Control of stored grain pest,Callosobruchus maculatus (F.) (Coleoptera: Bruchidae), using the essential oils isolated from Zingiber officinale (L.) and Mentha pulegium (L.) in laboratory condition

Fumigant activity of essential oil vapours distilled from Zingiber officinale (L.) and Mentha pulegium (L.) was tested against eggs, larvae and adults of Callosobruchus maculatus (F.). Fumigant toxicity was assessed at 27?±?1?°C and 60?±?5% RH, in dark condition. The influence of different concentrations of the essential oil vapours on egg hatchability, larval and adult mortality was significant. Data probit analysis showed that lethal concentration of the essential oil to kill 50% of the population (LC₅₀) for egg, larvae and adult was found to be 1.151, 2.336 and 2.183?μl/l air of Z. officinale, followed by 0.072, 0.113 and 0.093?μl/l air essential oil of M. pulegium, respectively. Between these essential oils, Z. officinale is almost more toxic than M. pulegium on all growth stages of C. maculatus. The present study suggests that essential oils from these medicinal plants may be potential grain protectants as botanical alternative fumigants and could be used in the management of various life stages of C. maculatus.     

Contact toxicity of Azadirachta indica (Adr. Juss.), Eucalyptus camaldulensis (Dehn.) and Laurus nobilis (L.) essential oils on mortality cotton aphids,Aphis gossypii Glover (Hem.: Aphididae)

Essential oils from three species of plants comprising three plant families were obtained by Clevenger-type water distillation. The major compounds in these essential oils were identified with GC-MS and their insecticidal activity against adult cotton aphid, Aphis gossypii Glover tested with dosage-mortality bioassays. We examined mortality only for viviparous adults because sizeable aphid populations on cucumber (Cucurbitaceae) hosts are largely produced by these wingless, parthenogenic females. Three of the oils were directly applied to aphid females in randomised blocks at 25?±?2?°C and 60?±?5% R.H. and under a L16:D8 photoperiod. Essential oils were mixed with a non-toxic emulsifying agent, Tween 80. Results show adverse contact effects of essential oils studied in the control of cotton aphid. Probit analysis and LC₅₀ at concentrations at different exposures showed aphids were incapacitated and killed by aliphatic aldehydes, phenols and monocyclic terpenes contained in Azadirachta indica, Eucalyptus camaldulensis and Laurus nobilis. LC₅₀ on cotton aphid, for azadirachtin eucalyptus and laurel essential oils were respectively 5389, 9515 and 13730?ppm. In the current study, efficacy in respect to the contact toxicity (LC₅₀) followed the order: A. indica?>?E. camaldulensis?>?L. nobilis after 24?h treatment. Our results show quantitative and qualitative differences in the chemical composition and insecticidal activities of our essential oils. All oils became insect toxic as concentration increased. According to the results, essential oils of all the three plants have the potential to be employed in the pest management programmes that can be used in protection of greenhouse conditions against cotton aphid.     

Chemical composition,aphicidal and antiacetylcholinesterase activities of essential oils against Aphis nerii Boyer de Fonscolombe (Hemiptera: Aphididae)

Aphids are important sucking insects that attack many crops and cause huge economic loss. Essential oils have been proposed to be appropriate alternative to synthetic insecticides due to their low impact on environment and human health. In this work, the chemical compositions of eight essential oils extracted from plants growing in Egypt were determined by gas chromatography/mass spectrometry (GC–MS). The aphicidal activities of the isolated oils were examined against the adults of oleander aphid, Aphis nerii by a leaf-dipping assay. The inhibitory effect of essential oils on acetylcholinesterase (AChE) activity was also tested in vitro. Chemical analyses showed the essential oils consisted mainly of monoterpene hydrocarbons, oxygenated monoterpenes, sesquiterpene hydrocarbons and oxygenated sesquiterpenes except the oil of Artemisia monosperma which contained high content of benzenes. The results of toxicity assay showed that the oils of A. monosperma and Citrus sinensis were the most potent toxicants displaying LC₅₀ value of 0.06 mg/L. The oils of Callistemon viminals, Schinus terebinthifolius and Schinus molle were also highly effective against aphid as their LC₅₀ values were lower than 1 mg/L. In addition, the highest inhibitory effect on AChE was recorded by 0.5 mg/L C. sinensis with inhibition of 49.33%, while 0.1 mg/L Citrus lemon oil recorded the lowest inhibitory effect with inhibition of 0.4%. In general, six of tested essential oils showed high toxicity against A. nerii and they might be applied in the IPM programs for this insect.     

