pests and diseases in Africa could be culled from the large volume of knowledge available in the scientific literature. To meet this challenge, data on plant uses have been compiled in a knowledge base and a software prototype was developed to navigate this trove of information. The present paper introduces this so-called Knomana Knowledge-Based System, while providing outputs related to Spodoptera frugiperda and Tuta absoluta, two invasive insect species in Africa. In early October 2020, the knowledge base hosted data obtained from 342 documents. From these articles, 11,816 uses—experimental or applied by farmers—were identified in the plant health field. In total, 384 crop pest species are currently reported in the knowledge base, in addition to 1547 botanical species used for crop protection. Future prospects for applying this interdisciplinary output to applications under the One Health approach are presented.

Momordica charantia L. extracts against Aedes aegypti larvae

Mormodica charantia (Curcubitaceae) is a plant with great medicinal potential, also used as an alternative of mosquitoes control as demonstrated by previous studies. We evaluated the larvicidal activity of crude extracts of ethyl acetate, methanol and hexane from flowers and fruits of M. charantia against Aedes aegypti (Culicidae). Flowers and fruits were macerated in methanol, ethyl acetate and hexane. Bioassays were performed with application of the extracts at final concentrations of 1 - 200 µg/mL in the middle of the third instar larvae of A. aegypti (L3). The results showed high toxicity to ethyl acetate extracts from flowers and fruits at concentrations of 200 µg/mL and 100 µg/mL, with 97% and 87% of larvae mortality (L3), respectively. Hexane extract demonstrated low toxicity, while methanol extract exhibited 78% larval mortality. The data suggested that the ethyl acetate extracts of flowers and fruits of M. charantia can effectively contribute to larvicidal activity. In addition, purification of M. charantia extracts may lead to a promising larvicidal activity to control the A. aegypti population.

Improved adulticidal activity against Aedes aegypti (L.) and Aedes albopictus (Skuse) from synergy between Cinnamomum spp. essential oils

Improved natural adulticidal agents against mosquito vectors are in urgent need, and essential oils from Cinnamomum plants can assume this role quite readily. Cinnamomum verum, C. cassia, and C. loureiroi essential oils (EOs) were extracted from the barks and evaluated for their chemical composition by GC–MS. The major constituent of the three EOs was cinnamaldehyde. WHO susceptibility tests on individual and combined EOs as well as cinnamaldehyde were conducted against female adults of Aedes aegypti and Aedes albopictus. All EO combinations exhibited a synergistic effect, manifesting a higher toxicity, with a synergistic value ranging from 2.9 to 6.7. Their increasing mortality value was improved between 16.0 to 41.7%. The highest synergistic effect was achieved by an EO combination of 0.5% C. cassia + 0.5% C. loureiroi, while the highest insecticidal activity was achieved by 2.5% C. verum + 2.5% C. cassia and 1% cinnamaldehyde, with a knockdown and mortality rate of 100% and a KT₅₀ between 0.7 and 2.1 min. This combination was more toxic to both mosquito species than 1% w/v cypermethrin. These findings demonstrate that cinnamaldehyde and synergistic combinations of C. verum + C. cassia EOs and C. cassia + C. loureiroi EOs have a high insecticidal efficacy against Aedes populations.

An approach to natural insect repellent formulations: from basic research to technological development

The incidence of dengue, Zika, chikungunya, yellow fever and malaria cases has increased significantly in the world. To avoid mosquito bites, one of the best strategies is the use of repellents. The interest in using plants as mosquito repellents has increased significantly. In this review, has been performed a bibliographic survey of the plants with repellent activity, evaluate the trends of natural repellent formulations in the scientific literature, those described in patents and commercially available products. Limonene, 1,8-cineole, geraniol, eugenol and citronellal are the active compounds that mostly appear in the essential oils of plants with repellent activity. The type of natural repellent formulation mostly widely marketed is the spray and lotion, respectively. In patents, classic formulation as emulsion was most frequently used, followed by lotions and sprays. Data collected from scientific articles and patents show that microparticles are the most widely used extended release systems nowadays for natural repellents. The citronella essential oil was the one mostly used among the classic commercially available formulations, as well as in the extended release systems described in the literature and patents. Future research must be conducted to the use of nanotechnology in the development of extended release systems containing essential oils with repellent activity produced from natural and biodegradable materials.

Ethnobotanical survey and evaluation of traditional mosquito repellent plants of Dai people in Xishuangbanna, Yunnan Province, China

ETHNOPHARMACOLOGICAL RELEVANCE

Dengue is one of the most important pervasive diseases in many regions of the world, including China. There is an urgent need for new repellents, including plant derivatives, due to the resistance, toxicity, and non-degradability of synthetic insecticides. Traditional plant-based remedies may provide potential avenues for developing new strategies.

AIMS OF THE STUDY

The aims of this study were to 1) document the traditional mosquitoes repellent plants used by the Dai people of Xishuangbanna, China; 2) screen out new efficient mosquito repellent plants as candidates for further study.

MATERIALS AND METHODS

During the period August 2016 to July 2017, five field surveys were conducted in 16 villages of Xishuangbanna. A total of 81 informants (44 males and 37 females) were interviewed using semi-structured questions to collect detailed information on the plants they use to prevent mosquito bites. Ten plants with higher popularity and larger resource were collected and extracts were prepared by hydro-distillation or with petroleum ether. Extracts were tested for adult Aedes albopictus repellency using a human-bait cage. Firstly, repellency was determined as the Minimum Effective Dosage (MED) per minute at which 1% of the mosquito bite through the treated cloth. Secondly, five plant extracts with lower MEDs were tested the repellent longevity of different concentrations.

