Fumigant activity of essential oils and their components from Eucalyptus codonocarpa and E. dives against Tetranychus urticae (Acari: Tetranychidae) at three temperatures

Essential oils derived from eighteen species of the Myrtaceae family native to Australia, and major constituents of two oils selected from these oils were tested for their fumigant activity against adult females and eggs of Tetranychus urticae Koch (Acari: Tetranychidae) at 5, 15 and 25°C. Essential oils of Eucalyptus codonocarpa and Eucalyptus dives showed the highest fumigant activity against female adults at 10 μl/l at 15 and 25°C. Among major constituents of the two essential oils, piperitone was the most effective against female adults, followed by terpinene‐4‐ol at 10 μl/l at all three temperatures. The two essential oils and these two constituents lowered egg hatchability at 10 μl/l at 25°C. Our results suggest that piperitone should be further investigated as a potential fumigant against T. urticae.     

Antimicrobial activity of certain essential oils against hindgut symbionts of the drywood termite Kalotermes flavicollis Fabr. and prevalent fungi on termite-infested wood

Abstract:  When the kalotermitid Kalotermes flavicollis Fabr. pseudergates exposed to Casuarina wood wafers treated separately with different concentrations (5, 15 and 30  μ l/2 g wood wafer) of the essential oils, their spirochaete and flagellate populations abnormally reduced in numbers and vigour. The lophomonadids Joenia sp. and Mesojoenia sp. were the most adversely affected flagellates followed by the polymastigid Foaina sp. and the trichomonadid Tricercomitus sp. The Taxodium distichum essential oil evidently appeared to have the greatest adverse effect on the flagellates (95–100% decline in numbers within 2–4 days) followed by the Eucalyptus citriodora (89–100%) and the Cupressus sempervirens oils (31–100%). While with the hindgut spirochaetes, the adverse effect seemed to be reversed where the E. citriodora essential oil had the greatest effect (54–100%) followed by C. sempervirens (46–100%) and T. distichum (8–100%) oils. Moreover, the essential oils were assayed for their antifungal activity, at 15, 20, 25, 30, and 50  μ l/1 ml acetone/15 ml Czapek-Dox medium, against isolates of four woodrotting fungi associated with Casuarina timber, Aspergillus sp., Penicillium sp., Fusarium sp. and Mucor sp. by a method based on inhibition of the fungus growth on agar plates. E. citriodora exhibited the most potent fungicidal activity against the tested four fungi, followed by T. distichum oil. While the C. sempervirens essential oil appeared to have the least significant antifungal property.     

Chemical constituents and fumigant toxicity of essential oil from Carum copticum against two stored product beetles

Plant secondary metabolites play an important role in plant-insect interactions and therefore such compounds may have insecticidal or antifeedant activity against insects. Carum copticum C. B. Clarke （Apiaceae） is one of these plants that have medicinal effects on humans. The chemical composition of the essential oil from dry seeds of C. copticum was studied by gas chromatography （GC） and gas chromatography mass spectrometry （GC-MS）. Thymol （41.34%）,α-terpinolene （17.46%） and ρ-cymene （11.76%） were found to be the major constituents of the oil. In fumigant toxicity tests with the essential oil against adults of Sitophilus oryzae （L.） and Tribolium castaneum （Herbst） at 27 ±1℃ and 60% ± 5% RH, it was observed that S. oryzae （LC50 = 0.91 μL/L） were significantly susceptible than T. castaneum （LC50 = 33.14 μL/L）. The mortalities of the insect species reached 100% at concentrations higher than 185.2 μL/L and 12-h exposure time. The findings indicate the strong insecticidal activity of C. copticum oil and its potential role as a fumigant for storedproduct insects.     

