Toxicity of plant essential oils and their components against Lycoriella ingenua (Diptera: Sciaridae)

Plant essential oils from 20 plant species were tested for their insecticidal activity against larvae of Lycoriella ingenua (Dufour) (Diptera: Sciaridae) by using a fumigation bioassay. Good insecticidal activity (>90%) against larvae of L. ingenua was achieved with essential oils of caraway seed Carum carvi (L.)], lemongrass [Cymbopogon citratus (D.C.) Stapf.], mandarine (Citrus reticulate Blanco), nutmeg (Myristica fragrans Houtt), cade (Juniperus oxycedrus L.), spearmint (Mentha spicata L.), cumin (Cuminum cyminum L.), and thyme red [Thymus vulgaris (L.)] oils at 30 X 10-3 mg/1 air. Among them, caraway seed, spearmint, cumin, and thyme red essential oils were highly effective against L. ingenua at 20 x 10(-3) mg/ml air. Analysis by gas chromatography-mass spectrometry led to identification of 4, 9, 8, and 17 compounds from caraway seed, spearmint, cumin, and thyme red oils, respectively. These compounds were tested individually for their insecticidal activities against larvae of L. ingenua, and compared with the toxicity of dichlorvos. Carvacrol, thymol, linalool, cuminaldehyde, p-cymen, terpinen-4-ol, and carvone was effective at 10 x 10(-3) mg/l. The insecticidal activity of dichlorvos was 60% at 10 x 10(-3) mg/ml. Effects of four selected plant essential oils on growth of oyster mushroom, Pleurotus ostreatus, also were investigated.     

Bioactivity of powders and essential oils of three Asteraceae plants as post-harvest grain protectants against three major coleopteran pests

Powders and essential oils were obtained from Achillea biebersteinii, A. fragrantissima and Ageratum conyzoides and tested for their insecticidal activity against Sitophilus oryzae, Rhyzopertha dominica and Tribolium castaneum. Composition of the oils was identified by gas chromatography (GC) and GC/mass spectrometry (MS). The tested plants showed adulticidal activity, where toxicity varied with dosage of the plant product, the insect tested and the exposure period. When mixed with grains as ground powders, a dosage of 20 g/kg grains killed 88.2, 73.6 and 64.4% of S. oryzae after 12 days of exposure with 79.6, 63.3 and 48% reduction in progeny for powders of A. biebersteinii, A. conyzoides and A. fragrantissima, respectively. Under the same assay conditions, A. biebersteinii and A. conyzoides powders killed 100% of R. dominica. T. castaneum was less susceptible to the plant powders. The LC₅₀ values for powders were 22.8, 31.6 and 39.7 mg/g grains for A. biebersteinii, 27.1, 35.4 and 47.8 mg/g grains for A. conyzoides and 36.9, 48.3 and 78.6 mg/g grains for A. fragrantissima against R. dominica, S. oryzae and T. castaneum, respectively. Upon fumigation, a dose of 60 μl/L air of A. biebersteinii and A. conyzoides oils was sufficient to kill 100% of R. dominica after 12 days of adult exposure, while 91.3% adult mortality was recorded in the case of A. fragrantissima oil. S. oryzae and T. castaneum showed a great susceptibility to the plant oils. Powders exhibited a moderate to strong residual activity where A. conyzoides showed the greatest grain protecting activity.     

Screening of insecticidal activity of plant essential oils and extract-based formulations against four agricultural insect pests and their risk assessment

Frankliniella occidentalis (Pergande), Myzus persicae (Sulzer), Plutella xylostella (L), and Spodoptera exigua (Hübner) are notorious agricultural insect pests worldwide. Due to the rapid development of resistance to the conventional insecticides, the number of available insecticides might be reduced in a near future, and botanical insecticides can be considered as one of the potential candidates to solve this problem. In the present study, test formulations were prepared using plant essential oils and extracts as main active ingredients, and their insecticidal activity and phytotoxicity were examined. Among the combinations tested, two oil-in-water formulations of NRS-13 containing thyme white oil and NRS-24 containing basil and rosemary oils were selected based on their notable insecticidal activity and low phytotoxicity. Chemical analyses on the active essential oils, the quantitative analysis of the major components in the formulations, insecticidal activities under pot and field conditions, their acute toxicity on mammals, and ecotoxicity on fish were also examined. The NRS-13 (BaechooSafer^TM) and NRS-24 (JindiOut^TM) formulations showed species-specific insecticidal activity against P. xylostella and M. persicae, respectively. In addition, both formulations produced low acute oral and dermal toxicity, skin and eye irritation, and fish toxicities, which suggests those formulations based on essential oils could be considered as insecticides for pest control in small-scale environments in organic farming.     

