Repellency Of Essential Oils Research Articles

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.

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 as environmentally friendly insecticides for controlling cotton mealybug, Phenacoccus solenopsis (Tinsley) (Hemiptera: Pseudococcidae)

Eight plant essential oils were extracted and tested for their efficiency as natural insecticides against the cotton mealybug, P. solenopsis (Tinsley). In-vitro bioassay, the contact toxicity of the tested oils to adult females and 2nd instar nymphs was determined. Also, repellence activity of the tested oils were tested. The most effective oil against adult female’s after 72 hrs of application was L. nobilis followed by Apium graveolens, M. longifolia, C. articulates, M. sativa, A. graveolens, O. vulgar, then F. vulgar. The 2nd instar nymphs showed more susceptibility for all tested essential. Regarding repellency, M. longifolia showed the highest repellency effect but unfortunately with high degradation rate. The most repellent essential oils with satisfactory stability were L. nobilis, F. vulgar and C. articulates. Also, the efficacy of the tested oils were tested against P. solenopsis in open field conditions. The most efficient oil at 72hrs after treatment was L. nobilis which showed great reduction percentage (89.3%) followed by Apium graveolens (88.6%), M. longifolia (88.6%), C. articulates (87.8%), M. sativa (87.7%), A. graveolens (86.9%), O. vulgar (85.9%) and F. vulgar (85.2%), respectively.

Chemical Diversity and Anti-Insect Activity Evaluation of Essential Oils Extracted from Five Artemisia Species.

As a source of aromatic plants, the genus Artemisia has long been considered to have the potential to develop plant pesticides. In this study, components of essential oils from A. dalai-lamae, A. tangutica, A. sieversiana, A. tanacetifolia and A. ordosica were identified by GC-MS. A total of 56 constituents were analysed, and each species consisted of 9 to 24 constituents. Principle component analysis (PCA) revealed that A. dalai-lamae, A. tangutica and A. tanacetifolia are characterised by monoterpene hydrocarbons and oxygenated monoterpenes. Hierarchical cluster analysis (HCA) showed the most remarkable similarity between A. sieversiana and A. ordosica, but the similarity was still lower than 50%. Contact toxicity and repellency of essential oils were evaluated by bioassays; A. ordosica oil exhibited the most substantial contact toxicity (LD50 = 52.11 μg/cm2) against Liposcelis bostrychophila, while A. tangutica oil showed the most potent contact toxicity (LD50 = 17.42 μg/adult) against Tribolium castaneum. Except for A. dalai-lamae, the other four species showed the same level (p > 0.05) of repellent activity as the positive control against both pests at high concentrations. The results indicated that these five Artemisia species had high chemical diversity and great potential to be developed into more effective and environmentally friendly anti-insect agents.

Fabrication of a vertical Y-tube olfactometer for the assessment of spatial repellency of essential oils against Helopeltis theivora waterhouse

Fabrication of a vertical Y-tube olfactometer for the assessment of spatial repellency of essential oils against Helopeltis theivora waterhouse

Repellent activity of essential oils on adults of Halyomorpha halys (Heteroptera: Pentatomidae) in different physiological‐behavioural phases

AbstractThe brown marmorated stink bug Halyomorpha halys is an invasive agricultural pest in North America and Europe, and also a dwelling nuisance in autumn, due to the overwintering adults aggregating inside buildings. The repellent potential of ginger, clove, vetiver and turmeric essential oils (EOs) was tested on H. halys adults of three different physiological‐behavioural phases: exiting overwintering (EXOV), active during summer (SUMM) and entering overwintering (ENOV). In a two‐choice apparatus, fresh food was used as an attractant in both sides, together with three males when testing ENOV individuals. A filter paper with different concentrations of the EOs was the treatment side, and a filter paper with ethanol acted as control. The position of the individually tested bugs was recorded after 1, 6 and 24 hr. All tested EOs were repellent at concentrations higher than 3%, independent of sex or length of exposure. Turmeric and clove were the most repellent EOs, whereas ginger and vetiver showed on average a medium‐to‐low repellency. Significant differences emerged among the physiological‐behavioural phases, with SUMM individuals showing a greater repellency to many of the tested concentrations, and EXOV individuals being overall the least susceptible to these substances. The response to vetiver oil was ambiguous, as at 25%, it elicited both a strong repellency in SUMM and a strong attraction in EXOV. Turmeric and clove EOs are promising candidates in integrated pest management strategies to reduce attacks by H. halys to susceptible crops especially during summer, as well as to prevent the entrance of overwintering bugs in buildings in autumn.

