Insecticidal and larvicidal activities of medicinal plant extracts against mosquitoes

Effect of nanoformulation Azadirachta indica on some factors associated with the vectorial capacity and competence of Anopheles aquasalis experimentally infected with Plasmodium vivax

Malaria remains a highly prevalent infectious disease worldwide, particularly in tropical and subtropical regions. Effectively controlling of mosquitoes transmitting of Plasmodium spp. is crucial in to control this disease. A promising strategy involves utilizing plant-derived products, such as the Neem tree (Azadirachta indica), known for its secondary metabolites with biological activity against various insect groups of agricultural and public health importance. This study investigated the effects of a nanoformulation prototype Neem on factors linked to the vector competence of Anopheles aquasalis, a malaria vector in Latin America. Different concentrations of the nanoformulation were supplied through sugar solution and blood feeding, assessing impacts on longevity, fecundity, fertility, and transgenerational survival from larvae to adults. Additionally, the effects of the Neem nanoformulation and NeemAZAL® formulation on the sporogonic cycle of P. vivax were evaluated. Overall, significant impacts were observed at 100 ppm and 1,000 ppm concentrations on adult survival patterns and on survival of the F1 generation. A trend of reduced oviposition and hatching rates was also noted in nanoformulation-consuming groups, with fertility and fecundity declining proportionally to the concentration. Additionally, a significant decrease in the infection rate and intensity of P. vivax was observed in the 1,000 ppm group, with a mean of 3 oocysts per female compared to the control's 27 oocysts per female. In the commercial formulation, the highest tested concentration of 3 ppm yielded 5.36 oocysts per female. Concerning sporozoite numbers, there was a reduction of 52 % and 87 % at the highest concentrations compared to the control group. In conclusion, these findings suggest that the A. indica nanoformulation is a potential as a tool for malaria control through reduction in the vector longevity and reproductive capacity, possibly leading to decreased vector population densities. Moreover, the nanoformulation interfered with the sporogonic development of P. vivax. However, further basic research on Neem formulations, their effects, and mechanisms of action is imperative to gain a more specific perspective for safe field implementation.

Ethnomedicinal uses, phytochemistry, and pharmacological relevance of Justicia procumbens (Oriental Water Willow) - A promising traditional plant

ETHNOPHARMACOLOGICAL RELEVANCE

Justicia procumbens L. (JP) (Oriental Water Willow, Shrimp plant, Acanthaceae) is a herbaceous plant that is commonly found in India, Taiwan, Australia, Southern China, Vietnam, and Korea. The plant has been primarily used to treat fever, asthma, edema, cough, jaundice, urinary tract infection, and sore throat, as well as for snake bites and as a fish-killer. In the present review, the reported phyto-chemical, ethno-pharmacological, biological, and toxicological studies on J. procumbens were summarized. Special focus had been given to its reported lignans, regarding their isolation, characterization, quantitative estimation, and biosynthesis.

MATERIALS AND METHODS

A survey of the literature was done using assorted databases and publishers; Scopus, Sci-Finder, Web of Science, PubMed, GoogleScholar, ScienceDirect, Wiley, Taylors&Francis, Bentham, Thieme, and Springer.

RESULTS

Currently, 95 metabolites have been separated fromJ. procumbens. Lignans and their glycosides were reported as main phyto-constituents of J. procumbens. Various methods are mentioned for quantitative estimation of these lignans. These phyto-constituents possessed wide pharmacological effectiveness, such as antiplatelet aggregation, antimicrobial, antitumor, and antiviral.

CONCLUSIONS

Many of the stated effects are harmonious with the reported traditional uses of this plant. This data could further support J. procumbens's utilization as a herbal remedy and drug lead. However, further study of J. procumbens toxicity, as well as preclinical and clinical investigation is required to ensure the safe usage of J. procumbens.

Mosquito larvicidal, pupicidal and ovicidal effects of the extracts of Peltophorum pterocarpum flowers on Aedes aegypti and Culex quinquefasciatus

Mosquitoes are the vectors of several diseases like dengue, chikungunya, malaria etc. The three important mosquito species in India are Aedes aegypti, Culex quinquefasciatus and Anopheles stephensi. Several plant extracts have been tested for their anti-mosquito activity. In this dissertation, the larvicidal, pupicidal and ovicidal activities of the successive hexane, chloroform and methanol extracts of Peltophorum pterocarpum (Fabaceae) on mosquitoes are reported. The larvicidal activity of those extracts on both Aedes aegypti and Culex quinquefasciatus mosquitoes was found to be in a decreasing order of hexane, methanol and chloroform - the LC50 values for these extracts were 111.81 and 104.84 ppm, 121.92 and 121.56 ppm, 357.2 and 352.0 ppm respectively. Their pupicidal activity on both mosquitoes was found in the order of methanol, chloroform and hexane - the LC50 values for these extracts being 172.8 and 162.35 ppm, 425.8 respectively. Their ovicidal activity on both mosquitoes was found to be very low, even at the higher concentration of 500 ppm. This is the first report on the effect of the extracts of Peltophorum pterocarpum flowers on the two mosquito species of Aedes aegypti, Culex quinquefasciatus. In the present work, the results showed that the hexane extract had the highest larvicidal activity, while methanol showed the highest pupicidal activity besides larvicidal activity. Hence, the methanol extract holds promise to be used as mosquitocidal agent against the above two vectors.

Insecticidal potential of a Consolida ajacis extract and its major compound (ethyl linoleate) against the diamondback moth, Plutella xylostella

The diamondback moth (Plutella xylostella) is one of the most destructive lepidopteran pests of cruciferous vegetables. However, DBM has developed resistance to current chemical and biological insecticides used for its control, indicating the necessity for finding new insecticides against it. Bio-insecticides derived from plant extracts are eco-friendly alternatives to synthetic pesticides. The aims of this study were to evaluate the insecticidal activity of Consolida ajacis seed extracts against DBM, the underlying mechanism of the control effect of promising extracts, and the identification of the main insecticidal compounds of these extracts. The results showed that ethyl acetate extract of C. ajacis seed exhibited strong contact toxicity (LC50: 5.05 mg/mL), ingestion toxicity, antifeedant, and oviposition deterrent activities against DBM, among the extracts evaluated. At 72 h, glutathiase, acetylcholinesterase, carboxylesterase, peroxidase, and superoxide dismutase activities were inhibited, but catalase activity was activated. The main compound identified from the extract was ethyl linoleate, which had the most significant insecticidal activity on the diamondback moths. This study's findings provide a better understanding of the insecticidal activity of ethyl acetate extract obtained from C. ajacis and its main component (ethyl linoleate). This will help in the development of new insecticides to control DBM.