Repellency and toxicity of oil from Artemisia annua to certain stored-product beetles

The essential oil of Artemisia annua L. was tested for its toxic repellent and development inhibitory activities against 2 economically important stored product insects: Tribolium castaneum (Herbst) and Callosobruchus maculatus (L.). Adult beetles of T. castaneum were repelled significantly by oil of A. annua at 1% concentration (vol:vol) and above in filter paper arena test. Dose-response relationship of A. annua oil revealed a significant negative correlation between larval survival; pupal survival and adult emergence of T. castaneum (i.e., increase in dose caused decrease in survival and adult emergence). Effective concentration (EC50) to reduce F1 progeny by 50% was calculated to be 2.6 and 4.1 microl/ml solvent against both the insect species, C. maculatus and T. castaneum, respectively. The relationship between bioactivity of oil from A. annua and responses of T. castaneum and C. maculatus is discussed. We found that oil from A. annua was largely responsible for both repellent (behavioral) and toxic (physiological) actions on 2 species of insect tested.     

Biological activity of some plant essential oils against <Emphasis Type="Italic">Varroa destructor</Emphasis> (Acari: Varroidae), an ectoparasitic mite of <Emphasis Type="Italic">Apis mellifera</Emphasis> (Hymenoptera: Apidae)

This experiment was conducted to evaluate acaricidal activity of the essential oils of Thymus kotschyanus, Ferula assa-foetida and Eucalyptus camaldulensis against Varroa destructor under laboratory conditions. Moreover, fumigant toxicity of these oils was tested on Apis mellifera. After preliminary dose-setting experiments, mites and honey bees were exposed to different concentrations of the oil, with 10 h exposure time. Essential oil of T. kotschyanus appeared the most potent fumigant for V. destructor (LC₅₀ = 1.07, 95% confidence limit (CL) = 0.87–1.26 μl/l air), followed by E. camaldulensis (LC₅₀ = 1.74, 95% CL = 0.96–2.50 μl/l air). The lowest acaricidal activity (LC₅₀ = 2.46, 95% CL = 2.10–2.86 μl/l air) was attributed to essential oil of F. assa-foetida. Surprisingly, among the three oils tested, essential oil of T. kotschyanus had the lowest insecticidal activity against A. mellifera (LC₅₀ = 5.08, 95% CL = 4.54–5.06 μl/l air). These findings proved that essential oil of T. kotschyanus has potential of practical value for use as alternative acaricide in the management of varroa in apiaries.     

Contact toxicity, feeding reduction, and repellency of essential oils from three plants from the ginger family (Zingiberaceae) and their major components against Sitophilus zeamais and Tribolium castaneum

The essential oils from rhizomes of Alpinia conchigera Griff, Zingiber zerumbet Smitt, Curcuma zedoaria (Berg.) Roscoe; their major compounds (camphene, camphor, 1,8-cineole, alpha-humulene, isoborneol, alpha-pinene, beta-pinene and terpinen-4-ol); and synthetic essential oils comprised of mixtures of major pure compounds in the same ratios as the extracted essential oils were tested for contact, feeding reduction, and repellency against Sitophilus zeamais Motschulsky and Tribolium castaneum (Herbst) adults. Via topical applications, the three extracted oils had similar toxicity against S. zeamais (LD50 fiducial limits: 18-24 microg oil/mg insect). T. castaneum had similar sensitivity to all three oils (35-58 microg/mg), and it was less sensitive than S. zeamais. The LD50 values of synthetic A. conchigera and synthetic Z. zerumbet oils were similar to those of their corresponding extracted essential oils. The synthetic C. zedoaria oils showed lower contact toxicity than the extracted C. zedoaria oils to both insects. Sitophilus zeamais and T. castaneum were sensitive to terpinen-4-ol and isoborneol in contact toxicity tests. In antifeedant tests, the three extracted oils were able to decrease the consumption of flour disks, especially Z. zerumbet oils, whereas both insect species could feed on the flour disks treated with three synthetic essential oils. Only terpinen-4-ol deterred feeding in both insects. In repellency tests, A. conchigera oils at highest concentration repelled S. zeamais and T. castaneum. None of the synthetic essential oils repelled S. zeamais (315 microl/cm2) and T. castaneum (31 microl/cm2) Only terpinen-4-ol showed repellent activity against both insects.     