Fumigant toxicity and repellency of some essential oils against Callosobruchus maculatus (Col.: Bruchidae).

Chemical composition and insecticidal activity and repellency of essential oils from Ferula gummosa Boiss., Cuminum cyminum L., Carum carvi L. and Pelargonium roseum Willd. against the adults of Callosobruchus maculatus (Coleoptera: Bruchidae) were studied. The gas chromatograph/mass spectrometry (GC/MS), bioassays, and olfactometer were respectively used to identify the components and determine the fumigant toxicity (in 50 mL vials containing 20 adult insects) and repellency of the essential oils. The main compounds of the essential oils were β-pinene (35.2%), α-pinene (9.4%), ρ-cymene (8.5%), and terpinene-4-ol (8.5%) for F. gummosa, cuminaldehyde (46.6%), ρ-cymene (18.4), γ-terpinene (12.2%) and α-terpinene-7-al (8.1%) for C. cyminum, carvone (46.2%), ρ-cymene (14.0%) and γ-terpinene (8.3%) for C. carvi, and β-citronellol (47.3%) and citronellyl formate (13.2%) for P. roseum. The fumigant toxicity of C. carvi and C. cyminum essential oils against C. maculatus was higher than the other two essential oils, and the repellent activity was observed for all essential oils tested against this pest. The repellency percentage of P. roseum, F. gummosa, C. cyminum and C. carvi essential oils was calculated as 41.66, 64.70, 70.17, and 66.29%, respectively. The results indicated that these essential oils could be considered as an effective alternative to control C. maculatus and possibly other storage coleopteran pests.

Effect of Citrus limonum essential oil against granary weevil, Sitophilus granarius and its chemical composition, biological activities and energy reserves

Stored grains could lose substantially their nutritional quality, and consequently its value, between storage and consummation because of insect’s infestation. One of the most frequent pests of wheat is the grain weevil (Sitophilus granarius L.). Cleverly hidden, the immature stages of this destructive pest are very difficult to identify. Protecting stored grains has become an agricultural challenge. In the present study, the essential oil (EO) distillated from Citrus limonum (L.) (Burm. F., 1768) and analyzed by gas chromatography-mass spectrometry (GC-MS) revealed the presence of 47 compounds with (Z)-citral (30.74%), dl-limonene (19.81%) and geranyl propionate (16.28%) as major components. In a second series of experiment, its fumigant (using filter paper), repellent (by semi circles joined discs) and residual (persistent insecticidal activity) activities were examined against Sitophilus granarius (L.) adults. The total nutrition (carbohydrates and lipids) depletion index (NDI) was also calculated. Residual toxicity and repellency of EO were demonstrated after fumigation against S. granarius with a dose-response relationship. The effectiveness of EO was exposure time dependent and its residual activity persisted up to 30 h following mortality. Moreover, data showed that treatment of S. granarius adults had adverse effects on the depletion of their energy reserves. C. limonum EO declined the lipid and carbohydrate contents in adults. Obtained data prove that botanical essential oils could be considered as potent biorational alternatives to synthetic insecticides for pest control of stored products in a sustainable manner.

Chemical diversity and biological activities of essential oils from native populations of Clinopodium menthifolium subsp. ascendens (Jord.) Govaerts.