RESULTS

Eighteen plants were documented as being used in traditional remedies against mosquitoes. The methods for controlling mosquitoes were diverse: direct burning was used for most plants (16 species), followed by smearing (5 species), and placing (5 species). Laboratory analyses confirmed that ten plants did exhibit mosquito repellent activity. Of them, Artemisia indica, Nicotiana tabacum, Blumea balsamifera, Vitex trifolia, and Chromolaena odorata showed good mosquito repellency with MEDs of 0.015, 0.061, 0.090, 0.090, and 0.105 mg/cm², respectively. The protection rate provided by A. indica is also the highest among five plants. Although it provides complete protection time of only 30 min at 0.45 mg/cm² concentration, its repellency within 2 h is not significantly different from that of DEET.

CONCLUSION

Dai villagers in Xishuangbanna have a rich, diverse and scientific knowledge of plant-based mosquito repellents. Laboratory experiments screened out several plants as candidates for mosquito repellents, of which Artemisia indica was the most promising candidate plant.

Pimpinella anisum Essential Oil Nanoemulsion Toxicity against Tribolium castaneum? Shedding Light on Its Interactions with Aspartate Aminotransferase and Alanine Aminotransferase by Molecular Docking

The insecticidal activity is the result of a series of complex interactions between toxic substances as ligands and insect’s enzymes as targets. Actually, synthetic insecticides used in pest control programs are harmful to the environment and may affect non-target organisms; thus, the use of natural products as pest control agents can be very attractive. In the present work, the toxic effect of aniseed (Pimpinella anisum L.) essential oil (EO) and its nanoemulsion (NE) against the red flour beetle Tribolium castaneum, has been evaluated. To assess the EO mode of action, the impact of sub-lethal concentrations of aniseed EO and NE was evaluated on enzymatic and macromolecular parameters of the beetles, including aspartate aminotransferase (AST), alanine aminotransferase (ALT), total protein, total lipids and glucose. Finally, a molecular docking study was conducted to predict the mode of action of the major EO and NE components namely E-anethole, Limonene, alpha-himalachalene, trans-Verbenol and Linalool at binding site of the enzymes AST and ALT. Herein, the binding location of the main compounds in both proteins are discussed suggesting the possible interactions between the considered enzymes and ligands. The obtained results open new horizons to understand the evolution and response of insect-plant compounds interactions and their effect predicted at the molecular levels and side effects of both animal and human.

Insecticidal properties and chemical composition of Piper aduncum L., Lippia sidoides Cham. and Schinus terebinthifolius Raddi essential oils against Plutella xylostella L

In the laboratory, were evaluated the effects (residual contact and feeding deterrence) of the essential oils from the leaves of Piper aduncum, Lippia sidoides and Schinus terebinthifolius, as well as eleven selected constituents and binary blends of oils in different proportions against 3rd instar larvae of Plutella xylostella (L.). The Piper oil demonstrated the greatest toxicity (LC50 = 0.31 µL/mL) and feeding deterrence (DC50 = 1.08 µL/mL) between oils tested. Dillapiole (LC50 = 1.01 µL/mL; DC50 = 1.10 µL/mL) and carvacrol (LC50 = 6.03 µL/mL; DC50 = 0.075 µL/mL) demonstrated the greatest toxicity and feeding deterrence between constituents tested, respectively. Based on the fractional effects indices for the blends, a synergistic interaction was found for the blend of the Lippia and Schinus oils at a proportion of 75 and 25%, respectively. The present findings indicate that this blend could be used in the control of P. xylostella, as the literature reports populations resistant to the active ingredient in the positive control, Premio®. Further studies are needed for the development of a new botanical insecticide based on the active ingredients in oils from L. sidoides and S. terebinthifolius to improve efficiency, stability and the cost-benefit in the control of P. xylostella.

Leaf Extract of Dillenia indica as a Source of Selenium Nanoparticles with Larvicidal and Antimicrobial Potential toward Vector Mosquitoes and Pathogenic Microbes

Chikungunya, dengue, Zika, malaria, Japanese encephalitis, filariasis, West Nile, etc. are mosquito transmitted diseases that have killed millions of people worldwide, and millions of people are at risk of these diseases. Control of the mosquitoes, such as Aedes aegypti and Culex quinquefasciatus, is challenging due to their development of resistance to synthetic insecticides. The habitats of the young mosquitoes are also the habitats for foodborne pathogens like Staphylococcus aureus (MTCC96) and Serratia marcescens (MTCC4822). The present study was aimed at synthesizing eco-friendly green nanoparticles using Dillenia indica leaf broth and analyzing its efficacy in controlling the vector mosquitoes A. aegypti and C. quinquefasciatus, as well as the microbial pathogens St. aureus and Se. marcescens. The formation of selenium nanoparticles (SeNps) was confirmed using UV-Vis spectroscopy (absorption peak at 383.00 nm), Fourier transform infrared radiation (FTIR spectrum peaks at 3177, 2114, 1614, 1502, 1340, 1097, 901, 705, and 508 cm−1), X-ray diffraction (diffraction peaks at 23.3 (100), 29.6 (101), 43.5 (012), and 50.05 (201)), and scanning electron microscopy (oval shaped). The size of the nanoparticles and their stability were analyzed using dynamic light scattering (Z-Average value of 248.0 nm) and zeta potential (−13.2 mV). The SeNps disorganized the epithelial layers and have broken the peritrophic membrane. Histopathological changes were also observed in the midgut and caeca regions of the SeNPs treated A. aegypti and C. quinquefasciatus larvae. The SeNps were also active on both the bacterial species showing strong inhibitory zones. The present results will explain the ability of SeNps in controlling the mosquitoes as well as the bacteria and will contribute to the development of multi potent eco-friendly compounds.

