Repellency Bioassay Research Articles

Biocidal action of silver oak (Grevillea robusta) leaf extract on the termite Heterotermes indicola Wasmann (Blattodea: Rhinotermitidae)

The subterranean termite Heterotermes indicola (Blattodea: Rhinotermitidae) is a serious pest to wood in service causing significant annual economic loss in Southeast Asia. In the present study, silver oak (Grevillea robusta A. Cunn.) (Proteaceae) leaf extract was investigated for its termiticidal properties against the termite H. indicola in laboratory tests. An ethanol-solvent system was used to remove the extract from dry leaf powder via Soxhlet apparatus. A dose-dependent foraging response and mortality was observed after continuous exposure to a dose range of 1–20 mg/mL of extract based on dry extract weight. Results indicated that maximum (>90%) termite mortality occurred at 20 mg/mL along with a significant reduction in termite tunneling activity. An LC50 was calculated at 5.47 mg/mL using the concentration series data. In filter paper antifeeding and repellency bioassays, a significant reduction in the total population of gut protozoa compared to untreated and negative controls (solvent) was observed. After 2 weeks of no-choice continuous feeding on filter paper treated at 20 mg/mL, hindgut protozoan population was reduced by 62.90%. The extract conveyed resistance to the non-durable cotton wood and chir pine after vacuum pressure treatment. At the highest concentration tested, 100% mortality was recorded after exposing termites to cotton wood and chir pine treated with silver oak leaf extract. HPLC-DAD-ESI-MS results of the extract showed high level of phenolic compound, alkyl-resorcinol. Results indicated that silver oak leaf extract has termiticidal properties and could be of value in the development of botanical insecticides for termite control in wood products.

Bioassay-guided isolation of active compounds from Adenosma buchneroides essential oil as mosquito repellent against Aedes albopictus

Ethnopharmacological relevanceA folk herb Adenosma buchneroides found in the previous ethnobotanical investigation plays an important role as an insect repellent among the Aini people in southwest of China, but the active compounds responsible for repellent activity of the plant have not yet been investigated. Aim of the studyThe main purpose of the study is to identify the active components of the essential oil which responsible for its repellent activity against Aedes albopictus to support the usage of the plant as mosquito repellent by Aini people. In addition, to supply a class of potential alternatives characterized carvacrol analogues to develop natural repellent products. Material and methodsThe essential oil from aerial part of Ad. buchneroides was extracted by hydrodistillation. A systematic bioassay-guided isolation of repellent compounds from the essential oil was conducted through chromatographic fractionation combined with in-cage mosquito repellent bioassay. The identification of the essential oil components was accomplished by GC-MS and GC-FID techniques. The structural elucidation of compounds was performed on the basis of IR, HR-ESI-MS and NMR. Larvicidal activity and cytotoxicity of all repellent compounds also tested by larval bioassays and MTS assays, respectively. Structure-activity relationship (SAR) of carvacrol analogues was investigated by in-cage mosquito repellent bioassay. ResultsThe essential oil of the plant showed strong mosquito repellent activity with minimum effective dosage (MED) of 0.019 ± 0.007 mg/cm2, compared to reference standard N,N-diethyl-3-methylbenzamide (DEET) (0.031 ± 0.014 mg/cm2). 26 compounds representing 97.8% of the essential oil were identified. Carvacrol, carvacrol methyl ether and a new fragrant compound, adenosmin A (1) were found to be repellent compounds by systematic bioassay-guided isolation, with MEDs in the range of 0.011–0.125 mg/cm2. An investigation on SAR of carvacrol analogues led to the discover of three analogues with further lower MEDs (0.002–0.009 mg/cm2) than that of DEET, and other three compounds with similar MEDs (0.029–0.039 mg/cm2) to that of DEET. Carvacrol (LD50 of 24.8 ppm) was the best larvicide among tested repellent compounds. The essential oil and repellent compounds against seven mammalian cell lines revealed low or no cytotoxicity. ConclusionsScientific evidences reported here validate the plant's traditional use as insect repellent and imply promising application of the essential oil and carvacrol analogues as natural mosquito repellents.

