Botanical repellents and pesticides traditionally used against hematophagous invertebrates in Lao People's Democratic Republic: a comparative study of plants used in 66 villages

Alternatives to Pyrethroid Resistance: Combinations of Cymbopogon nardus and Ocimum americanum Essential Oils Improve the Bioefficiency Control Against the Adults' Populations of Aedes aegypti (Diptera: Culicidae)

Dengue vector control strategies are mostly based on chemicals use against Aedes aegypti populations. The current study aimed at investigating the insecticidal effects of essential oils (EOs) obtained from five plant species, Cymbopogon citrates (D. C.) Stapf. (Poaceae), Cymbopogon nardus (Linn.) Rendle (Poaceae), Eucalyptus camaldulensis Linn. (Myrtaceae), Lippia multiflora Moldenke (Verbenaceae), and Ocimum americanum Linn. Lamiaceae, and combinations of Cymbopogon nardus and Ocimum americanum on Ae. aegypti populations from Bobo-Dioulasso. For this purpose, adults of the susceptible and field strains of Ae. aegypti were tested in WHO tubes with EO alone and binary combinations of O. americanum (OA) and C. nardus (CN; scored from C1 to C9). The extraction of the essential oils was done by hydrodistillation, and their components were determined by GC/MS. Among the 5 EOs tested, L. multiflora essential oil was the most efficient, with KDT50 values below 60 min on all Ae. aegypti strains tested, and also with a rate of mortality up to 100 and 85% for Bora Bora and Bobo-Dioulasso strains, respectively. This efficacy may be due to its major compounds which are with major compounds as β-caryophyllene, p-cymene, thymol acetate, and 1.8 cineol. Interestingly, on all strains, C8 combination showed a synergistic effect, while C2 showed an additive effect. These combinations exhibit a rate of mortality varying from 80 to 100%. Their toxicity would be due to the major compounds and the putative combined effects of some major and minor compounds. More importanly, L. multiflora EO and combinations of C. nardus and O. americanum EO, may be used as alternatives against pyrethroid resistant of Ae. aegypti.

Cananga odorata (Magnoliales: Annonaceae) Essential Oil Produces Significant Avoidance Behavior in Mosquitoes

Essential oil of Cananga odorata Hook. F. & Tomson is a source of insect repellent, but contact irritancy and noncontact repellency actions that stimulate insect's avoidance behavior (escape away from chemical source after direct physical contact or without making physical contact, respectively) have not been investigated. Therefore, an excito-repellency test chamber was used for measuring avoidance behavior of four insectary-reared mosquito species (Diptera: Culicidae) that escape from esposure to four concentrations (0.5, 1.0, 2.5, and 5.0% v/v) of C. odorata oil. The oil strongly repelled both Culex quinquefasciatus Say (85-97% escape) and Anopheles minimus Theobald (97-99%) at high concentrations (2.5-5.0%). For Anopheles dirus Peyton & Harrison and Aedes aegypti (L.), highest repellency (64 and 39% escape, respectively) was demonstrated at 2.5% concentration. For contact irritancy, the oil produced relatively high percent escape found in Cx. quinquefasciatus (90-100% escape) and An. minimus (83-100%). Whereas moderate contact irritancy was observed against An. dirus (40-50% escape) and Ae. aegypti (51-59%). The percent escape was then adjusted with repellency to estimate the effect of contact irritancy alone. We found that highest contact irritancy was presented at 0.5% concentration against An. minimus (67% escape). Knockdown and toxic actions were only found in Anopheles mosquitoes at 5.0% concentration. The results revealed that An. minimus and Cx. quinquefasciatus were more prone to be repelled by C. odorata oil. Detailed analysis of oil identified primary compounds as methyl benzoate (14.6%), α-gurjunene (12.8%), p-methyl-anisole (11.3%), and benzyl acetate (9.9%). Further investigations are needed to assess excito-repellency actions of these compounds alone or in combination.