Insecticidal activity of polycaprolactone nanocapsules loaded with Rosmarinus officinalis essential oil in Tribolium castaneum (Herbst)

In this study, the opportunity to enhance the insecticidal activity of Rosmarinus officinalis essential oil was studied for effective management of the red flour beetle, Tribolium castaneum , as a stored product pest beetle. Nanoprecipitation method was used to prepare rosemary oil‐loaded nanocapsules. Bioassays were conducted at 27–30°C temperature and 70–75 % relative humidity in the dark. Fumigant toxicity of the non‐formulated oil and nanocapsules of R. officinalis were investigated at 13.20, 15.92, 19.12, 23.04, and 27.76 μL/L air after 24 and 72 h exposure and the contact toxicity of the non‐formulated oil and nanocapsules were investigated at 4.28, 3.55, 2.95, 2.45 and 2.36 μL/cm² after 24 h exposure. The major constituents of the essential oil of rosemary were α‐Pinene, 1,8‐cineol, camphor, and cis‐verbenone. Nanocapsules presented an average size (145 ± 15 nm) (± standard error [SE]) with a polydispersity index below 0.3, a negative zeta potential (?11.0 ± 0.5 mV), and a high encapsulation efficiency (78.20 ± 0.93 %). Scanning electron microscope photomicrograph of rosemary oil‐loaded nanocapsules showed the presence of spherical nanocapsules with regular and homogeneous surfaces. In fumigant and contact toxicity, there were significant differences between non‐formulated and rosemary oil‐loaded nanocapsules in all the concentrations and times. The results suggested that nanoencapsulated essential oils from R. officinalis can be used for effective control in T. castaneum . When this technique is used, it can produce pesticides that have controlled‐release properties and reduce the concentration of the applied doses and number of applications.     

Bioactivities of the leaf essential oil of Curcuma longa (var. ch-66) on three species of stored-product beetles (Coleoptera)

Essential oil extracted from the leaves of turmeric, Curcuma longa L., was investigated for contact and fumigant toxicity and its effect on progeny production in three stored-product beetles, Rhyzopertha dominica F. (lesser grain borer), Sitophilus oryzae L. (rice weevil), and Tribolium castaneum Herbst (red flour beetle). Oviposition-deterrent and ovicidal actions of C. longa leaf oil were also evaluated against T. castaneum. The oil was insecticidal in both contact and fumigant toxicity assays. The adults of R. dominica were highly susceptible to contact action of C. longa leaf oil, with LD50 value of 36.71 microg/mg weight of insect, whereas in the fumigant assay, adults of S. oryzae were highly susceptible with LC50 value of 11.36 mg/liter air. Further, in T. castaneum, the C. longa oil reduced oviposition and egg hatching by 72 and 80%, respectively at the concentration of 5.2 mg/cm2. At the concentration of 40.5 mg/g food, the oil totally suppressed progeny production of all the three test insects. Nutritional indices indicate >81% antifeedant action of the oil against R. dominica, S. oryzae and T castaneum at the highest concentration tested.     

Antimicrobial activity of essential oils and structurally related synthetic food additives towards Clostridium perfringens

Aims:  To assess the potential of essential oils and structurally related synthetic food additives in inhibiting the growth of Clostridium perfringens for the control of necrotic enteritis in chickens.
Methods and Results:  The antimicrobial activity of essential oils/compounds was measured by determining the inhibition of bacterial growth. Thirty-three of 66 oils/compounds exhibited ≥80% inhibition. Seven with the highest potency were further studied. The oils/compounds had MIC₉₅ values between 167 and 425  μ g ml⁻¹. Most of them were tolerant to low pH (2·0) and exhibited minor or no inhibition of Lactobacillus isolates from the chicken intestine. When mixed with chicken ileal digesta, the oils/compounds retained their efficacy against C . perfringens , but had little effect on the total number of lactobacilli and anaerobic bacteria in the digesta.
Conclusions:  Some essential oils/compounds demonstrated good potential in controlling C . perfringens .
Significance and Impact of the Study:  This study has identified candidates of essential oils/compounds for in vivo studies for the control of necrotic enteritis in chickens.     

