Chemical Composition of Essential Oils from Natural Populations of Artemisia scoparia Collected at Different Altitudes: Antibacterial, Mosquito Repellent, and Larvicidal Effects.

The current study aimed to evaluate the presence of chemical variations in essential oils (EOs) extracted from Artemisia scoparia growing at different altitudes and to reveal their antibacterial, mosquito larvicidal, and repellent activity. The gas chromatographic-mass spectrometric analysis of A. scoparia EOs revealed that the major compounds were capillene (9.6-31.8%), methyleugenol (0.2-26.6%), ß-myrcene (1.9-21.4%), γ-terpinene (1.5-19.4%), trans-ß-caryophyllene (0.8-12.4%), and eugenol (0.1-9.1%). The EO of A. scoparia collected from the city of Attock at low elevation was the most active against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, and Pseudomonas aeruginosa bacteria (minimum inhibitory concentration of 156-1250 µg/mL) and showed the best mosquito larvicidal activity (LC50, 55.3 mg/L). The EOs of A. scoparia collected from the high-altitude areas of Abbottabad and Swat were the most repellent for females of Ae. aegypti and exhibited repellency for 120 min and 165 min, respectively. The results of the study reveal that different climatic conditions and altitudes have significant effects on the chemical compositions and the biological activity of essential oils extracted from the same species.

Chemical Composition, Toxicity, and Repellency of Essential Oils from Three Hedychium Species Against Stored-Product Insects.

Stored products are constantly infested by insects, so finding eco-friendly bioinsecticides for insect management is important. The work aimed to assess the insecticidal and repellent activity of essential oil (EO) from Hedychium glabrum S. Q. Tong, Hedychium coronarium Koen., and Hedychium yunnanense Gagnep. against Tribolium castaneum, Lasioderma serricorne, and Liposcelis bostrychophila. Results showed that 88 chemical components were identified in the extracted Hedychium EOs, indicating that they exhibited diversity in components. According to principal component analysis (PCA), the composition of the EO from the H. yunnanense stem and leaf (EOHYSL) was significantly different from other EOs due to the different organs and species. The biological activity also varied continuously with plant species and organs. Only the EO of H. yunnanense (EOHY) showed strong fumigant toxicity. While in the contact tests, EOHGR showed the strongest toxicity effect on L. bostrychophila, with a LC50 value of 71.76 µg/cm2, which was closest to the positive control (Pyrethrin). All EOs had remarkable repellent activities against the three target insects, and repellency increased with concentration. According to the results of the comprehensive score, EOHY had the highest potential, which ranged from 0.7999 to 0.8689. Thus, Hedychium EOs possess potential biorational traits to be biological insecticides.

Development of terpenoid repellents against Aedes albopictus: a combined study of biological activity evaluation and computational modelling.

To explore novel terpenoid repellents, 22 candidate terpenoid derivatives were synthesized and tested for their electroantennogram (EAG) responses and repellent activities against Aedes albopictus. The results from the EAG experiments revealed that 5-(2-hydroxypropan-2-yl)-2-methylcyclohex-2-en-1-yl formate (compound 1) induced distinct EAG responses in female Aedes albopictus. At concentrations of 0.1, 1, 10, 100, and 1000 mg/L, the EAG response values for compound 1 were 179.59, 183.99, 190.38, 193.80, and 196.66 mV, demonstrating comparable or superior effectiveness to DEET. Repellent activity analysis indicated significant repellent activity for compound 1, closest to the positive control DEET. The in silico assessment of the ADMET profile of compound 1 indicates that it successfully passed the ADMET evaluation. Molecular docking studies exhibited favourable binding of compound 1 to the active site of the odorant binding protein (OBP) of Aedes albopictus, involving hydrophobic forces and hydrogen bond interactions with residues in the OBP pocket. The QSAR model highlighted the influential role of hydrogen-bonding receptors, positively charged surface area of weighted atoms, polarity parameters of molecules, and maximum nuclear-nuclear repulsion force of carbon-carbon bonds on the relative EAG response values of the tested compounds. This study holds substantial significance for the advancement of new terpenoid repellents.