Novel Essential Oils Blend as a Repellent and Toxic Agent against Disease-Transmitting Mosquitoes

Bio-insecticidal research has focused on long-term vector control using essential oils (EOs). This study examined the larvicidal, oviposition-deterrent, and repellent properties of five medicinal herb-based EO formulations (EOFs) on mosquitoes that are vectors of dengue, filariasis, and malaria. EOFs were significantly more toxic to the larvae and pupae of Culex quinquefasciatus, Anopheles stephensi, and Aedes aegypti with LC₅₀ = 9.23, 12.85, and 14.46 ppm, as well with 10.22, 11.39, and 12.81 ppm, with oviposition active indexes of -0.84, -0.95, and -0.92, respectively. Oviposition-deterrent repellence was found in 91.39%, 94.83%, and 96.09%. EOs and N, N-Diethyl-3-methylbenzamide (DEET) were prepared at various concentrations for time duration repellent bioassays (6.25-100 ppm). Ae. aegypti, An. stephensi, and Cx. quinquefasciatus were monitored for 300, 270, and 180 min, respectively. At 100 ppm, EOs and DEET had comparable repellence in terms of test durations. EOF's primary components d-limonene (12.9%), 2,6-octadienal, 3,7-dimethyl, (Z) (12.2%), acetic acid, phenylmethyl ester (19.6%), verbenol (7.6%), and benzyl benzoate (17.4%) may be combined to make a mosquito larvicidal and repellant equivalent to synthetic repellent lotions. In the molecular dynamics simulations, limonene (-6.1 kcal/mol) and benzyl benzoate (-7.5 kcal/mol) had a positive chemical association with DEET (-6.3 kcal/mol) and interacted with the OBP binding pocket with high affinity and stability. This research will help local herbal product manufacturers and the cosmetics industry in developing 100% herbal insect repellent products to combat mosquito-borne diseases, including dengue, malaria, and filariasis.

Hydroxyapatite-binding Silver/Titanium Dioxide as a Potential Control Compound Against Mosquito Vectors, Aedes aegypti (Diptera: Culicidae) and Anopheles dirus (Diptera: Culicidae)

Controlling mosquitoes is vital for counteracting the rising number of mosquito-borne illnesses. Vector control requires the implementation of various measures; however, current methods lack complete effectiveness, and new control agents or substances are urgently needed. Therefore, this study developed a nonwoven fabric sheet coated with hydroxyapatite-binding silver/titanium dioxide compound (hydroxyapatite-binding silver/titanium dioxide sheet [HATS])and evaluated its effectiveness on all stages of laboratory Aedes aegypti (Linnaeus); Diptera: Culicidae and Anopheles dirus (Peyton & Harrison); Diptera: Culicidae. We reared larvae with HATS and control sheets and assessed their mortality, emergence, and hatching rates. The submersion rates of engorged female mosquitoes in submerged HATS and control sheets were also compared. The HATS strongly affected mosquito development, resulting in high mortality rates (mean ± SE) of 99.66 ± 0.58% (L1-L2) and 91.11 ± 9.20% (L3-L4) for Ae. aegypti and 100% of both stages for An. dirus. In contrast, mosquitoes raised in the control sheet showed relatively high survival rates of 92.33 ± 3.21% (L1-L2) and 95.67 ± 0.58% (L3-L4) for Ae. aegypti and 86.07 ± 3.53% (L1-L2) and 92.01 ± 8.67% (L3-L4) for An. dirus. Submersion of engorged females was found in the HATS oviposition cup, leading to a decreased number of eggs and a low hatching rate compared to that of the control. Overall, HATS may be a useful new control method for Ae. aegypti and An. dirus.

Role of antioxidant activity of essential oils in their acaricidal activities against Rhipicephalus annulatus

Essential oils of Origanum majorana and Satureja thymbra as well as carvacrol are natural products that are known to have potent antioxidant activities. The current study was designed to investigate the role of the antioxidant properties of these natural products in their acaricidal activities against Rhipicephalus annulatus larvae. The synergistic and/or antagonistic effects of the addition of vitamins E and C and hydrogen peroxide (H2O2) to these natural products were also evaluated. Larval packet tests were used to evaluate the acaricidal activities against the larvae of R. annulatus. The antioxidant effectiveness of these products was determined by a DPPH (2,2-diphenyl-1-picrylhydrazyl) free radical scavenging assay. The addition of vitamin E at 100 mg/mL to O. majorana and S. thymbra decreased the concentrations required to achieve the death of half of the larvae (LC50) to 0.44 and 0.47%, respectively. The combination of O. majorana and S. thymbra attained the LC50 at 1.54% which was decreased to 0.69% after addition of vitamin E. Also, the addition of vitamin E to carvacrol reduced the LC50 to 0.27%. The total antioxidant activity of these natural products increased significantly in presence of vitamin E. The addition of H2O2 inhibited the acaricidal activity of all tested materials, especially at low concentrations. All treatments induced an increase in lipid peroxidation, whereas carvacrol-treated larvae revealed the lowest values for the superoxide dismutase. Glutathione peroxidase and catalase activity decreased in larvae treated with S. thymbra combined with vitamin E. In conclusion, the addition of vitamins E and C increased the acaricidal activities of the tested compounds, whereas the addition of H2O2 decreased these activities. The antioxidant activities of essential oils and their active components may play an important role in mediating their acaricidal activities.

Insecticidal effect of ethnobotanical plant extracts against Anopheles arabiensis under laboratory conditions

Background

The emergence and spread of resistant strains of malaria vectors to chemical insecticides are becoming major problems for malaria vector management. Natural plant products have a vital role to play in the current challenge of malaria control. The current study was conducted to evaluate insecticidal effect of ethnobotanical plant extracts against the primary malaria vector, Anopheles arabiensis in northwestern Ethiopia.

