Essential oils: effects of application rate and modality on potential for combating northern fowl mite infestations

The northern fowl mite (NFM), Ornithonyssus sylviarum (Mesostigmata: Macronyssidae), is the primary blood‐feeding ectoparasite found on poultry in the U.S.A. Three experiments were conducted in vitro to test the acaricidal properties of cade, garlic, lavender, lemongrass, pine and thyme essential oils against NFM, and to evaluate whether these effects are altered by adjusting oil application rates and application modality (direct vs. vapour contact). Applied at the rate of 0.21 mg/cm², the essential oils of cade, thyme, lemongrass and garlic resulted in higher NFM mortality at 24 h post‐application than lavender and pine oils, and the untreated and ethanol‐treated controls. Cade and thyme were the most consistent and fast‐acting of the essential oils in terms of toxicity to NFM. Cade applied at 0.21 mg/cm² and 0.11 mg/cm² and thyme applied at 0.21 mg/cm² were effective in eliminating NFM within 2 h through direct contact. The modality of application did not affect the efficacy of cade and thyme essential oils. The results suggest that essential oils may be utilized as alternatives to chemical pesticides and could be used as fumigants for the control of NFM.     

Essential oils against multidrug resistant gram-negative bacteria

Multi-drug resistant uropathogens are responsible for urinary tract infections. The antibacterial activity of seven essential oils, oregano, thyme, clove, arborvitae, cassia, lemongrass, tea tree) was investigated by agar diffusion method, followed by determination of minimum inhibitory (MIC) and bactericidal (MBC) concentrations against five multidrug resistant isolates namely Pseudomonas aeruginosa, Escherichia coli, Enterobacter cloaceae, Morganella morganii, Proteus mirabilis. Oregano, thyme, cassia had antibacterial activity with inhibition zones ranging 25–39 mm; clove, arborvitae, tea tree and lemongrass 12–15 mm. The essential oils showed antibacterial activities with MICs ranged from 0.005% (w/v) to 0.5% (w/v). Thyme had the same MIC and MBC on all strains. The effects of the vapors of the essential oils were also tested by placing the oils on the underside of the Petri dish lid. Thyme, oregano and cassia essential oils strongly inhibited the growth of the clinical strains of bacteria tested in vapor phase. This study demonstrates the potential of investigated essential oils as natural alternatives for further application in hospital therapies in order to retard or inhibit the bacterial growth. For the first time antibacterial effects of essential oils (clove, arborvitae, tea tree, lemongrass, and cassia) were evaluated against Enterobacter cloaceae and Morganella morganii clinical isolates.     

Antifungal activity of essential oils evaluated by two different application techniques against rye bread spoilage fungi

AIMS: To study how antifungal activity of natural essential oils depends on the assay method used. METHODS AND RESULTS: Oils of bay, cinnamon leaf, clove, lemongrass, mustard, orange, sage, thyme and two rosemary oils were tested by two methods: (1) a rye bread-based agar medium was supplemented with 100 and 250 microl l-1 essential oil and (2) real rye bread was exposed to 136 and 272 microl l-1 volatile oil in air. Rye bread spoilage fungi were used for testing. Method 1 proved thyme oil to be the overall best growth inhibitor, followed by clove and cinnamon. On the contrary, orange, sage and rosemary oils had very limited effects. Mustard and lemongrass were the most effective oils by the volatile method, and orange, sage and one rosemary showed some effects. Oil compositions were analysed by gas chromatography-mass spectrography. CONCLUSIONS: Antifungal effects of the essential oils depended on the application method. Larger phenolic compounds such as thymol and eugenol (thyme, cinnamon and clove) had best effect applied directly to medium, whereas smaller compounds such as allyl isothiocyanate and citral (mustard and lemongrass) were most efficient when added as volatiles. SIGNIFICANCE AND IMPACT OF THE STUDY: This study proves that the method used for screening essential oils as potential antimicrobials should correspond with the application sought.     