The Odorant Receptor Recognizing Camphor in a Camphor Tree Specialist Orthaga achatina (Lepidoptera: Pyralidae).

Camphor has been used as an effective repellent and pesticide to stored products for a long history, but Orthaga achatina (Lepidoptera: Pyralidae) has evolved to specifically feed on the camphor tree Cinnamomum camphora. However, the behavioral response of O. achatina to camphor and the molecular basis of camphor perception are totally unknown. Here, we demonstrated that both male and female adults were behaviorally attracted to camphor, suggesting the adaptation of O. achatina to and utilization of camphor as a signal of C. camphora. Second, in 40 O. achatina OR genes obtained by analyzing antenna transcriptomes, only OachOR16/Orco significantly responded to camphor in the Xenopus oocyte system. Finally, by molecular docking analysis and site-directed mutagenesis, the Ser209 residue is confirmed to be essential for binding of the oachOR16 with camphor. This study not only reveals the camphor-based host plant choice and olfactory mechanisms of O. achatina but also provides a molecular target for screening more potential insect repellents.

Rational design, synthesis and binding mechanisms of novel benzyl geranate derivatives as potential eco-friendly aphid repellents.

BACKGROUND: The push-pull strategy is considered as a promising eco-friendly method for pest management. Plant volatile organic compounds (PVOCs) act as semiochemicals constitute the key factor in implementing this strategy. Benzyl alcohol and geraniol, as functional PVOCs, were reported to regulate insect behavior, showing the potential application in pest control. Using geraniol as lead, a geraniol derivative 5i with fine repellent activity was discovered in our previous work. In order to explore novel, eco-friendly aphid control agents, a series of benzyl geranate derivatives was designed and synthesized using 5i as the lead and benzyl alcohol as the active fragment. RESULTS: Benzyl alcohol was firstly evaluated to have repellent activity to Acyrthosiphon pisum. Based on this repellent fragment, a series of novel benzyl geranate derivatives was rationally designed and synthesized using a scaffold-hopping strategy. Among them, compound T9, with a binding affinity (Kd = 0.43 µm) and a substantial repellency of 64.7% against A. pisum, is the most promising compound. Molecule docking showed that hydrophobic and hydrogen-bonding interactions substantially influenced the binding affinity of compounds with ApisOBP9. Additionally, T9 exhibited low-toxicity to honeybees and ladybugs. CONCLUSION: Using a simple scaffold-hopping strategy combined with active fragment benzyl alcohol, a new derivative T9, with high aphid-repellency and low-toxicity to nontarget organisms, can be considered as a novel potential eco-friendly aphid control agent for sustainable agriculture. © 2023 Society of Chemical Industry.

Repellency and Toxicity of Vapor-Active Benzaldehydes against Aedes aegypti.

Chemical screening efforts recently found that 3-phenoxybenzaldehyde, a breakdown product of alpha-cyano pyrethroids, was a potent spatial repellent against Aedes aegypti mosquitoes in a glass tube repellency assay. In order to characterize this molecule further and identify structure-activity relationships, a set of 12 benzaldehyde analogues were screened for their repellency and toxicity in vapor phase exposures at 100 µg/cm2. Dose-response analyses were performed for the most active compounds in order to better characterize their repellent potency and toxicity compared to those of other commercially available toxicants. The three most toxic compounds (LC50 values) were 3-chlorobenzaldehyde (CBA) (37 µg/cm2), biphenyl-3-carboxaldehyde (BCA) (48 µg/cm2), and 3-vinylbenzaldehyde (66 µg/cm2), which makes them less toxic than bioallethrin (6.1 µg/cm2) but more toxic than sandalwood oil (77 µg/cm2), a repellent/toxic plant essential oil. The most repellent analogues with EC50 values below 30 µg/cm2 were 3-phenoxybenzaldehyde (6.3 µg/cm2), isophthalaldehyde (23 µg/cm2), BCA (17 µg/cm2), and CBA (22 µg/cm2), which makes them about as active as N,N-diethyl-3-methylbenzamide (25.4 µg/cm2). We further investigated the activity of a select group of these benzaldehydes to block the firing of the central nervous system of A. aegypti larvae. Compounds most capable of repelling and killing mosquitoes in the vapor phase were also those most capable of blocking nerve firing in the larval mosquito nervous system. The results demonstrate that benzaldehyde analogues are viable candidate repellent and insecticidal molecules and may lead to the development of future repellent and vapor toxic vector control tools.