Methods

Primarily, ethnobotanical plants used for Anopheles mosquito control were surveyed in Dangur district, northwestern Ethiopia. Insecticide-susceptible strains of Anopheles arabiensis mosquito were reared in the insectary of the Tropical and Infectious Diseases Research Centre, Assosa University. After surveying plants used for mosquito control in local people, four frequently used plants were identified for extraction. The larvicidal and adulticidal potential of frequently used plant extracts against susceptible strains of the laboratory colony were evaluated.

Results

A total of 15 plants were identified as ethnobotanical plants that help local people with mosquito control. Azadirachta indica, Ocimum lamiifolium, Ocimum americanum, Moringa olifeira leaf, and Moringa olifeira seed species of local plants were found to be frequently used to kill and/or repel mosquitoes in the study district. All the plant extracts were found to have potential larvicidal activity against fourth instar larvae of An. arabiensis and only ethanol and methanol extract of Azadirachta indica and Ocimum lamiifolium were found to have potential adulticidal effect against adult of An. arabiensis. The highest larvicidal activity was observed in ethanol extract of Azadirachta indica with 95% larval mortality and lowest Lethal Concentration 50 (LC 50) of 40.73parts per million (ppm) and LC90 of 186.66 ppm. The highest adulticidal activity was observed in methanol extract of Azadirachta indica with 75% adult mortality at 300 ppm and lowest LC50 of 106.65 ppm and LC90 of 1,293 ppm. The lowest larvicidal and adulticidal activity was observed in methanol extracts of Ocimum lamiifolium with 63.35% larval mortality and leaf extract of Moringa olifeira with 50% adult mortality at 300 ppm, respectively.

Conclusion

Ethanol extract of Azadirachta indica exerted a remarkable larvicidal effect against An. arabiensis and thus it can be used for botanical mosquito insecticide development. Since the current finding is based on susceptible strain of An. arabiensis, further work on wild mosquitoes is recommended.

Green synthesis and characterization of titanium dioxide nanoparticles using leaf extract of Pouteria campechiana and larvicidal and pupicidal activity on Aedes aegypti

The frequent application of synthetic insecticides creates resistance among insects, including mosquitoes, and causes environmental pollution and health issues. The current work aim at assessing the possibilities to produce and characterize the titanium dioxide (TiO₂) nanoparticles (TiO₂ NPs) mediated through the aqueous leaf extract of Pouteria campechiana, and their larvicidal and pupicidal activities against Aedes aegypti. The attained results showed that the aqueous leaf extract of P. campechiana had the efficiency to fabricate TiO₂ NPs from TiO₂. Under the UV-vis spectrum analysis, a sharp peak was recorded at 320 nm, which indicated the production of TiO₂ NPs by the plant extract. The SEM analysis revealed that the synthesized TiO₂ NPs were spherical, and 5 dissimilar diffractions were detected in the XRD spectrum analysis related to the TiO₂ NPs. In FTIR analysis, a prominent peak was found at 1052.41 cm^-1, corresponding to alcohol, and confirmed metal reduction. In the EDX analysis, there was a signal of around 58.44%, confirming the decrease in Ti from TiO₂ NPs, and the remaining percentages were Ca, Al, and Mg. About 900 μg mL^-1 of TiO₂ NPs had excellent lethal activity against various larvae and pupa stages of Ae. aegypti. The attained results showed that the P. campechiana aqueous leaf extract could reduce TiO₂ into TiO₂ NPs and could be considered a mosquito control agent. Furthermore, this is the initial report about the aqueous leaf extract of P. campechiana effectively synthesizing the TiO₂ NPs with anti-mosquito activity.

Selection of candidate reference genes for RT-qPCR analysis in Argulus siamensis and their validation through screening of drugs and drug targets

Argulus spp. are economically important fish ectoparasites. The development of antiparasitic drugs is thus important and real time PCR is an indispensable tool in drug development. The analytical potential of RT-PCR depends upon accurate normalisation by the use of stable reference genes. Here, we identified stable reference genes of Argulus siamensis for validation of efficacy of drugs and drug targets. Seven candidate genes were evaluated by evaluating their expression under different states of Argulus using the RefFinder tool. The four algorithms together generated a comprehensive ranking with elongation factor-1 alpha (EF-1α) being the most stable and 18S ribosomal protein (18S) the least stable gene. Taking EF-1α and 18S genes as references, the effectiveness of six anti-parasitic compounds against Argulus was evaluated by studying their effect on the expression pattern of few ion channel genes; this was to understand their mode of action, besides validating the reference genes. EF-1α was found to be the most stable gene in the validation. Collectively, this study is the first report to validate the optimal reference genes of A. siamensis for normalisation, and the potential of the ion channel genes for evaluating effective drug targets in parasite control.

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.

Target and non-target toxicity of fern extracts against mosquito vectors and beneficial aquatic organisms

Dengue and malaria are significant mosquito-borne diseases that are rapidly spread worldwide, mainly in temperate countries. Pteridophytes were identified to be a significant source of novel mosquitocidal agents. The present research was to explore the eco-friendly larvicides from methanol extracts of ferns, viz., Actiniopteris radiata, Adiantum caudatum, Cheilanthes swartzii, Hemionitis arifolia and Lycopodium clavatum. The larvicidal potential of the extracts screened using larvae of dengue vector Aedes aegypti (III and IV instar) and malarial vector Anopheles stephensi (III and IV instar), showed 10-100% mortality rates. Biosafety assessment was made on embryos of Danio rerio and Artemia nauplii. The phyto-constituents of the methanol extract of A. radiata leaves were identified through gas chromatography-mass spectrometry (GC-MS). Methanolic leaf extracts of A. radiata, A. caudatum and C. swartzii exhibited larvicidal activity against III and IV instar larvae of Ae. aegypti (LC₅₀: 37.47, 74.51 and 152.38 and 67.58, 95.89 and 271.46 ppm) and An. stephensi (LC₅₀: 70.35, 112.12 and 301.05 and 113.83, 175.30 and 315.19 ppm), respectively. The GC-MS of the methanol extract of A. radiata leaves revealed the presence of 7 phyto-components among which, Carbamic acid, phenyl-, (2-Nitrophenyl) methyl ester (1), Benzoic acid, 3- methylbenzoate (2) and 4-(benzylimino)- 1,4-dihydro-1-(p-toluoylmethyl) pyridine (3) were dominant. Biosafety assessment of methanol extract of A. radiata leaves on embryos of Danio rerio (Zebra fish) and Artemia nauplii (micro crustacean) revealed that there were no destructive or teratogenic effects. To conclude, the larvicidal activity and insignificant toxicity to non-target aquatic organisms of A. radiata leaves makes it a potential and environment safe biocontrol agent against dengue and malarial vectors.