Insecticidal and repellent properties of novel trifluoromethylphenyl amides II

This project focused on the design, synthesis, and testing of trifluoromethylphenyl amides (TFMPAs) as potential mosquitocides and repellents. Fourteen compounds were evaluated for toxicity against larvae and adults of Aedes aegypti. Several compounds were toxic against Aedes aegypti (larval, adult and feeding bioassays) and Drosophila melanogaster (glass-surface contact assay), but were much less toxic than fipronil, with toxicity ratios ranging from 100-fold in the larval assay to 100,000-fold for topical application to adult insects. In repellency bioassays to determine minimum effective dosage (MED), compound N-(2,6-dichloro-4-(trifluoromethyl)phenyl)-2,2,3,3,3-pentafluoropropanamide (7b) repelled Ae. aegypti females at lower concentration, 0.017 (±0.006) μmol/cm2, than N, N-diethyl-meta-toluamide (DEET) 0.026 (±0.005) μmol/cm2. 2-Chloro-N-(3-(trifluoromethyl)phenyl)acetamide (6a) performed better than DEET against two species of mosquitoes: it repelled Ae. aegypti females at 0.013 (±0.006) μmol/cm2 and Anopheles gambiae females (in a warm body repellent assay), at a standard exposure of 2 nmol/cm2. These studies revealed novel active structures that could further lead to compounds with better repellent activity.

Mosquito and tick repellency of two Anthemis essential oils from Saudi Arabia

The essential oils (EOs) of Anthemis melampodina (Am) and Anthemis scrobicularis (As) (Asteraceae) were extracted from the aerial parts of the plants by hydrodistillation, and their chemical compositions were analyzed using GC-FID and GC-MS. Fifty-six components representing 85.5% of the oil composition of Anthemis melampdina were identified, and the major components were α-pinene (17.1%) and β-eudesmol (13.8%). Forty-one components representing 86% of the oil composition of Anthemis scrobicularis were identified, and the major component was β-eudesmol (12.8%). Laboratory bioassays were conducted to determine repellency of Am and As EOs against the yellow fever mosquito Aedes aegypti L. and the lone star tick Amblyomma americanum L. The minimum effective doses (MEDs) of the Am and As EOs against mosquitoes were 0.187 ± 0.000 and 0.312 ± 0.063 mg/cm2 respectively, which were significantly higher than that of DEET (0.023 ± 0.000 mg/cm2) in human-based repellent bioassays. The As EO was more repellent than Am EO against nymphal ticks but was less effective than DEET in vertical paper bioassays.

Ecological applications of Pseudomonas as a biopesticide to control two-spotted mite Tetranychus urticae: chitinase and HCN production

Abstract The two-spotted spider mite (Tetranychus urticae Koch) is an important pest of many horticultural crops. A study was conducted to evaluate the effect of three fluorescent Pseudomonas isolates obtained from rhizospheric soil of tomato (Solanum lycopersicon) in Agadir, Morocco: Q110B, Q036B and Q172B, as potential biological control agents for T. urticae. Both acaricide and repellent activities were assessed on homogenous adult mites. The acaricidal activity test evaluated five concentrations of bacterial suspensions: 0 (control), 102, 104, 106, 108, and 1010 cfu · ml−1, while only the 1010 cfu ∙ ml−1 concentration of each bacterium was used for the repellent bioassay. The mortality rate and repellentindex were recorded 24, 48 and 72 h after application. Results indicated that the survival rate of T. urticae was reduced (p ≤ 0.01) by all three bacterial isolates compared to control. Within the 24–72 h time period the mortality rates ranged from 8 to 87%, 16 to 99%, and 13 to 89%, for Q110B, Q036B and Q172B isolates, respectively. The isolate Q036B (LC50 = 0.598 cfu · ml−1) provided higher mortality rates than Q172B and Q110B with LC50 values of 90,846 and 169,585 cfu · ml−1, respectively. Repellent activity was also the highest with Pseudomonas Q036B having a 71% repellence index at 48 h after application. Regarding the mechanism of action, all three isolates produced hydrogen cyanide, and exhibited protease and cellulose activities, although only Q036B and Q172B had potential chitinase action. Identification analysis showed that the isolates were either Pseudomonas putida (Q172B) or P. fluorescens (Q110B and Q036B). Our results indicate that the P. fluorescens isolate Q036B is a promising candidate for biological control of T. urticae, and has potential to contribute to an integrated pest management program to control this important pest. Then the fruits produced will be qualified as safe for consumers and the environment. The present work was customized to give support for policy decision makers as an agroecological potential meeting needs of industries and ecological balance.