Control of coleopteran insect pests through RNA interference

Commercial biotechnology solutions for controlling lepidopteran and coleopteran insect pests on crops depend on the expression of Bacillus thuringiensis insecticidal proteins, most of which permeabilize the membranes of gut epithelial cells of susceptible insects. However, insect control strategies involving a different mode of action would be valuable for managing the emergence of insect resistance. Toward this end, we demonstrate that ingestion of double-stranded (ds)RNAs supplied in an artificial diet triggers RNA interference in several coleopteran species, most notably the western corn rootworm (WCR) Diabrotica virgifera virgifera LeConte. This may result in larval stunting and mortality. Transgenic corn plants engineered to express WCR dsRNAs show a significant reduction in WCR feeding damage in a growth chamber assay, suggesting that the RNAi pathway can be exploited to control insect pests via in planta expression of a dsRNA.     

Synergistic repellent activity of hot and cool thermal-sense compounds against two stored product insect pests

The repellent activities of one hot thermal-sense compound, vanillyl butyl ether (VBE), and two cool thermal-sense compounds, menthoxypropanediol (MPD) and (?)-isopulegol (IPG), against two stored product insects, Tribolium confusum and Liposcelis bostrychophila, were investigated. Such thermal-sense compounds affect mammals through transient receptor potential (TRP) channels, and both types of agonists (VBE and menthol) exhibited mutually inhibitory effects on mammalian TRPV1 and TRPM8 channels. Each compound exhibited repellent activity against both T. confusum and L. bostrychophila in a dose-dependent manner. Furthermore, synergistic effects were observed between VBE and MPD or IPG. The composition of TRP channels is different between mammals and insects. These results suggest that the use of thermal-sense compounds might serve as an alternative to essential oils in stored products protection.     

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.     

Bactericidal activities of essential oils of basil and sage against a range of bacteria and the effect of these essential oils on Vibrio parahaemolyticus

Basil and sage essential oils were examined for bactericidal activity against a range of Gram-positive and Gram-negative bacteria by viable count determinations. Generally, Gram-positive bacteria showed higher resistance to basil and sage essential oils than Gram-negative bacteria. Vibrio species showed a high sensitivity to both essential oils. Stationary growth phase cells of selected bacteria showed higher resistance to these essential oils than exponential growth phase cells. Basil-resistant (b21) and sage-resistant (s20) strains of Vibrio parahaemolyticus were isolated. Both strains showed higher resistance to heat and H2O2 than parent strain. Conversely, heat-adapted V. parahaemolyticus also showed a higher resistance to these essential oils than nonadapted cells.     

Activity of essential oils and individual components against acetyl- and butyrylcholinesterase

We have tested acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory activities of nineteen essential oils obtained from cultivated plants, namely one from Anethum graveolens L. (organic fertilizer), two from Foeniculum vulgare Mill. collected at fully-mature and flowering stages (organic fertilizer), two from Melissa officinalis L. (cultivated using organic and chemical fertilizers), two from Mentha piperita L. and M. spicata L. (organic fertilizer), two from Lavandula officinalis Chaix ex Villars (cultivated using organic and chemical fertilizers), two from Ocimum basilicum L. (green and purple-leaf varieties cultivated using only organic fertilizer), four from Origanum onites L., O. vulgare L., O. munitiflorum Hausskn., and O. majorana L. (cultivated using organic fertilizer), two from Salvia sclarea L. (organic and chemical fertilizers), one from S. officinalis L. (organic fertilizer), and one from Satureja cuneifolia Ten. (organic fertilizer) by a spectrophotometric method of Ellman using ELISA microplate-reader at 1 mg/ml concentration. In addition, a number of single components widely encountered in most of the essential oils [gamma-terpinene, 4-allyl anisole, (-)-carvone, dihydrocarvone, (-)-phencone, cuminyl alcohol, cumol, 4-isopropyl benzaldehyde, trans-anethole, camphene, iso-borneol, (-)-borneol, L-bornyl acetate, 2-decanol, 2-heptanol, methyl-heptanol, farnesol, nerol, iso-pulegol, 1,8-cineole, citral, citronellal, citronellol, geraniol, linalool, alpha-pinene, beta-pinene, piperitone, iso-menthone, menthofurane, linalyl oxide, linalyl ester, geranyl ester, carvacrol, thymol, menthol, vanilline, and eugenol] was also screened for the same activity in the same manner. Almost all of the essential oils showed a very high inhibitory activity (over 80%) against both enzymes, whereas the single components were not as active as the essential oils.     