Structural Exploration of Novel Pyrethroid Esters and Amides for Repellent and Insecticidal Activity against Mosquitoes.

The emergence of pyrethroid-resistant mosquitoes is a worldwide problem that necessitates further research into the development of new repellents and insecticides. This study explored the modification of existing pyrethroid acids to identify structural motifs that might not be affected by kdr active site mutations that elicit pyrethroid resistance. Because synthetic pyrethroids almost always contain activity-dependent chiral centers, we chose to focus our efforts on exploring alkoxy moieties of esters obtained with 1R-trans-permethrinic and related acids, which we showed in previous studies to have repellent and/or repellent synergistic properties. To this end, compounds were synthesized and screened for spatially acting repellency and insecticidal activity against the susceptible, Orlando, and pyrethroid-resistant, Puerto Rico, strains of Aedes aegypti mosquito. Screening utilized a high-throughput benchtop glass tube assay, and the compounds screened included a mixture of branched, unbranched, aliphatic, halogenated, cyclic, non-cyclic, and heteroatom-containing esters. Structure-activity relationships indicate that n-propyl, n-butyl, n-pentyl, cyclobutyl, and cyclopentyl substituents exhibited the most promising repellent activity with minimal kdr cross resistance. Preliminary testing showed that these small alcohol esters can be synergistic with phenyl amides and pyrethroid acids. Further derivatization of pyrethroid acids offer an interesting route to future active compounds, and while mosquitoes were the focus of this work, pyrethroid acids and esters have potential for use in reducing pest populations and damage in cropping systems as well.

The essential oil of Kochia scoparia (L.) Schrad. as a potential repellent against stored-product insects.

Chemical composition of the essential oil from Kochia scoparia (L.) Schrad. (syn. Bassia scoparia (L.) A. J. Scott) was analyzed in quality and quantity by GC-MS and GC-FID. Repellent activities of the essential oil from K. scoparia (KSEO) were evaluated against two common species of stored-product insects Tribolium castaneum Herbst and Liposcelis bostrychophila Badonnel. Results indicated that KSEO mainly consisted of eugenol, ß-caryophyllene, and α-humulene, accounting for 75.6%, 8.2%, and 1.4% of the total oil, respectively. KSEO and the three major components were repellent to T. castaneum and L. bostrychophila adults. Notably, KSEO exerted significant effects, comparable to the positive control DEET at 2 and 4 h post-exposure. Eugenol at 63.17-2.53 nL/cm2 exhibited high percentage repellency ranging from 96 to 70% against L. bostrychophila during 4-h exposure. To gain further insights into the repellent activity, molecular docking simulation was performed with eugenol as the ligand and an odorant binding protein TcOBPC12 (gene: TcOBP10B) from the model insect T. castaneum as the receptor. Docking calculation results revealed that TcOBPC12 had binding affinity to eugenol (△G = - 4.52 kcal/mol) along with a hydrogen bond of 0.18 nm (1.8 Å) long forming between them, which could be an important target protein associated with identifying volatile repellent molecules. This work highlights the promising potential of KSEO as a botanical repellent for controlling stored-product insects.

Assessment of Contact Toxicity and Repellent Effects of Essential Oils from Piper Plants Piper yunnanense and Piper boehmeriifolium against Three Stored-Product Insects.