Bioinsecticidal Activity of Eucalyptol and 1R-Alpha-Pinene Rich Acetonic Oils of <i>Eucalyptus saligna</i> on <i>Sitophilus zeamais</i> Motschulsky, 1855 (Coleoptera: Curculionidae)

Exploration of plants, animals, microbes and their products for green pesticides have been the mainstay of modern agriculturalists. Plant bioactive oils have been utilized in formulation of green pesticides, which are less toxic, least deleterious on biocontrol agents, readily biodegraded and have no or few ecological effects as compared to synthetic equivalents. This study evaluated the bioinsecticidal activity of Eucalyptol and 1R-Alpha-Pinene rich acetonic essential oils of dry leaves of the Sydney Blue gum (Eucalyptus saligna Smith) on common granivorous maize weevil. Fresh leaves of Eucalyptus saligna were harvested and the essential oils extracted from its dry powder by hydrodistillation. The chemical composition of the essential oil was analyzed by tandem GC/MS. Twelve components were identified, and the main components were Eucalyptol (34.36%) and 1R-alpha pinene (17.92%). Acetonic essential oils of 2µL, 4µL, 6µL and 8µL in 1ml acetone were used in contact toxicity, fumigant and repellent bioassays. In contact toxicity, 8µL/ml oil exerted a rapid effect on the weevils giving 100% mortality in the first day of exposure; 6µL/ml achieved 100% mortality 96 hours after treatment. Both fumigant and repellent activities showed a gradual increase in insect mortality and repellency with time of exposure as the concentrations of the essential oils were increased; 100% repellency was achieved at 8µL in the second hour and this remained constant with time. The lowest repellency of 20% was obtained at 2µL. In fumigant toxicity, the highest mortality was 70% recorded at 8µL on the third day of exposure. The results indicated that the acetonic essential oil of dry Eucalyptol and 1R-Alpha-Pinene rich Eucalyptus saligna leaves can be developed into a bioinsecticide for controlling maize weevil as a repellent, toxicant and fumigant candidate.

Insecticides for Suppression of Nylanderia fulva.

Nylanderia fulva (Mayr) is an invasive ant that is a serious pest in the southern United States. Pest control operators and homeowners are challenged to manage pest populations below acceptable thresholds. Contact and bait insecticides are key components of an Integrated Pest Management (IPM) strategy, however, little is known about their efficacy. In repellency and efficacy bioassays, N. fulva were not completely repelled by any insecticide tested, although fewer ants crossed a surface treated with Temprid®. Few insecticides provided rapid control. Termidor® and Temprid® were the best performing with mean mortality of 100% in 13.4 and 19.0 days, respectively. In no-choice bait acceptance studies, it was shown that N. fulva generally had greater acceptance of carbohydrate-based ant baits (Advion®, InTiceTM (gel), and InTiceTM (granular)). However, mortality was low for the InTiceTM baits in a 7-day bioassay. Maxforce® Ant Killer Bait Gel and Advance® 375A in the spring and Maxforce® Complete in the summer and fall required the fewest days to reach 100% mortality. Bait active ingredients that resulted in the highest mortality were hydramethylnon and fipronil. These data on the efficacy of commercially available contact and bait insecticides provide valuable information to manage this invasive pest.

Toxicological effects of Sphaeranthus indicus Linn. (Asteraceae) leaf essential oil against human disease vectors, Culex quinquefasciatus Say and Aedes aegypti Linn., and impacts on a beneficial mosquito predator.