Fumigant toxicity of Laurus nobilis and Myrtus communis essential oils on larvae and adults of the Red flour beetle,Tribolium castaneum Herbst (Col.: Tenebrionidae)

Considering the invasion to food commodities by insects and harmful effect of chemical pesticides, essential oils are among the best known substances tested against stored product pests. These compounds may act as fumigants, contact insecticides, repellents or anti-feedants. In present study, fumigant toxicity of essential oils from Laurus nobilis L. and Myrtus communis L. was assessed on larvae and adults of Tribolium castaneum Herbst at 27?±?2?°C, 60?±?5% RH in darkness. Each essential oil was tested in five concentrations with three replicates. The LC₅₀ values of L. nobilis and M. communis against adults of beetle were calculated 243.78 and 56.11?μl/l and LC₉₅ values for them were 685.85 and 144.01?μl/l, respectively. For the larvae of T. castaneum, the LC₅₀ values for L. nobilis and M. communis were 211.64 and 69.63 and LC₉₅ values were 656.84 and 183.65?μl/l, respectively. Results showed that these essential oils may have potential as botanical control agents against larvae and adults of T. castaneum.     

Toxicity of plant essential oils to different life stages of the poultry red mite,Dermanyssus gallinae,and non‐target invertebrates

Seven essential oils with potential as acaricides for use against the poultry red mite, Dermanyssus gallinae (De Geer) (Acari: Dermanyssidae), were selected for study. These products (essential oils of manuka, cade, pennyroyal, thyme, garlic, clove bud and cinnamon bark) were deployed against different life stages of D. gallinae in laboratory tests at the (lethal concentration) LC₅₀ level for adult mites. For all essential oils tested, toxicity to D. gallinae juveniles was as high as toxicity to adults, if not higher. However, at the LC₅₀ level determined for adults, some oils were ineffective in preventing hatching of D. gallinae eggs. The essential oils were also tested under laboratory conditions at their LC₉₀ levels for D. gallinae adults on two model non‐target species, the brine shrimp, Artemia salina (L.), and the mealworm beetle, Tenebrio molitor (L.). Results showed that not all essential oils were as toxic to A. salina and T. molitor as they were to D. gallinae, suggesting that it may be possible to select certain oils for development as acaricides against D. gallinae that would have minimal impact on non‐target organisms. However, the level of toxicity to A. salina and T. molitor was not consistent across the selected essential oils.     

Estimation of mortality by entomophages on exotic Harmonia axyridis versus native Adalia bipunctata in semi-field conditions in northern Italy

A semi-field experiment was carried out in two peach orchards in northern Italy to assess mortality due to predators and parasitoids on the exotic coccinellid Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) in comparison with the native coccinellid Adalia bipunctata L. (Coleoptera: Coccinellidae). The experiments were conducted in cages to avoid the possible escape of the exotic ladybird (not yet established in Italy). Two kinds of cage experiments were included: ‘exclusion cages’ (access by walking predators impeded) and ‘free cages’ (walking predators free to enter). The cages, containing all the stages of the two ladybird species, were placed in two localities and left for 24 h. All ladybird stages used for the semi-field experiments came from a laboratory rearing. The eggs of H. axyridis experienced less mortality than those of A. bipunctata. The ant workers were the most frequent predators in ‘free cages’ but A. bipunctata cannibalism on eggs was also detected. Larvae of both coccinellid species were predated equally but larval predation of L1 and L2 was higher in comparison to predation of L3 and L4. Pupae and adults of both exotic and native ladybirds were never attacked by predators. Predation on younger larval stages was higher in the ‘free cages’ in comparison with ‘exclusion cages’. No ladybird parasitisation was observed. The ‘free cage’ technique seems to provide a standardised and realistic estimation of predation impact but more studies are needed to evaluate ladybird parasitisation in semi-field conditions.     