Ultrasonic Technology Applied against Mosquito Larvae

The effective management of mosquito vectors is a timely challenge for medical and veterinary entomology. In this study, we evaluated the acoustic Larvasonic device to control young instars of the mosquito Aedes aegypti in diverse freshwater environments. Under laboratory conditions, we investigated the effect of exposure time and distance from the transducer on the mortality of larvae and pupae of Ae. aegypti. Furthermore, we evaluated the effectiveness of the ultrasound window of the electromagnetic spectrum under different field conditions. Results showed that first and second instar larvae were more sensitive to the frequency range of 18–30 kHz of the Larvasonic device. Ultrasonic waves applied for 180 s at a frequency from 18 to 30 kHz caused 100% larval mortality at a distance of 60 cm from the transducer. No mortality was observed in the non-target copepod Megacyclops formosanus. The exposure to the soundwaves produced by the acoustic larvicidal device over different distances effectively damaged Ae. aegypti through destruction of the larval dorsal tracheal trunk, thorax and abdomen. Overall, results indicated that the Larvasonic device tested can provide an alternative tool to reduce young instar populations of Ae. aegypti, without any effects on non-target aquatic invertebrates like copepods. It turned out to be a useful device for mosquito biocontrol. This technology has a relevant potential to fight the spread of mosquito-borne diseases.

Bioactivity of Common Pesticidal Plants on Fall Armyworm Larvae (Spodoptera frugiperda)

The fall armyworm (FAW), Spodoptera frugiperda (Lepidoptera: Noctuidae) is a recent invasive pest species that has successfully established across sub-Saharan Africa where it continues to disrupt agriculture, particularly smallholder cereal production. Management of FAW in its native range in the Americas has led to the development of resistance to many commercial pesticides before its arrival in Africa. Pesticide use may therefore be ineffective for FAW control in Africa, so new and more sustainable approaches to pest management are required that can help reduce the impact of this exotic pest. Pesticidal plants provide an effective and established approach to pest management in African smallholder farming and recent research has shown that their use can be cost-beneficial and sustainable. In order to optimize the use of botanical extracts for FAW control, we initially screened ten commonly used plant species. In laboratory trials, contact toxicity and feeding bioassays showed differential effects. Some plant species had little to no effect when compared to untreated controls; thus, only the five most promising plant species were selected for more detailed study. In contact toxicity tests, the highest larval mortality was obtained from Nicotiana tabacum (66%) and Lippia javanica (66%). Similarly, in a feeding bioassay L. javanica (62%) and N. tabacum (60%) exhibited high larval mortality at the highest concentration evaluated (10% w/v). Feeding deterrence was evaluated using glass-fibre discs treated with plant extracts, which showed that Cymbopogon citratus (36%) and Azadirachta indica (20%) were the most potent feeding deterrents among the pesticidal plants evaluated. In a screenhouse experiment where living maize plants infested with fall armyworm larvae were treated with plant extracts, N. tabacum and L. javanica were the most potent species at reducing foliar damage compared to the untreated control whilst the synthetic pesticide chlorpyrifos was the most effective in reducing fall armyworm foliar damage. Further field trial evaluation is recommended, particularly involving smallholder maize fields to assess effectiveness across a range of contexts.

Toxicity and repellency of two anthranilates against Aedes albopictus Skuse (Diptera: Culicidae)

The ability of Aedes albopictus Skuse to transmit several pathogens to humans makes it a very important mosquito with public health significance. Ecofriendly products as alternatives to synthetic chemicals for the control of mosquito vectors are needed. Therefore, the larvicidal and repellent effects of two nontoxic chemicals, butyl anthranilate (BA) and ethyl anthranilate (EA), at different concentrations were compared in A. albopictus. The repellency persistence of BA and three commercial mosquito repellent products (Liushen repellent spray, DKB Korean, Raid repellent spray) against A. albopictus was compared. The results showed that 0.1% concentrations of BA and EA solutions were highly toxic to A. albopictus larvae, and the mortality rate was >90% after 4 h of treatment. We found that BA was more repellent than EA, and at 0.1% BA and 1% EA, and the repellency rates were 53.62% and 38.47%, respectively. Overall, 5% BA presented a significantly longer repellency time than the three commercial repellent products against female A. albopictus. These results indicate that BA has significant larvicidal and repellent effects and can be exploited further for the development of ecofriendly alternatives to existing toxic chemicals currently used for mosquito control.

Lichen Parmelia sulcata mediated synthesis of gold nanoparticles: an eco-friendly tool against Anopheles stephensi and Aedes aegypti

The gold nanoparticles (AuNPs) were synthesized using the lichen Parmelia sulcata extract (PSE) and characterized. The peaks of ultraviolet spectrophotometer and Fourier transmission infrared confirmed the formation of nanoparticles and the bioactive compounds of the lichen being responsible for reducing and capping of the particles. The face-centered cubic particles were determined by XRD peaks at 111, 200, 220, and 311. The elemental composition and spherical shape of AuNPs were confirmed by energy-dispersive spectroscopy and transmission electron microscopy. The average particle size is 54 nm, and the zeta potential - 18 was ascertained by dynamic light scattering. The potential effect of synthesized nanoparticles and lichen extracts was evaluated for antioxidant bioassays like DPPH and H₂O₂ and tested for mosquitocidal activity against Anopheles stephensi. Results showed that the lichen extract and AuNPs have the capability to scavenge the free radicals with the IC₅₀ values of DPPH being 1020 and 815 μg/ml and the IC₅₀ values of H₂O₂ being 694 and 510 μg/ml, respectively. The mosquitocidal experimental results in this study showed the inhibition of A. stephensi and A. aegypti against the larvae (I-IV instar), pupae, adult, and egg hatching. On comparison, A. stephensi showed effective inhibition than A. aegypti even at low concentration. Based on the obtained results, gold nanoparticles synthesized using PSE showed an excellent mosquitocidal effect against Anopheles stephensi.

