In the arm-in-cage test, topical repellents activate mosquitoes to disengage upon contact instead of repelling them at distance.

Topical repellents provide protection against mosquito bites and their efficacy is often assessed using the arm-in-cage test. The arm-in-cage test estimates the repellent's protection time by exposing a repellent-treated forearm to host-seeking mosquitoes inside a cage at regular intervals until the first confirmed mosquito bite. However, the test does not reveal the repellents' behavioural mode of action. To understand how mosquitoes interact with topical repellents in the arm-in-cage test, we used a 3D infrared video camera system to track individual Aedes aegypti and Anopheles stephensi females during exposure to either a repellent-treated or an untreated forearm. The repellents tested were 20% (m/m) ethanolic solutions of N, N-diethyl-meta-toluamide, p-menthane-3,8-diol, icaridin and ethyl butylacetylaminopropionate. All four repellents substantially reduced the number of bites compared to an untreated forearm, while the flight trajectories indicate that the repellents do not prevent skin contact as the mosquitoes made multiple brief contacts with the treated forearm. We conclude that, in the context of the arm-in-cage test, topical repellents activate mosquitoes to disengage from the forearm with undirected displacements upon contact rather than being repelled at distance by volatile odorants.

Sustainable Natural Resources for Aphid Management: ß-Ionone and Its Derivatives as Promising Ecofriendly Botanical-Based Products.

ß-Ionone, sustainably derived from Petunia hybrida as a natural bioresource, was identified as a lead compound for integrated aphid management. A series of ß-ionone derivatives containing ester groups were designed and synthesized for the purpose of discovering renewable botanical-based products. The odorant-binding protein (OBP) binding test indicated that ß-ionone and its derivatives displayed binding affinities with Acyrthosiphon pisum OBP9 (ApisOBP9) and Harmonia axyridis OBP15 (HaxyOBP15). Bioactivity assays revealed that most ß-ionone derivatives exhibited a higher repellent activity than that of ß-ionone. ß-Ionone and derivatives 4g and 4l displayed attractiveness to H. axyridis. Specifically, 4g was a highly promising derivative, possessing good repellent activity against A. pisum and attractiveness to H. axyridis. Molecular dynamics simulations revealed that integrating the hydrophobic ester group into the ß-ionone framework strengthened the van der Waals interactions of 4g with ApisOBP9/HaxyOBP15, improving the binding affinity with OBPs and producing higher push-pull activity than ß-ionone; 4g also had low toxicity toward nontarget organisms. Thus, 4g is a potential ecofriendly, botanical-based option for aphid management.

Optokinetic response in D. melanogaster reveals the nature of common repellent odorants.

Animals' ability to orient and navigate relies on selecting an appropriate motor response based on the perception and integration of the environmental information. This is the case, for instance, of the optokinetic response (OKR) in Drosophila melanogaster, where optic flow visual stimulation modulates head movements. Despite a large body of literature on the OKR, there is still a limited understanding, in flies, of the impact on OKR of concomitant, and potentially conflicting, inputs. To evaluate the impact of this multimodal integration, we combined in D. melanogaster, while flying in a tethered condition, the optic flow stimulation leading to OKR with the simultaneous presentation of olfactory cues, based on repellent or masking compounds typically used against noxious insect species. First, this approach allowed us to directly quantify the effect of several substances and of their concentration on the dynamics of the flies' OKR in response to moving gratings by evaluating the number of saccades and the velocity of the slow phase. Subsequently, this analysis was capable of easily revealing the actual effect, i.e. masking vs. repellent, of the compound tested. In conclusion, we show that D. melanogaster, a cost-affordable species, represents a viable option for studying the effects of several compounds on the navigational abilities of insects.

Repellency, Fumigant Toxicity, Antifeedent and Residual Activities of Coridothymus capitatus and Its Main Component Carvacrol against Red Flour Beetle.