Zingiber cernuum (Zingiberaceae) essential oil as effective larvicide and oviposition deterrent on six mosquito vectors, with little non-target toxicity on four aquatic mosquito predators

Mosquitoes are responsible for the transmission of many pathogens and parasites, which cause serious diseases in humans and animals. Currently, botanical products have been suggested as alternative tools in the fight against arthropod vectors. In this study, the essential oil (EO) extracted from Zingiber cernuum was tested as larvicide and oviposition deterrent on six mosquito species of public health relevance, including malaria and Zika virus vectors. The EO showed high toxicity on third instar larvae of Anopheles stephensi (LC₅₀ = 41.34 μg/ml), Aedes aegypti (LC₅₀ = 44.88 μg/ml), Culex quinquefasciatus (LC₅₀ = 48.44 μg/ml), Anopheles subpictus (LC₅₀ = 51.42 μg/ml), Aedes albopictus (LC₅₀ = 55.84 μg/ml), and Culex tritaeniorhynchus (LC₅₀ = 60.20 μg/ml). In addition, low doses of Z. cernuum EO reduced oviposition rates in six mosquito species. The acute toxicity of Z. cernuum EO on four mosquito predators was scarce; LC₅₀ ranged from 3119 to 11,233 μg/ml. Overall, our results revealed that the Z. cernuum EO can be considered for the development of effective and environmental-friendly mosquito larvicides and oviposition deterrents.

The bioefficacy of crude extracts of Azadirachta indica (Meliaceae) on the survival and development of myiasis-causing larvae of Chrysomya bezziana (Diptera: Calliphoridae)

Myiasis is a type of parasitosis originating from the invasion of tissues of live humans and other vertebrates by dipteran larvae. The Old World screwworm fly—Chrysomya bezziana—is known worldwide in the tropical regions for causing myiasis among man and domestic animals, thereby leading to health hazards and severe economic losses to the dairy farmers. Management techniques for controlling populations of the fly are needed to minimize these losses. Plant-derived materials have been increasingly evaluated these days in controlling the insects of medical and veterinary importance. This study evaluated the efficacy of crude extracts of the plant neem, Azadirachta indica, against C. bezziana. The dried leaves of the plant were extracted successively with four different solvents viz. petroleum ether, chloroform, ethyl acetate and methanol and were evaluated against the third instar larvae of C. bezziana using dipping method and thin film application technique. In the dipping method, larvae were dipped in four different concentrations of plant extracts for 30 s, whereas in the thin film application, they were exposed to a thin film of plant extracts. The results showed that all the extracts had toxic effect on the larvae in both the techniques. In the dipping method, the highest mortalities were recorded in methanol extract followed by chloroform, petroleum ether and ethyl acetate extracts with LC50 values 1.07 g/100 ml, 1.7 g/100 ml, 3.39 g/100 ml and 4.9 g/100 ml, respectively. In the thin film application method, methanol extract showed the highest mortalities followed by chloroform, ethyl acetate and petroleum ether with LC50 values 0.4 mg/cm2, 0.6 mg/cm2, 2.1 mg/cm2 and 2.5 mg/cm2. It is concluded that the crude extracts of A. indica can be used in controlling the larvae of C. bezziana by using the dipping as well as thin film application technique.

Characterization and bioassay for larvicidal activity of Anacardium occidentale (cashew) shell waste fractions against dengue vector Aedes aegypti

Recent studies regarding the harmful effects of synthetic larvicides initiated the need to investigate for unconventional measures that are environmentally safe and target-specific against Aedes aegypti larvae. Thus, the main objectives of the study are to evaluate the larvicidal toxicity of the solvent fractions of Anacardium occidentale shell wastes against the third and fourth instar larvae of A. aegypti and to compare the results with the commercial larvicide product. The shell wastes were extracted with 95% EtOH followed by polarity-based fractionation. The fractions were tested for larvicidal activity according to the World Health Organization bioassay method. These were then characterized by quantitative thin-layer chromatographic (TLC) fingerprinting. The hexane fraction gave the strongest activity among the fractions with an LC50 of 4.01 mg/L and LC90 of 11.29 mg/L highly comparable to the commercial larvicide, which exhibited an LC50 of 1.71 mg/L and LC90 of 8.41 mg/L. The dichloromethane fraction exhibited 9.70 mg/L LC50 and 18.44 mg/L LC90. The remarkable toxicity effects exhibited by these fractions indicate their potential to provide core structures from which sustainable and environmentally safe plant-based larvicidal agents can be synthesized.

Larvicidal activity of Persea americana Mill. against Aedes aegypti

OBJECTIVE

To evaluate the toxicity of the ethanol and hexane extracts of the different parts of Persea americana Mill. (P. americana) toward third and fourth instars larvae of Aedes aegypti (Ae. aegypti) and to characterize the ethanol extract by qualitative phytochemical analysis.

METHODS

The seeds, peels and pulp of P. americana were processed for crude extraction using 95% ethanol and n-hexane. Crude extracts were bio-assayed for larvicidal activity against Ae. aegypti following the World Health Organization standard bioassay method. The mortality was observed at 24 h and 48 h after treatment and data were subjected to probit analysis to determine lethal concentrations (LC50 and LC90). The ethanol extract was characterized by phytochemical analysis.

RESULTS

Both the hexane and ethanol extracts from the different parts of P. americana exhibited evidence of larvicidal toxicity. The hexane extract from the seeds exhibited the highest toxicity with LC50 and LC90 values of 9.82 mg/L and 22.19 mg/L, respectively, while the ethanol seed extract exhibited LC50 of 16.48 mg/L and LC90 45.77 mg/L, respectively. This was closely followed by the ethanol extract of the peels with an LC50 of 10.35 mg/L and LC90 of 26.29 mg/L. The pulp extracted with ethanol also yielded great larvicidal toxicity with LC50 of 21.32 mg/L and LC90 of 59.45 mg/L. Results of the phytochemical analysis of the ethanol seed extract indicated presence of alkaloids, tannins, saponins, unsaturated steroids and triterpenoids, flavonoids (leucoanthocyanins), fats and oils.