Storage is a crucial part during grain production for the massive spoilage caused by stored product insects. Essential oils (EOs) of plant origin have been highly recommended to combating insects which are biodegradable and safe mode of action. Hence, to make the fullest use of natural resources, essential oils of different parts from Piper yunnanense (the whole part, PYW; fruits, PYF; leaves, PYL) and Piper boehmeriifolium (leaves, PBL) were extracted by steam distillation method in the present study. Gas chromatography-mass spectrometry (GC-MS) characterization revealed bicyclogermacrene (PYW), γ-muurolene (PYF), δ-cadinene (PYL) and methyl 4,7,10,13,16,19-docosahexaenoate (PBL) as the principal compound of each essential oil. Sesquiterpene hydrocarbons were also recognized as the richest class accounting for 56.3 %-94.9 % of the total oil. Three storage pests, Tribolium castaneum, Lasioderma serricorne and Liposceis bostrychophila, were exposed to different concentrations of EOs to determine their insecticidal effects. All tested samples performed modest contact toxicity in contrast to a bioactive ingredient pyrethrin, among which the most substantial effects were observed in PYF EOs against T. castaneum (35.84 µg/adult), PBL EOs against L. serricorne (15.76 µg/adult) and PYW EOs against L. bostrychophila (57.70 µg/cm2 ). In terms of repellency tests, essential oils of PYF at 78.63 nL/cm2 demonstrated to have a remarkable repellence against T. castaneum at 2h and 4h post-exposure. The investigations indicate diverse variations in the chemical profiles and insecticidal efficacies of P. yunnanense and P. boehmeriifolium EOs, providing more experimental evidence for the use of the Piper plants.

Extraction and chemical characterisation of agro-waste from turmeric leaves as a source of bioactive essential oils with insecticidal and antioxidant activities.

Turmeric (Curcuma longa L.) is a significant crop that has historically been used worldwide as a medicinal plant, spice, food colouring agent, and a significant ingredient in cosmetic industries. After harvesting rhizomes, leaves are considered waste material. This research study aims to extract and chemically characterise the essential oil from the leaves waste of turmeric with an evaluation of different insecticidal, antioxidant, and phytotoxic activities. Subsequently, the contact toxicity, fumigant toxicity, and repellent activity were evaluated against two key stored grain insect species. The gas chromatography-mass spectrometry (GC-MS) characterisation revealed that α-phellandrene (28.95%), 2-carene (16.51%), eucalyptol (10.54%) and terpinolene (10.24%) were the major chemical constituents. The study's findings on the insecticidal effects of essential oils extracted from turmeric leaves revealed noteworthy repellent, contact (at 24 h, LC50 = 6.51 mg/cm2 for Tribolium castaneum and LC50 = 4.74 mg/cm2 for Rhyzopertha dominica) and fumigant toxicities (at 24 h, LC50 = 2.57 mg/L air for T. castaneum and LC50 = 2.83 mg/L air for R. dominica), against two key stored grain insects. In addition, turmeric leaf essential oil showed notable antioxidant activity (IC50 = 10.04 ± 0.03 µg/mL for DPPH assay; IC50 = 14.12 ± 0.21 µg/mL for ABTS assay. Furthermore, a phytotoxicity study was carried out on stored paddy seeds and no toxic effects were found on germination rate and seedling growth. So, it might be expected that the essential oils extracted from the turmeric leaf waste could be valorised and demonstrate their potential as safe botanical insecticides against stored-product insects, with noble antioxidant properties.

Analysis of Essential Oils Components from Aromatic Plants Using Headspace Repellent Method against Aedes aegypti Mosquitoes.