Tribolium castaneum is a challenging pest of stored products, causing significant economic losses. The present study explored the efficacy of Coridothymus capitatus essential oil and its primary constituent, carvacrol, as eco-friendly alternatives for managing this pest. To evaluate their insecticidal potential, repellency, fumigant toxicity, and antifeedant properties, progeny inhibition assays were performed. Carvacrol exhibited superior repellency compared to the essential oil, achieving a 92% repellency rate at 2 mg/cm2. Both compounds demonstrated significant fumigant toxicity against T. castaneum, with LC50 values of 168.47 and 106.5 µL/L for the essential oil and carvacrol, respectively, after 24 h. Carvacrol also outperformed the essential oil in antifeedant activity, inducing an 80.7% feeding deterrence at 1.17 mg/g. Moreover, both treatments effectively suppressed the development of the pest's progeny. These results collectively underscore the potent insecticidal properties of C. capitatus essential oil and carvacrol, particularly carvacrol, as promising candidates for the sustainable management of T. castaneum in stored product protection.

Molecular basis of camphor repellency in Hyphantria cunea.

The plant-derived camphor has been used as a natural insect repellent against various insects for >500 years. However, the repellency mechanism behind camphor remains less understood. In this study, we aimed to identify the camphor receptor in Hyphantria cunea by deorphanizing 7 odorant receptors (ORs). The results showed that HcunOR46 is narrowly tuned to Camphor and is only conserved within the family Noctuidae. Further analysis through behavioral and electroantennograms (EAG) assays indicated that H. cunea adults are more sensitive to camphor than larvae, both behaviorally and electrophysiologically. This difference may be due to the lower expression of HcunOR46 at the larval stage. Additionally, a feeding assay indicated that camphor repellency could be related to camphor toxicity to larvae, with the lethal concentration 50 (LC50) value of 69.713 µg/µL. These results suggest that H. cunea may detect camphor through a distinct olfactory pathway from Culicinae mosquitos, providing a novel camphor-based pest management strategy for H. cunea.

Mentha arvensis oil exhibits repellent acute toxic and antioxidant activities in Nauphoeta cinerea.

Mentha arvensis is an herbaceous plant commonly known as peppermint or Japanese mint. This study investigated the toxic potential and repellent efficacy of M. arvensis essential oil (MaEO) at varying concentrations (15.625-250 mg/mL) in Nauphoeta cinerea, along with its impact on biochemical parameters in N. cinerea. The potential of the major compounds as a new analgesic target was investigated using molecular docking. The essential oil was analyzed by gas Chromatography-mass spectrometry (GC-MS) and the toxic potential, repellent property, and changes in lipid peroxidation (LPO) levels were evaluated as markers of oxidative stress. GC-MS results revealed that the main components were oxygenated monoterpenes such as menthol (71.31%), mentone (13.34%) and isomentone (5.35%). MaEO significantly reduced lipid peroxidation (LPO), the levels of non-protein thiols and iron(II) at the concentration of 125 mg/mL in N. cinerea. Furthermore, the major components, L-(-)-Menthol and menthone demonstrated high gastrointestinal absorption and high affinity with the target protein, suggesting possible links that contribute to the analgesic effect of MaEO.

Stereoselective Oxidation of α-Copaene, a Fire Ant Repellent Sesquiterpene from the Essential Oil of Dipterocarpus turbinatus.

Imported fire ants are significant agricultural pests. Repellents can be used to prevent foraging fire ants from entering sensitive areas, including electrical equipment, nursing homes, and hospitals. Bioassay-guided fractionation of the essential oil extracted from gurjun balsam (Dipterocarpus turbinatus) resulted in the identification of (-)-α-copaene (1) as the repellent constituent with a minimum repellent effective dose (MRED) of 15.6 µg/g against both red imported fire ants (Solenopsis invicta) and hybrid imported fire ants (Solenopsis invicta × Solenopsis richteri). Stereoselective oxidation of 1 via autoxidation and chemical methods produced (-)-5R-hydroperoxy-α-copaene (2), (+)-3S-hydroperoxycopa-4-ene (3), (-)-α-copaene oxide (4), (+)-ß-copaen-4α-ol (5), copaenediol (6), and copaene ketol (7). Reduction of 2 and 3 with triphenylphosphine afforded (-)-5R-hydroxy-α-copaene (2a) and (+)-3S-hydroxycopa-4-ene (3a), respectively, which led to the structural revision of copa-3-en-2α-ol and copa-2-en-4-ol as 2a and 3, respectively. The configurational assignment of compound 4 in the literature was also clarified by the detailed analysis of 2D NMR spectroscopic data. Compounds 2-7 showed repellency with MREDs ranging from 3.9 to 15.6 µg/g against hybrid and red imported fire ants, indicating that chemical modification can enhance the repellent effect of (-)-α-copaene.