This study is focused on the analysis of regional variation of the chemical compositions of three Clinopodium menthifolium subsp. ascendens (Jord.) Govaerts Tunisian accession, as well as their inhibition toward fungi and insect pests. The diversity of the chemical constituents and biological activities in front of the aforementioned variations was found to be remarkable. Essential oils were obtained by hydrodistillation of the aerial parts and analyzed by gas chromatography-mass spectrometry (GC-MS). A total of 41, 42, and 30 compounds were identified respectively from Clinopodium menthifolium essential oils harvested from three Tunisian regions, namely Ain-Draham (ADEO), Babouch (BEO), and Tabarka (TEO). All analyzed oils were rich in oxygenated monoterpenes with different major constituents. Piperitenone (34.5%), cis-piperitone oxide (26.1%), and pulegone (47.9%) were the dominant compounds in the three volatile oils, respectively. The antifungal activity was investigated in vitro using six targeted fungal strains (Aspergillus flavus, Aspergillus terreus, Candida albicans, Microsporum canis, Microsporum gypseum, and Trichophyton mentagrophytes). The toxicity and repellency of essential oils were evaluated against the stored product pest Tribolium confusum. The tested samples were differently effective toward the target fungi and the pest depending on the variability of their chemical compositions. BEO exhibited the highest fungitoxic properties toward A. terreus mold, M. canis dermatophyte, and C. albicans yeast (the MIC values ranged from 40 to 400 μg mL-1). In addition, the data showed that TEO repelled T. confusum moderately (PR = 42.5% at 2 h after exposure). Concerning the contact treatment, both ADEO and BEO were proved to possess slightly toxic effects toward T. confusum pest (% of mortality 27.5-32.5% at 5% concentration). The results showed that the geographic origin greatly influenced the chemical composition and the associated bioactivities of Clinopodium menthifolium subsp. ascendens.

Toxicity and repellency of essential oils in the management of Sitophilus zeamais

ABSTRACT This study had the following objectives: to identify and quantify the constituent compounds of essential oils from Cymbopogon winterianus Jowitt, Eucalyptus globulus Labill., Eucalyptus staigeriana F. Muell. ex F.M. Bailey, Foeniculum vulgare Mill., Ocimum basilicum L., Ocimum gratissimum L., and Piper hispidinervum C. DC., investigate their toxicity and repellency to S. zeamais and evaluate the toxicity of P. hispidinervum to immature S. zeamais. Individual tests for each essential oil were conducted with a completely randomized design with five concentrations for each oil and four replicates. Gas chromatography-mass spectrometry revealed the presence of citronellal in C. winterianus, 1,8-cineole in E. globulus, limonene in E. staigeriana, limonene in F. vulgare, linalool in O. basilicum, (E)-anethole in O. gratissimum, and safrole in P. hispidinervum. The median lethal concentration required to kill 50% of the insect (LC50) in contact and ingestion toxicity tests ranged from 5.12 to 78.89 μL 40g-1 corn in P. hispidinervum and C. winterianus, respectively. In adult fumigation tests, the LC50 ranged from 2.1 to 19.4 µL L-1 air, and in immature fumigation tests, the egg stage was susceptible to essential oil, whereas larval and pupal phases were tolerant. All of the oils repelled S. zeamais.

Toxicity and repellency of essential oils against rice weevil Sitophilus oryzae (L.)

Contact, fumigant, persistence toxicities and repellant activity of three plant essential oils viz., cinnamon (Cinnamomum verum J. Presl), eucalyptus (Eucalyptus obliqua L'Her) and orange oil (Citrus sinensis L.) against rice weevil, Sitophilus oryzae L. were evaluated under laboratory condition. Chemical profiling of tested essential oils through GC-MS studies showed presence of various chemical constituents wherein, eugenol (82.68%), eucalyptol (64.80%) and D-limonene (83.35%) were the major component of cinnamon, eucalyptus and orange oils, respectively. Contact toxicity results indicated that at 120 hours after treatment (HAT), eucalyptus oil caused significantly maximum mortality (100%) of S. oryzae when treated with 0.75 μl/cm2 concentration in comparison to fumigant toxicity (83%) at 2 μl/500 cm3 concentration. The present study demonstrated that among the treated oils, eucalyptus oil has higher contact, fumigant and repellent toxicity and hence it can be harnessed for integrated management of S. oryzae under storage condition.

Toxicity and repellency of essential oil from Evodia lenticellata Huang fruits and its major monoterpenes against three stored-product insects