This research serves as the basis for developing essential oil-based repellent activity tests against Aedes aegypti mosquitoes. The method used for the isolation of essential oils was the steam distillation method. Virus-free Aedes aegypti mosquitoes were used as test animals by applying the 10% essential oil repellent on the arms of volunteers. The analysis of the essential oils activities and aromas' components was carried out using headspace repellent and GC-MS methods. Based on the results, the yields of essential oil from 5000 g samples for cinnamon bark, clove flowers, patchouli, nutmeg seed, lemongrass, citronella grass, and turmeric rhizome were 1.9%, 16%, 2.2%, 16.8%, 0.9%, 1.4%, and 6.8%, respectively. The activity test showed that the average repellent power of 10% essential oils, patchouli, cinnamon, nutmeg, turmeric, clove flowers, citronella grass, and lemongrass, was 95.2%, 83.8%, 71.4%, 94.7%, 71.4%, 80.4%, and 85%, respectively. Patchouli and cinnamon had the best average repellent power. Meanwhile, the aroma activities showed that the average repellent power of the patchouli oil was 96%, and the cinnamon oil was 94%. From the GC-MS analysis, nine components were identified in the patchouli essential oil aromas' with the highest concentration being patchouli alcohol (42.7%), Azulene, 1,2,3,5,6,7,8,8a-octahydro-1,4-dimethyl-7-(1-methylethenyl)-, [1S-(1α,7α,8aß)] (10.8%), α-guaiene (9.22%), and seychellene (8.19%)., whereas using the GC-MS headspace repellent method showed that there were seven components identified in the patchouli essential oil aroma with a high concentration of the components, which were patchouli alcohol (52.5%), Seychellene (5.2%), and α-guaiene (5.2%). The analysis results of cinnamon essential oil using the GC-MS method showed that there were five components identified in the aroma, with E-cinnamaldehyde (73%) being the highest component, whereas using the GC-MS headspace repellent method showed that there were five components identified in the aroma, with highest concentrations of cinnamaldehyde (86.1%). It can be concluded that the chemical compounds contained in patchouli and cinnamon bark have the potential to be environmentally friendly repellents in controlling and preventing Aedes aegypti mosquitoes.

Chemical composition and repellent activity of essential oils of Tithonia diversifolia (Asteraceae) leaves against the bites of Anopheles coluzzii.

Tithonia diversifolia is widely used in African traditional medicine for the treatment of a large number of ailments and disorders, including malaria. In the present study, we evaluated the repellent activity of essential oils (EO) of this plant against Anopheles coluzzii, a major vector of malaria in Africa. Fresh leaves of T. diversifolia were used to extract EO, which were used to perform repellency assays in the laboratory and in the field using commercially available N,N-Diethyl-meta-toluamide (DEET) and Cymbopogon (C.) citratus EO as positive controls and vaseline as negative control. The repellency rates and durations of protection of the human volunteers involved were used as measures of repellent activity. Chemical composition of the T. diversifolia EO was established further by gas chromatography coupled with mass spectrometry. The moisture content and oil yield were 81% and 0.02% respectively. A total of 29 compounds in the T. diversifolia EO was identified, with D-limonene (20.1%), α-Copaene (10.3%) and o-Cymene (10.0%) as the most represented. In field studies, the mean time of protection against mosquito bites was significantly lower in T. diversifolia EO-treated volunteers compared to treatments with C. citratus EO (71 min versus 125 min, p = 0.04), but significantly higher when compared with the non-treated volunteers (71 min vs 0.5 min, p = 0.03). The same pattern was found in laboratory repellency assays against A. coluzzii. In contrast, repulsion rates were statistically similar between T. diversifolia EO and positive controls. In conclusion, the study suggests promising repellent potential of leaves of T. diversifolia EO against A. coluzzii.

Comparative Bioactivity Evaluation of Chemically Characterized Essential Oils Obtained from Different Aerial Parts of Eucalyptus gunnii Hook. f. (Myrtaceae).