Plant extracts for developing mosquito larvicides: From laboratory to the field, with insights on the modes of action

In the last decades, major research efforts have been done to investigate the insecticidal activity of plant-based products against mosquitoes. This is a modern and timely challenge in parasitology, aimed to reduce the frequent overuse of synthetic pesticides boosting resistance development in mosquitoes and causing serious threats to human health and environment. This review covers the huge amount of literature available on plant extracts tested as mosquito larvicides, particularly aqueous and alcoholic ones, due to their easy formulation in water without using surfactants. We analysed results obtained on more than 400 plant species, outlining that 29 of them have outstanding larvicidal activity (i.e., LC₅₀ values below 10 ppm) against major vectors belonging to the genera Anopheles, Aedes and Culex, among others. Furthermore, synergistic and antagonistic effects between plant extracts and conventional pesticides, as well as among selected plant extracts are discussed. The efficacy of pure compounds isolated from the most effective plant extracts and - when available - their mechanism of action, as well as the impact on non-target species, is also covered. These belong to the following class of secondary metabolites: alkaloids, alkamides, sesquiterpenes, triterpenes, sterols, flavonoids, coumarins, anthraquinones, xanthones, acetogenonins and aliphatics. Their mode of action on mosquito larvae ranges from neurotoxic effects to inhibition of detoxificant enzymes and larval development and/or midugut damages. In the final section, current drawbacks as well as key challenges for future research, including technologies to synergize efficacy and improve stability - thus field performances - of the selected plant extracts, are outlined. Unfortunately, despite the huge amount of laboratory evidences about their efficacy, only a limited number of studies was aimed to validate their efficacy in the field, nor the epidemiological impact potentially arising from these vector control operations has been assessed. This strongly limits the development of commercial mosquito larvicides of botanical origin, at variance with plant-borne products developed in the latest decades to kill or repel other key arthropod species of medical and veterinary importance (e.g., ticks and lice), as well as mosquito adults. Further research on these issues is urgently needed.

Insecticidal activity of essential oils in controlling fall armyworm, Spodoptera frugiperda

ABSTRACT: Fall armyworm, Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae) is one of the main pests in maize crop with developing resistance to chemical products and Bt technology. Therefore, alternative control methods such as essential oils are important steps in the implementation management strategies for this pest. This study aimed to evaluate the efficiency of essential oils (EOs) of Corymbia citriodora, Myrciaria dubia (Myrtaceae), Lippia microphylla (Verbenaceae) and Piper umbelattum (Piperaceae) in controlling S. frugiperda. The OEs were extracted and mortality tests were conducted with topic and volatile applications, in 30 second-instar caterpillars originated from insect rearing and artificial diet. As a control, we conducted tests with distilled water and acetone. EOs that provided mortality rates above 80% were submitted to chemical analysis for constituent identification. The efficient EOs were only those of C. citriodora and L. microphylla. For EO of C. citriodora, the LD80 was 7.06 ± 0.73 mg.g-1 in topical application and 5.85 ± 0.75 µL via volatile application. On the other hand, for EO of L. microphylla, DL80 was 9.95 ± 1.25 mg.g-1 in topical application and 18.56 ± 3.55 µL via volatile application. Chemical analysis showed that the main constituents were citronella for the EO of C. citriodora and (E)-caryophyllene and (E)-nerolidol to the EO of L. microphylla. EOs of C. citriodora and L. microphylla are promising for controlling S. frugiperda, with emphasis on the volatile effect of C. citriodora oil.

Arboviruses in South Africa, known and unknown

The emergence of novel arboviruses of zoonotic potential in South Africa (SA) threatens human health and animal welfare, and affects economic growth and development. These viruses cause severe infections in animals and humans, including neurological diseases, such as encephalitis, resulting in high morbidities, mortalities and economic losses. With increasing reports of Middelburg, Shuni, Sindbis, West Nile and Wesselsbron virus infections in animals and humans in SA, this article reviews and discusses known and currently emerging arboviruses in the country. These reports underscore the need for increased surveillance, vector control management, public health preparedness, focused research, community awareness programs, and the development of rapid and sensitive diagnostic approaches. Furthermore, appropriate medical personnel training and strengthening initiatives for a one-health approach are required to understand and mitigate the emerging arboviral threat to public health.

An online survey of personal mosquito-repellent strategies

Background

Mosquito repellents can be an effective method for personal protection against mosquito bites that are a nuisance and carry the risk of transmission of mosquito-borne pathogens like plasmodia, dengue virus, chikungunya virus, and Zika virus. A multitude of commercially available products are currently on the market, some of them highly effective while others have low or no efficacy. Many home remedies of unknown efficacy are also widely used.

Methods

We conducted a survey study to determine what kind of mosquito repellents and other mosquito control strategies people use. Our online survey was focused on unconventional methods and was answered by 5,209 participants.

Results

The majority of participants resided in the United States, were female (67%), had higher education (81% had a university degree), and were 18 to 37 years old (50%). The most commonly used repellent was DEET spray (48%), followed closely by citronella candles (43%) and ‘natural’ repellent sprays (36%). We collected a plethora of home remedies and other strategies people use that warrant further research into their effectiveness.

Discussion

Our study lays the foundation for future research in alternative, unconventional methods to repel mosquitoes that may be culturally acceptable and accessible for people.

Pimpinella anisum essential oil nanoemulsions against Tribolium castaneum-insecticidal activity and mode of action

The red flour beetle, Tribolium castaneum Herbst (Coleoptera: Tenebrionidae), is an economically important pest of stored products. As possible alternative to conventional insecticides for its management, plant essential oils have gained interest owing to their effectiveness and eco-friendly features. However, they also show some drawbacks, such as low stability, poor water solubility and diffusion, and limited persistence in the environment. A good strategy to overcome these disadvantages is represented by green nanotechnologies. Herein, we developed a nanoemulsion based on the essential oil from Pimpinella anisum L. (Apiaceae) containing 81.2% of (E)-anethole and evaluated its toxicity on T. castaneum adults and F₁ progeny, as well as its morphological and histological impact. The aniseed oil nanoemulsion was characterized by the formation of a semi-solid interphase between oil and water; mean drop size was 198.9 nm, PDI was 0.303, zeta potential was - 25.4 ± 4.47 mV, and conductivity was 0.029 mS/cm. The nanoemulsion showed toxicity on T. castaneum (LC₅₀ = 9.3% v/v), with a significant impact on its progeny. Morphological and histological damages triggered by feeding and exposure to the aniseed nanoemulsion were analyzed by scanning electron microscopy (SEM) and light microscopy. Overall, our findings showed that the development of nanoemulsions allows to improve the stability of P. anisum essential oil enhancing its efficacy against stored grain pests and contributing to reduce the use of harmful synthetic insecticides.