In Vitro and Molecular Docking Evaluation of Larvicidal Effects of Essential Oils of Five Aromatic Plants on the Fall Armyworm Spodoptera frugiperda JE. Smith (Lepidoptera: Noctuidae) from Ivory Coast

Faced with the serious consequences resulting from the abusive and repeated use of synthetic chemicals, today rethinking crop protection is more than necessary. It is in this context that the essential oils of the Lamiaceae Ocimum gratissimum and Ocimum canum, the Poaceae Cymbopogon citratus and nardus and a Rutaceae Citrus sp. of known chemical compositions were experimented. The evaluation of the larvicidal potential of the essential oils was done by the method of topical application of the test solutions, on the L1−L2 stage larvae from the first generation of S. frugiperda obtained after rearing in an air-conditioned room. Lethal concentrations (LC₁₀, LC₅₀ and LC₉₀) were determined after 48 h. After assessing the larvicidal potential of essential oils, molecular docking was carried out to study protein-ligand interactions and their propensity to bind to insect enzyme sites (AChE). The essential oil of O. gratissimum was the most effective with the lowest lethal concentrations (LC₁₀=0.91 %, LC₅₀=1.91 % and LC₉₀=3.92 %). The least toxic oil to larvae was Citrus sp. (LC₁₀=5.44 %, LC₅₀=20.50 % and LC₉₀=77.41 %). Molecular docking revealed that p-cymene and thymol from O. gratissimum essential oil are structurally similar and bind to the AChE active site via predominantly hydrophobic interactions and a H-bond with Tyr374 in the case of thymol. The essential oil of O. gratissimum constitutes a potential candidate for the development of biological insecticides for the fight against insect pests and for the protection of the environment.     

Predation and avoidance behaviour in aphid‐ladybird interactions of native and invasive ladybirds in Europe

1. While detrimental effects of invasive predators on native species are well documented, we often lack a mechanistic understanding of the invasion success. Lack of prey avoidance behaviour can lead to higher consumption rates by invasive predators compared to native predators. This competitive advantage is expected to contribute to the invasion success of non‐native predators.
2. We compared aphid consumption and cue avoidance behaviour of aphids between four native ladybird species (Coccinella septempunctata, Adalia bipunctata, Propylea quatuordecimpunctata, and Hippodamia variegata) and the invasive Asian ladybird Harmonia axyridis.
3. The invasive H. axyridis and the native C. septempunctata consumed more aphids than the three smaller native ladybird species. In line with our expectations, aphids avoided leaves bearing cues of most native ladybird species but not of the invasive H. axyridis.
4. Our results indicate that body size rather than ladybird origin determined aphid predation rates. The lack of aphid avoidance behaviour towards cues of H. axyridis indicates that they were not able to recognise the chemical cues of the invasive predator.
5. Relatively large body size and the absence of cue avoidance in aphids might benefit the invasive H. axyridis, particularly in comparison to smaller native ladybird species. The absence of avoidance behaviour in aphids might lead to even higher predation rates of H. axyridis under more natural conditions.