Use of environmentally friendly, decomposable natural products for effective vector control has gained considerable momentum in modern society. In this study, essential oil of Sphaeranthus indicus (Si-EO) was extracted and further phytochemical screening revealed fourteen compounds with prominent peak area percentage of 24.9 and 22.54% in 3,5-di-tert-butyl-4-hydroxybenzaldehyde and benzene,2-(1,1-dimethylethyl)-1,4-dimethoxy, respectively. The Si-EO was further evaluated for their larvicidal response against Culex quinquefasciatus and Aedes aegypti at different dosages (62.5, 125, 250 and 500ppm). The Si-EO displayed prominent larvicidal activity at higher concentration (500ppm) against both species of mosquitoes. The LC50 and LC90 values of oils were observed at 130 and 350ppm against C. quinquefasciatus larvae and at 140 and 350ppm against A. aegypti larvae, respectively. Repellent bioassay established higher protection rate at 200ppm up to 120min against both the mosquitoes. However, adulticidal response displayed higher mortality rate only at 700 and 800ppm against C. quinquefasciatus and A. aegypti, respectively. Toxicological screening against mosquito predator Toxorhynchites splendens revealed that the Si-EO was harmless even at the concentration of 1500ppm. Overall, these results suggest that the Si-EO plays a significant role as a new bio-rational product against ecological burden mosquito vectors which provides an eco-friendly alternative to synthetic pesticides.

Screening for insecticidal potential and acetylcholinesterase activity inhibition of Urginea maritima bulbs extract for the control of Sitophilus oryzae (L.)

Interest in botanical insecticides derived from plants has increased as a result of environmental concerns and insect resistance to chemical insecticides. In this study, we explored the insecticidal activity of Urginea maritima bulbs extract and its inhibitory effect on acetylcholinesterase enzyme system in the rice weevil Sitophilus oryzae (L.) (Coleoptera: Curculionidae). Phytochemical screening and HPLC-ESI/TOF-MS analysis revealed the presence of bioactive molecules with high insecticidal potential. Content of polyphenols (130.88±0.44mgGAE/g FW), flavonoids (50.81±0.25mgRE/g FW) as well as alkaloids (12.09±0.16mgAE/g FW) were high. HPLC-ESI/TOF-MS analysis results demonstrated that ferulic acid (124.19μg/g FW), vanillic acid (75.84μg/g FW) and 4-hydroxybenzoic acid (59.73μg/g FW) were the major phenolic compounds of U. maritima bulbs extract. The toxic potential against the rice weevil using contact and repellent bioassays showed the highest insecticidal potential of U. maritima bulbs extract. The LD50, LC50 and RC50 values were 19.03μg/insect, 2.35μg/cm2 and 0.009μg/cm2 for contact bioassay by topical application, contact bioassay by treated filter paper method and repellent bioassay, respectively. Furthermore, U. maritima bulbs extract inhibited acetylcholinesterase (AChE) activity and median inhibition concentration IC50 was evaluated to 66.08μg/ml. The findings of the present investigation confirmed that Urginea maritima may be recommended as an eco-friendly alternative to synthetic insecticides.

Comparative Evaluation of a Silicone Membrane as an Alternative to Skin for Testing Mosquito Repellents.

Repellents prevent mosquito bites and help reduce mosquito-borne disease, a global public health issue. Laboratory-based repellent bioassays predict the ability of compounds to deter mosquito feeding, but the variety of repellent bioassays and statistical analysis methods makes it difficult to compare results across methodologies. The most realistic data are collected when repellents are applied on the skin; however, this method exposes volunteers to chemicals and mosquito bites. Silicone membranes were investigated as an alternative to human skin in assays of repellent efficacy. Results from module system bioassays conducted in vitro with a silicone membrane were compared with in vivo bioassays conducted with N,N-diethyl-3-methylbenzamide (referred to as DEET), 1-piperidinecarboxylic acid 2-(2-hydroxyethyl)-1-methylpropylester (referred to as Picaridin), ethyl 3-[acetyl(butyl)amino]propanoate (referred to as IR3535), and para-menthane-3,8-diol (referred to as PMD) applied directly on the skin of the leg. No significant difference in mosquito feeding was found when comparing skin and volunteer-worn membrane controls using blood; however, feeding was significantly lower in unworn membrane controls using either 10% sucrose or blood, indicating that worn membranes are a possible surrogate for untreated human skin. Pooled data from six volunteers were used to generate dose-response curves of blood-feeding activity. Results from skin-applied repellents were modeled to determine if membranes could provide a predictive correlate for skin. Goodness-of-fit comparisons indicated that the nonlinear dose-response curves for the skin and membrane differed significantly for DEET and Picaridin, but did not differ significantly for IR3535 and PMD. With knowledge of the dose-response relationships and further modifications to this system, the membrane-based tests could be used for standardized repellent testing with infected vectors.