In this work, the essential oil (EO) was extracted from the fruits of Evodia lenticellata, and the fumigant toxicity, contact toxicity and repellency against three stored-product insect species were evaluated for the obtained EO and several of its chemical components. The target insects were the adults of Tribolium castaneum (Coleoptera: Tenebrionidae), Lasioderma serricorne (Coleoptera: Anobiidae) and Liposcelis bostrychophila (Psocoptera: Liposcelididae). The EO was obtained with hydrodistillation and its chemical components were analyzed with the gas chromatography-mass spectrometry (GC-MS). Twenty-seven compounds, accounting for 83.1% of the total amount of the oil, were identified from the EO sample. The main compounds included linalool (12.0%), β-pinene (11.5%), 3-carene (9.6%), caryophyllene oxide (8.7%) and β-caryophyllene (7.9%). Among them, the amounts of monoterpenes and sesquiterpenes were as high as 52.7% and 22.7% to the total amount of EO respectively. The results of bioactivity test showed that the EO and its testing compounds had interspecific toxicity and repellent activity. So that, it might be expected that the EO extracted from the fruits of E. lenticellata could be developed to a new type of eco-friendly natural insecticide or repellent for the control of stored-product insects.

Odorant-binding protein-based identification of natural spatial repellents for the African malaria mosquito Anopheles gambiae

There is increasing interest in the development of effective mosquito repellents of natural origin to reduce transmission of diseases such as malaria and yellow fever. To achieve this we have employed an in vitro competition assay involving odorant-binding proteins (OBPs) of the malaria mosquito, Anopheles gambiae, with a predominantly female expression bias to identify plant essential oils (EOs) containing bioactive compounds that target mosquito olfactory function. EOs and their fractions capable of binding to such OBPs displayed repellence against female mosquitoes in a laboratory repellent assay. Repellent EOs were subjected to gas chromatographic analysis linked to antennogram (EAG) recordings from female A. gambiae to identify the biologically active constituents. Among these compounds cumin alcohol, carvacrol, ethyl cinnamate and butyl cinnamate proved as effective as DEET at an equivalent dose in the repellent assay, and combinations of carvacrol with either butyl cinnamate or cumin alcohol proved to be significantly more effective than DEET in the assay. When tested as spatial repellents in experimental shelters housing sleeping humans in northern Nigeria a binary mixture of carvacrol plus cumin alcohol caused mosquitoes to leave shelters in significantly higher numbers to those induced by DEET in female Anopheles spp. and in numbers equivalent to that of DEET in Culex spp. mosquitoes. These findings indicate an approach for the identification of biologically active molecules of natural origin serving as repellents for mosquitoes.

Repellency of essential oils against Nephotettix cincticeps: Laboratory and glasshouse assays

AbstractFour oils from Piper nigrum, Litsea cubeba, Zanthoxylum bungeanum and Curcuma longa were obtained by ethanol extraction. The repellency of these oils and two major compounds (linalool and piperine) was evaluated against female adult and third‐instar nymphs of the rice pest, Nephotettix cincticeps, under laboratory and glasshouse conditions. Paired‐choice and no‐choice assays were used for each treatment, with essential oils evaluated after 24 and 48 hr of exposure and chemical compounds evaluated after 12 and 24 hr of exposure. The potential effects of essential oils on activities of glutathione S tranferase (GST), carboxyl esterase (CarE) and acetyl cholinesterase (AchE) were also evaluated after 48 hr of exposure to leafhoppers. The constituents of the essential oils were determined using GC‐MS. The results showed that the major components in the oils were piperine (34.75%) for P. nigrum, 9,12‐octadecadienoic acid (Z,Z) (18.74%) for L. cubeba, ethanone, 1‐(2‐hydroxy‐4,6‐dimethoxyphenyl) (18.51%) for Z. bungeanum and turmerone (15.89%) for C. longa. In all cases, the essential oils repelled female adults and third‐instar nymphs of N. cincticeps. The repellency of the tested oils and chemicals compounds in the paired‐choice assay was higher than in the no‐choice assay. In all experimental conditions, P. nigrum and C. longa oils were the most and the least potent, respectively. Linalool was the best repellent among the single‐tested compounds under laboratory conditions. In the glasshouse study, the highest repellency was observed in the mixture of linalool and piperine. GST and CarE activities of leafhoppers were significantly enhanced by exposure to the four essentials oils; AchE activity increased significantly only in the P. nigrum and L. cubeba assays. Our results clearly indicate that the tested oils and chemical compounds are promising agents for developing plant‐based pesticides to control N. cincticeps.