Essential oils (EOs) obtained by hydro-distillation from different parts of twigs (EOT), leaves (EOL), and fruits (EOF) of Eucalyptus gunnii Hook. f. were screened for their chemical composition, insecticidal, repellence, and antibacterial properties. Based on GC and GC/MS analysis, 23 constituents were identified across the twigs, leaves, and fruits, with 23, 23, and 21 components, respectively. The primary significant class was oxygenated monoterpenes (82.2-95.5%). The main components were 1,8-cineole (65.6-86.1%), α-terpinyl acetate (2.5-7.6%), o-cymene (3.3-7.5%), and α-terpineol (3.3-3.5%). All three EOs exhibited moderate antibacterial activities. EOL was found to have higher antibacterial activity against all tested strains except Dickeya solani (CFBP 8199), for which EOT showed more potency. Globally, Dickeya solani (CFBP 8199) was the most sensitive (MIC ≤ 2 mg/mL), while the most resistant bacteria were Dickeya dadantii (CFBP 3855) and Pectobacterium carotovorum subsp. carotovorum (CFBP 5387). Fumigant, contact toxicity, and repellent bioassays showed different potential depending on plant extracts, particularly EOT and EOL as moderate repellents and EOT as a medium toxicant.

The structure of AgamOBP5 in complex with the natural insect repellents Carvacrol and Thymol: Crystallographic, fluorescence and thermodynamic binding studies.

Among several proteins participating in the olfactory perception process of insects, Odorant Binding Proteins (OBPs) are today considered valid targets for the discovery of compounds that interfere with their host-detection behavior. The 3D structures of Anopheles gambiae mosquito AgamOBP1 in complex with the known synthetic repellents DEET and Icaridin have provided valuable information on the structural characteristics that govern their selective binding. However, no structure of a plant-derived repellent bound to an OBP has been available until now. Herein, we present the novel three-dimensional crystal structures of AgamOBP5 in complex with two natural phenolic monoterpenoid repellents, Carvacrol and Thymol, and the MPD molecule. Structural analysis revealed that both monoterpenoids occupy a binding site (Site-1) by adopting two alternative conformations. An additional Carvacrol was also bound to a secondary site (Site-2) near the central cavity entrance. A protein-ligand hydrogen-bond network supplemented by van der Waals interactions spans the entire binding cavity, bridging α4, α6, and α3 helices and stabilizing the overall structure. Fluorescence competition and Differential Scanning Calorimetry experiments verified the presence of two binding sites and the stabilization effect on AgamOBP5. While Carvacrol and Thymol bind to Site-1 with equal affinity in the submicromolar range, they exhibit a significantly lower and distinct binding capacity for Site-2 with Kd's of ~7 µΜ and ~18 µΜ, respectively. Finally, a comparison of AgamOBP5 complexes with the AgamOBP4-Indole structure revealed that variations of ligand-interacting aminoacids such as A109T, I72M, A112L, and A105T cause two structurally similar and homologous proteins to display different binding specificities.

Chemical Composition, Toxicity and Repellency of Inula graveolens Essential Oils from Roots and Aerial Parts against Stored-Product Beetle Tribolium castaneum (Herbst).

In this work, essential oils extracted from roots and aerial parts of Inula graveolens by hydrodistillation and their fractions obtained by chromatographic simplification were first investigated for their chemical composition by GC/MS and then evaluated for the first time for their repellency and contact toxicity properties against Tribolium castaneumadults. Twenty-eight compounds were identified in roots essential oil (REO), which accounted for 97.9 % of the total oil composition, with modhephen-8-ß-ol (24.7 %), cis-arteannuic alcohol (14.8 %), neryl isovalerate (10.6 %) and thymol isobutyrate (8.5 %) as major constituents. Twenty-two compounds were found in the essential oil from aerial parts (APEO), which accounted for 93.9 % of the total oil, with borneol (28.8 %), caryophylla-4(14),8(15)-dien-6-ol (11.5 %), caryophyllene oxide (10.9 %), τ-cadinol (10.5 %) and bornyl acetate (9.4 %) as main compounds.REO and APEO displayed stronger repellency after 2 h of exposure (80.0 and 90.0 %, respectively) against T. castaneum at the concentration of 0.12 µL/cm2 . After fractionation, fractions R4 and R5 exhibited greater effects (83.3 % and 93.3 %, respectively) than the roots essential oil. Furthermore, the fractions AP2 and AP3 showed higher repellency (93.3 and 96.6 %, respectively) than the aerial parts oil. The LD50 values of oils from roots and aerial parts topically applied were 7.44 % and 4.88 %, respectively. Results from contact toxicity assay showed that fraction R4 was more effective than the roots oil with LD50 value of 6.65 %. These results suggests that essential oils of roots and aerial parts from I. graveolens may be explored as potential natural repellent and contact insecticides against T. castaneum in stored products.