Repellent activities of dichloromethane extract of Allium sativum (garlic) (Liliaceae) against Hyalomma rufipes (Acari).

Dichloromethane (DCM) extract of garlic (Allium sativum Linn.) bulbs was assessed for its repellent effect against the hard tick, Hyalomma rufipes (Acari: Ixodidae) using two tick behavioural bioassays; Type A and Type B repellency bioassays, under laboratory conditions. These bioassays exploit the questing behaviour of H. rufipes, a tick that in nature displays ambush strategy, seeking its host by climbing up on vegetation and attaching to a passing host. One hundred microlitres (100 µL) of the test solution containing DCM extract of garlic bulbs and DCM at concentrations of 0.35%, 0.7% or 1.4% w/v were evaluated. DCM only was used for control. Tick repellency increased significantly (R2 = 0.98) with increasing concentration (40.03% – 86.96%) yielding an EC50 of 0.45% w/v in Type B repellency bioassay. At concentration of 1.4% w/v, the DCM extract of garlic bulbs produced high repellency index of 87% (male ticks) and 87.5% (female ticks) in the Type A repellency bioassay. Only 4% avoidance of male ticks or female ticks was recorded in the Type B repellency bioassay. In the corresponding controls, the mean numbers of non-repelled male or female ticks were 80% and 41 males or 38 females of 50 ticks in the Type A and Type B repellency bioassays, respectively. The variations in the results could be attributed to the difference in tick repellent behaviours that were assessed by the two repellency bioassays; the Type A repellency bioassay assessed repellent effect of garlic extracts without discriminating between deterrence and avoidance whereas the Type B repellency bioassay only assessed avoidance response. Generally, DCM extract of garlic was repellent against H. rufipes, albeit weak tick repellency was obtained in the Type B repellency bioassay. Furthermore, this study established that the tick repellent activity of garlic extracts is predominantly by deterrence.

Repellency to ticks (Acari: Ixodidae) of extracts of Nigella sativa (Ranunculaceae) and the anti-inflammatory DogsBestFriend™.

Motivated by observations that the canine anti-inflammatory cream DogsBestFriend™ (DBF) appeared to deter flies, mosquitoes, and ticks from treated animals, repellent efficacy bioassays using four species of ticks were conducted with three extracts of Nigella sativa L. (Ranunculaceae), a constituent of DBF. The DBF cream was tested against nymphs of lone star tick, Amblyomma americanum (L.). In vertical filter paper assays, the three extracts applied at 0.413mgextract/cm(2) filter paper repelled 96.7-100% of brown dog tick, Rhipicephalus sanguineus (Latreille) nymphs, whereas, at the same rate, only one extract repelled >90% A. americanum nymphs. Adult (mixed sexes) American dog ticks, Dermacentor variabilis (Say), required a higher concentration to be repelled effectively; two extracts, applied at 0.827mgextract/cm(2) filter paper, repelled ≥90% of the D. variabilis. In contrast, all extracts applied at much lower concentration (0.206mgextract/cm(2) filter paper) repelled 100% adult blacklegged ticks, Ixodes scapularis Say (only females tested). Of the two more repellent extracts, one lost most of its activity against A. americanum nymphs in <4h when applied at 0.827mgextract/cm(2) filter paper, whereas the other repelled 66.7% of the nymphs at 192h after application. At 0.206mgextract/cm(2) filter paper, one extract was as repellent as deet against A. americanum nymphs. In a vertical bioassay in which nylon organdy was substituted for filter paper, DBF, at the rates of 1.67 and 0.835mgcream/cm(2), repelled 76.7 and 30.0% A. americanum nymphs, respectively. These findings indicate that when applied appropriately DBF should afford some protection to canines against tick bites.

Attractiveness of volatiles from different body parts to the malaria mosquito Anopheles coluzzii is affected by deodorant compounds.