Unravelling the genomic landscape reveals the presence of six novel odorant-binding proteins in whitefly Bemisia tabaci Asia II-1.

Genome wide analysis identified 14 OBPs in B. tabaci Asia II-1, of which six are new to science. Phylogenetic analysis traced their diversity and evolutionary lineage among Hemipteran insects. Comparative analysis reclassified the OBP gene families among B. tabaci cryptic species: Asia I, II-1, MEAM1, and MED. The 14 OBPs were clustered on four chromosomes of B. tabaci. RT-qPCR showed high expression of OBP3 and 8 across all body tissues and OBP10 in the abdomen. Molecular docking showed that OBP 3 and 10 had high affinity bonding with different candidate ligands, with binding energies ranging from -5.0 to -7.7 kcal/mol. Competitive fluorescence binding assays revealed that ß-caryophyllene and limonene had high binding affinities for OBP3 and 10, with their IC50 values ranging from 9.16 to 14 µmol·L-1 and KD values around 7 to 9 µmol·L-1. Behavioural assays revealed that ß-caryophyllene and carvacrol were attractants, ß-ocimene and limonene were repellents, and γ-terpinene and ß-ocimene were oviposition deterrents to B. tabaci. Functional validation by RNAi demonstrated that OBP3 and OBP10 modulated host recognition of B. tabaci. This study expands our understanding of the genomic landscape of OBPs in B. tabaci, offering scope for developing novel pest control strategies.

Multifaceted computational profiling of thymol and geraniol against the human proteome for bio-repellent alternatives: Toxicity predictions, degradation analysis, and quantum mechanical approaches.

With growing interest in natural compounds as alternative mosquito repellents, assessing the toxicity and structure of potential repellent naturals like thymol (monoterpene phenol) and geraniol (monoterpene alcohol) is vital for understanding their stability and human impact. This study aimed to determine the structural, toxicity, and binding profiles of thymol and geraniol using computational predictions, xTB metadynamics, quantum mechanics, and principal component analysis. Toxicity studies using Protox-II, T.E.S.T, and SwissADME indicated that thymol and geraniol belong to toxicity class 4 and 5, respectively, with low toxicity predictions in other endpoints. Overall pharmacokinetic profile was generated via pkCSM. Off-target predictions via SwissTarget Predictions, LigTMap, Pharmapper, and SuperPred showed that these molecules can bind to 614 human proteins. The degradation of thymol and geraniol were performed using xTB metadynamics and the outcomes showed that the degradants for both compounds were stable and had lower toxicity profile. Nine tautomers were generated via quantum mechanics for thymol and four for geraniol, with RMSD ranging from 3.8 to 6.3 Å for thymol and 3.6 to 4 Å for geraniol after superimpositions. DFT studies found that HOMO-LUMO values and electronegativity parameters of thymol and geraniol did not differ significantly from their isomers. Binding affinity studies against 614 proteins, analysed via PCA and violin plots, highlighted the probable range of binding. These multifaceted in-silico findings corroborate the stability and potential utility of thymol and geraniol as safer alternatives in repellent applications.

Insecticidal and Repellent Activity of Essential Oils from Copaifera reticulata, Citrus paradisi, Lavandula hybrida and Salvia sclarea Against Immature and Adult Stages of Ctenocephalides felis felis.

PURPOSE: The flea Ctenocephalides felis (Siphonaptera: Pulicidae), parasitizes dogs and cats globally, acting as a vector for various pathogens affecting both animals and humans. Growing interest in environmentally friendly, plant-based products prompted this study. The aim of the study was to determine the chemical composition of essential oils (EOs) from Copaifera reticulata, Citrus paradisi, Lavandula hybrida and Salvia sclarea, assessing their insecticidal and repellent properties, determining lethal concentrations (LC50 and LC90), and evaluating residual efficacy in vitro against Ctenocephalides felis felis. METHODS: Gas Chromatography with Flame Ionization Detector analyzed EO composition. In vitro tests involved preparing EO solutions at various concentrations. Ten specimens from each life stage (egg, larva, pupa, adult) were used for insecticidal activity assessment. Adulticidal activity was assessed using 10 cm2 filter paper strip, each treated with 0.200 mL of the test solution. Immature stages activities were evaluated using 23.76 cm2 discs of the same filter paper, each treated with 0.470 mL of the test solution. Mortality percentage was calculated using (number of dead insects × 100) / number of incubated insects. Probit analysis calculated LC50 values with a 95% confidence interval. RESULTS: Major EO constituents were ß-caryophyllene (EOCR), linalool (EOLH), linalyl acetate (EOSS), and limonene (EOCP). LC50 values were obtained for all stages except for the essential oil of C. paradisi. All oils showed repellent activity at 800 µg/cm2. OECR exhibited greater residual efficacy. CONCLUSION: Each EO demonstrated superior insecticidal activity against specific C. felis felis stages.