Biopesticidal value of selected essential oils against pathogenic fungus, termites, and nematodes

The biopesticidal potential of six plant-derived essential oils (mint [Mentha arvensis], ajwain [Carum capticum], lemongrass [Cymbopogon citrates], clove [Eugenia caryophyllata], cedarwood [Cedrus deodara], and eucalyptus [Eucalyptus globulas]) was evaluated against Odontotermes obesus (termites), Fusarium oxysporum (plant pathogenic fungi), and Meloidogyne incognita (nematodes). In the case of termites, a “no-choice” bioassay revealed that the mint oil gave the best results (100% mortality in 30 min with 10% oil and in 10 h with 0.12% oil) followed by the lemongrass and ajwain oils. The disc diffusion method was adopted to test the anti-fungal activity of the essential oils and it was found that the clove oil gave the maximum inhibition measured in terms of the average inhibition zone diameter (5.3 ± 0.2 cm with 10% oil and 6.6 ± 0.9 cm with 20% oil), followed by the ajwain oil. To check the anti-nematicidal activity of the essential oil, in-vitro growth chamber experiments revealed that eucalyptus oil was the most efficient (100% mortality in 6 h with 1000 ??l l⁻¹ oil and in 30 h with 125 ??l l⁻¹ oil), followed by the ajwain oil. The use of the crude oils at low concentrations provided satisfactory results at the laboratory level against these pathogens, and needs further evaluation in field trials.     

Temperature-dependent fumigant activity of essential oils against twospotted spider mite (Acari: Tetranychidae)

Fumigant activity of 34 commercial essential oils was assessed on female adults and eggs of twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) at three temperatures (5, 15, and 25 degrees C). Common thyme, cinnamon, and lemongrass oils were equally effective on twospotted spider mite adults showing 85.8-100% mortality at 5 and 10 microl/liter air at 25 degrees C. At a lower temperature of 15 degrees C, lemongrass and peppermint resulted in > or =90% mortality of adults at 10 microl/liter air. Only lemongrass was relatively active at 5 microl/liter air, at 15 degrees C. At 5 degrees C, lemongrass and peppermint caused significantly higher adult mortality than controls but only at 10 microl/liter air. Common thyme oil showed the highest ovicidal activity at 5 microl/liter air at 25 degrees C. Among the main components of common thyme and lemongrass oils, citral was lethal to twospotted spider mite adults at all tested temperatures. Carvacrol, thymol, and citral caused the same inhibitory effects on the hatch of twospotted spider mite eggs at 25 degrees C. However, citral was more active than other compounds to twospotted spider mite eggs at 15 degrees C. Therefore, we conclude that citral has the best potential for development as a fumigant against twospotted spider mite on agricultural products harvested late in the growing season.     

Effect of some essential oils on mycelial growth of <Emphasis Type="Italic">Penicillium digitatum</Emphasis> Sacc.

The antifungal action of four essential oils of Foeniculum vulgare (fennel), Thymus vulgaris (thyme), Eugenia caryophyllata (Clove) and Salvia officinalis (sage) was tested in vitro against Penicillium digitatum Sacc. Direct contact and vapour phase were used to test the antifungal activity of these essential oils against P. digitatum that is responsible for green mould rot of citrus fruits. The vapour phase and direct contact of clove and thyme essential oils exhibited the strongest toxicity and totally inhibited the mycelial growth of the test fungus. Thyme and clove essential oils completely inhibited P. digitatum growth either when added into the medium 600 μl l⁻¹ or by their volatiles with 24 μl per 8 cm diameter Petri dish. In in vitro mycelial growth assay showed fungistatic and fungicidal activity by clove and thyme essential oils. Sage and fennel oils did not show any inhibitory activity on this fungus. Scanning electron microscopy (SEM) was done to study the mode of action of clove oil in P. digitatum and it was observed that treatment with the oil leads to large alterations in hyphal morphology.     

Nematicidal Activity of Plant Essential Oils against Bursaphelenchus xylophilus (Nematoda: Aphelenchoididae)

The nematicidal activity and poisoning symptoms of 88 plant essential oils against Bursaphelenchus xylophilus were examined by an immersion bioassay. Results were compared with those of three trunk-injection nematicides: fenitrithion, levamisol hydrochloride, and morantel tartrate. As judged by 24 h LC₅₀ values, cinnamon bark oil (0.12 mg/ml) was the most effective nematicide, followed by coriander herb oil (0.14 mg/ml). Potent nematicidal activity was also observed with lemongrass, oregano, thyme red, and clove bud oils (LC₅₀, 0.57-0.88 mg/ml). Fenitrothion was ineffective (LC₅₀, > 10 mg/ml). In typical poisoning symptoms in B. xylophilus, these essential oils exerted rapid nematicidal action and the nematodes killed usually showed an extended shape, whereas levamisole hydrochloride and morantel tartrate usually exhibited semicircular and coiling shapes, respectively. The essential oils described merit further study as botanical nematicides for the control of pine wilt disease caused by B. xylophilus.     