CONCLUSIONS

Both the hexane and ethanol extracts of P. americana showed promising potential as an alternative source of a more sustainable, non-toxic and environmentally friendly solution for the control of dengue vector, Ae. aegypti.

Evaluation of plant-mediated synthesized silver nanoparticles against vector mosquitoes

Diseases transmitted by blood-feeding mosquitoes, such as dengue fever, dengue hemorrhagic fever, Japanese encephalitis, malaria, and filariasis, are increasing in prevalence, particularly in tropical and subtropical zones. To control mosquitoes and mosquito-borne diseases, which have worldwide health and economic impacts, synthetic insecticide-based interventions are still necessary, particularly in situations of epidemic outbreak and sudden increases of adult mosquitoes. Green nanoparticle synthesis has been achieved using environmentally acceptable plant extract and eco-friendly reducing and capping agents. In view of the recently increased interest in developing plant origin insecticides as an alternative to chemical insecticide, in the present study, the adulticidal activity of silver nanoparticles (AgNPs) synthesized using Heliotropium indicum plant leaf extract against adults of Anopheles stephensi, Aedes aegypti, and Culex quinquefasciatus was determined. Adult mosquitoes were exposed to varying concentrations of aqueous extract of H. indicum and synthesized AgNPs for 24 h. AgNPs were rapidly synthesized using the leaf extract of H. indicum, and the formation of nanoparticles was observed within 6 h. The results recorded from UV-vis spectrum, Fourier transform infrared, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy support the biosynthesis and characterization of AgNPs. The maximum efficacy was observed in synthesized AgNPs against the adult of A. stephensi (lethal dose (LD)₅₀ = 26.712 μg/mL; LD₉₀ = 49.061 μg/mL), A. aegypti (LD₅₀ = 29.626 μg/mL; LD₉₀ = 54.269 μg/mL), and C. quinquefasciatus (LD₅₀ = 32.077 μg/mL; LD₉₀ = 58.426 μg/mL), respectively. No mortality was observed in the control. These results suggest that the leaf aqueous extracts of H.indicum and green synthesis of AgNPs have the potential to be used as an ideal eco-friendly approach for the control of the A. stephensi, A. aegypti, and C. quinquefasciatus. This is the first report on the adulticidal activity of the plant extracts and AgNPs.

Tropical Plant Extracts as Sources of Grain-Protectant Compounds Against Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae)

The toxicity of organic plant extracts to Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) was assessed for three tropical plant species: branches, leaves, and seeds of Annona montana (Annonaceae), branches of Aristolochia paulistana (Aristolochiaceae), and leaves and branches of Casearia sylvestris (Salicaceae). The screening assay resulted that the extracts of A. montana seeds obtained with hexane (LC50 = 534.75 mg kg(-1) and LT50 = 6.10 days) and with dichloromethane (LC50 = 424.67 mg kg(-1) and LT50 = 5.03 days) were the most promising treatments, followed by the extract prepared from A. montana leaves with hexane (LC50 = 837.70 mg kg(-1) and LT50 = 4.90 days). Moreover, extracts (at 1,500 mg kg(-1)) prepared from C. sylvestris branches with dichloromethane and A. paulistana with hexane caused significant mortality (37% and 41.5%, respectively) beyond sublethal effects on S. zeamais. Therefore, based on the biological assays, extraction yield, and evaluation of the chromatographic profile of the crude extracts by TLC, the hexane extract of A. montana seeds was selected and fractioned using liquid-liquid partitioning. The hydroalcoholic fraction caused mortality of 55.5%, significantly superior to dichloromethane fraction, which caused 35.5% of mortality. Chemical analyses ((1)H NMR, HPLC, and TLC) were performed, and the results showed the presence of alkaloids and acetogenins in both active fractions, which have been associated with bioactivity. Therefore, extracts prepared from A. montana seeds (especially) is an interesting source of new compounds with promising grain-protectant properties.

Screening for adulticidal activity against Anopheles arabiensis in ten plants used as mosquito repellent in South Africa

BACKGROUND

Due to the development of resistance to synthetic insecticides, adverse effects to human health, non-target organisms and the environment, there is an urgent need to develop new insecticides, which are effective, safe, biodegrable and target-specific. This study was undertaken to evaluate the adulticidal activity of 10 plants used traditionally as mosquito repellents in South Africa.

METHODS

The dried plant materials were extracted with dichloromethane (DCM) and ethanol (EtOH). The extracts were evaluated for adulticidal activity against Anopheles arabiensis mosquitoes, a potent malaria vector in South Africa. Adult mortality was observed after 24 hours of exposure.

RESULTS

All the extracts showed adulticidal activity. The highest activity was observed in both DCM and EtOH extracts of Aloe ferox leaves with 98 and 86% mosquito mortality, respectively. The DCM extract of A. ferox leaves was then subjected to a dose-dependent bioassay to determine the EC50 value. The extract exhibited an EC50 value of 4.92 mg/ml.

CONCLUSION

The results of the present study showed that the DCM extract of A. ferox leaves may have the potential to be used as an insecticide against An. arabiensis. Further studies to isolate and identify active compounds are in progress.

Bioefficacy of plant-mediated gold nanoparticles and Anthocepholus cadamba on filarial vector, Culex quinquefasciatus (Insecta: Diptera: Culicidae)

Mosquito-borne diseases in India, e.g., malaria, dengue, chikungunya, filariasis, and Japanese encephalitis cause thousands of deaths per year. Mosquito control is to enhance the health and quality of life of county residents and visitors through the reduction of mosquito populations. Mosquito control is of serious concern in developing countries like India due to the lack of general awareness, development of resistance, and socioeconomic reasons. Noble metal nanoparticles have been used because of their unique optical properties; especially gold and silver have a broad absorption band in the visible region of electromagnetic spectrum. Synthesis of gold nanoparticles using Cymbopogan citratus is an ecofriendly approach for safer environment. C. citratus leaf broth was a good reducing agent that converted chloroauric acid (HAuCl(4)) to metal gold and further heating converted it into nanoparticles. Characterization using UV spectrophotometer, X-ray diffraction, Fourier transform infrared spectroscopy, particle size analyzer, and transmission electron microscopy confirmed that the particles are gold nanoparticles ranging between 10 and 110 nm with an average particles size of 20 nm. Further biosynthesized gold nanoparticles and Anthocephalus cadamba were experimented for the larvicidal effect on the filarial vector, Culex quinquefasciatus. Results showed that the gold nanoparticles are much toxic than the plant extract. Observed lethal concentrations (LC(50) and LC(90)) were 1.08 and 2.76 ppm for gold nanoparticles and 21.82 and 79.52 ppm for the third instar of C. quinquefasciatus.