Enhanced repellent and anti-nutritional activities of polymeric nanoparticles containing essential oils against red flour beetle, Tribolium castaneum.

Encapsulation of essential oils (EOs) is an important strategy that can be applied to intensify the stability and efficiency of these compounds in integrated pest management. The present study aimed to investigate the sub-lethal activity of polymer-based EOs nanoparticles against red flour beetle, Tribolium castaneum adults as an important critical pest of stored products. Chitosan nanoparticles (CSNPs) containing garlic and cinnamon essential oils (GEO and CEO) prepared using the ionic cross-link technique. Stability of nano-formulations evaluated over temperature and storage time. The fumigant effect (LC10, LC20, LC30) and contact toxicity (LC10, LC15, LC25) determined. In addition, the contact toxicities of EOs and their nanoparticles on nutritional indices evaluated. An olfactometer used to assess the repellent activity of EOs and EOs loaded in CSNPs (EOs@CSNPs) in sub-lethal fumigant concentrations. Characterization results showed GEO loaded in CSNPs has particle size of 231.14 ± 7.55 nm, polydispersity index (PDI) value of 0.15 ± 0.02, encapsulation efficiency (EE) percentage of 76.77 ± 0.20 and zeta potential of - 18.82 ± 0.90 mV, in which these values for the CEO loaded in CSNPs (CEO@CSNPs) changed to 303.46 ± 0.00 nm, 0.20 ± 0.05, 86.81 ± 0.00% and - 20.16 ± 0.35 mV, respectively. A lower PDI value for both CSNPs showed an appropriate NPs size distribution. Furthermore, NPs size and encapsulation efficiency did not change in various temperatures and during four months which confirm good stability of the EOs@CSNPs. In LC30 of GEO@CSNPs, the maximum repellency was determined as 66.66 ± 3.33. Among nutritional indices, in LC25 of GEO@CSNPs, the relative growth rate (RGR) (0.011 ± 0.003 mg.mg-1.day-1), relative consumption rate (RCR) (0.075 ± 0.004 mg.mg-1.day-1) and feeding deterrence index (FDI) (54.662 ± 1.616%) were more affected, so GEO@CSNPs was more effective than CEO@CSNPs. The results of repellent and anti-dietary activities of EOs and EOs@CSNPs confirmed the higher repellency and adverse effectivity on nutritional indices of Tribolium castaneum pest treated with EOs@CSNPs compared to free EOs. In conclusion, the NPs form of GEO and CEO can be a novel and efficient carrier for improving the repellent and anti-nutritional activities of EOs.

Designing thermoreversible gels for extended release of mosquito repellent.

Mosquito-borne diseases are responsible for 700 000 deaths annually. Current outdoor protective strategies primarily focus on direct skin application of commercial repellents (i.e., aerosol sprays or topical lotions) which are typically limited to efficacy times of ≤10 hours due to rapid evaporation and dermal absorption. Consequently, frequent reapplication for continuous protection can increase associated health hazards and cause noncompliance. This study utilizes Hansen solubility parameter modeling to design physical gels composed of insect-repelling N,N-diethyl-meta-toluamide (DEET) and modacrylic copolymer poly(acrylonitrile-co-vinyl chloride) (P(AN-VC)). The P(AN-VC)/DEET composites exhibit tunable and reversible sol-gel transition temperatures that can meet the thermomechanical stability demands of the intended application and permit facile transition to commercial melt processing techniques such as injection molding, filament spinning, or film casting. P(AN-VC)/DEET gel films demonstrate mosquito repellency for more than half a year-performing longer than any other known material to date-due to the high reservoir of repellent and its desorption hindrance from the polymer matrix. Therefore, P(AN-VC)/DEET gels hold significant potential for extended protection against mosquitos and other biting arthropods.