Behavioral Responses of the Potato Psyllid (Hemiptera: Triozidae) to Volatiles from Dimethyl Disulfide and Plant Essential Oils

The behavioral responses of the potato psyllid, Bactericera cockerelli (Sulc) to dimethyl disulfide (DMDS) and to 12 plant essential oils were examined in a glass Y-tube olfactometer. DMDS at doses of 0.5, 1, 2 and 5 g showed a significant repellent effect on the psyllids. Cedar wood, lime, savory, thyme and tea tree oils significantly repelled adults over a wide range of doses tested (1, 10, 100, 500, 1,000 and 2,000 μl). The oils of clove and peppermint also had a significant repellent effect on adults at all doses except at the lowest dose (1 μl). The residual effect of 1 g of DMDS persisted for 10 consecutive days whereas five oils (thyme, tea tree, peppermint, savory and clove) remained repellent for the 20-day longevity residual trial.     

Antifungal activity of volatile compounds generated by essential oils against fungi commonly causing deterioration of bakery products

AIMS: To investigate the volatile fractions of 16 essential oils for activity against the more common fungi causing spoilage of bakery products, Eurotium amstelodami, E. herbariorum, E. repens, E. rubrum, Aspergillus flavus, A. niger and Penicillium corylophilum. METHODS AND RESULTS: The study applied 50 microl of pure essential oils in a sterilized filter paper, were carried out at pH 6 and at different water activity levels (0.80-0.90). First, a wheat flour based agar medium was used, where cinnamon leaf, clove, bay, lemongrass and thyme essential oils where found to totally inhibit all microorganisms tested. These five essential oils were then tested in sponge cake analogues, but the antifungal activity detected was much more limited. CONCLUSION: Five essential oils showed potential antifungal capacity against all species tested, over a wide range of water availability. Their activity, however, seems to be substrate-dependent. More research is needed to make them work in real bakery products, as in the preliminary study limited effectiveness was found. SIGNIFICANCE AND IMPACT OF THE STUDY: The potential of the cinnamon leaf, clove, bay, lemongrass and thyme essential oils against species belonging to Eurotium, Aspergillus and Penicillium genus has been demonstrated.     

Bactericidal activity of some plant essential oils against Ralstonia solanacearum infection

Potato plants and their tubers in Egypt are affected by one of the most renowned soil-borne pathogen, Ralstonia solanacearum, that caused brown rot in potato tubers and wilt in plants. There is no efficient therapeutic bactericide so; control of bacterial wilt is very rough.The study investigated three different concentrations of seven essential plant oils under in vitro and in vivo conditions as a result of their effects on Ralstonia solanacearum growth and their possibility use as potato seed pieces dressing for controlling bacterial wilt disease incidence. In vitro, anise oil at the three tested different concentrations (0.04, 0.07, and 0.14% vol/vol) was the most effective one inhibiting the growth of T4 and W9 isolates of Ralstonia solanacearum then pursued by thyme, lemongrass, and clove oils. On the other hand, rocket oil at the tested concentration was the least effective one followed by fennel oil. However, wheat germ oil was not completely effective. In vivo, experiment revealed that anise oil at the three concentrations significantly reduced disease incidence and severity in sponta and hermes potato cultivars and their effect was associated with increase of peroxidase, polyphenoloxidase, phenols and the foliar fresh weight of treated plants as well as the weight of tubers/plant followed by thyme and lemongrass oils compared to the infected untreated control.Morphological differences in bacterial cell structure have been observed using a transmission electron microscope (TEM). Anise oil at higher concentration caused of cell wall rupture and degraded cellular components.     

Acaricidal activities of bicyclic monoterpene ketones from Artemisia iwayomogi against Dermatophagoides spp.