Managing mosquitoes and ticks in a rapidly changing world - Facts and trends

Vector-borne diseases transmitted by mosquitoes and ticks are on the rise. The effective and sustainable control of these arthropod vectors is a puzzling challenge for public health worldwide. In the present review, I attempted to provide a concise and updated overview of the current mosquito and tick research scenario. The wide array of control tools recently developed has been considered, with special reference to those approved by the World Health Organization Vector Control Advisory Group (WHO VCAG), as well as novel ones with an extremely promising potential to be exploited in vector control programs. Concerning mosquitoes, a major focus has been given on genetically modified vectors, eave tubes, attractive toxic sugar baits (ATSB) and biocontrol agents. Regarding ticks, the recent development of highly effective repellents and acaricides (including nanoformulated ones) as well as behavior-based control tools, has been highlighted. In the second part of the review, key research questions about biology and control of mosquitoes and ticks have been critically formulated. A timely research agenda outlining hot issues to be addressed in mosquito and tick research is provided. Overall, it is expected that the present review will contribute to boost research and applications on successful mosquito and tick control strategies, along with an improved knowledge of their biology and ecology.

Ethnobotanical survey of plants used as repellents against housefly, Musca domestica L. (Diptera: Muscidae) in Budondo Subcounty, Jinja District, Uganda

BACKGROUND

The housefly, Musca domestica L., is a major public health and domestic pest that spoils food and causes irritation and is a vector of many infectious disease pathogens of medical and veterinary importance. Currently, its control relies largely on chemical pesticides. However, the adverse health and environmental effects of pesticides, risk of development of insect resistance, and bioaccumulation through the food chain emphasize the need to search for environmentally friendly alternatives. This study aimed at documenting traditional knowledge about plants used as repellents against the houseflies by the people of Budondo Subcounty, Uganda.

METHODS

An ethnobotanical survey was conducted between November 2016 and June 2017. A total of 372 household members were interviewed on knowledge and use of traditional insect repellents, through face-to-face interviews guided by semi-structured questionnaires administered in nine villages in Budondo Subcounty.

RESULTS

Overall, only 24.5% of the respondents had ample knowledge about insect repellent plants. A chi-square analysis shows a significant association between respondents' knowledge of insect repellent plants and age, educational status, occupation, religion, and marital status although not with gender. Overall, eight plants from seven families and eight genera were mentioned as repellents. The growth forms encountered were tree, shrub, and herb. Plants that were commonly mentioned by respondents were Cupressus sempervirens L. (16.9%), followed by Lantana camara L.(16.1%), Eucalyptus globulus Labill. (11.0%), Carica papaya L. (8.6%), Cymbopogon citratus (de Candolle) Stapf (4.3%), Mentha × piperita L. (2.4%), Azadirachta indica A. Juss (2.2%), and Ocimum kilimandscharicum Gürke (0.8%) in descending order. Leaves were the most commonly used plant part (76.9%), followed by the stem/bark (19.8%), flowers (2.2%), and root (1.1%). Burning of the plant materials in order to generate smoke was the most popular method of application.

CONCLUSIONS

This study has shown that there are many locally available plants in use by the people of Budondo Subcounty with potency for repelling houseflies. Further studies are needed to identify bioactive compounds responsible for the repellent activity in the different species which could be promoted as sustainable housefly control tools in these remotely located communities of Budondo. Furthermore, studies on the efficacy of these repellent plants or plant parts and their potential toxicological properties should be considered a priority.

Mosquito oviposition deterrents

Mosquitoes are well-known vectors of disease and threaten the health of millions of people annually. While synthetic insecticides have been relied on to combat these diseases, insecticide resistance and environmental concerns have directed attention towards novel and more targeted mosquitocides derived from botanicals. Research on the activity of botanical derivatives has focused on mosquito larvae and adults with little attention given to their potential as oviposition deterrents against gravid female mosquitoes. This review explores the influence of chemical and biological factors on deterrence and examines issues relating to environmental persistence and non-target effects. With very few discoveries of new insecticide pathways, the answer to effective mosquito control may well reside within other ancient plant-based organisms that have co-resided and evolved with this ubiquitous pest.

High toxicity of camphene and γ-elemene from Wedelia prostrata essential oil against larvae of Spodoptera litura (Lepidoptera: Noctuidae)

The development of eco-friendly biopesticides in the fight against agricultural pests is an important challenge nowadays. The essential oil of Wedelia prostrata Hemsl. is known for its multipurpose biological activities in Chinese folk medicine. However, limited efforts attempted to understand the potential insecticidal activity of its main individual constituents and related mechanism of action. In this research, we investigated the insecticidal activity of W. prostrata against the crop pest Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae). Toxicity on 4th instar larvae was assessed after 24 h of exposure. The LC₅₀ and LC₉₀ of the W. prostrata essential oil were 167.46 and 322.12 μg/ml, respectively. GC-MS analyses were carried out to shed light on the oil chemical composition. Main constituents were the monoterpene camphene (9.6%) and the sesquiterpenes γ-elemene (7.6%), α-humulene (6.9%), and (E,E)-α-farnesene (7.3%). The pure constituents were evaluated for their insecticidal activity on S. litura 4th instar larvae. The most toxic molecule was camphene (LC₅₀ = 6.28 μg/ml), followed by γ-elemene, (LC₅₀ = 10.64 μg/ml), α-humulene (LC₅₀ = 12.89 μg/ml), and (E,E)-α-farnesene (LC₅₀ = 16.77 μg/ml). Overall, our experiments highlighted the promising potential of camphene and γ-elemene from W. prostrata essential oil against larvae of S. litura, allowing us to propose these two compounds for the development of newer pesticides in the fight against crop pests. Further studies aimed at evaluating the potential synergy between these two molecules, as well as their stability in field conditions are ongoing.