Antibiofilm activity of selected plant essential oils and their major components

The aim of the study was to examine the antibiofilm activity of selected essential oils (EO): Lavandula angustifblia (LEO), Melaleuca alternifolia (TTO), Melissa officinalis (MEO) and some of their major constituents: linalool, linalyl acetate, alpha-terpineol, terpinen-4-ol. Biofilms were formed by Staphylococcus aureus ATCC 29213 and Escherichia coli NCTC 8196 on the surface of medical biomaterials (urinary catheter, infusion tube and surgical mesh). TTC reduction assay was used for the evaluation of mature biofilm eradication from these surfaces. Moreover, time-dependent eradication ofbiofilms preformed in polystyrene 96-well culture microplates was examined and expressed as minimal biofilm eradication concentration (evaluated by MTT reduction assay). TTO, alpha-terpineol and terpinen-4-ol as well as MEO, showed stronger anti-biofilm activity than LEO and linalool or linalyl acetate. Among the biomaterials tested, surgical mesh was the surface most prone to persistent colonization since biofilms formed on it, both by S. aureus and E. coli, were difficult to destroy. The killing rate studies of S. aureus biofilm treated with TTO, LEO, MEO and some of their constituents revealed that partial (50%) destruction of 24-h-old biofilms (MBEC50) was achieved by the concentration 4-8 x MIC after 1 h, whereas 2-4 x MIC was enough to obtain 90% reduction in biomass metabolic activity (MBEC90) after just 4 h of treatment. A similar dose-dependent effect was observed for E. coli biofilm which, however, was more susceptible to the action of phytochemicals than the biofilms of S. aureus. It is noteworthy that an evident decrease in biofilm cells metabolic activity does not always lead to their total destruction and eradication.     

Antifungal properties of essential oils and their main components uponCryptococcus neoformans

Cryptococcus neoformans opportunistic fungus met in the last phasis of AIDS is inhibited in vitro by several essential oils on natural volatile compounds. The minimal inhibitory concentration may reach 100 µl/l and minimal fungicidal concentration 200 µl/l with Palmarosa or Cinnamon oils. Among phenolic compounds, thymol and carvacrol are most fungitoxic. Terpenoids, citral, geraniol, and citronellol show best activities.     

Toxicity of plant essential oil vapours to aphid pests and their coccinellid predators

The comparative toxicity of five essential oil vapours was tested against four aphid species, the black bean aphid Aphis fabae, the pea aphid Acyrthosiphon pisum, the chrysanthemum aphid Macrosiphoniella sanborni, the green peach aphid Myzus persicae and on two of the most common coccinellid predators, the seven-spotted ladybird Coccinella septempunctata and the two-spotted ladybird Adalia bipunctata. All essential oils were highly toxic to the aphid species tested with LC₅₀ and LC₉₉ values ranging between 0.17 and 1.92 and 0.44 and 4.83 µL/L air, respectively, depending on the aphid species and on the essential oil. Coccinellid predators were also highly susceptible to the essential oil vapours and the selective toxicity ratio varied depending on aphid species, coccinellid predator and essential oil. The possibilities for the utililization of essential oils as aphicides, especially in IPM programmes in glasshouses are discussed with regard to the present findings.     

Evaluation of some medicinal plants and their mixtures for their bio-efficacy against crop and stored product pests

Plant based insecticides are gaining importance for their environmental safety. But their efficacy is greatly reduced in the field due to several factors. This study was undertaken to assess the insecticidal properties of medicinal plants viz., Cassia tora, Clerodendron enermi, Calotropis gigantea, Aloe vera, Vitex negundo and Andrographis paniculata, commonly found on farmlands and their mixtures. The extracts and mixtures were bio-assayed against a lepidopteran larva (Heliothis armigera) by modified leaf dip bioassay, and its effect on larval growth, development and survival; the oviposition deterrent effect against moths of H. armigera, and efficacy against the sucking pest Aphis gossypii and a stored product pest Callosobruchus chinensis were studied. The insecticidal activity in descending order was as follows: NSKE 10% > NSKE 5%, Botanical mixture II > A. paniculata > V. negundo > Botanical mixture I > C. gigantea > C. tora > C. enermi > A. vera. All botanicals showed greater ovipositional deterrence than insecticidal activity exhibiting 40–100% inhibition compared to untreated control. A. paniculata showed the highest activity against the store product pest C. chinensis. The complex of compounds in botanical mixtures could be synergistically used in eco-friendly pest management and botanical mixtures with neem as one of the ingredients, which could have a potential role as insect growth regulator.     