The acaricidal properties of 1,7,7-trimethylbicyclo[2.2.1]heptan-2-one isolated from Artemisia iwayomogi and its structural analogues were evaluated against Dermatophagoides farinae and D. pteronyssinus, and their effects were compared with that of the commercial acaricide benzyl benzoate. Based on the 50 % lethal dose (LD₅₀) values against D. farinae, 1,7,7-trimethylbicyclo[2.2.1]heptan-2-one (0.82 μg/cm²) was 9.71 times more effective than benzyl benzoate (7.96 μg/cm²), followed by (1R)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-one (1.03 μg/cm²), (1S)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-one (1.58 μg/cm²), and (1R)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-one oxime (3.05 μg/cm²) in a filter paper bioassay. The acaricidal activities of 1,7,7-trimethylbicyclo[2.2.1]heptan-2-one and its structural analogues against D. pteronyssinus were similar to those against D. farinae. These results demonstrate that naturally occurring A. iwayomogi-isolated 1,7,7-trimethylbicyclo[2.2.1]heptan-2-one and its structural analogues are suitable for the production of natural acaricides against house dust mites.     

Essential oils as spatial repellents for the brown marmorated stink bug,Halyomorpha halys (Stål) (Hemiptera: Pentatomidae)

The brown marmorated stink bug (BMSB), Halyomorpha halys (Stål), native to Northeastern Asia, is a serious invasive pest in the United States, Canada, Switzerland, Germany and France. Several common essential oils and their compositions were tested against BMSBs as potential repellents. All the tested individual essential oils and a ternary oil blend showed significant repellency to both BMSB nymphs and adults. Clove oil, lemongrass oil, spearmint oil, ylang‐ylang oil, and the ternary oil mixture (clove, lemongrass and spearmint) almost completely blocked attraction of BMSBs to the stink bug attractant‐baited traps; whereas wintergreen oil, geranium oil, pennyroyal oil and rosemary oil resulted in 60–85% trap catch reductions. Over 20 BMSB antennally active compounds were identified from SPME headspace samples of the eight repellent essential oils using GC‐EAD and GC‐MS techniques. Among the synthetic EAD‐active compounds tested in the field, eugenol, l‐carvone, p/l‐menthone, pulegone, methyl salicylate, trans/cis‐citral, methyl benzoate and β‐caryophyllene significantly reduced trap catches of BMSBs by 72–99%; these compounds are likely responsible for the repellency of their corresponding essential oils. Surprisingly, a synthetic mixture of the predacious spined soldier bug (SSB) [Podisus maculiventris (Say)] aggregation pheromone (trans‐2‐hexenal, α‐terpineol and benzyl alcohol) also showed a significant inhibition of BMSB response to its attractants. These repellent essential oils and their active compounds, as well as the synthetic SSB pheromone, are potentially useful as part of an efficient, environmentally sound semiochemical‐based IPM programme to combat this serious invasive stink bug.     

Acaricidal Activity of Eugenol Based Compounds against Scabies Mites

Backgound

Human scabies is a debilitating skin disease caused by the “itch mite” Sarcoptes scabiei. Ordinary scabies is commonly treated with topical creams such as permethrin, while crusted scabies is treated with topical creams in combination with oral ivermectin. Recent reports of acaricide tolerance in scabies endemic communities in Northern Australia have prompted efforts to better understand resistance mechanisms and to identify potential new acaricides. In this study, we screened three essential oils and four pure compounds based on eugenol for acaricidal properties.

Methodology/Principal Findings

Contact bioassays were performed using live permethrin-sensitive S. scabiei var suis mites harvested from pigs and permethrin-resistant S. scabiei var canis mites harvested from rabbits. Results of bioassays showed that clove oil was highly toxic against scabies mites. Nutmeg oil had moderate toxicity and ylang ylang oil was the least toxic. Eugenol, a major component of clove oil and its analogues –acetyleugenol and isoeugenol, demonstrated levels of toxicity comparable to benzyl benzoate, the positive control acaricide, killing mites within an hour of contact.

Conclusions

The acaricidal properties demonstrated by eugenol and its analogues show promise as leads for future development of alternative topical acaricides to treat scabies.     

Investigations on influencing plant-associated bacteria in tissue cultures of black locust (<Emphasis Type="Italic">Robinia pseudoacacia</Emphasis> L.)

During tissue culture of black locust (Robinia pseudoacacia L.), serious problems with plant-associated bacteria led to a reduction of propagation potential in several clones. Four dominant strains of plant-associated bacteria could be isolated and were assigned to the genera Acidovorax, Dyella, Microbacterium and Sphingomonas. Out of five essential oils tested, thyme and lemongrass oil at a concentration of 0.03% each and 0.015% of both oils in combination clearly inhibited the growth of these bacteria strains on bacteriologic medium. There were no significant differences in total bacterial population density when penicillin, thyme and lemongrass oil or thyme plus lemongrass oil were added to the plant propagation media. The use of lemongrass oil changed the proportion of dominant bacterial strains.     