Mosquito control with green nanopesticides: towards the One Health approach? A review of non-target effects

The rapid spread of highly aggressive arboviruses, parasites, and bacteria along with the development of resistance in the pathogens and parasites, as well as in their arthropod vectors, represents a huge challenge in modern parasitology and tropical medicine. Eco-friendly vector control programs are crucial to fight, besides malaria, the spread of dengue, West Nile, chikungunya, and Zika virus, as well as other arboviruses such as St. Louis encephalitis and Japanese encephalitis. However, research efforts on the control of mosquito vectors are experiencing a serious lack of eco-friendly and highly effective pesticides, as well as the limited success of most biocontrol tools currently applied. Most importantly, a cooperative interface between the two disciplines is still lacking. To face this challenge, we have reviewed a wide number of promising results in the field of green-fabricated pesticides tested against mosquito vectors, outlining several examples of synergy with classic biological control tools. The non-target effects of green-fabricated nanopesticides, including acute toxicity, genotoxicity, and impact on behavioral traits of mosquito predators, have been critically discussed. In the final section, we have identified several key challenges at the interface between "green" nanotechnology and classic biological control, which deserve further research attention.

Eco-friendly and cost-effective Ag nanocrystals fabricated using the leaf extract of Habenaria plantaginea: toxicity on six mosquito vectors and four non-target species

Recently, the biofabrication of metal nanoparticles has gained wide interest owing to its inherent features such as swift, simplicity, eco-friendliness, and cheaper costs. Different green-reducing agents led to the production of nanoparticles with varying toxicity on insects. In the current study, silver nanoparticles (AgNPs) were successfully synthesized using Habenaria plantaginea leaf extract. Ag nanoparticles were studied by UV-Vis spectroscopy (UV-Vis), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS), and transmission electron microscopy (TEM). H. plantaginea extract and AgNPs were tested for mosquito larvicidal activity on Anopheles stephensi, Aedes aegypti, Culex quinquefasciatus, An. subpictus, Ae. albopictus, and Cx. tritaeniorhynchus. LC₅₀ values were 102.51, 111.99, 123.47, 123.96, 136.56, 149.42 μg/ml and 12.23, 13.38, 14.78, 14.37, 15.39, 16.89 μg/ml, respectively. Moreover, H. plantaginea aqueous extract and AgNPs were tested against the non-target species Anisops bouvieri, Diplonychus indicus, Poecilia reticulata, and Gambusia affinis obtaining LC₅₀ values ranging from 831.82 to 36,212.67 μg/ml. Overall, this study showed the effectiveness of H. plantaginea-fabricated nanoparticles on a wide range of important mosquito vectors, highlighting their scarce toxicity on four natural enemies predating mosquito larvae and pupae.

Curzerene, trans-β-elemenone, and γ-elemene as effective larvicides against Anopheles subpictus, Aedes albopictus, and Culex tritaeniorhynchus: toxicity on non-target aquatic predators

A wide number of studies dealing with mosquito control focus on toxicity screenings of whole plant essential oils, while limited efforts shed light on main molecules responsible of toxicity, as well as their mechanisms of action on non-target organisms. In this study, GC-MS shed light on main essential oil components extracted from leaves of the Suriname cherry Eugenia uniflora, i.e., curzerene (35.7%), trans-β-elemenone (11.5%), and γ-elemene (13.6%), testing them on Anopheles subpictus, Aedes albopictus, and Culex tritaeniorhynchus larvae. Non-target toxicity experiments were carried out on four species of aquatic larvivorous organisms, including fishes, backswimmers, and waterbugs. The essential oil from E. uniflora leaves tested on An. subpictus, Ae. Albopictus, and Cx. tritaeniorhynchus showed LC₅₀ of 31.08, 33.50, and 36.35 μg/ml, respectively. Curzerene, trans-β-elemenone, and γ-elemene were extremely toxic to An. subpictus (LC₅₀ = 4.14, 6.13, and 10.53 μg/ml), Ae. albopictus (LC₅₀ = 4.57, 6.74, and 11.29 μg/ml), and Cx. tritaeniorhynchus (LC₅₀ = 5.01, 7.32, and 12.18 μg/ml). The essential oil from E. uniflora leaves, curzerene, trans-β-elemenone, and γ-elemene showed low toxicity to larvivorous fishes, backswimmers, and waterbugs, with LC₅₀ ranging from 303.77 to 6765.56 μg/ml. Predator safety factor (PSF) ranged from 55.72 to 273.45. Overall, we believe that curzerene isolated from the essential oil from E. uniflora leaves can represent an ideal molecule to formulate novel mosquito larvicides, due to its extremely low LC₅₀ on all tested mosquito vectors (4.14-5.01 μg/ml), which far encompasses most of the botanical pesticides tested till now. Notably, the above-mentioned LC₅₀ did not damage the four aquatic predators tested in this study.

Clausena anisata and Dysphania ambrosioides essential oils: from ethno-medicine to modern uses as effective insecticides

Dysphania ambrosioides (L.) Mosyakin & Clemants (Amaranthaceae) and Clausena anisata (Willd.) Hook. f. ex Benth. (Rutaceae) are two aromatic species traditionally used in Cameroon to repel and kill insects. The present work was carried out to substantiate this traditional use and to evaluate the possible incorporation in commercial botanical insecticides of their essential oils (EOs). The EOs were distilled from leaves of C. anisata and aerial parts of D. ambrosioides and analyzed by gas chromatography-mass spectrometry (GC-MS). The insecticidal activity of both EOs was investigated against the filariasis vector, Culex quinquefasciatus, and the housefly, Musca domestica. As possible mode of action, the inhibition of acetylcholinesterase (AChE) by the two EOs was investigated as well. The D. ambrosioides EO was characterized by the monoterpene peroxide ascaridole (61.4%) and the aromatic p-cymene (29.0%), whereas the C. anisata EO was dominated by the phenylpropanoids (E)-anethole (64.6%) and (E)-methyl isoeugenol (16.1%). The C. anisata EO proved to be very toxic to third instar larvae of C. quinquefasciatus showing LC₅₀ of 29.3 μl/l, whereas D. ambrosioides EO was more toxic to adults of M. domestica showing a LD₅₀ of 51.7 μg/adult. The mixture of both EOs showed a significant synergistic effect against mosquito larvae with LC₅₀ estimated as 19.3 μl/l, whereas this phenomenon was not observed upon application to M. domestica adults (LD₅₀ = 75.9 μg/adult). Of the two EOs, the D. ambrosioides one provided a good inhibition of AChE (IC₅₀ = 77 μg/ml), whereas C. anisata oil was not effective. These findings provide new evidences supporting the ethno-botanical use of these two Cameroonian plants, and their possible application even in synergistic binary blends, to develop new eco-friendly, safe and effective herbal insecticides.