Mosquitoes display biting preferences among different sites of the human body. In addition to height or convection currents, body odour may play a role in the selection of these biting sites. Previous studies have shown that skin emanations are important host-finding cues for mosquitoes. In this study, skin emanations were collected from armpits, hands and feet; the volatile profiles were analysed and tested for their attractiveness to the malaria mosquito Anopheles coluzzii. Skin emanations collected from armpits were less attractive to An. coluzzii compared to hands or/and feet. The difference may have been caused by deodorant residues, which were found in the armpit samples and not in those of hands and feet. In a subsequent experiment, volunteers were asked to avoid using skincare products for five days, and thereafter, no differences in attractiveness of the body parts to mosquitoes were found. The detected deodorant compound isopropyl tetradecanoate inhibited mosquito landings in a repellent bioassay. It is concluded that the volatiles emanated from different body parts induced comparable levels of attraction in mosquitoes, and that skincare products may reduce a person’s attractiveness to mosquitoes.

Larvicidal and repellent potential of Zingiber nimmonii (J. Graham) Dalzell (Zingiberaceae) essential oil: an eco-friendly tool against malaria, dengue, and lymphatic filariasis mosquito vectors?

Mosquitoes (Diptera: Culicidae) are important vectors of terms of public health relevance, especially in tropical and sub-tropical regions. The continuous and indiscriminate use of conventional pesticides for the control of mosquito vectors has resulted in the development of resistance and negative impacts on non-target organisms and the environment. Therefore, there is a need for development of effective mosquito control tools. In this study, the larvicidal and repellent activity of Zingiber nimmonii rhizome essential oil (EO) was evaluated against the malaria vector Anopheles stephensi, the dengue vector Aedes aegypti, and the lymphatic filariasis vector Culex quinquefasciatus. The chemical composition of the EO was analyzed by gas chromatography-mass spectroscopy (GC-MS). GC-MS revealed that the Z. nimmonii EO contained at least 33 compounds. Major constituents were myrcene, β-caryophyllene, α-humulene, and α-cadinol. In acute toxicity assays, the EO showed significant toxicity against early third-stage larvae of An. stephensi, Ae. aegypti, and Cx. quinquefasciatus, with LC50 values of 41.19, 44.46, and 48.26μg/ml, respectively. Repellency bioassays at 1.0, 2.0, and 5.0mg/cm(2) of Z. nimmonii EO gave 100% protection up to 120, 150, and 180min. against An. stephensi, followed by Ae. aegypti (90, 120, and 150min) and Cx. quinquefasciatus (60, 90, and 120min). Furthermore, the EO was safer towards two non-target aquatic organisms, Diplonychus indicus and Gambusia affinis, with LC50 values of 3241.53 and 9250.12μg/ml, respectively. Overall, this research adds basic knowledge to develop newer and safer natural larvicides and repellent from Zingiberaceae plants against malaria, dengue, and filariasis mosquito vectors.

An astigmatid defence volatile against a phytoseiid mite

AbstractNumerous semiochemicals have been isolated from several species of astigmatid mites with various identified or unidentified functions. Alarm pheromonal activity is widespread with neryl formate and neral, being the most common compounds eliciting alarm response in conspecifics. The cosmopolitan astigmatid mite Suidasia medanensis (= S. pontifica) Oudemans (Acari: Suidasidae) has been reported to use neral as an alarm pheromone, but neral can also act as an allomone towards predators of oribatid mites. Suidasia medanensis can be utilised as a factitious prey for mass‐rearing of the phytoseiid predatory mite Amblyseius (= Typhlodromips) swirskii (Athias‐Henriot) (Acari: Phytoseiidae), which is used for biological control of insect and mite pests in protected crops. This study investigated the potential defence properties of the S. medanensis volatiles against A. swirskii, comparing the repellency to pollen‐reared (naïve) vs. S. medanensis‐reared (experienced) predators using a synthetic blend of the isomers neral and geranial (1:1) as a model compound. In a repellency bioassay, the synthetic blend elicited a significant repellence to A. swirskii with no difference between naïve and experienced predators. During capture success studies, S. medanensis under repeated attack could release sufficient quantities of the defence volatile to deter 1–5 attacks from A. swirskii, whereas hexane‐treated S. medanensis artificially depleted of volatiles were significantly more vulnerable to an attack. This is the first report of an astigmatid defence volatile with repellent activity to a phytoseiid mite and the starting point to understanding semiochemical interactions in any current or novel factitious predator‐prey mass‐rearing system.