Integration of botanicals and microbials for management of crop and human pests

Insect pests inflict damage to humans, farm animals, and crops. Human and animal pests put more than 100 million people and 80 million cattle at risk worldwide. Plant pests are the main reason for destroying one fifth of the world's total crop production annually. Anopheles stephensi is the major vector of human malaria in Middle East and South Asian regions. Spodoptera litura is a polyphagous pest of vegetables and field crops. Because of its broad host range, this insect is also known as cluster caterpillar, common cutworm, cotton leafworm, tobacco cutworm, tobacco caterpillar, and tropical armyworm. The toxic effects of methanolic extract of Senna alata and microbial insecticide, Bacillus sphericus, were tested against the polyphagous crop pest, S. litura (Fab.), and the malarial vector, A. stephensi. Results from the present study states that B. sphericus is more toxic than S. alata to both the crop pest and mosquito. The malarial vector, A. stephensi, was found to be susceptible than the crop pest, S. litura. Both the botanical and microbial insecticide showed excellent larvicidal, pupicidal, longevity, fecundity, and growth regulatory activities. Median lethal concentrations of B. sphericus and methanolic extract of S. alata observed to kill the third instar of S. litura were 0.52 and 193.09 ppm and A. stephensi were 0.40 and 174.64 ppm, respectively.

Chemical Constituents and Pharmacology of the Aristolochia ( mădōu ling) species

Aristolochia ( mădōu ling) is an important genus widely cultivated and had long been known for their extensive use in traditional Chinese medicine. The genus has attracted so much great interest because of their numerous biological activity reports and unique constituents, aristolochic acids (AAs). In 2004, we reviewed the metabolites of Aristolochia species which have appeared in the literature, concerning the isolation, structural elucidation, biological activity and literature references. In addition, the nephrotoxicity of aristolochic acids, biosynthetic studies, ecological adaptation, and chemotaxonomy researches were also covered in the past review. In the present manuscript, we wish to review the various physiologically active compounds of different classes reported from Aristolochia species in the period between 2004 and 2011. In regard to the chemical and biological aspects of the constituents from the Aristolochia genus, this review would address the continuous development in the phytochemistry and the therapeutic application of the Aristolochia species. Moreover, the recent nephrotoxicity studies related to aristolochic acids would be covered in this review and the structure-toxicity relationship would be discussed.

Mosquito larvicidal activity of alkaloids and limonoids derived from Evodia rutaecarpa unripe fruits against Aedes albopictus (Diptera: Culicidae)

In recent years, uses of environment friendly and biodegradable natural insecticides of plant origin have received renewed attention as agents for vector control. During a screening program for new agrochemicals from Chinese medicinal herbs and local wild plants, the ethanol extract of Evodia rutaecarpa Hook f. et Thomas (Rutaceae) unripe fruits was found to possess larvicidal activity against the mosquitoes. The aim of this research was to determine larvicidal activity of the ethanol extract of E. rutaecarpa unripe fruits and the isolated constituents against the larvae of the Culicidae mosquito Aedes albopictus. The powder, 5 kg of the fruit material, was extracted with 30 l of 95 % ethanol, filtered, and evaporated to dryness in a rotary vacuum evaporator. The crude extract was then partitioned between methanol-water and n-hexane. The n-hexane fraction was evaporated off to given n-hexane extract. The aqueous layer was repartitioned with chloroform to provide chloroform extract after evaporation of the solvent. Further partitioning with ethyl acetate gave a residue after evaporation of the solvent. Bioactivity-directed chromatographic separation of chloroform extract on repeated silica gel columns led to the isolation of three alkaloids (evodiamine, rutaecarpine, and wuchuyuamide I) and two limonoids (evodol and limonin). The structures of the constituent compounds were elucidated based on high-resolution electron impact mass spectrometry and nuclear magnetic resonance. Evodiamine, rutaecarpine, and wuchuyuamide I exhibited strong larvicidal activity against the early fourth instar larvae of A. albopictus with LC(50) values of 12.51, 17.02, and 26.16 μg/ml, respectively. Limonin and evodol also possessed larvicidal activity against the Asian tiger mosquitoes with LC(50) values of 32.43 and 52.22 μg/ml, respectively, while the ethanol extract had a LC(50) value of 43.21 μg/ml. The results indicated that the ethanol extract of E. rutaecarpa and the five isolated constituents have a good potential as a source for natural larvicides.

Repellent effect of Salvia dorisiana, S. longifolia, and S. sclarea (Lamiaceae) essential oils against the mosquito Aedes albopictus Skuse (Diptera: Culicidae)

Aedes albopictus (Diptera: Culicidae) has been one of the fastest spreading insects over the past 20 years. Its medical importance is due to the aggressive daytime human-biting behavior and the ability to vector many viruses, including dengue, LaCrosse, Eastern Equine encephalitis and West Nile viruses. In this research, the essential oils (EOs) extracted from fresh air dried leaves of Salvia dorisiana, S. longifolia, and S. sclarea (Lamiaceae) were evaluated for their repellent activity against A. albopictus by using the human-bait technique. The EOs chemical composition was also investigated, and EOs were divided in three different profiles on the basis of their chemical composition: EO with large amount of monoterpenes from S. sclarea, EO rich in oxygenated sesquiterpenes from S. dorisiana, and S. longifolia EO characterized by similar percentages of monoterpenes and sesquiterpenes. The efficacy protection from S. dorisiana, S. longifolia, and S. sclarea EOs, at dosages ranging from 0.004 to 0.4 μL cm(-2) of skin, was evaluated during 120 min of observation. Results indicated that S. dorisiana, S. longifolia, and S. sclarea EOs had a significant repellent activity (RD(50) =0.00035, 0.00049, and 0.00101 μL cm(-2), respectively), with differences in repellency rates, as a function of oil, dosage, and observation time. S. dorisiana was the most effective oil: at the two higher dosages, it gave almost complete protection (with a protective efficacy of 90.99% and 95.62%, respectively) for 90 min. The best protection time was achieved with S. dorisiana essential oil. It ranged from 9.2 to 92.4 min. Protection times of S. longifolia and S. sclarea oils ranged from 3.2 to 60 min, and from 3.6 to 64.2 min, respectively. Our findings clearly reveal that these EOs have a good repellent activity against A. albopictus, therefore they can be proposed to improve the efficacy of repellent formulations against the Asian tiger mosquito.