The crop-residue of fiber hemp cv. Futura 75: from a waste product to a source of botanical insecticides

In the attempt to exploit the potential of the monoecious fiber hemp cv. Futura 75 in new fields besides textile, cosmetics and food industry, its crop-residue given by leaves and inflorescences was subjected to hydrodistillation to obtain the essential oils. These are niche products representing an ideal candidate for the development of natural insecticides for the control and management of mosquito vectors, houseflies and moth pests. After GC-MS analysis highlighting a safe and legal chemical profile (THC in the range 0.004-0.012% dw), the leaf and inflorescence essential oils were investigated for the insecticidal potential against three insect targets: the larvae of Culex quinquefasciatus and Spodoptera littoralis and the adults of Musca domestica. The essential oil from inflorescences, showing (E)-caryophyllene (21.4%), myrcene (11.3%), cannabidiol (CBD, 11.1%), α-pinene (7.8%), terpinolene (7.6%), and α-humulene (7.1%) as the main components, was more effective than leaf oil against these insects, with LD₅₀ values of 65.8 μg/larva on S. littoralis, 122.1 μg/adult on M. domestica, and LC₅₀ of 124.5 μl/l on C. quinquefasciatus larvae. The hemp essential oil moderately inhibited the acetylcholinesterase (AChE), which is a target enzyme in pesticide science. Overall, these results shed light on the future application of fiber hemp crop-residue for the development of effective, eco-friendly and sustainable insecticides.

Towards green oviposition deterrents? Effectiveness of Syzygium lanceolatum (Myrtaceae) essential oil against six mosquito vectors and impact on four aquatic biological control agents

Essential oils (EOs) from plants may be alternative sources of molecules toxic against mosquito vectors of public health relevance. Most of researches in this field focused on EOs as larvicides or ovicides, while limited efforts focused on the exploitation of EOs as oviposition deterrents. In the present study, the larvicidal and oviposition deterrent activity of Syzygium lanceolatum leaf EO was evaluated against six mosquito species, Anopheles stephensi, An. subpictus, Aedes aegypti, Ae. albopictus, Culex quinquefasciatus, and Cx. tritaeniorhynchus. The chemical composition of the S. lanceolatum EO was analyzed by GC-MS analysis, showing the presence of phenyl propanal, β-caryophyllene, α-humulene, and caryophyllene oxide as major constituents. S. lanceolatum EO showed high acute toxicity on An. stephensi (LC₅₀ = 51.20 μg/ml), Ae. aegypti (LC₅₀ = 55.11 μg/ml), Cx. quinquefasciatus (LC₅₀ = 60.01 μg/ml), An. subpictus (LC₅₀ = 61.34 μg/ml), Ae. albopictus (LC₅₀ = 66.71 μg/ml), and Cx. tritaeniorhynchus (LC₅₀ = 72.24 μg/ml) larvae. Furthermore, the EO was effective as oviposition deterrent against the six tested mosquito species, with OAI on An. stephensi, An. subpictus, Ae. aegypti, Ae. albopictus, Cx. quinquefasciatus, and Cx. tritaeniorhynchus reaching -0.83, -0.81, -0.84, -0.83, -0.84, and -0.86, respectively. The toxicity of S. lanceolatum EO against several biological control agents of mosquitoes, including water bugs (Anisops bouvieri and Diplonychus indicus) and fishes (Gambusia affinis and Poecilia reticulata), was extremely low, with LC₅₀ ranging between 4148 and 15,762 μg/ml. Overall, our results pointed out the promising potential of the S. lanceolatum leaf EO as a source of environmental-friendly oviposition deterrents and larvicides effective against a wide number of mosquito species of importance for parasitology.

Biophysical characterization of Acacia caesia-fabricated silver nanoparticles: effectiveness on mosquito vectors of public health relevance and impact on non-target aquatic biocontrol agents

Mosquito-borne diseases lead to serious public health concerns in tropical and sub-tropical countries worldwide, due to development of mosquito resistance to synthetic pesticides, non-target effects of pesticides, and socioeconomic reasons. Currently, green nanotechnology is a promising research field, showing a wide range of potential applications in vector control programs. The employ of natural products as reducing agents to fabricate insecticidal nanocomposites is gaining research attention worldwide, due to low costs and high effectiveness. Interestingly, biophysical features of green-synthesized nanoparticles strongly differ when different botanicals are employed for nanosynthesis. In this study, a cheap Acacia caesia leaf extract was employed to fabricate silver nanoparticles (Ag NPs) with ovicidal, larvicidal, and adulticidal toxicity against three mosquito vectors, Anopheles subpictus, Aedes albopictus, and Culex tritaeniorhynchus. Ag NPs were analyzed by various biophysical methods, including spectroscopy (UV-visible spectrophotometry, XRD, FTIR, EDX) and microscopy (SEM, TEM, AFM) techniques. High acute larvicidal potential was observed against larvae of An. subpictus (LC₅₀ = 10.33 μg/ml), Ae. albopictus (LC₅₀ = 11.32 μg/ml), and Cx. tritaeniorhynchus (LC₅₀ = 12.35 μg/ml). Ag NPs completely inhibited egg hatchability on three vectors at 60, 75, and 90 μg/ml, respectively. In adulticidal assays, LD₅₀ values were 18.66, 20.94, and 22.63 μg/ml. If compared to mosquito larvae, Ag NPs were safer to three non-target aquatic biocontrol agents, with LC₅₀ ranging from 684 to 2245 μg/ml. Overall, our study highlights the potential of A. caesia as an abundant and cheap bioresource to fabricate biogenic Ag NPs effective against mosquito young instars and adults, with moderate impact on non-target aquatic biocontrol agents.