Chemical composition and fumigant toxicity of the essential oils from 16 species of Eucalyptus against Haematobia irritans (Diptera: Muscidae) adults

Oils extracted from various species of Eucalyptus (Eucalyptus badjensis Beuzev & Welch, Eucalyptus badjensis x Eucalyptus nitens, Eucalyptus benthamii variety dorrigoensis Maiden & Cambage, Eucalyptus botryoides Smith, Eucalyptus dalrympleana Maiden, Eucalyptus fastigata Deane & Maiden, Eucalyptus nobilis L.A.S. Johnson & K. D. Hill, Eucalyptus polybractea R. Baker, Eucalyptus radiata ssp. radiata Sieber ex Spreng, Eucalyptus resinifera Smith, Eucalyptus robertsonii Blakely, Eucalyptus rubida Deane & Maiden, Eucalyptus smithii R. Baker, Eucalyptus elata Dehnh, Eucalyptus fraxinoides Deane & Maiden, E. obliqua L'Hér) were obtained by hydrodistillation. The chemical composition of essential oils was determined by gas chromatography coupled to mass spectrometry. Essential oils were mainly composed of 1,8-cineole, alpha-pinene, alpha-terpineol, 4-terpineol, and p-cymene. Vapors from these essential oils and their major components were found to be toxic to Haematobia irritans (L.) (Diptera: Muscidae) adults. An aliquot of each oil was placed in a cylindrical test chamber, and the number of knocked down flies was recorded as a function of time. Knockdown time 50% was then calculated. Results showed that essential oil of E. polybractea had the highest knockdown activity of 3.44 min. A correlation was observed between the content of 1,8-cineole in the Eucalyptus essential oils and the corresponding toxic effect.     

Sensitivity of two greenhouse pests to vapours of essential oils

Vapours of essential oils extracted from cumin, Cuminum cyminum L., anise, Pimpinella anisum L., oregano, Origanum syriacum var bevanii (Holmes) Ietswaart and eucalyptus, Eucalyptus camaldulensis Dehn., were found to be toxic to two greenhouse pests, viz. the carmine spider mite, Tetranychus cinnabarinus (Boisd.) (Tetranychidae, Tetranychini) and cotton aphid, Aphis gossypii Glov. (Aphididae, Aphidini). In general, a minimum dose of 0.5 µl/l air and 2–3 days of exposure was required for 99% mortality using essential oils of the first three plants.     

Insecticidal activity of essential oils from eleven Eucalyptus spp. and two hybrids: lethal and sublethal effects of their major components on Blattella germanica

The aim of the current study was to evaluate the fumigant activity of the essential oils from 11 species of the genus Eucalyptus and two of their hybrids on first instar of Blattella germanica L. The fumigant activity and repellence of the four major monoterpene components of these essential oils also were tested. Fumigant activity was evaluated by exposing nymphs to the vapors emitted by 50 microl of essential oil or monoterpene in a closed container. The lowest knockdown time 50% (KT50) values, expressed in minutes, were elicited by the essential oils of the Eucalyptus grandis X Eucalyptus tereticornis (57.9) hybrid, Eucalyptus sideroxylon A. Cunn (62.0), E. grandis X Eucalyptus camaldulensis (63.8) hybrid, Eucalyptus viminalis Labill (64.1), Eucalyptus dunnii Maiden (64.5), and Eucalyptus grandis (Hill) ex Maiden (68.7). The KT50 values for the remaining essential oils ranged between 74.5 (E. saligna Smith) and 161.4 min (E. tereticornis Smith). The essential oil from the hybrid E. grandis X E. tereticornis was 3.7 times less toxic than dichlorvos (positive control). The KT50 values of monoterpenes were 38.8 for alpha-pinene, 55.3 for 1,8-cineole, 175.6 for p-cymene, and 178.3 for gamma-terpinene. Alpha-pinene was 2.5 times less toxic than dichlorvos. There was a strong positive correlation between the fumigant activity of essential oils and their corresponding 1,8-cineole and alpha-pinene concentration. Repellency was quantified using a video tracking system. Two concentrations of monoterpenes were studied (7 and 70 microg/cm2). All compounds produced a light repellent effect but only when applied at 70 microg/cm2. In all cases, the repellent effect was less than that produced by the broad-spectrum insect repellent N,N-diethyl-3-methylbenzamide (positive control).     