Mosquito Shield™, a transfluthrin passive emanator, protects against pyrethroid-resistant Anopheles gambiae sensu lato in central Benin.

BACKGROUND: Spatial repellents can provide personal and household protection against biting vector mosquitoes by volatizing repellents into the air within a given area. Mosquito Shield™ is a transfluthrin passive emanator undergoing evaluation for malaria control. Studies evaluating its entomological impact against different local malaria vector populations would help guide its deployment in endemic countries. METHODS: A two-arm single-blinded small-scale household randomised entomological trial was conducted to assess the impact of Mosquito Shield™ on the human landing rate of wild pyrethroid-resistant Anopheles gambiae sensu lato (s.l.) vector mosquitoes in houses in the Ganhoua village of the Zakpota District of central Benin. From a total of 30 houses, 15 were randomly allocated to receive Mosquito Shield™, while the remainder received a placebo product. The trial lasted through the life of the Mosquito Shield™ product (32 days). Mosquito sampling was performed by human landing catches at baseline and at 6 timepoints post-intervention (days 0-1, 7-8, 14-15, 21-22, 28-29 and 31-32). Collections were performed for 2 nights at each sampling time point. WHO cylinder bioassays were conducted during the trial with F1 An. gambiae s.l. mosquitoes that emerged from larvae from the study area to assess the intensity of resistance to pyrethroids in the wild vector population. RESULTS: The vector population in the study area showed a high intensity of resistance to pyrethroids. Baseline An. gambiae s.l. human landing rates were similar in houses in both study arms before product application (11.53/person/night vs 11.67/person/night, p > 0.05). A total of 5736 mosquitoes were collected in the placebo control arm and 3862 in the Mosquito Shield™ arm post-intervention. Overall An. gambiae s.l. post-intervention human landing rates were significantly lower in houses in the Mosquito Shield™ arm (18.13/person/night) compared to the houses in the placebo control arm (26.84/person/night, IRR = 0.658, p < 0.001). Over the lifespan of the product, Mosquito Shield™ provided a significant protective efficacy of 34.2% (22.1-44.4%, p < 0.001) against wild pyrethroid-resistant An. gambiae s.l. vectors compared to the placebo. Human landing rates of other nuisance vector mosquito species (Culex and Mansonia) were also reduced in houses treated with Mosquito Shield™ compared to the placebo. CONCLUSION: Mosquito Shield™, a transfluthrin passive emanator, provided significant protection against pyrethroid-resistant malaria vectors to households in Benin. The spatial repellent shows potential to reduce malaria transmission by pyrethroid-resistant An. gambiae s.l. vector mosquitoes and cover gaps in malaria control when deployed to complement existing vector control interventions.

Rancid rumors or Native wisdom: Evaluating the efficacy of animal fats as insect repellents attributed to historic-period Native Americans.

Little is known about Native American adaptations to blood-sucking arthropods prior to and following European contact. Multiple accounts starting in the 16th century suggest that rancid animal grease was employed by Gulf Coast indigenes as a mosquito repellent. Although many Native American ethnobotanical remedies for biting insects have been recorded, the use of animal products for this purpose is not well documented. Moreover, few traditional Native American mosquito repellents have been examined using controlled laboratory methods for repellency testing. In this study, we tested the repellent efficacy of fats derived from alligator, bear, cod, and shark that were aged to various stages of rancidity. Using yellow fever mosquitoes, (Aedes aegypti), we performed an arm-in-cage assay to measure the complete protection times resulted from these fats, when applied to human skin. We used a Y-tube olfactometer assay to evaluate long-distance repellency and tested tick-repellency in a crawling assay. Our results suggest that rancid animal fats from cod, bear, and alligator are potent albeit short-lived mosquito repellents. We found that both rancid and fresh fats do not repel ticks. Our findings show the validity of traditional ethnozoological knowledge of Native American people and support aspects of the ethnohistorical record.

Repellency, Toxicity, and Chemical Composition of Plant Essential Oils from Myrtaceae against Asian Citrus Psyllid, Diaphorina citri Kuwayama (Hemiptera Liviidae).