     

Fumigant toxicity of essential oil of Mugwort (Artemisia vulgaris L.) against three major stored product beetles

Application of plants essential oil for the evaluation of their fumigant toxicity and insecticidal properties is the goal of many researches. In this study, aerial parts of Artemisia vulgaris L. were subjected to hydrodistillation using a Clevenger-type apparatus, and the chemical composition of the volatile oils was studied by gas chromatography–mass spectrometry. Alpha-Pinene (23.56) was the main component of the essential oil. Insecticidal activity of the oil was evaluated against Tribolium castaneum (Herbst), Callosobruchus maculatus (F.) and Rhizopertha dominica (F.) after 24, 48 and 72 h. After 24-h exposure time, C. maculatus was more susceptible (LC₅₀ = 52.47 μl/l air) and T. castaneum was more tolerant (LC₅₀ = 279.86 μl/l air) than other species. LT₅₀ values were indicated using highest concentration of LC₅₀ tests for three species. In general, mortality increased as the doses of essential oil and exposure time increased. These results proposed that A. vulgaris oil might have potential as a control agent against T. castaneum, R. dominica and especially C. maculates in storages.     

Larvicidal effects of some essential oils against Aedes aegypti (L.), the vector of dengue fever in Saudi Arabia

Essential oils are very popular among organic growers because they are ecologically safe, do not have mammalian toxicity, and cannot be resistant to a variety of contaminants. Four essential oils, Lemon, Lavender, Peppermint, and Neem, were tested for larvicide efficacy against the dengue fever vector Aedes aegypti larvae under laboratory conditions using dipping bioassay techniques. Among the essential oils tested, lemon, peppermint, and lavender oils showed high larvicidal activity against larvae of Ae. aegypti. Lemon oil showed the highest effects (LC₅₀ 10.676 ppm), while Peppermint, Lavender and Neem oil showed the lowest effects (LC₅₀ 21.380, 29.818 and 38.058 ppm, respectively). As a result, the mixture of lemon oil (LC₅₀) with Peppermint oil (LC₂₅) showed the highest co-toxicity factor, whereas the mixture of Lemon oil (LC₅₀) with Diesel oil (LC₂₅) showed the lowest co-toxicity factor. Based on the results of this study, it appears that essential oils may be useful as larvicides against Ae. aegypti larvae. In search of new natural larvicides, these compounds may provide an alternative to Synthetic insecticides as these are environmentally safe insecticides.     

Acute toxicity of kaolin and essential oils from Mentha pulegium and Zingiber officinale against different stages of Callosobruchus maculatus under laboratory conditions

Naturally derived compounds such as essential oils and natural mineral are relatively cheap, non-toxic to food grains and environmentally friendly and would be suitable alternatives for currently used chemical insecticides if they have high insecticidal effectiveness. In the present study, acute toxicity of kaolin and essential oils from Mentha pulegium and Zingiber officinale were assessed on different stages of Callosobruchus maculatus at 28?±?2?°C, 65?±?5% R. H and dark condition. The calculated LC₅₀ values on the egg, larvae and adult stages of C. maculatus were 1.15, 2.33 and 2.18?μl/ml air for Z. officinale and 0.07, 0.11 and 0.09?μl/ml air for M. pulegium, respectively. The result showed that M. pulegium was more effective essential oil against different stages of C. maculatus compared with the Z. officinale, and also the egg and adult stages of C. maculatus were more susceptible against essential oils compared with larval stage. The LC₅₀ values of kaolin were 0.71 and 0.18?mg/cm² on egg and adult of C. maculatus, respectively. The combination of tested essential oils with kaolin increased mortality of C. maculatus adults compared with their application alone. It was found that tested essential oils and kaolin had high potential in controlling different stages of C. maculatus.     

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

Plant 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.     