Activity studies of sesquiterpene oxides and sulfides from the plant Hyptis suaveolens (Lamiaceae) and its repellency on Ixodes ricinus (Acari: Ixodidae).

Hyptis suaveolens (Lamiaceae), a plant traditionally used as a mosquito repellent, has been investigated for repellent properties against nymphs of the tick Ixodes ricinus. Essential oils and volatile compounds of fresh and dried leaves, from plants originating from Laos and Guinea-Bissau, were identified by GC-MS and tested in a tick repellency bioassay. All the essential oils were strongly repellent against the ticks, even though the main volatile constituents differed in their proportions of potentially tick repellent chemicals. (+)/(-)-sabinene were present in high amounts in all preparations, and dominated the emission from dry and fresh leaves together with 1,8-cineol and α-phellandrene. 1,8-Cineol and sabinene were major compounds in the essential oils from H. suaveolens from Laos. Main compounds in H. suaveolens from Guinea-Bissau were (-)-sabinene, limonene and terpinolene. Among the sesquiterpene hydrocarbons identified, α-humulene exhibited strong tick repellency (96.8 %). Structure activity studies of oxidation or sulfidation products of germacrene D, α-humulene and β-caryophyllene, showed increased tick repellent activity: of mint sulfide (59.4 %), humulene-6,7-oxide (94.5 %) and caryophyllene-6,7-oxide (96.9 %). The substitution of oxygen with sulfur slightly lowered the repellency. The effects of the constituents in the oils can then be regarded as a trade off between the subsequently lower volatility of the sesquiterpene derivatives compared to the monoterpenes and may thus increase their potential usefulness as tick repellents.

Discovery and structure activity relationships of 2-pyrazolines derived from chalcones from a pest management perspective

Synthesis of chalcones and 2-pyrazoline derivatives has been an active field of research due to the established pharmacological effects of these compounds. In this study, a series of chalcone (1a–i), 2-pyrazoline-1-carbothioamides (2a–i), and 2-pyrazoline-1-carboxamide derivatives (3a–g) were synthesized and screened for their potential pesticide activities. The proposed structures of all the synthesized compounds were confirmed using the elemental analysis, UV, IR, 1H-NMR, and mass spectroscopy. Among the total of 25 tested compounds, compounds 1g and 2a and 2e with Biting Deterrence Index (BDI) values of 0.85, 0.83, and 0.8, respectively, at 25 nmol/cm2 showed the highest biting deterrent activity against Aedes aegypti, which was comparable to N,N-diethyl-3-methylbenzamide (DEET). Compounds 1g, 2a and 2e were subsequently tested in human-based repellent bioassays, and they showed MED (minimum effective dose) values of 0.375, 0.094, and 0.375 mg/cm2, respectively. Compound 1e was the most toxic compound (LC50 = 2.58 ppm), followed by 1f (LC50 = 5.69 ppm) and 2g (LC50 = 15.14 ppm), against 1-day-old Ae. aegypti larvae. Compounds 1f and 2h 1f and 2h showed the greatest growth inhibition against Colletotrichum gloeosporioides (97.6 and 98.5 %, respectively) at the lowest dose (0.3 μM), which was greater antifungal activity than with standard commercial fungicides captan and azoxystrobin. Compounds 2d, 2g and 2h produced 79.5, 98.3, and 82.3 % growth inhibition, respectively, at 30.0 μM against Botrytis cinerea, which was similar to captan in the antifungal activity. The active fungicidal compounds (2d, 2g, and 2h) were weaky phytotoxic, with little or no phytotoxicity at concentrations that were fungitoxic. Compound 2h stimulated the growth of Lemma paucicostata at concentrations that are fungitoxic to several plant pathogens.