Potential of the neonicotinoid imidacloprid and the oxadiazine indoxacarb for controlling five coleopteran pests of stored grain

Abstract The potential for using imidacloprid (a neonicotinoid) and indoxacarb (an oxadiazine) as grain protectants was investigated in bioassays against resistant strains of five stored grain beetles. The species investigated were Rhyzopertha dominica (F.) (the lesser grain borer), Sitophilus oryzae (L.) (the rice weevil), Tribolium castaneum (Herbst) (the rust‐red flour beetle), Oryzaephilus surinamensis (L.) (the saw tooth flour beetle), and Cryptolestes ferrugineus (Stephens) (the flat grain beetle). Each of these species has developed resistance to one or more protectants, including organophosphorus insecticides, synthetic pyrethroids and the juvenile hormone analogue methoprene. Mortality and reproduction after a 2‐week exposure of adults to treated wheat depended on species, dose and insecticide. Imidacloprid had no effect on S. oryzae at any dose, but none of the other species produced any live progeny at 10 mg/kg. Indoxacarb had no effect on T. castaneum at any dose, but none of the other species produced any live progeny at 5 mg/kg. The results show that although both imidacloprid and indoxacarb can control at least four of the five key pests tested at doses comparable to those used for organophosphorus protectants, more potent neonicotinoid or oxadiazine insecticides would be needed than either of these to provide broad spectrum protection of stored grain.     

Cardioacceleratory action of tachykinin-related neuropeptides and proctolin in two coleopteran insect species

Several cardioactive peptides have been identified in insects and most of them are likely to act on the heart as neurohormones. Here we have investigated the cardioactive properties of members of a family of insect tachykinin-related peptides (TRPs) in heterologous bioassays with two coleopteran insects, Tenebrio molitor and Zophobas atratus. Their effects were compared with the action of the pentapeptide proctolin. We tested the cardiotropic activity of LemTRP-4 isolated from the midgut of the cockroach Leucophaea maderae, CavTK-I and CavTK-II isolated from the blowfly Calliphora vomitoria. The semi-isolated hearts of the two coleopteran species were strongly stimulated by proctolin. We observed a dose dependent increase in heartbeat frequency (a positive chronotropic effect) and a decrease in amplitude of contractions (a negative inotropic effect). In both beetles the TRPs are less potent cardiostimulators and exert lower maximal frequency responses than proctolin. LemTRP-4 applied at 10(-9)-10(-6) M was cardiostimulatory in both species inducing an increase of heart beat frequency. The amplitude of contractions was stimulated only in Z. atratus. CavTK-I and CavTK-II also exerted cardiostimulatory effects in Z. atratus at 10(-9)-10(-6) M. Both peptides stimulated the frequency, but only CavTK-II increased the amplitude of the heart beat. In T. molitor, however, the CavTKs induced no significant effect on the heart.Immunocytochemistry with antisera to the locust TRPs LomTK-I and LomTK-II was employed to identify the source of TRPs acting on the heart. No innervation of the heart by TRP immunoreactive axons could detected, instead it is possible that TRPs reach the heart by route of the circulation. The likely sources of circulating TRPs in these insects are TRP-immunoreactive neurosecretory cells of the median neurosecretory cell group in the brain with terminations in the corpora cardiaca and endocrine cells in the midgut.In conclusion, LemTRP-4, CavTK-I and CavTK-II are less potent cardiostimulators than proctolin and also exert stimulatory rather than inhibitory action on amplitude of contractions. The differences in the responses to proctolin and TRPs suggest that the peptides regulate heart activity by different mechanisms.     