Prolonged Repellent Activity of Plant Essential Oils against Dengue Vector, Aedes aegypti.

Repellents are effective personal protective means against outdoor biting mosquitoes. Repellent formulations composed of EOs are finding increased popularity among consumers. In this study, after an initial screening of 11 essential oils (EOs) at the concentration of 33 µg/cm2, five of the most repellent EOs, Perovskia atriplicifolia, Citrus reticulata (fruit peels), C. reticulata (leaves), Mentha longifolia, and Dysphania ambrosioides were further investigated for repellent activity against Aedes aegypti mosquitoes in time span bioassays. When tested at the concentrations of 33 µg/cm2, 165 µg/cm2 and 330 µg/cm2, the EO of P. atriplicifolia showed the longest repellent effect up to 75, 90 and 135 min, respectively, which was followed by C. reticulata (peels) for 60, 90 and 120 min, M. longifolia for 45, 60 and 90 min, and C. reticulata (leaves) for 30, 45 and 75 min. Notably, the EO of P. atriplicifolia tested at the dose of 330 µg/cm2 showed complete protection for 60 min which was similar to the commercial mosquito repellent DEET. Gas chromatographic-mass spectrometric analyses of the EOs revealed camphor (19.7%), limonene (92.7%), sabinene (24.9%), carvone (82.6%), and trans-ascaridole (38.8%) as the major constituents of P. atriplicifolia, C. reticulata (peels), C. reticulata (leaves), M. longifolia, and D. ambrosioides, respectively. The results of the present study could help develop plant-based commercial repellents to protect humans from dengue mosquitoes.

Essential oils of four wild plants inhibit the blood seeking behaviour of female Aedes aegytpi.

Aedes aegypti (Diptera: Culicidae) mosquito is an important vector of many disease-causing pathogens. An effective way to escape from these mosquito-borne diseases is to prevent mosquito bites. In the current study, essential oils of Lepidium pinnatifidum, Mentha longifolia, Origanum vulgare, and Agrimonia eupatoria were evaluated for their repellent potential against Ae. aegypti females. Essential oils were extracted using steam distillation from freshly collected aerial parts of the plants and tested against 4-5 day old females of Ae. aegypti through the human bait technique for repellency and repellent longevity assays. The chemical composition of extracted essential oils was explored by gas chromatography coupled with mass spectrometry (GC-MS). The essential oils of L. pinnatifidum, M. longifolia, O. vulgare, and A. eupatoria at a dose of 33 µg/cm2 showed 100%, 94%, 87%, and 83% mosquito repellent activity, respectively. Furthermore, M. longifolia and O. vulgare essential oils exhibited 100% repellency at a dose of 165 µg/cm2, whereas A. eupatoria essential oil showed 100% repellency only at 330 µg/cm2. In the time-span bioassay, M. longifolia and O. vulgare essential oils showed protection against Ae. aegypti bites for 90 and 75 min, respectively whereas both A. eupatoria and L. pinnatifidum were found active for 45 min. Phenylacetonitrile (94%), piperitone oxide (34%), carvacrol (20%) and α-pinene (62%) were the most abundant compounds in L. pinnatifidum, M. longifolia, O. vulgare and A. eupatoria essential oils, respectively. The current study demonstrates that M. longifolia and O. vulgare essential oils possess the potential to be used as an alternative to synthetic chemicals to protect humans from mosquito bites.

Experimental evaluation and structure-activity relationship analysis of bridged-ring terpenoid derivatives as novel Blattella germanica repellent.