Ethnobotanical survey of plants traditionally used against hematophagous invertebrates by ethnic groups in the mountainous area of Xishuangbanna, Southwest China

Hematophagous invertebrates such as mosquitoes, leeches, mites, ticks, lice and bugs cause various problems for humans. Considering reports on insecticide resistance and requirements for improved environmental and toxicological profiles, there is a continuing need to discover and develop new insecticides and repellents. Ethnobotanical surveys of traditional plant-based repellents provide a direct method of identifying plants for potential use. During five field surveys in Bulang, Jinuo and Lahu villages between August 2018 and July 2019, semi-structured interviews were conducted with 237 informants (151 male, 86 female; mean age 63). Frequency of citation, use value, informant consensus factor and Jaccard index were employed to statistically analyze the collected data. A total of 709 use reports relating to 32 plant species and 71 remedies were collected. Similarities and differences between the three groups, as well as the Dai and Hani of Xishuangbanna, who were studied earlier, were shown through network analysis. These five ethnic groups living in the same area have a common understanding of traditional botanical knowledge against hematophagous invertebrates, but each group also possesses unique knowledge. Recording and protecting this traditional knowledge is potentially useful for protecting this cultural diversity and related biodiversity and can also have important practical applications. In this study, traditional knowledge provided us with many new potential plants for follow-up research for the development of new insecticides and repellents, among which Artemisia indica, Nicotiana tabacum and Clausena excavata are the most promising.

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.

Considerations for Human Blood-Feeding and Arthropod Exposure in Vector Biology Research: An Essential Tool for Investigations and Disease Control

Eventually there may be a broadly acceptable, even perfected, substitute for the human host requirement for direct feeding experiments by arthropods, most notably mosquitoes. However, for now, direct and indirect feeding on human volunteers is an important, if not essential, tool in vector biology research (VBR). This article builds on the foundational publication by Achee et al. (2015) covering considerations for the use of human participants in VBR pursuits. The authors introduced methods involving human participation in VBR, while detailing human-landing collections (catches) as a prime example. Benedict et al. (2018) continued this theme with an overview of human participation and considerations for research that involves release of mosquito vectors into the environment. In this study, we discuss another important aspect of human use in VBR activities: considerations addressing studies that require an arthropod to feed on a live human host. Using mosquito studies as our principal example, in this study, we discuss the tremendous importance and value of this approach to support and allow study of a wide variety of factors and interactions related to our understanding of vector-borne diseases and their control. This includes establishment of laboratory colonies for test populations, characterization of essential nutrients that contribute to mosquito fitness, characterization of blood-feeding (biting) behavior and pathogen transmission, parameterization for modeling transmission dynamics, evaluation of human host attraction and/or agents that repel, and the effectiveness of antivector or parasite therapeutic drug studies.

Before it disappeared: ethnobotanical study of fleagrass (Adenosma buchneroides), a traditional aromatic plant used by the Akha people

BACKGROUND

Fleagrass, Adenosma buchneroides, is an aromatic perennial herb that occupies an important position in the life of the Akha people. They regard it as a tribal symbol and a gift of love. Fleagrass also has many medicinal uses, and there is considerable potential for its development as an insect repellent. Traditionally, Akha people plant it in swidden fields, but there are few swidden fields in China now. Therefore, the first question this study aims to answer is as follows: how is fleagrass planted and utilized now? At present, fleagrass is only reported to be used by Akha people in Mengla. We also try to understand the following questions: Is fleagrass used in nearby area? If so, how is fleagrass used in nearby area? Furthermore, why is fleagrass used in that way?

METHODS

From August 2016 to July 2018, field surveys were conducted six times. The ethnobotanical and ethnopharmacological uses of A. buchneroides in 13 Akha villages were investigated by means of semi-structured interviews. We assessed the responses of a total of 64 interviewees (32 men and 32 women; mean age, 58.6) from the Xishuangbanna Dai Autonomous Prefecture, southwest China, and from Phongsaly Province, Laos. To explain the bases for the ethnobotanical uses of fleagrass, we used Google Scholar, Web of Science, and China National Knowledge Infrastructure to review the bioactivities of the chemical constituents of A. buchneroides.

RESULTS

With the vanishing of swidden agriculture and the development of modern products, fleagrass cultivation is disappearing in China. However, most Akha people in Xishuangbanna still remember and yearn for its traditional uses, and Akha people in a nearby area (northern Laos) continue to plant and utilize it. We documented ten uses of A. buchneroides within five discrete categories. The whole plant of fleagrass has a distinct strong aroma, of which Akha villagers are particularly fond. Akha villagers mostly use this aromatic property as a decoration, perfume, and insect repellent. A. buchneroides is also used as a condiment and for medicinal and ritual purposes, including its use as a cure for insect bites, headaches, influenza, and diarrhoea, and as a part of pray ritual for a bumper harvest. From our literature review, we identified many major chemical compounds contained in the essential oil of A. buchneroides, including thymol, carvacrol, 3-carene, and p-cymene, which have insecticidal or insect-repellent, antimicrobial, and anti-inflammatory properties.