Fumigation and repellency of essential oils against Callosobruchus maculatus (Coleoptera: Chrysomelidae: Bruchinae) in cowpea

Abstract: The objective of this work was to assess the fumigant and repellent effects of essential oils on adults of Callosobruchus maculatus and to identify the chemical composition of two of the tested essential oils. For the fumigation test, the oils of Schinus terebinthifolius, Piper aduncum, Syzygium aromaticum, Piper hispidinervum, Cymbopogon citratus, Cinnamomum zeylanicum, and the eugenol compound were tested at different concentrations on C. maculatus adults. For the repellency test, the oils of S. terebinthifolius, P. aduncum, P. hispidinervum, S. aromaticum, Jatropha curcas, and Ricinus communis were evaluated. In the fumigation test, it was observed that P. aduncum and eugenol showed the highest and lowest LC50s, of 169.50 and 0.28 μL L-1 air, respectively. In the repellency test, the oils of S. aromaticum and P. hispidinervum were repellent to C. maculatus. Gas chromatography coupled to mass spectrometry (GC-MS) analysis of these two oils identified 42 compounds, of which safrole was the main component of P. hispidinervum and eugenol of S. aromaticum. The essential oils of S. aromaticum, C. zeylanicum, and the eugenol compound are the most promising to control C. maculatus, via fumigation.

Behavioural responses of Vespula germanica (Hymenoptera: Vespidae) wasps exposed to essential oils

AbstractSecondary plant metabolites such as those present in essential oils can be toxic to herbivorous insects and also repel attack, given they play a role in selection and acceptance of host plants. However, few studies have dealt with the use of plant‐based repellents to manage invasive wasps. The objective was to assess essential oils with potential as wasp repellents, and to gain further insight as to how they affect the learning capacities of these insects. Five essential oils were tested on Vespula germanica (Fabricius) wasps in field choice and no‐choice tests. When given a choice, foragers avoided the treated baits almost completely. Wind tunnel bioassays demonstrated that wasps recognise the repellent essential oils through olfactory cues, leading to a dose‐dependent decreased response to the food stimulus. The effect of the repellents on the cognitive ability of V. germanica workers was also studied in relation to food search efficiency. Naive workers landed on the treated baits, although it took them longer than to land on control baits. When workers were allowed to forage on a food bait twice before a repellent was added, an effect on relocation behaviour was observed. The returning workers arriving to a feeding site with essential oil were reticent to land on it, suggesting that there is indeed a repellent effect and not just masking of the food source. A push–pull system combining attractive baits with the use of plant‐based repellents is a promising management strategy in urban settings for this insect pest.

Potential of <em>Olax zeylanica</em> leaves in the suppression of <em>Sitophilus oryzae</em> L. infestations

In spite of the growth of paddy production, significant losses occur globally during post harvest storage of rice, due to the rice weevil Sitophilus oryzae attack, which is considered the major insect pest of stored rice. In order to develop green alternative to synthetic insecticides, the repellent and toxic properties of Olax zeylanica leaf powder, solvent extracts and essential oil were tested against S. oryzae under laboratory conditions. Laboratory reared one week old adults were used to determine the efficacy of plant products. Repellent effect was evaluated within an hour of exposure using a contact-repellency chamber by admixing leaf powder with 30g of rice grains at 4 doses (1, 3, 5 and 7 g). Repellency of leaf-solvent extracts (methanol, ethyl acetate, hexane and water) was investigated at 10%, 50% and 100% (v/v) while the repellency of essential oil was assessed at same concentrations using area-preference method and all the observations were recorded after 30 minutes. Observations on contact and fumiga-tion toxicity of the essential oil were made 30 and 60 minutes after exposure to weevils. All tested plant products elicited significantly very high responses in S. oryzae when compared with the controls (0.00%). Leaf powder of O. zeylanica evoked 100% repellency at the highest dose (23.33% w/w) and the repellent rate increased with the in-crease in dose. In repellency assays using leaf extracts, methanol extract was found to be the most effective causing 96% repellency in the weevils, followed by ethyl acetate (95%) and hexane (89%) whereas the aqueous extract was least effective (70%) indicating the lowest level of repellency. Furthermore, three concentrations of the essen-tial oil evoked extremely high repellent action in weevils (94%, 99%, and 100% respectively) within 30 minutes. Both contact and fumigant toxicity effects with the essential oil were dose dependent and 100% adult mortalities were observed at the highest concentration after one hour of exposure. The overall results of the present study indicate that, O. zeylanica leaves could be utilized as a very successful candidate in the development of bio-insecticides in controlling S. oryzae infestations.