Vibrational spectroscopic studies to acquire a quality control method of Eucalyptus essential oils

This article presents a novel and original approach to analyze in situ the main components of Eucalyptus oil by means of Raman spectroscopy. The obtained two-dimensional Raman maps demonstrate a unique possibility to study the essential oil distribution in the intact plant tissue. Additionally, Fourier Transform (FT)-Raman and attenuated total reflection (ATR)-IR spectra of essential oils isolated from several Eucalyptus species by hydrodistillation are presented. Density Functional Theory (DFT) calculations were performed in order to interpret the spectra of the essential oils of the Eucalyptus species. It is shown that the main components of the essential oils can be recognized by both vibrational spectroscopic techniques using the spectral information of the pure terpenoids. Spectroscopic analysis is based on the key bands of the individual volatile substances and therefore allows one to discriminate different essential oil profiles of several Eucalyptus species. It has been found that the presented spectroscopic data correlate very well with those obtained by gas chromatography (GC) analysis. All these investigations are helpful tools to generate a fast and easy method to control the quality of the essential oils with vibrational spectroscopic techniques in combination with DFT calculations.     

Effects of Essential Oils from Eucalyptus globulus Leaves on Soil Organisms Involved in Leaf Degradation

The replacement of native Portuguese forests by Eucalyptus globulus is often associated with deleterious effects on terrestrial and aquatic communities. Several studies have suggested that such a phenomenon is linked with the leaf essential oils released into the environment during the Eucalyptus leaf degradation process. However, to date, the way these compounds affect leaf degradation in terrestrial systems i.e. by direct toxic effects to soil invertebrates or indirectly by affecting food of soil fauna, is still unknown. In order to explore this question, the effect of essential oils extracted from E. globulus leaves on terrestrial systems was investigated. Fungal growth tests with species known as leaf colonizers (Mucor hiemalis, Alternaria alternata, Penicillium sp., Penicillium glabrum and Fusarium roseum) were performed to evaluate the antifungal effect of essential oils. In addition, a reproduction test with the collembolans Folsomia candida was done using a gradient of eucalyptus essential oils in artificial soil. The influence of essential oils on feeding behaviour of F. candida and the isopods Porcellio dilatatus was also investigated through food avoidance and consumption tests. Eucalyptus essential oils were lethal at concentrations between 2.5–20 µL/mL and inhibited growth of all fungal species between 1.25–5 µL/mL. The collembolan reproduction EC₅₀ value was 35.0 (28.6–41.2) mg/kg and both collembola and isopods preferred leaves without oils. Results suggested that the effect of essential oils in leaf processing is related to direct toxic effects on fungi and soil fauna and to indirect effects on the quality and availability of food to soil invertebrates.     

Interspecific hybridization of Eucalyptus as a potential tool to improve the bioactivity of essential oils against permethrin-resistant head lice from Argentina

The essential oils extracted from Eucalyptus grandis, Eucalyptus camaldulensis, Eucalyptus tereticornis, and the hybrids E. grandisxE. camaldulensis, and E. grandisxE. tereticornis were analyzed by GC-MS, and evaluated for their fumigant and repellent effects on permethrin-resistant head lice. Fumigant activity of both hybrids was higher than that for pure species. E. grandisxE. tereticornis and E. grandisxE. camaldulensis showed KT50 values of 12.99 and 13.63min, respectively. E. grandis, E. camaldulensis, and E. tereticornis showed KT50 values of 25.57, 35.01, and 31.31, respectively. A simple regression analysis revealed a significant correlation between KT50 data and % of 1,8-cineole in these essential oils. Repellency varied from 47.80+/-16% to 80.69+/-6% for the five Eucalyptus essential oils tested. Interspecific hybridization improves the pediculicidal activity of Eucalyptus essential oils.     