Mosquito repellent activity of essential oils and extracts from Chamomile flowers

Aedes aegypti L. is the major vector for dengue and yellow fever. In order to discover plant based mosquito repellents, the n-hexane, ethyl acetate extracts and essential oils from the flowers of German chamomile (Matricaria chamomilla L.), Roman chamomile (Chamaemelum nobile L.) and Juhua (Chrysanthemum morifolium Ramat.) were screened for the repellent activity against Ae. aegypti. In human based “cloth patch” repellent bioassays, German chamomile essential oils showed the highest activity. Thus, we determined chemical differences between these three chamomile essential oils using GC-FID and GC-MS. Two Roman chamomile oil samples were characterized by the isobutyl angelate, 2-butenyl angelate and 3-methyl pentyl angelate, whereas all four German chamomile essential oils were characterized by α-bisabolol oxide A and α-bisabolol oxide B, bisabolone oxide A, (E)-β-farnesene and chamazulene. Borneol, ar-curcumene and bornyl acetate were found as principle compounds in Juhua essential oil. In this study, the major compound α-bisabolol oxide A and some of polyacetylenes which have a history of insecticidal activity were investigated for their biting deterrent activity using in vitro K & D system against Ae. Aegypti.

Toxicity and repellency of Hoslundiaopposita Vahl (Lamiaceae) leaves' essential oil against rust-red flour beetle, Triboliumcastaneum Herbst (Coleoptera: Tenebrionidae)

The insecticidal properties of Hoslundia opposita Vahl (Lamiaceae) leaves' essential oil (EO) against Tribolium castaneum were investigated using contact toxicity and repellency bioassays. Mortality progressed with exposure period and ranged from 61.13% observed at 24 h after treatment (HAT) to 88.86% at 168 HAT. The LT50 (lethal time for 50% of treated adults) of H. opposita EO against T. castaneum was 10.42 h. Application of EO at 20–30 μL/30 cm2 caused significantly (P < 0.05) higher percentage repellency than what was observed in control, 10 and 15 μL/30 cm2 at 1 and 3 HAT, with significant repellency at 24 HAT regardless of dosage. Repellency class increased with EO dosage, with class V observed at 30 μL/30 cm2, regardless of exposure duration. The RD50 (repellency dose for 50% of treated adults) of 15.88 and 13.37 μL/30 cm2 for 1 and 2 HAT, respectively, was significantly higher than 0.09 μL/30 cm2 at 24 HAT.

Toxicity and repellent effects of leaf extracts of four Kenyan plants against nymphs and adults of Rhipicephalus appendiculatus (Neuman 1901)

Ticks are important arthropod vectors of diseases of man and farm animals in Africa and in spite of the efforts to control them using synthetic acaricides, they continue to be amongst the leading vectors of disease-causing agents. Unfortunately, over-reliance on synthetic acaricides for tick control has led to problems including acaricide resistance, environmental pollution, and acaricide residues in products destined for human consumption. These problems highlight the need for alternative tick control methods that are environment friendly and yet effective. In the current study, the repellency and toxic effects of essential oils extracted from four Kenyan plants namely;Tagetes minuta L.(Asteraceae), Fuerstia. africana T.C.E. Friers (Lamiaceae), Tephrosia vogelii Hook. f. (Leguminosae) and Sphaeranthus ukambensis against the ixodid tick Rhipicephalus appendiculatu were determined. Essential oils were extracted by steam distillation from fresh plants using Clevenger apparatus. Host seeking nymphs (2-3 weeks old)and adult ticks were used and fumigant toxicity bioassay was done using four concentrations (0.1µ/ml, 0.01 µ/ml, 0.001 µ/ml, and 0.0001µ/ml) of the essential oils, each in four replicates and with ten ticks per replicate. In the control experiment, ticks were exposed to n- hexane. Mortality was recorded every 48 hours for 2 weeks. In repellency bioassay, a Y tube olfactometer and same concentrations as above were used. Treated paper discs were placed in one arm and control (discs treated with hexane) in the other. Ticks were introduced at the main arm and allowed to make choices on the direction of movement. Ticks on the two arms were counted after 30 minutes. The essential oils showed dose dependant mortality and repellency values. The highest repellency value for R. appendiculatus adults was observed with T. vogelii (93.8% at 0.01µ/ml) while for the nymphs, both S. ukambensis and T. vogelii recorded the highest repellency values of 100% and 95% respectively both at 0.1µ/ml concentration. Essential oils from Fuerstia. africana recorded the highest mortality values for nymph (97.8% at 0.1µ/ml) and adult (53.2 % 0.1µ/ml) Rhipicephalus appendiculatus . The present study has demonstrated that Tephrosia vogelii, Tagetes minuta and Sphaeranthus ukambensis have repellent and toxic effects on Rhipicephalus appendiculatus and therefore can