CONCLUSION

Fleagrass is an aromatic plant that is widely used by Aka people. Its chemical composition also has a variety of biological activities. With the vanishing of swidden agriculture and the development of modern products, fleagrass utilization in China is disappearing and its cultural importance is reduced. However, its economic and medicinal value is assignable.

Biochemical efficacy, molecular docking and inhibitory effect of 2, 3-dimethylmaleic anhydride on insect acetylcholinesterase

Evolution of resistance among insects to action of pesticides has led to the discovery of several insecticides (neonicotinoids and organophosphates) with new targets in insect nervous system. Present study evaluates the mode of inhibition of acetylchlonesterase (AChE), biochemical efficacy, and molecular docking of 2,3-dimethylmaleic anhydride, against Periplaneta americana and Sitophilus oryzae. The knockdown activity of 2,3-dimethylmaleic anhydride was associated with in vivo inhibition of AChE. At KD₉₉ dosage, the 2,3-dimethylmaleic anhydride showed more than 90% inhibition of AChE activity in test insects. A significant impairment in antioxidant system was observed, characterized by alteration in superoxide dismutase and catalase activities along with increase in reduced glutathione levels. Computational docking programs provided insights in to the possible interaction between 2,3-dimethylmaleic anhydride and AChE of P. americana. Our study reveals that 2,3-dimethylmaeic anhydride elicits toxicity in S. oryzae and P. americana primarily by AChE inhibition along with oxidative stress.

Potential mode of action of a novel plumbagin as a mosquito repellent against the malarial vector Anopheles stephensi, (Culicidae: Diptera)

Plumbagin was isolated and characterized from the roots of Plumbago zeylanica using chromatography: TLC, Column chromatogram, HPLC, FTIR and ¹H NMR. The isolated pure compounds were assayed for potency as inhibitors of: acetylcholine esterase (AchE), glutathione S-transferases (GST), superoxide dismutase (SOD), cytochrome P450 and α, β-esterase, and for repellency with Anopheles stephensi at four different concentrations (25, 50, 75 and 100ppm). The enzyme assay against the pure compound reveals that the level of esterase and SOD was decreased significantly in contrast the level of GST and cytochrome P450 was increased significantly. Our results suggests that novel Plumbagin has significantly alters the level of enzyme comparable to the control. Evaluations resulted in Plumbagin producing maximum repellency scores against An. stephensi mosquitoes in dose dependent manner with highest repellence was observed in the 100ppm. Histological examination showed that the midgut, hindgut and muscles are the most affected tissues. These tissues affected with major changes including separation and collapse of epithelial layer and cellular vacuolization. The results support the utility of plant compound Plumbagin for vector control as an alternative to synthetic insecticides, however, more vigorous field trials are needed to determine viability under natural conditions.

Evaluation of a Noncontact, Alternative Mosquito Repellent Assay System

A novel noncontact repellency assay system (NCRAS) was designed and evaluated as a possible alternative method for testing compounds that repel or inhibit mosquitoes from blood feeding. Deet and Aedes aegypti were used in a controlled laboratory setting. Using 2 study designs, a highly significant difference were seen between deet-treated and untreated skin placed behind the protective screens, indicating that deet was detected and was acting as a deterrence to mosquito landing and probing behavior. However, a 2nd study showed significant differences between protected (behind a metal screen barrier) and unprotected (exposed) deet-treated forearms, indicating the screen mesh might restrict the detection of deet and thus influences landing/biting response. These findings indicate the prototype NCRAS shows good promise but requires further evaluation and possible modification in design and testing protocol to achieve more desirable operational attributes in comparison with direct skin-contact repellency mosquito assays.

Plants traditionally used as mosquito repellents and the implication for their use in vector control

Numerous plants with insect repelling properties are native to the tropics where they are produced for a wide range of medicinal purposes. In Thailand, these native plant species have a history of use for personal protection against biting insects. From our investigation we identified 37 plant species within 14 plant families that showed some mosquito repellent properties. Of these, 9 plant species were characterized using an excito-repellency test system against several Thai mosquito species. Results from these studies revealed that five essential oils extracted from plants demonstrated promising insect repellent activity. These active ingredients show promise for further development into formulations that may serve as alternatives to DEET or possibly be used as natural bio-pesticides to kill mosquitoes.