Bioactivity of selected essential oils and some components on Listeria monocytogenes biofilms

Listeria monocytogenes is a Gram-positive bacterium, able to survive and grow in water, soil, agricultural products, various foods and the food-processing environment. The ubiquitous nature of the organism, coupled with its ability to colonise food-processing surfaces by forming biofilms, causes it to be of a major concern to the industry. Increased foodborne pathogen resistance and negative consumer perceptions regarding the use of synthetic bacteriocides, has resulted in natural antimicrobials being sourced from the plant kingdom. The listerial antibiofilm activities of Syzygium aromaticum (clove), Mentha spicata (spearmint), Lippia rehmannii and Cymbopogon citratus (lemongrass) essential oils and their major components were evaluated using the crystal violet assay and confocal scanning laser microscopy. Listerial biofilms treated with S. aromaticum or M. spicata essential oils, or the pure compounds nerol and citral, exhibited a similar biofilm biomass to the positive control. However, the essential oils of lemongrass, L. rehmannii, eugenol and R-carvone caused biofilm enhancement, rather than inhibition. L. rehmannii and lemongrass essential oils did not display any antibiofilm properties. Results obtained were confirmed by microscopic observations indicating either a reduction (inhibition) or an increase (enhancement) in biofilm biomass when exposed to the essential oils or pure compounds. The present study revealed that M. spicata and S. aromaticum essential oils as well as pure citral and nerol are good candidates for further development of ecofriendly disinfectants.     

Novel strategies of essential oils,chitosan, and nano- chitosan for inhibition of multi-drug resistant: E. coli O157:H7 and Listeria monocytogenes

Despite the wide range of available antibiotics, food borne bacteria demonstrate a huge spectrum of resistance. The current study aims to use natural components such as essential oils (EOs), chitosan, and nano-chitosan that have very influential antibacterial properties with novel technologies like chitosan solution/film loaded with EOs against multi-drug resistant bacteria. Two strains of Escherichia coli O157:H7 and three strains of Listeria monocytogenes were used to estimate antibiotics resistance. Ten EOs and their mixture, chitosan, nano-chitosan, chitosan plus EO solutions, and biodegradable chitosan film enriched with EOs were tested as antibacterial agents against pathogenic bacterial strains. Results showed that E. coli O157:H7 51,659 and L. monocytogenes 19,116 relatively exhibited considerable resistance to more than one single antibiotic. Turmeric, cumin, pepper black, and marjoram did not show any inhibition zone against L. monocytogenes; Whereas, clove, thyme, cinnamon, and garlic EOs exhibited high antibacterial activity against L. monocytogenes with minimum inhibitory concentration (MIC) of 250–400 μl 100^?1 ml and against E. coli O157:H7 with an MIC of 350–500 μl 100^?1 ml, respectively. Among combinations, clove, and thyme EOs showed the highest antibacterial activity against E. coli O157:H7 with MIC of 170 μl 100^?1 ml, and the combination of cinnamon and clove EOs showed the strongest antibacterial activity against L. monocytogenes with an MIC of 120 μl 100^?1 ml. Both chitosan and nano-chitosan showed a promising potential as an antibacterial agent against pathogenic bacteria as their MICs were relatively lower against L. monocytogenes than for E. coli O157:H7. Chitosan combined with each of cinnamon, clove, and thyme oil have a more effective antibacterial activity against L. monocytogenes and E. coli O157:H7 than the mixture of oils alone. Furthermore, the use of either chitosan solution or biodegradable chitosan film loaded with a combination of clove and thyme EOs had the strongest antibacterial activity against L. monocytogenes and E. coli O157:H7. However, chitosan film without EOs did not exhibit an inhibition zone against the tested bacterial strains.     

Screening for inhibitory activities of essential oils on the growth of Colletotrichum gloeosporioides (Penz.) Penz. & Sacc., the causal agent of leaf spot disease of Murraya koenigii L.