Diaphorina citri Kuwayama (D. citri) is one of the major pests in the citrus industry, which spreads Citrus Huanglongbing disease. It has developed resistance to chemical insecticides. Therefore, searching for greener solutions for pest management is critically important. The main aim of this study was to evaluate the repellent and insecticidal efficacy of essential oils (EOs) from four species of Myrtaceae plants: Psidium guajava (PG), Eucalyptus robusta (ER), Eucalyptus tereticornis (ET), and Baeckea frutescens (BF) against D. citri and to analyze their chemical compositions. GC-MS analysis was performed, and the results indicated that the EOs of PG, ER, ET, and BF were rich in terpenoids, ketones, esters, and alcohol compounds. The repellent rate of all four EOs showed that it decreased with exposure time but increased with the concentration of EOs from 80.50% to 100.00% after treating D. citri for 6 h with four EOs at 100% concentration and decreased to 67.71% to 85.49% after 24 h of exposure. Among the compounds from the EOs tested, eucalyptol had the strongest repellent activity, with a 24 h repellency rate of 100%. The contact toxicity bioassay results showed that all EOs have insecticidal toxicity to D. citri; the LC50 for nymphs was 36.47-93.15 mL/L, and for adults, it was 60.72-111.00 mL/L. These results show that when PG is used as the reference material, the ER, ET, and BF EOs have strong biological activity against D. citri, which provides a scientific basis for the further development of plant-derived agrochemicals.

Synergism of (E)-ß-farnesene and Its Analogue to Insecticides against the Green Peach Aphid Myzus persicae.

With high aphid-repellent activity but low stability, (E)-ß-farnesene (EßF), the major component of the aphid alarm pheromone, can be used as a synergist to insecticides. Some EßF analogues possess both good aphid-repellent activity and stability, but the synergistic effect and related mechanism are still unclear. Therefore, this study investigated the synergistic effect and underlying mechanism of the EßF and its analogue against the aphid Myzus persicae. The results indicated that EßF and the analogue showed significantly synergistic effects to different insecticides, with synergism ratios from 1.524 to 3.446. Mechanistic studies revealed that EßF and the analogue exhibited effective repellent activity, significantly upregulated target OBP genes by 161 to 731%, increased aphid mobility, and thereby enhanced contact with insecticides. This research suggests that the EßF analogue represents a novel synergist for insecticides, with the potential for further application in aphid control owing to its enhanced bioactivity and the possibility of reducing insecticide doses.

Field evaluation of a volatile pyrethroid spatial repellent and etofenprox treated clothing for outdoor protection against forest malaria vectors in Cambodia.

Cambodia's goal to eliminate malaria by 2025 is challenged by persistent transmission in forest and forest fringe areas, where people are exposed to Anopheles mosquito bites during the day and night. Volatile pyrethroid spatial repellents (VPSRs) and insecticide-treated clothing (ITC) could address these gaps. This study evaluated the outdoor application of one passive transfluthrin-based VPSR, four etofenprox-ITCs paired with a picaridin topical repellent, and a combination of VPSR and ITC against wild Anopheles landing in Cambodia. A 7 × 7 Latin-square study was conducted over 49 collection nights in temporary open structures in Mondulkiri Province. All interventions substantially reduced Anopheles landing, with protective efficacy ranging from 61 to 95%. Mathematical modeling showed significant reductions in vectoral capacity, especially with the combined ITC and VPSR and VPSR alone, albeit with decreased effectiveness over time. These interventions have the potential to reduce outdoor and daytime Anopheles biting, offering valuable contributions to malaria elimination efforts in Cambodia and the Greater Mekong Subregion, contingent upon achieving effective coverage and adherence.

Repellency, toxicity, and physiological actions of low molecular weight basic amines in mosquitoes.