Repellent activity of some essential oils against Simulium species in India

Use of repellents seems to be most reliable method of personal protection against annoyance and infections associated with haematophagous insects. We have investigated the biting activity of Simulium and tested the repellency of five essential oils extracted from Homalomena aromatica Schott (Alismatales: Araceae), Pogostemon heyneanus Bentham (Lamiales: Lamiaceae), Citrus aurantifolia Swingle (Sapindales: Rutaceae), Vitex negundo L. (Lamiales: Lamiaceae), and Ageratum conzoides L. (Asterales: Asteraceae) on the human volunteers against Simulium (blackflies) in three locations of Arunachal Pradesh, India. Blackflies preferred biting legs (> 79%) as compared to hand and face with profound biting activity during 1000-1100 h (> 23%) and 1500 - 1600 h (> 28%). The essential oil extracted from Homalomena aromatica, Vitex negundo and Ageratum conizoides provided > 2 h protection at 5% concentration and > 5 h protection at 10% concentration in all the three testing locations. The repellency of Homalomena aromatica, Vitex negundo and Ageratum conizoides essential oils after 6 h application was > 50% at 5% concentration and > 90% at 10% concentration. The study provides evidence for the potential of these essential oils in developing new repellents against blackflies.

Larvicidal activity of medicinal plant extracts and lignan identified in Phryma leptostachya var. asiatica roots against housefly (Musca domestica L.)

Medicinal plant extracts from 27 plant species in 20 families were tested for their larvicidal activity against housefly, Musca domestica (L.). Responses varied with plant material and concentration. Among plant species tested, Phryma leptostachya var. asiatica showed 100% larvicidal activity against M. domestica at 10 mg/g concentration. Larvicidal activities of Atractylodes japonica, Saussurea lappa, Asiasarum sieboldi, and Gleditsia japonica var. koraiensis were 89.3%, 85.3%, 93.3%, and 96.6% at 10 mg/g concentration, respectively. Extracts of Prunus persica, Curcuma longa, and Paeonia moutan produced moderate activity. Larvicidal activity of other plant extracts was less than 50%. Among test plant species, P. leptostachya var. asiatica showed the most potent larvicidal activity. The active constituent of P. leptostachya var. asiatica roots was identified as the leptostachyol acetate by spectroscopic analysis. The LC(50) values of leptostachyol acetate against M. domestica larvae were 0.039 mg/g. Naturally occurring medicinal plant extracts and P. leptostachya var. asiatica root-derived compounds merit further study as potential housefly larval control agents or lead compounds.

Larvicidal activity of lignans from Phryma leptostachya L. against Culex pipiens pallens

The larvicidal activity of crude petroleum ether, ethyl acetate, and methanol extracts of the whole plants of Phryma leptostachya L. was assayed for its toxicity against the early fourth instar larvae of Culex pipiens pallens. The larval mortality was observed after 24 h of exposure. Among three solvent extracts from Phyrma leptostachya L., the petroleum ether extract exhibited the best larvicidal activity. The corresponding LC₅₀ values of petroleum ether, ethyl acetate, and methanol extracts were 3.23, 5.23, and 61.86 ppm against the early fourth instar larvae of Culex pipiens pallens. The petroleum ether extract was successively subjected to column chromatography and preparative high performance liquid chromatography, and yielded the three lignans, phrymarolin-I, haedoxane A, and haedoxane E, which were isolated and identified as new mosquito larvicidal compounds. Phrymarolin-I, haedoxane A, and haedoxane E showed high larvicidal activity, for which the lethal doses LC₅₀ were estimated at 1.21, 0.025, and 0.15 ppm against the early fourth instar larvae of Culex pipiens pallens, respectively. The structures were elucidated by analyses of IR, UV, MS, and NMR spectral data. This is the first report on the mosquito larvicidal activity of the three compounds, phrymarolin-I, haedoxane A, and haedoxane E from Phyrma leptostachya L.

First report on susceptibility of wild Aedes aegypti (Diptera: Culicidae) using Carapa guianensis (Meliaceae) and Copaifera sp. (Leguminosae)

Oils of Carapa guianensis and Copaifera spp. are well known in the Amazonian region as natural insect repellent, and studies have reported their efficiency as larvicide against some laboratory mosquito species. However, in wild populations of mosquitoes, these oils have not yet been evaluated. Thus, the objective of this study was to investigate their efficiency as larvicide in wild populations of Aedes aegypti with a history of exposure to organophosphate. The susceptibility of larvae was determined under three different temperatures, 15°C, 20°C, and 30°C. For each test, 1,000 larvae were used (late third instar and early fourth instar-four replicates of 25 larvae per concentration). Statistical tests were used to identify significant differences. The results demonstrated that as the laboratory A. aegypti, the wild populations of A. aegypti were also susceptible to C. guianensis and Copaifera sp. oils. The lethal concentrations for Copaifera sp. ranged from LC(50) 47 to LC(90) 91 (milligrams per liter), and for C. guianensis, they were LC(50) 136 to LC(90) 551 (milligrams per liter). In relation to different temperature, the effectiveness of the oils on larvae mortality was directly related to the increase of temperature, and better results were observed for temperature at 25°C. The results presented here indicate the potential larvicidal activity of C. guianensis and species of Copaifera, in populations of A. aegypti from the wild. Therefore, the results presented here are very important since such populations are primarily responsible for transmitting the dengue virus in the environment.