Toxic effects of some insecticides,herbicides, and plant essential oils against Tribolium confusum Jacquelin du val (Insecta: Coleoptera: Tenebrionidae)

Cereals are staple food for many countries and are grown on millions of hectares of land, but much of the harvest is wasted due to losses by pests. To minimize these losses, many pesticides are used which are damaging to the environment and human health. There are debates to get rid of these chemicals but they are still in use at large scale. An alternative control strategy for insect pests in storage houses is the use of botanicals. In this study, four plant essential oils, two plant extracts, two herbicides, and two insecticides were used against Tribolium confusum and the comparison of toxicity was made by calculating LC₅₀ and LT₅₀ values. LC₅₀ values were higher for abamectin (2.09–10.23 mg/L) and cypermethrin (3.41–11.78 mg/L) insecticides followed by neem essential oil (7.39–19.24 mg/L) and citrus extract (10.14–24.50 mg/L). However, LC₅₀ values were maximum in case of jaman plant extract (22.38–176.42 mg/L) followed by two herbicides, Logran (19.66–39.72 mg/L) and Topik (29.09–47.67 mg/L) However, LC₅₀ values were higher for topic herbicide (24.098 ppm) and jaman essential oil (16.383 ppm) after four days of treatment. Abamectin and cypermethrin insecticides, neem essential oil and citrus plant extract also killed adults of T. confusum quicker as compared other essential oils, extracts and herbicides. Results revealed that botanical formulations being environmentally safe could be used instead of highly hazardous pesticides for stored products’ pests. This study also elaborates the non-host toxicity of herbicides commonly applied in our agroecosystem.     

Insecticidal and feeding deterrent activities of essential oils in the cabbage looper,Trichoplusia ni (Lepidoptera: Noctuidae)

Ten essential oils were tested against the cabbage looper, Trichoplusia ni larvae for contact, residual and fumigant toxicities and feeding deterrent effects. Against third instar T. ni, Syzygium aromaticum (LD₅₀ = 47.8 μg/larva), Thymus vulgaris (LD₅₀ = 52.0 μg/larva) (the two positive controls) and Cinnamomum glanduliferum (LD₅₀ = 76.0 μg/larva) were the most toxic via topical application. Litsea pungens (LD₅₀ = 87.1 μg/larva), Ilex purpurea (LD₅₀ = 94.0 μg/larva), Cinnamomum cassia (LD₅₀ = 101.5 μg/larva) and Litsea cubeba (LD₅₀ = 112.4 μg/larva) oils were equitoxic. Thymus vulgaris (LC₅₀ = 4.8 mg/ml) and S. aromaticum (LC₅₀ = 6.0 mg/ml) oils were the most toxic in residual bioassays. Cymbopogon citratus (LC₅₀ = 7.7 mg/ml) and C. cassia (LC₅₀ = 8.5 mg/ml) oils were equitoxic followed by Cymbopogon nardus (LC₅₀ = 10.1 mg/ml) in this bioassay. The remaining five oils showed little or no residual effects. In a fumigation bioassay, L. cubeba (LC₅₀ = 16.5 μl/l) and I. purpurea (LC₅₀ = 22.2 μl/l) oils were the most toxic. Cinnamomum glanduliferum (LC₅₀ = 29.7 μl/l) and Sabina vulgaris (LC₅₀ = 31.2 μl/l) oils were equitoxic. Interestingly, S. aromaticum did not exhibit any fumigant toxicity. Cymbopogon citratus, C. nardus and C. cassia strongly deterred feeding by third instar T. ni (DC₅₀s = 26.9, 33.8 and 39.6 μg/cm², respectively) in a leaf disc choice bioassay. The different responses of T. ni larvae to the oils in different bioassays suggest that these essential oils exhibit different modes of action. Based on their comparable efficacy with essential oils already used as active ingredients in many commercial insecticides (i.e. clove oil and thyme oil), some of these essential oils may have potential as botanical insecticides against T. ni.     

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.     