Evaluation of Origanum vulgare L. essential oil as a source of toxicant and an inhibitor of physiological parameters in diamondback moth, Plutella xylustella L. (Lepidoptera: Pyralidae)

The effect of essential oil of Origanum vulgare L. a medicinal plant was studied on toxicity, physiology and biochemical characteristics of diamondback moth Plutella xylustella L. in controlled condition. The LC10, LC30 and LC50 values were estimated 0.234, 0.710 and 1.528 percent (v/v) respectively for 3rd instar larvae. Repellency of essential oil under LC10 and LC30 concentrations was 22.8±6.64 and 49.8±6.95 percent respectively. Effect of plant essential oil on feeding efficiency was also evaluated under LC10 and LC30 concentrations. Approximately Digestibility (AD), Efficacy of Conversion of Ingested Food (ECI), Efficacy of Conversion of Digested Food (ECD), Relative Consumption Rate (RCR) and Relative Growth Rate (RGR) of the treated larvae showed a significant difference compared with the control. The effectiveness of plant essential oil on digestive enzymes under LC50 concentration for the survivors after 24 and 48h after treatment was analyzed. Total protein and triglycerides were decreased significantly compared with the control. Activity of alkaline phosphatase and protease in treated larvae decreased compared with the controls. The lipase was increased 24h after treatment compared with the control. Significant differences in detoxifying enzymes such as glutathione S-transferase and esterase were noted compared to controls. It is concluded that the essential oil used in the present experiment shows toxicity in higher doses. It is also concluded that the essential oil used did show considerable changes in repellency, feeding efficiency, reduced larval weight and changes in biochemical properties which may nominate it for further investigation in key insect pests.

Toxicity, behavior impairment, and repellence of essential oils from pepper‐rosmarin and patchouli to termites

AbstractPlant essential oils are potential sources of insecticidal compounds, but have rarely been explored for their effect on termites. In the present study, we assessed the chemical composition of essential oils of Lippia sidoides Cham. (pepper‐rosmarin; Verbenaceae) and Pogostemon cablin (Blanco) Benth. (patchouli; Lamiacaeae) and evaluated their toxicity, behavioral impairment, and repellence to termite species of the genera Amitermes and Microcerotermes (Isoptera: Termitidae: Termitinae). The main components of essential oils of L. sidoides and P. cablin were thymol (44.6%) and patchouli alcohol (36.6%), respectively. The essential oil of P. cablin was most potent against Amitermes cf. amifer Silvestri and had the lowest LD50 (0.63 μg mg−1). There was no difference in toxicity for Microcerotermes indistinctus Mathews between the essential oils of L. sidoides (LD50 = 1.49 μg mg−1) and P. cablin (LD50 = 1.67 μg mg−1). Pogostemon cablin essential oil was the most toxic to M. indistinctus (LC50 = 0.32 μl ml−1) and A. cf. amifer (LC50 = 0.29 μl ml−1). The essential oils analyzed exhibited high toxicity and repellence to the termites, in addition to reducing behavioral interactions among individuals, thus constituting potential termiticides.

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

In tropical countries, netting is an effective sustainable tool for protecting horticultural crops against Lepidoptera, although not against small pests such as Bemisia tabaci, while smaller mesh netting can be used in temperate regions. A solution is to combine a net with a repellent. Previously we identified repellent essential oils: lemongrass (Cymbopogon citratus), cinnamon (Cinnamomum zeylanicum), cumin (Cuminum cyminum) and citronella (Cymbopogon winternarius). The present study was designed to identify the active compounds of these essential oils, characterise their biological activity and examine their potential for coating nets. We investigated the efficiency and toxicity of nets dipped in different solutions. We then studied the repellent effect with an olfactometer and the irritant effect by videotracking. Geraniol and citronellol were the most promising net coatings owing to their repellent effect. The repellency, irritancy or toxicity varied with the product and concentration, and these features were independent, indicating that the repellent and the irritant/toxic mechanisms were not the same. The combined effects of these different compounds account for the bioactivity of the mixture, suggesting interactions between the compounds. This new sustainable strategy for protecting vegetable crops against whiteflies is discussed, in addition to the use of companion plants that could produce such bioactive compounds.