The inhibition of Candida albicans by selected essential oils and their major components

Many volatile oils are known to possess antifungal properties and are potentially applicable as antimycotic agents. By studying the efficacy of essential oils against different pathogenic mycetes, we have evaluated the in-vitro inhibiting activity of some essential oils and their main constituents against a strain of Candida albicans. Sixteen commercial essential oils and forty-two pure constituents (alcohols, aldehydes, ketons, phenols and hydrocarbons), were tested by using a semisolid agar antifungal susceptibility (SAAS) method. Gas chromatography/mass spectroscopy analyses of the oils tested were performed. The essential oils of Origanum vulgare, Satureja montana, Mentha piperita, Cinnamomum verum, Cymbopogon flexuosus showed maximum inhibitory activity (MIC = 500 ppm) after 7 days. According to the results of the examination of pure constituents, -phellandrene proved to be the most interesting component among cyclic monoterpenic hydrocarbons as it showed a strong activity (MIC = 50 ppm). The most active of phenols was carvacrol (MIC 100 ppm). The open-chain alcohol 1-decanol was the most active of alcohols at 50 ppm. Finally, among aldehydes, a strong activity was shown by trans-cynnamaldehyde (MIC 50 ppm).     

害虫生物型及其遗传机理

以农作物上5种重要害虫的生物型为例,简单地概括了分子标记在害虫生物型研究中的应用,重点阐述几种重要害虫如黑森瘿蚊,麦二叉蚜,褐飞虱,稻瘿蚊和烟粉虱等的生物型遗传变异机理。黑森瘿蚊、麦二叉蚜和稻瘿蚊的生物型由单基因控制,特定害虫生物型与作物基因型之间存在“基因_基因”关系;褐飞虱的致害性为多基因控制的数量性状;烟粉虱生物型的遗传变异机理尚不明确。还指出生物型遗传研究中待进一步解决的问题如生物型的遗传组成差异与致害力的关系等。     

植物耐虫性研究进展

本文简要介绍了植物耐虫性的含义、发生范围、耐虫性的进化过程和遗传特性、耐虫性机理以及影响植物耐虫性表达的非生物和生物因子。植物耐虫性机理的研究涉及光合作用能力变化、同化产物的再分配、内源激素的变化、休眠分生组织的激活和补偿生长、储藏器官的利用、植物物候学和植株株型结构的变化等。研究表明,植物受害后光合作用强度的变化与其耐虫性没有相关性,有些耐虫植物受害后光合作用能力增加,有些植物光合作用强度无明显影响或者下降较少; 害虫取食为害可促进耐虫植物的同化产物得到最大程度利用,能激活耐虫植物的休眠分生组织,产生超补偿作用; 耐虫植物受害部位细胞分裂素含量显著升高; 虫害引起物候学变化小的植物具有较强的耐虫性; 植物的冠层结构、叶形态、根茎比、茎蘖数等植株株型变化与耐虫性有关。影响植物耐虫性表达的因子主要有温度、大气CO₂浓度、土壤营养水平、农用化学物质、植株年龄、害虫分布类型和取食方式、植物共生物等。不同植物在相同温度下对同一种害虫的耐害性差异大,其主要原因可能是由于温度的变化引起同化产物的分配和再分配以及气孔关闭对气体交换和光合作用能力的影响; 生长在高CO₂含量大气中的植物,对害虫的为害有较强耐受性。土壤营养水平对植物耐虫性表达的影响大于温度,增施磷、钾肥可增加植物的耐虫性。聚集分布型害虫为害对植物造成的损失大于随机分布型和均匀分布型害虫,害虫的取食方式、传粉昆虫的活动、植物内生真菌和菌根真菌的感染均影响到植物耐虫性的表达水平。文中最后讨论了植物耐虫性在害虫综合治理中的重要性及应用前景。     

Larvicidal activity of Amyris balsamifera,Daucus carota and Pogostemon cablin essential oils and their components against Culex pipiens pallens

Larvicidal activities of Amyris balsamifera, Daucus carota, and Pogostemon cablin essential oils were tested against Culex pipiens pallens. All three oils showed 100% larvicidal activity against C. pipiens pallens at 0.1 mg/mL. Among the tested oils, the larvicidal activity of D. carota oil was the strongest followed by P. cablin and A. balsamifera. Four active compounds such as β-eudesmol, elemol, patchoulol, and carotol were isolated from the three oils by open column chromatography. These compounds showed > 90% mortality against C. pipiens pallens at 0.1 mg/mL. In acute toxicity testing of the water flea, Daphnia magna, P. cablin oil was the most toxic followed by A. balsamifera, and D. carota. Among the isolated compounds, carotol was the most toxic to water fleas. The residues of P. cablin, A. balsamifera, and D. carota in water were 67.8%, 59.5%, and 51.2% at 2 days after treatment, respectively. High concentrations of elemol and patchoulol were detected 2 days after treatment compared to those of β-eudesmol and elemol. Whole oils and compounds tested were detected at < 50% after 7 days in water.