BACKGROUND: This study investigated the behavioral responses and toxicity of three basic amines: 1-methylpiperazine, 1-methylpyrrolidine, and triethylamine (TEA), compounds suggested previously to be anosmic in vapor exposures to caged mosquitoes. RESULTS: These compounds showed repellency of Aedes aegypti mosquitoes, followed by flightlessness, knockdown, and paralysis, all increasing with exposure time and dosage. Electrophysiological experiments showed a blocking effect on nerve discharge of the Drosophila melanogaster larval central nervous system (CNS) with little evidence of hyperexcitation. Blockage of voltage-gated (Kv2) potassium channel currents under patch clamp occurred at similar concentrations. Involvement of K+ channels in the action of basic amines was supported by behavior and CNS recordings of a Shaker Kv1 mutant exposed to TEA, where instead of blockage, a hyperexcitation of nerve firing was observed. Experiments on cockroach leg mechanoreceptors demonstrated neuronal excitation and on mosquito antennae strong electroantennogram (EAG) signals with an augmentation of blank air responses after a single puff of basic amine. CONCLUSIONS: The neurophysiological effects of basic amines are consistent with K+ channel block, whereas the antennal EAG response was not obviously associated with anosmia. The low-dose effects of basic amines appear to be repellency and bradykinesia. Overall, the findings provide key insights into the mechanisms underlying the biological activity of basic amines. © 2024 Society of Chemical Industry.

Actividad repelente e insecticida de cuatro aceites esenciales de plantas recolectadas en Chocó-Colombia contra Tribolium castaneum / Repellent and insecticidal activity of four essential oils from plants recolleted in Chocó-Colombia against Tribolium castaneum

This study aimed to determine the repellent and insecticidal activity of four essential oils (EOs) from plants collected in the Chocó rain forest, Colombia, against T. castaneum . Conventional hydrodistillation was used to obtain the EOs. The repellent and insecticidal activities were evaluated by the preference area and gas dispersion methods, espectively. Statistical differences (p<0.05) were determined by applying a student's t-test. EOs of Siparuna guianensis, S. conica, Piper marginatum, and Nectandra acutifolia showed excellent repellent properties as the main findings, highlighting S. conicaEO with 84% repellency (1-hµL/cm2), while P. marginatum showed to be bioactive to the dose of 500 µL/mL (72 h), inducing mortality of 100% of the exposed population. In conclusion, the results evidenced the repellent properties of the EOs evaluated against T. castaneum , which allows us to conclude that these plant species are potential natural sources producing bio-repellents that contribute to the integrated control of T. castaneum.

Se evaluaron cuatro aceites esenciales (AEs) de plantas recolectadas en la selva pluvial del Chocó, Colombia, para determinar su actividad repelente e insecticida contra T. castaneum. Los AEs fueron obtenidos por hidrodestilación convencional. Las actividades repelentes e insecticidas se evaluaron por los métodos de área de preferencia y dispersión de gas, respectivamente. Las diferencias significativas (p<0,05) fueron determinadas aplicando una prueba t de student. Los AEs de Siparuna guianensis, S. conica, Piper marginatum y Nectandra acutifolia mostraron excelentes propiedades repelentes, destacando el AE de S. conicacon un 84% de repelencia (1µL/cm2), mientras que el AE de P. marginatummostró ser bioactivo a la dosis de 500 µL/mL (72 h) al inducir la mortalidad del 100% de la población expuesta. Se concluye que estas especies de plantas son fuentes naturales potencialmente viables para la producción de biorepelentes que contribuyan en el control integrado de T. castaneum.

Repellency of N,N-diethyl-3-methylbenzamide (DEET) during host-seeking behavior of bed bugs (Hemiptera: Cimicidae) in binary choice olfactometer assays.

The bed bug (Cimex lectularius L.) is one of the most prolific and burdensome indoor pests, and suppression of bed bug populations is a global priority. Understanding bed bug behavior is important to the development of new tactics for their control. Major gaps exist in our understanding of how host cues, insecticide resistance, and exposure modality impact the repellency of formulated products to bed bugs. Here, we validate the use of a binary choice olfactometer for assessing bed bug repellency behaviors using N,N-diethyl-3-methylbenzamide (DEET) in a dose-dependent manner, while considering the role of host-associated stimuli (with vs. without CO2), exposure modality (olfactory vs. olfactory and contact), and resistance status (susceptible vs. resistant) on repellency. We observed that host-seeking insecticide-susceptible bed bugs were repelled only when olfactorily exposed to high concentrations of DEET. However, exposure to DEET by contact repelled insecticide-susceptible bed bugs at 100-fold lower dose of DEET. Further, we demonstrate for the first time that insecticide-resistant bed bugs were significantly more responsive to DEET than susceptible bed bugs. We conclude that the 2-choice olfactometer is an effective tool for assessing the behavioral responses of bed bugs to spatial and contact repellents.