Anti-fungal activity of essential oils of Ceylon Eucalyptus species for the control of Fusarium solani and Sclerotium rolfsii

The essential oils were extracted from the leaves of Eucalyptus microcorys, Eucalyptus grandis and Eucalyptus robusta which were grown in Sri Lanka and their major chemical compounds were determined. 1,8-Cineole and α-pinene were identified as major aroma compounds in these oils. In this study, the anti-fungal activity of essential oils of E. microcorys, E. grandis and E. robusta, ethanol extract of E. microcorys and 1,8-cineole were evaluated against Sclerotium rolfsii, a fungi responsible for leaf spot disease of indoor plants and Fusarium solani, a fungi responsible for dry rot diseases of potato by poisoned food technique, and minimum inhibitory concentrations (MICs) were determined. The essential oils from three Eucalyptus species showed significant inhibitory effect against S. rolfsii and F. solani than the ethanol extract of E. microcorys. Of treatments, the essential oil of E. grandis showed the best anti-fungal activity with the MIC values of less than 0.1% for S. rolfsii and 0.5% for F. solani. The MICs of the oils of E. microcorys and E. robusta were between 0.3–0.5% against S. rolfsii and 0.5–0.75% for F. solani. The 1,8-cineole did not exhibit inhibition activity as much of Eucalyptus essential oils and hence, it can be assumed that minor chemical components of the oils contribute to the growth inhibition of the tested fungi. This is the first report of anti-fungal activity of Sri Lankan oils of E. microcorys, E. grandis and E. robusta and ethanol extract of E. microcorys against S. rolfsii and F. solani. These findings would be useful for the designing of natural fungicide for agriculture- and food-based industries.     

Insecticidal activity of Artemisia sieberi,Eucalyptus camaldulensis,Thymus persicus and Eruca sativa oils against German cockroach,Blattella germanica (L.)

The German cockroach, Blattella germanica (L.) (Blattodea: Blattellidae), has been recognized as a serious health problem because of its potential to harbor and transmit human disease-causing pathogens. The development of new and environmentally friendly control agents is essential as alternative tool to conventional chemical insecticides. The aim of the current study was to determine the fumigant and contact toxicity of essential oils (EOs), Artemisia sieberi Besser, Eucalyptus camaldulensis Dehn. and Thymus persicus (Ronniger ex Rech. f.) and cold press oil of Eruca sativa (Miller) (ESO) against first instar nymphs and adults. According to results, the LC₅₀ values of EOs were between 15.01 and 28.80 μl/l air for fumigant toxicity, 2202.8 and 5600.2 mg/l for dipping toxicity and 9484.2 and 34,421.1 mg/l for applied surface toxicity. Fumigant activity of the oils were significantly more toxic than other methods. In general, the toxicity of A. sieberi was higher than other EOs. Also, the first instar nymphs were more susceptible than adults. Additionally, the results showed that the EOs were significantly more toxic than ESO in both fumigant and dipping methods. In addition to contact effects, the fumigant activity of ESO was proved, although the toxicity was lower than the EOs. Hence, it is important to consider the production cost benefit of ESO in comparison with the EOs. So, the ESO could be considered as a good candidate in control of the cockroach but in enclosed spaces such as inaccessible cockroach hiding places, the EO of A. sieberi can be useful.     

Biological activity of two juvenoids and two ecdysteroids against three stored product insects