Synergistic larvicidal and repellent effects of essential oils of three Origanum species on Rhipicephalus annulatus tick

Ticks are of great economic importance worldwide, both because they represent major obstacles to livestock productivity and because of their ability to transmit diseases to humans and animals. Although synthetic acaricides are the most common method for tick control, their overuse has led to the development of resistance as well as unacceptable residual levels in animal products and in the environment in general. There is therefore an urgent need to identify alternative treatments. Among such alternative approaches for tick control is plant essential oil (EO) therapy. In the present study, we investigated the synergistic effect of EOs of three oregano species—Origanum onites, O. majorana and O. minutiflorum—against Rhipicephalus annulatus larvae. Gas chromatography–mass spectrometry profiles of the three EOs revealed that carvacrol was their major component, with a concentration of 86.2% in O. majorana, 79.1% in O. minutiflorum and 77.4% in O. onites. The results of larvicidal assays revealed that the doses that lead to the death of 50% of the ticks (LC₅₀) were 22.99, 25.08 and 27.06 µL/mL for O. majorana, O. minutiflorum and O. onites EOs, respectively, whereas the doses that lead to the death of 99% (LC₉₉) were 41.26, 43.62 and 48.96 µL/mL. In addition, the LC₅₀ and LC₉₉ of the three oils combined was lower (viz., 4.01 and 6.97 µL/mL) than that of each oil alone. The tested EOs were also able to repel larvae of R. annulatus to varying degrees, with O. onites oil exhibiting the greatest repellent effect, as shown by the lowest RC₅₀ dose, followed by O. minutiflorum and O. majorana. Interestingly, this means that the oil that was least effective in killing the larvae was the most effective in repelling them. The calculated synergistic factor of any combination was higher than 1 which means that combinations have a synergistic effect. In conclusion, the combination of all three oils showed higher toxic and repellent activities than either oil separately or combinations of any two oils, suggesting synergistic effects with low doses. Further studies including field trials and the establishment of the mode of action and side effects are urgently needed to expand on these findings, and other tick stages such as adults should also be tested.

     

Effect of some plant extracts on two coccinellid predators of the cowpea aphid,Aphis craccivora (Hom.: Aphididae)

This study was conducted to examine the effects of some aphicidal biologically active plant compounds on the natural enemies of the cowpea aphid,Aphis craccivora Koch. In the laboratory, acetone extracts ofCymbopogon citratus (DC) Stapf.,Momordica charantia L.,Zingiber officinale Rose andAframomum melegueta (Rose) K. Schum, were tested for toxicity to two coccinellid species,Cheilomenes lunata (Fabricius) andCheilomenes vicina (Mulsant) predaceous on the aphid. All the extracts were highly ovicidal to eggs of the two coccinellid predators. None of the extracts caused mortality of eitherC. lunata orC. vicina fourth-instar larvae after 24 h. Larvae treated with the extracts consumed fewer aphids in 24 h than untreated larvae. Ability to pupate was also significantly reduced in larvae treated with the extracts. No morphological deformities were observed in adults emerging from treated larvae.     

Essential oils of catmint (<Emphasis Type="Italic">Nepeta meyeri</Emphasis> Benth.) induce oxidative stress in early seedlings of various weed species

The essential oils from the aerial parts of catmint (Nepeta meyeri Benth.) were analyzed by hydrodistillation with GC–MS. Fourteen compounds were identified in the yellowish essential oil of the plant, representing more than 99.07% of the oil, of which the major components were found to be 4aα,7α,7aβ-nepetalactone (83.4%) and 4aα,7α,7aα-nepetalactone (8.83%). The oils were characterized by relatively high content of oxygenated monoterpenes, and were tested on the germination and antioxidative systems in early seedlings of seven weed species (Amaranthus retroflexus L., Bromus danthoniae Trin., Bromus intermedius Guss., Chenopodium album L., Cynodon dactylon L., Lactuca serriola L., and Portulaca oleracea L.) and autotoxicity. The essential oil of N. meyeri inhibited seed germination by more than 50% in three weed species (B. danthoniae, B. intermedius, and L. serriola) when applied at a concentration of 0.01%. When the same oils were applied at 0.02% concentration, the inhibition of germination was more than 70% in two weeds (C. album and C. dactylon) and was 100% in four weeds (A. retroflexus, B. danthoniae, B. intermedius, and L. serriola). The essential oils increased CAT activity in all the weed species and decreased SOD activity, except in A. retroflexus. POX activity did not exhibit a revealing situation in the weed species tested. The essential oils increased the level of lipid peroxidation and hydrogen peroxide (H₂O₂) concentration in all the weeds studied. Our results show that the essential oils of N. meyeri have an important phytotoxic effect on seed germination and, consequently, seedling growth by exhausting antioxidative system of the weeds. The phytotoxic activity of the essential oils may be attributed to their relatively high content of oxygenated monoterpenes, especially 4aα,7α,7aβ-nepetalactone. It can be suggest that the essential oils of N. meyeri have the potential to be used as a bioherbicide.     