Naturally occurring bioactive compounds from four repellent essential oils against Bemisia tabaci whiteflies

BACKGROUND

In tropical countries, netting is an effective sustainable tool for protecting horticultural crops against Lepidoptera, although not against small pests such as Bemisia tabaci, while smaller mesh netting can be used in temperate regions. A solution is to combine a net with a repellent. Previously we identified repellent essential oils: lemongrass (Cymbopogon citratus), cinnamon (Cinnamomum zeylanicum), cumin (Cuminum cyminum) and citronella (Cymbopogon winternarius). The present study was designed to identify the active compounds of these essential oils, characterise their biological activity and examine their potential for coating nets. We investigated the efficiency and toxicity of nets dipped in different solutions. We then studied the repellent effect with an olfactometer and the irritant effect by videotracking.

RESULTS

Geraniol and citronellol were the most promising net coatings owing to their repellent effect. The repellency, irritancy or toxicity varied with the product and concentration, and these features were independent, indicating that the repellent and the irritant/toxic mechanisms were not the same. The combined effects of these different compounds account for the bioactivity of the mixture, suggesting interactions between the compounds.

CONCLUSION

This new sustainable strategy for protecting vegetable crops against whiteflies is discussed, in addition to the use of companion plants that could produce such bioactive compounds.

Synergistic repellent and irritant effect of combined essential oils on Aedes aegypti (L.) mosquitoes

This study was designed to compare the behavioral responses of Aedes aegypti to a single essential oil and to a mixture of two or three essential oils using an excito-repellency test chamber. Mixtures were prepared from essential oils extracted from Litsea cubeba (LC), Litsea salicifolia (LS), and Melaleuca leucadendron (ML). In general, the mixture of essential oils produced a much stronger escape response by Ae. aegypti, regardless of the test conditions. No significant difference in escape responses was seen when the mixture of oils was compared with a standard commercial product containing DEET. Greater contact irritancy was seen from mixed oils of LC and LS than with other mixed oils. Mixtures of LC and LS at 0.075% showed the highest synergistic action (65.5% escaped) compared to that with unmixed oil alone at the same concentration (LC/20% and LS=32.2%). In addition, mixtures of LC and LS at 0.075% demonstrated the highest non-contact repellency (62.7%) and showed a greater effect than the use of LC (20%) or LS (20.3%) alone. We conclude that mixtures of two essential oils show potential as active ingredients for mosquito repellents.

Repellent, irritant and toxic effects of 20 plant extracts on adults of the malaria vector Anopheles gambiae mosquito

Pyrethroid insecticides induce an excito-repellent effect that reduces contact between humans and mosquitoes. Insecticide use is expected to lower the risk of pathogen transmission, particularly when impregnated on long-lasting treated bednets. When applied at low doses, pyrethroids have a toxic effect, however the development of pyrethroid resistance in several mosquito species may jeopardize these beneficial effects. The need to find additional compounds, either to kill disease-carrying mosquitoes or to prevent mosquito contact with humans, therefore arises. In laboratory conditions, the effects (i.e., repellent, irritant and toxic) of 20 plant extracts, mainly essential oils, were assessed on adults of Anopheles gambiae, a primary vector of malaria. Their effects were compared to those of DEET and permethrin, used as positive controls. Most plant extracts had irritant, repellent and/or toxic effects on An. gambiae adults. The most promising extracts, i.e. those combining the three types of effects, were from Cymbopogon winterianus, Cinnamomum zeylanicum and Thymus vulgaris. The irritant, repellent and toxic effects occurred apparently independently of each other, and the behavioural response of adult An. gambiae was significantly influenced by the concentration of the plant extracts. Mechanisms underlying repellency might, therefore, differ from those underlying irritancy and toxicity. The utility of the efficient plant extracts for vector control as an alternative to pyrethroids may thus be envisaged.

Repellency of DEET, picaridin, and three essential oils to Triatoma rubida (Hemiptera: Reduviidae: Triatominae)

The kissing bug, Triatoma rubida (Uhler) is a common hematophagous bug in Tucson, AZ, and is responsible for causing severe allergic reactions in some bitten individuals. DEET, picaridin, tea tree oil, peppermint oil, and citronella oil were tested for repellency to T. rubida and its ability to probe and feed on a small restrained rat. No long range repellency was observed with any of the test materials. The lowest repellent concentrations observed were: 10% DEET, 7% picaridin; 30% tea tree oil, 3.3% peppermint oil, and 0.165% citronella oil. Only citronella oil was able to stop all probing and feeding by T. rubida. Citronella oil appears to be a promising potential repellent to prevent sleeping people from being bitten by kissing bugs.