Evaluation of time toxicity, residual effect, and growth-inhibiting property of Carapa guianensis and Copaifera sp. in Aedes aegypti

Oils of Carapa guianensis and Copaifera spp. are well-known in the Amazonian region as natural insect repellents, and studies have reported their efficiency as larvicide against some mosquito species. However, toxicity persistence and effect on mosquito development have not yet been evaluated. Thus, the objective of this study was to evaluate the initial time of larvicidal activity, residual effect, and the effect of very low concentrations of these oils on Aedes aegypti. Different concentrations of the oils were used to evaluate the initial time of larval mortality and residual effect, as well as, the development of larvae, pupae, and adults. Results demonstrated that the lethal effect started mainly between the first 2 and 3 h of larvae exposure to oils, when using concentrations which ranged from 500 mg/L of C. guianensis and 90 mg/L of Copaifera sp. The toxic effect remained with total efficiency (100% mortality) until the sixth day for Copaifera sp. and 12th day for C. guianensis. When using sublethal dosages (ranging from 140 mg/L of C. guianensis to 26 mg/L of Copaifera sp.) mortality was observed after the larval molt. Also, imperfection of pupae and adult development and unsuccessful emergence of adults were observed. A product of botanical origin that could break the development of immature stage of mosquitoes and inhibit the emergence of adults should be essential in vector control. Thus, our results provide new information for a better understanding in using C. guianensis and Copaifera sp. oils with a potential to be used as a natural insecticide.

Biolarvicidal compound gymnemagenol isolated from leaf extract of miracle fruit plant, Gymnema sylvestre (Retz) Schult against malaria and filariasis vectors

Owing to the fact that the application of synthetic larvicide has envenomed the surroundings as well as non-target organisms, natural products of plant origin with insecticidal properties have been tried as an indigenous method for the control of a variety of insect pests and vectors in the recent past. Insecticides of plant origin have been extensively used on agricultural pests and, to a very limited extent, against insect vectors of public health importance, which deserve careful and thorough screening. The use of plant extracts for insect control has several appealing features as these are generally more biodegradable, less hazardous and a rich storehouse of chemicals of diverse biological activities. Moreover, herbal sources give a lead for discovering new insecticides. Therefore, biologically active plant materials have attracted considerable interest in mosquito control study in recent times. The crude leaf extracts of Gymnema sylvestre (Retz) Schult (Asclepiadaceae) and purified gymnemagenol compound were studied against the early fourth-instar larvae of Anopheles subpictus Grassi and Culex quinquefasciatus Say (Diptera: Culicidae). In the present study, bioassay-guided fractionation of petroleum ether leaf extract of G. sylvestre led to the separation and identification of gymnemagenol as a potential new antiparasitic compound. Phytochemical analysis of G. sylvestre leaves revealed the presence of active constituents such as carbohydrates, saponins, phytosterols, phenols, flavonoids and tannins. However, cardiac glycosides and phlobatannins are absent in the plant extracts. Quantitative analysis results suggested that saponin (5%) was present in a high concentration followed by tannins (1.0%). The 50 g powder was loaded on silica gel column and eluted with chloroform-methanol-water as eluents. From that, 16 mg pure saponin compound was isolated and analysed by thin layer chromatography using chloroform and methanol as the solvent systems. The structure of the purified triterpenoid fraction was established from infrared (IR), ultraviolet (UV), (1)H nuclear magnetic resonance (NMR), (13)C NMR and mass spectral data. The carbon skeleton of the compound was obtained by (13)C NMR spectroscopy. The chemical shift assignments obtained for gymnemagenol from (1)H NMR correspond to the molecular formula C(30)H(50)O(4). The compound was identified as 3β, 16β, 28, 29-tetrahydroxyolean-12-ene (gymnemagenol sapogenin). Parasite larvae were exposed to varying concentrations of purified compound gymnemagenol for 24 h. The results suggested that the larval mortality effects of the compound were 28%, 69%, 100% and 31%, 63%, 100% at 6, 12 and 24 h against A. subpictus and C. quinquefasciatus, respectively. In the present study, the per cent mortality were 100, 86, 67, 36, 21 and 100, 78, 59, 38 and 19 observed in the concentrations of 1,000, 500, 250, 125 and 62.75 ppm against the fourth-instar larvae of A. subpitcus and C. quinquefasciatus, respectively. The purified compound gymnemagenol was tested in concentrations of 80, 40, 20, 10 and 5 ppm, and the per cent mortality were 100, 72, 53, 30 and 15 against A. subpitcus and 100, 89, 61, 42 and 30 against C. quinquefasciatus, respectively. The larvicidal crude leaf extract of G. sylvestre showed the highest mortality in the concentration of 1,000 ppm against the larvae of A. subpictus (LC(50) = 166.28 ppm, r (2) = 0.807) and against the larvae of C. quinquefasciatus (LC(50) = 186.55 ppm, r (2) = 0.884), respectively. The maximum efficacy was observed in gymnemagenol compound with LC(50) and r (2) values against the larvae of A. subpictus (22.99 ppm, 0.922) and against C. quinquefasciatus (15.92 ppm, 0.854), respectively. The control (distilled water) showed nil mortality in the concurrent assay.

Mosquito larvicidal activity of citrus limonoids against Aedes albopictus

Citrus limonoids, nomilin and limonin, were used for larvicidal assay against Aedes albopictus utilizing WHO methodology. LC(50s) were 305.83, 176.08, and 136.07 μM for nomilin and 850.09, 600.72, and 407.09 μM for limonin after 24, 48, and 72 h, respectively. LT(50) assays exhibited that Savage citrange oil was the best at all concentrations (400, 500, 600, and 700 ppm) while Fairchild and Cassa grande were the weakest oils at 400 ppm, but at 500, 600, and 700 ppm, Carrizo citrange remained at the bottom with highest LT(50) values. Results exhibited that nomilin was more toxic than limonin and therefore provided a clear indication that limonoids in sample oils influenced the potential of respective oil. Out of the 10 tested citrus seed oils, Savage citrange (Citrus sinensis) comprised the maximum amount of limonin (2823.59 μg/ml) followed by grapefruit, Sacaton citrumelo, and Jaffa. When this oil (Savage citrange) was evaluated for bioassay against larvae of Ae. albopictus, it reflected complete dominance (LC(50) and LT(50)) as compared to rest of the oils. Although Jaffa (Citrus paradisi) was found to contain nomilin and limonin, it was found less effective as compared to Savage citrange. The oils from Minneola and Chinese lime did not contain limonin and nomilin, and were therefore weak in terms of LC(50) values. Presence of limonin and nomilin in plant products is therefore a significant indicator of the pest control that needs to be exploited in other plants as well.