Seven essential oils namely clove, cedar wood, lemongrass, peppermint, eucalyptus, citronella and neem oils were tested for their inhibitory effect on spore germination, growth of germ tube and mycelial growth of Colletotrichum gloeosporioides isolated from diseased Murraya koenigii. All essential oils inhibited the germination and growth of germ tube at different concentrations. However, significant reduction in colony growth was observed with citrus, lemongrass and peppermint oils at 1000, 1500 and 2000 ppm concentrations, respectively. Citrus oil at 1360 ppm inhibited the maximum growth of the fungus followed by lemongrass oil at 1720 ppm and peppermint at 2260 ppm, respectively. The effect of essential oils on mycelial dry weight also showed antifungal activity on the growth of Colletotrichum gloeosporioides. The study revealed the possible utilisation of these essential oils for foliar spray for the management of leaf spot disease of Murraya koenigii.     

The effects of clove oil on the enzyme activity of Varroa destructor Anderson and Trueman (Arachnida: Acari: Varroidae)

Varroa destructor, a key biotic threat to the Western honey bee, has played a major role in colony losses over the past few years worldwide. Overuse of traditional acaricides, such as tau-fluvalinate and flumethrin, on V. destructor has only increased its tolerance to them. Therefore, the application of essential oils in place of traditional pesticides is an attractive alternative, as demonstrated by its high efficiency, lack of residue and tolerance resistance. To study the acaricidal activity of essential oils, we used clove oil (Syzygium aromaticum L.), a typical essential oil with a wide range of field applications, and examined its effects on the enzyme activities of Ca²⁺-Mg²⁺-ATPase, glutathione-S-transferase (GST) and superoxide dismutase (SOD) and its effects on the water-soluble protein content of V. destructor body extracts after exposure to 0.1 μl and 1.0 μl of clove oil for 30 min. Our results showed that the water-soluble protein content significantly decreased after the treatments, indicating that the metabolism of the mites was adversely affected. The bioactivity of GSTs increased significantly after a low dosage (0.1 μl) exposure but decreased at a higher dosage (1.0 μl), while the activities of SOD and Ca²⁺-Mg²⁺-ATPase were significantly elevated after treatments. These results suggest that the protective enzyme SOD and detoxifying enzymes Ca²⁺-Mg²⁺-ATPase and GST contributed to the stress reaction of V. destructor to the essential oils and that the detoxification ability of V. destructor via GST was inhibited at higher dosages. Our findings are conducive to understanding the physiological reactions of V. destructor to treatment with essential oils and the underlying mechanisms behind the acaricidal activities of these natural products.     

Progeny of the maize weevil,Sitophilus zeamais,is affected by parental exposure to clove and cinnamon essential oils

The interest in and utilization of botanical insecticides, particularly essential oils, has become increasingly relevant to the control of insect pests. However, the potential ecotoxicological risks or flaws (including sublethal effects on the targeted pest generation and its subsequent progeny) of this pest control tool have been neglected frequently. Here, we evaluated the effects of sublethal exposure to clove, Syzygium aromaticum (L.) Merrill & Perry (Myrtaceae), and cinnamon, Cinnamomum verum J. Presl (Lauraceae), essential oils on adult (F0) maize weevils, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae), and the physiology (e.g., body mass, respirometry, and grain consumption) and population dynamics (e.g., daily emergence and sex ratio) of their progeny. Longevities of the parents were negatively affected by the essential oils in a concentration‐dependent manner. Parental sublethal exposure to clove oil (0.17 μl cm^?2) accelerated offspring emergence but delayed the emergence of females compared to males. Parents that were sublethally exposed to clove (0.17 μl cm^?2) or cinnamon (0.35 μl cm^?2) essential oils produced heavier offspring. Parental sublethal exposure to cinnamon essential oil accelerated offspring emergence (at 0.70 μl cm^?2), delayed female emergence (at 0.17 μl cm^?2), and enhanced grain consumption (at 0.35 and 0.70 μl cm^?2) of the progeny. Thus, our findings indicate that sublethal exposure to clove and cinnamon essential oils is capable of promoting transgenerational effects in S. zeamais that can negatively impact the control efficacy of such products.     

Adverse Effect of Essential Oil Fumigation on Proisotoma minuta (Collembola: Entomobryoidae)

Eighteen essential oils were tested for their fumigant toxicity towards Proisotoma minuta (Tullberg). The essential oils of citronella (LD₅₀=0.65 μL/L air), petitgrain (LD₅₀=2.3 μL/L air), and thyme (LD₅₀=2.8 μI/L air) produced potent activity towards the species.