The insecticidal activity of juvenile hormone agonists methoprene and pyriproxyfen, and the ecdysone agonists RH-5849 and tebufenozide was evaluated against susceptible and actellic-resistant strains of Tribolium castaneum and susceptible strains of Rhyzopertha dominica and Sitophilus oryzae. Concentrations ranging from 0.1 to 20 ppm of the analogues were mixed in the food medium to which the tested insects were exposed. The results showed that all these compounds could affect the development of the tested species to differing extents but had no effect on the mortality of parental adults. The two JH analogues did not prolong the life span of R. dominica and S. oryzae, but very greatly extended that of T. castaneum. The extension led to the production of giant larvae and failure to pupate. Actellic-resistant strain of T. castaneum showed some cross-resistance to methoprene and pyriproxyfen, but not to RH-5849 and tebufenozide. Pyriproxyfen was the most effective compound among the four IGRs; a concentration of 0.1 ppm could completely inhibit the F(1) adult occurrence of both S- and R-strains of T. castaneum and its LC(90)s for controlling R. dominica and S. oryzae were 0.1 and 1.2 ppm, respectively. Methoprene was highly effective against R. dominica, but less active on S. oryzae. RH-5849 could achieve almost complete control of F(1) adults of T. castaneum and R. dominica at 10 ppm, but was less potent on S. oryzae. Tebufenozide appeared to be much less active on these three species compared with the other three compounds. The percentage reductions of F(1) adults for S- and R-strains of T. castaneum at a concentration of 20 ppm were 80 and 99%, respectively.     

Insecticidal and synergistic effects of Majorana hortensis essential oil and some of its major constituents

The essential oil from leaves of Majorana hortensis Moench (Lamiaceae) was isolated by hydrodistillation with a yield of 1.6% (wt/wt). The insecticidal activity of the oil was evaluated against fourth instars of Spodoptera littoralis Boisduval (Lepidoptera: Noctuidae) and adults of Aphis fabae L. (Hemiptera: Aphididae). The oil showed a remarkable toxic effect against S. littoralis in a topical application assay (LD₅₀ = 2.48 μg per larva) and in a residual film assay (LC₅₀ = 3.14 g/l). The oil of M. hortensis also exhibited a pronounced toxic effect against A. fabae adults with LC₅₀ values of 1.86 and 2.27 g/l in rapid dipping and residual film assays, respectively. Gas chromatography-mass spectrometry analyses of M. hortensis essential oils revealed the presence of 31 compounds and the main components were terpinen-4-ol (30.0%), γ-terpinene (11.3%), and trans -sabinene hydrate (10.8%). Repeated column chromatography of M. hortensis oil on silica gel led to the isolation of two major constituents, which were characterized based on ¹H-nuclear magnetic resonance and mass spectrometric data, as terpinen-4-ol and γ-terpinene. These two components were examined for their insecticidal and synergistic activities towards S. littoralis and A. fabae . Terpinen-4-ol and γ-terpinene exhibited a significant insecticidal activity against both insects, but γ-terpinene was more toxic than terpinen-4-ol. When tested in a binary mixture with the synthetic insecticides profenofos and methomyl, it was found that both compounds enhanced the insecticidal activity of these insecticides by two- to threefold. These results show that terpinen-4-ol and γ-terpinene have a synergistic effect on the insecticidal activities of synthetic insecticides profenofos and methomyl.     

Bioactivities of l-carvone, d-carvone, and dihydrocarvone toward three stored product beetles

The rice weevil, Sitophilus oryzae L., adults were highly susceptible by contact to l-carvone, d-carvone, and dihydrocarvone when compared with the lesser grain borer, Rhyzopertha dominica F., adults and red flour beetle, Tribolium castaneum (Herbst.). Adults of R. dominica were more susceptible than the other species to fumigant vapors of l-carvone, d-carvone, and dihydrocarvone. The three larval stages (14-, 16-, and 18-d-old) of T. castaneum progressively became more susceptible with age toward contact toxicity of three test compounds but in fumigant toxicity, 16-d-old larvae of T. castaneum were more susceptible to the three compounds. Comparison of contact and fumigant toxicity of the test compounds indicates that l-carvone and d-carvone possess 24 times more fumigant toxicity toward adults of R. dominica than its contact toxicity. Overall order of toxicity was l-carvone > d-carvone > dihydrocarvone. Egg hatching and subsequent larval and adult survival of T. castaneum were significantly reduced when the eggs of T. castaneum were treated with l-carvone, d-carvone, and dihydrocarvone. l-Carvone completely suppressed egg hatching at the concentration of 7.72 mg/cm2. Data on feeding-deterrent indices indicate the high potency of l-carvone as feeding-deterrent in order of S. oryzae adults > T. castaneum adults > R. dominica adults > T. castaneum larvae.