A fly in the ointment: evaluation of traditional use of plants to repel and kill blowfly larvae in fermented fish

Introduction

In rural areas in Laos, fly larvae infestations are common in fermenting fish. Blowflies (Chrysomya megacephala, Diptera: Calliphoridae) are attracted to oviposit (and/or larviposit) onto fermenting fish which results in infestations with fly larvae. Knowledge of traditional use of plants to repel larvae during the production of fermented fish is common and widespread in Lao PDR.

Research Questions

How effective are the most salient species in repelling, and killing fly larvae in fermenting fish?

Material and Methods

The three plant species most frequently reported to repel fly larvae during an ethnobotanical survey throughout Lao PDR were tested for repellence and larvicidal activity of fly larvae infesting fermented fish. The lethality and repellence of Tadehagi triquetrum (L.) H. Ohashi (Fabaceae), Uraria crinita (L.) Desv. ex DC. (Fabaceae) and Bambusa multiplex (Lour.) Raeusch. ex Schult. & Schult. f. (Poaceae) were tested in an experimental design using fermenting fish in Vientiane, Lao PDR.

Results

The repellent effect of fresh material of T. triquetrum and U. crinita, and the larvicidal effect of fresh B. multiplex, is significantly more effective than that of dried material of the same species, and the total effect (repellence and larvicidal effect combined) for each of the three species was significantly more effective for fresh than for dry material. Fresh material of T. triquetrum, U. crinita, or B. multiplex added on top of the fermenting fish repelled 50%, 54%, 37%, and killed 22%, 28%, and 40% of fly larvae. The total effect was not significantly different per species at 72%, 82%, and 77%, respectively.

Discussion and Conclusions

The three most salient species are effective in repelling and killing fly larvae in the production of fermented fish, and may be essential to augment food safety during traditional fermentation in open jars.

Acaricidal effect of an isolate from Hoslundia opposita vahl against Amblyomma variegatum (Acari: Ixodidae)

BACKGROUND

Hoslundia opposita Vahl. (Lamiaceae), a common local shrub in Ghana, is traditionally known not only for its pharmacological benefits but also for its insecticidal properties. Its acaricidal property, however, has not been investigated.

OBJECTIVE

To test the acaricidal effects of the crude extract and fractions of H. opposita leaves as well as to isolate and characterize the acaricidal principles.

MATERIALS AND METHODS

The crude methanolic extract, pet. ether, ethyl acetate and aqueous fractions of the leaves of H. opposita were tested against the larvae of the cattle tick, Amblyomma variegatum, using the Larval Packet Test. A bioassay-guided isolation was carried out to identify the acaricidal principle obtained from the ethyl acetate fraction.

RESULTS

The active principle was characterised as ursolic acid, a triterpene previously isolated from the leaves of the same plant. The extract and fractions were less potent than the control, malathion (LC(50) 1.14 × 10(-4) mg/ml). Among the plant samples however the crude methanolic extract exhibited the highest effect against the larvae (LC(50) 5.74 × 10(-2) mg/ml), followed by the ethyl acetate fraction (LC(50) 8.10 × 10(-2) mg/ml). Ursolic acid, pet. ether and aqueous fractions however showed weak acaricidal effects with LC(50) values of 1.13 mg/ml, 8.96 × 10(-1) mg/ml and 1.44 mg/ml, respectively.

CONCLUSION

Ursolic acid was not as potent as the crude methanolic extract and the ethyl acetate fraction from which it was isolated. The overall acaricidal effect of H. opposita may have been due to synergy with other principles having acaricidal properties.

Toxicity of aqueous extract of Euphorbia tirucalli latex on catfish, Heteropneustes fossilis

A four-day static renewal acute toxicity test was performed to determine the LC(50) value of aqueous extract of Euphorbia tirucalli latex for the freshwater fish, Heteropneustes fossilis. The LC(50) values, their upper and lower confidence limits and slope functions were calculated. The LC(50) values for aqueous extract of E. tirucalli latex at various exposure periods are 3.450 μl/L for 24 h, 2.516 μl/L for 48 h, 1.623 μl/L for 72 h and 1.315 μl/L for 96 h. The toxicity of aqueous extract of E. tirucalli latex exhibits a positive correlation between fish mortality and exposure periods. It is concluded that latex of E. tirucalli has higher piscicidal activity as compared with other synthetic pesticides, organophosphates and pyrethroids for the fish H. fossilis. Hence, adequate precautions must be exercised when E. tirucalli latex is being used near fish-inhabiting water reservoirs.