Cockroaches are urban pests that are very difficult to control. Using repellents is a green, safe and effective strategy for their control. In order to find novel cockroach repellents, the repellent activity of 45 bridged-ring terpenoid derivatives synthesized from ß-pinene against Blattella germanica was tested. The relationship between the molecular structure of these bridged-ring terpenoid derivatives and their repellent activity against Blattella germanica was also analysed. The results show that some of the bridged-ring terpenoid derivatives exhibit good repellent activity against Blattella germanica, and six compounds (RR = 60.44-87.32%) show higher repellent activity against Blattella germanica than DEET (RR = 54.77%), making them promising for development as new cockroach repellents. Quantitative structure-activity relationship (QSAR) analysis revealed that the HOMO-1 energy, Kier and Hall index (order 2), Balaban index, and relative positive charged surface area of bridged-ring terpenoid derivatives have effects on repellent activity against Blattella germanica. The present study may provide a theoretical basis for the high-value use of ß-pinene and can be helpful to the development of novel repellents against Blattella germanica.

Hierarchical Virtual Screening and Binding Free Energy Prediction of Potential Modulators of Aedes Aegypti Odorant-Binding Protein 1.

The Aedes aegypti mosquito is the main hematophagous vector responsible for arbovirus transmission in Brazil. The disruption of A. aegypti hematophagy remains one of the most efficient and least toxic methods against these diseases and, therefore, efforts in the research of new chemical entities with repellent activity have advanced due to the elucidation of the functionality of the olfactory receptors and the behavior of mosquitoes. With the growing interest of the pharmaceutical and cosmetic industries in the development of chemical entities with repellent activity, computational studies (e.g., virtual screening and molecular modeling) are a way to prioritize potential modulators with stereoelectronic characteristics (e.g., pharmacophore models) and binding affinity to the AaegOBP1 binding site (e.g., molecular docking) at a lower computational cost. Thus, pharmacophore- and docking-based virtual screening was employed to prioritize compounds from Sigma-Aldrich® (n = 126,851) and biogenic databases (n = 8766). In addition, molecular dynamics (MD) was performed to prioritize the most potential potent compounds compared to DEET according to free binding energy calculations. Two compounds showed adequate stereoelectronic requirements (QFIT > 81.53), AaegOBP1 binding site score (Score > 42.0), volatility and non-toxic properties and better binding free energy value (∆G < −24.13 kcal/mol) compared to DEET ((N,N-diethyl-meta-toluamide)) (∆G = −24.13 kcal/mol).

Repellency, contact toxicity, and anti-oviposition effects of three ethanol-extracted plant essential oils on Bemisia tabaci (Hemiptera: Aleyrodidae).

There are more than 1200 species of whiteflies found across the globe. Due to the high level of resistance of whitefly against synthetic insecticides, alternate pest management measures have their significance. Plant essential oils (EOs) affect insect pests in many ways, such as via stimulatory, deterrent, toxic, and hormonal effects. This study was designed to determine the repellency of EOs, toxicity, and oviposition deterrent activities of Allium ascalonicum, Cinnamomum camphora, and Mentha haplocalyx against adult whiteflies. In repellency determination experiments, a single tomato plant was treated with 10 ml of ethanol-extracted EO with 1000 ppm concentration. Results showed that C. camphora EO was the most repellent for whitefly compared to M. haplocalyx and A. ascalonicum. The oviposition deterrent experiments revealed that C. camphora has the highest oviposition deterrent effect, followed by M. haplocalyx and A. ascalonicum. A single plant treatment method was used to assess the contact toxicity of three EOs against whitefly after 12, 24, 48, and 72 h of exposure. The results revealed that C. camphora is more toxic to whitefly than M. haplocalyx and A. ascalonicum. After determining the antagonistic effects of these EOs, the oils were analyzed using gas chromatography/mass spectrometry to identify the chemical components. It can be concluded that C. camphora is the most effective oil EO in terms of toxicity, repellence, and oviposition deterrence, followed by M. haplocalyx and A. ascalonicum under greenhouse conditions. Our results introduce some new eco-friendly plant EOs to control whiteflies.