Boswellia ovalifoliolata (Burseraceae) essential oil as an eco-friendly larvicide? Toxicity against six mosquito vectors of public health importance, non-target mosquito fishes, backswimmers, and water bugs

The use of synthetic pesticides to control vector populations is detrimental to human health and the environment and may lead to the development of resistant strains. Plants can be alternative sources of safer compounds effective on mosquito vectors. In this study, the mosquito larvicidal activity of Boswellia ovalifoliolata leaf essential oil (EO) was evaluated against Anopheles stephensi, Anopheles subpictus, Aedes aegypti, Aedes albopictus, Culex quinquefasciatus, and Culex tritaeniorhynchus. GC-MS revealed that the B. ovalifoliolata EO contained at least 20 compounds. The main constituents were β-pinene, α-terpineol, and caryophyllene. In acute toxicity assays, the EO was toxic to larvae of An. stephensi, Ae. aegypti, Cx. quinquefasciatus, An. subpictus, Ae. albopictus, and Cx. tritaeniorhynchus with LC₅₀ values of 61.84, 66.24, 72.47, 82.26, 89.80, and 97.95 μg/ml, respectively. B. ovalifoliolata EO was scarcely toxic to mosquito fishes, backswimmers, and water bugs predating mosquito larvae with LC₅₀ from 4186 to 14,783 μg/ml. Overall, these results contribute to develop effective and affordable instruments to magnify the reliability of Culicidae control programs.

High efficacy of (Z)-γ-bisabolene from the essential oil of Galinsoga parviflora (Asteraceae) as larvicide and oviposition deterrent against six mosquito vectors

The eco-friendly management of mosquitoes with novel and effective larvicides and oviposition deterrents is a crucial challenge to prevent outbreaks of mosquito-borne diseases. However, most of the herbal formulations tested in these years showed LC₅₀ values higher of 40 ppm, and significant oviposition deterrent activity only when tested at relatively higher doses (> 50 μg/ml). Herein, we studied the chemical composition of the Galinsoga parviflora essential oil (EO). This plant is an annual herb native to South America naturalized all over the world. We tested the EO larvicidal and oviposition deterrent action on 6 mosquito species. Totally 37 compounds were identified in the EO of G. parviflora by GC and GC-MS analyses. The major constituent was (Z)-γ-bisabolene (38.9%). The G. parviflora EO and (Z)-γ-bisabolene showed acute toxicity on An. stephensi (LC₅₀ = 31.04 and 2.04 μg/ml, respectively), Ae. aegypti (LC₅₀ = 34.22 and 2.26 μg/ml, respectively), Cx. quinquefasciatus (LC₅₀ = 37.10 and 2.47 μg/ml, respectively), An. subpictus (LC₅₀ = 40.97 and 4.09 μg/ml, respectively), Ae. albopictus (LC₅₀ = 45.55 and 4.50 μg/ml, respectively) and Cx. tritaeniorhynchus (LC₅₀ = 49.56 and 4.87 μg/ml, respectively) larvae. Furthermore, the oviposition deterrent potential of the G. parviflora EO and (Z)-γ-bisabolene was studied on six mosquito vectors, showing that 25 μg/ml of (Z)-γ-bisabolene led to an Oviposition Activity Index lower of - 0.79 in all tested mosquito vectors. Overall, all larvicidal LC₅₀ values estimated for (Z)-γ-bisabolene were lower than 5 μg/ml. This result far encompasses current evidences of toxicity reported for the large majority of botanical products currently tested against mosquito young instars, allowing us to propose this compound as an highly effective mosquito larvicide and oviposition deterrent.

Larvicidal activity of selected plant extracts and their combination against the mosquito vectors Culex quinquefasciatus and Aedes aegypti

In order to develop an environment-friendly botanical mosquito larvicide alternative to the chemical larvicides, extracts were made from the leaves of Hyptis suaveolens, Lantana camara, Nerium oleander, and Tecoma stans with three organic solvents such as methanol (ME), chloroform (CH), and petroleum ether (PE) using a Soxhlet extractor. The plant extracts were screened for larvicidal activity individually and in combination against the larvae of Aedes aegypti and Culex quinquefasciatus as per WHO protocol. Among the extracts, the maximum larvicidal activity was shown by the PE extract of L. camara (LC₅₀ 10.63 mg/L) followed by the PE extract of T. stans (LC₅₀ 19.26 mg/L), ME extract of N. oleander (LC₅₀ 35.82 mg/L), and PE extract of H. suaveolens (LC₅₀ 38.39 mg/L) against Cx. quinquefasciatus. In the case of Ae. aegypti, the PE extract of T. stans showed maximum activity with LC₅₀ value of 55.41 mg/L followed by H. suaveolens (LC₅₀ 64.49 mg/L), PE extract of L. camara (LC₅₀ 74.93 mg/L), and ME extract of N. oleander (LC₅₀ 84.09). A blend of these four extracts resulted in a combination with corresponding LC₅₀ values of 4.32 and 7.19 mg/L against Cx. quinquefasciatus and Ae. aegypti. The predator safety factors were 12.55 and 20.88 for Gambusia affinis with respect to Aedes and Culex larvae for the extract combination. Chemical constituents in extracts were also identified by FT-IR and GC-MS data. The present investigations suggest the possible use of this blend of botanical extracts as an ideal ecofriendly, larvicide against Ae. aegypti and Cx. quinquefasciatus larvae.