Fumigant Toxicity of Plant Essential Oils to Plutella xylostella (Lepidoptera: Yponomeutidae) and Cotesia glomerata (Hymenoptera: Braconidae)

The fumigant toxicity of 66 plant essential oils to Plutella xylostella (L.) larvae and Cotesia glomerata (L.) adults was examined using a vapor-phase toxicity bioassay and compared with that of dichlorvos. Responses varied according to oil and insect species used. Based on 24 h LD₅₀ values, pennyroyal oil [10.77 mg/filter paper (4.25 cm diameter)] was the most toxic fumigant, followed by rosemary and sage (Dalmatin) oils (15.15 mg/paper). Potent fumigant toxicity was also produced from armoise, buchu leaf, cedarleaf, coriander, eucalyptus, howood, lavender, myrtle, niaouli, peppermint, and rosewood oils (LD₅₀, 21.29–27.31 mg/paper). All essential oils were less effective than dichlorvos (LD₅₀, 0.52 mg/paper). Against adult C. glomerata, dichlorvos (LD₅₀, 0.03 mg/paper) was the most toxic fumigant, whereas the LD₅₀ values of the 14 essential oils ranged from 1.59 to 8.51 mg/paper. Based on selective toxicity ratio (STR, P. xylostella LD₅₀/C. glomerata LD₅₀), the 14 essential oils (STR, 2.5–14.5) are more selective than dichlorvos (STR, 17.3). The essential oils tested merit further study as potential fumigants for the control of P. xylostella in greenhouses because of their selective toxicity to adult C. glomerata and their much greater activity as a fumigant.     

Yield,chemical composition,and bioactivity of essential oils from 12 species of Eucalyptus on Aedes aegypti larvae

The insecticidal activity of essential oils from 12 species of Eucalyptus (Myrtaceae) was evaluated on larvae of Aedes aegypti (L.) (Diptera: Culicidae), the most important vector of dengue and yellow fever in the Americas. Oils were obtained by hydrodistillation and their chemical composition was determined by gas chromatography coupled to mass spectrometry; yields ranged from 0.2 to 2.5%. Essential oils were mainly composed of 1,8‐cineole, α‐pinene, α‐phellandrene, β‐phellandrene, γ‐terpinene, 4‐terpineol, α‐terpineol, p‐cymene, and spathulenol. Larvicidal effects were tested on susceptible third or fourth stage Ae. aegypti larvae, determining median lethal concentration (LC₅₀) and median effective concentration (EC₅₀). Essential oils from Eucalyptus dunnii (Maiden), Eucalyptus gunnii (Hook), Eucalyptus tereticornis (Smith), Eucalyptus camaldulensis (Dehn), and Eucalyptus saligna (Smith) showed the best larvicidal activities with LC₅₀ values of 25.2, 21.1, 22.1, 26.8, and 22.2, respectively. No significant differences were observed between LC₅₀ and EC₅₀ values of the same oil. Regression analysis revealed a significant relationship between total essential oil yields and 1,8‐cineole concentration. Significant relationships were also revealed between larval mortality and the concentration of 1,8‐cineole and p‐cymene. This indicated that Eucalyptus species with high oil yields have higher 1,8‐cineole concentrations and lower p‐cymene concentrations and have less effect on Ae. aegypti. Our results suggest the potential of controlled crossing methods to obtain Eucalyptus trees with chemical profiles having enhanced activity against this mosquito.