Absence of farnesol in strawberry and hop foliage

The farnesol content of foliage has been proposed as an indicator of susceptibility to the two-spotted spider mite in various crops. The use of this chemical marker was investigated for strawberry and hop varieties. No farnesol was detectable in any of the varieties tested. The techniques necessary for analysis and identification of farnesol from foliage are discussed.     

Strawberry resistance toTetranychus urticae Koch: Effects of flower,fruit, and foliage removal—comparisons of air- vs. nitrogen-entrained volatile compounds

An increase in resistance to the two-spotted spider mite (TSSM),Tetranychus urticae Koch, is observed in field-grown strawberry plants during the period from flowering to postharvest. This seasonal phenomenon was investigated to determine the influence of the metabolic sink, that is, fruiting in the plant. Removal of flowers and fruit and partial removal of foliage did not alter the pattern of resistance of the strawberry plant to TSSM. Bioassays were conducted in concert with chemical analyses. Headspace chemicals emitted from foliage samples were entrained in air and trapped on Tenax, identified, and compared with those entrained in nitrogen and trapped. Terpenes were among the major compounds entrained in air, whereas alcohols were obtained with nitrogen. The air-entrained headspace compounds did not appear to correlate quantitatively with the development of mite resistance in the control plants or those subjected to metabolic sink (flower and fruit) removal. Evidence was obtained for the presence of heretofore unreported strawberry foliage headspace components, namely, (Z)-3-hexenyl 2-meth-ylbutyrate, (Z)-3-hexenyl tiglate, (E)--ocimene, (Z)--ocimene, -farnesene, and germacrene D.     

Prior exposure to carbaryl alters behavior ofTetranychus urticae Koch on acaricide-treated leaf surfaces

Preadult exposure to carbaryl affected the subsequent behavior of two-spotted spider mites (Tetranychus urticae Koch) on leaf surfaces with discontinuous acaricide residues. In dicofol bioassays, preexposure to carbaryl caused a loss of avoidance behavior (eliminating the tendency of mites to feed and stand longer off treated areas). In amitraz bioassays, preexposure to carbaryl had the opposite effect. It increased the propensity of mites to feed and stand off amitraz-treated areas, resulting in increased avoidance of amitraz. Carbaryl preexposure therefore resulted in diametrically opposed behavioral changes in subsequent encounters with two acaricides. These effects provide additional evidence of the unpredictable nature of interactions between pesticides and show how a chemical, irrespective of degree of toxicity, can alter the behavior of arthropods in response to subsequent chemical encounters.     

Role of cucurbitacin C in resistance to spider mite (Tetranychus urticae) in cucumber (Cucumis sativus L.)

Cucurbitacins are bitter triterpenoid compounds that are toxic to most organisms and occur widely in wild and cultivated Cucurbitaceae. The only cucurbitacin identified in Cucumis sativus is cucurbitacin C. The bitter taste of cucumber has been correlated with resistance to the spider mite Tetranychus urticae, but a quantitative relationship has not been established. We determined the spider mite resistance and cucurbitacin C content in the dihaploid progeny derived from the F₁ generation of a cross between a bitter, spider-mite-resistant cucumber line and a bitter-free, spider-mite-susceptible line. The ratio of the number of bitter to bitter-free dihaploids conformed to the expected 1:1 ratio, based on a monogenic segregation pattern. Genetic analysis ascribed 69% of the variance of the difference in spider mite survival rate to the bitterness locus. Within the group of bitter dihaploids, cucurbitacin C content was significantly correlated with spider mite resistance. Thus, a quantitative relationship between cucurbitacin C content and spider mite resistance could be established.     

Insect feeding and oviposition deterrents from western red cedar foliage

The feeding deterrent activity of fractions from the foliage of western red cedar,Thujaplicata Donn, was studied in laboratory bioassays using the white pine weevil,Pissodes strobi Peck, as a test insect. The most active fraction was the volatile mixture that comprises the leaf oil of this tree species. Further fractionation of the leaf oil indicated feeding deterrent activity in the monoterpene hydrocarbon, thujone, and terpene alcohol fractions. When tested alone, both (–)-3-isothujone and (+)-3-thujone, which made up 75–88% and 5–10% of the leaf oil, respectively, deterred feeding by the weevils. Western red cedar leaf oil also showed antifeedant activity with the alder flea beetle,Altica ambiens (Le Conte), and served as an oviposition deterrent for the onion root maggot,Hylemya antiqua Meigen. The leaf oil, however, had no inhibitory effect on the feeding of the leaf roller,Epinotia solandriana L., and the red-backed sawfly,Eriocampa ovata L.Research supported by the Natural Science and Engineering Research Council, Canada, Co-op Grant No. A0243 and Operating Grant Nos. A3881 and A3706, and by the British Columbia Ministry of Labour Youth Employment Program.     

Analysis of trichome exudate from mite-resistant geraniums

Trichome exudate from mite-resistant geraniums (Pelargonium horlorum) was analyzed, principally by mass spectrometry and NMR spectroscopy. The exudate was found to consist of two anacardic acid derivatives,o-pentadecenylsalicylic acid ando-heptadecenylsalicylic acid. Bioassays established a moderate toxicity of these compounds to the two-spotted spider mite,Tetranychus urticae. The production of these compounds in geraniums was correlated with the two complementary dominant genes previously reported for host resistance to spider mites.     

Behavior ofHeliothis virescens (F.) in presence of oviposition deterrents from elderberry

Extracts prepared from elderberry,Sambucus simpsonii Rehd., leaves with either acetone, dichloromethane, distilled water, ethanol, hexane, or methanol deterred oviposition byHeliothis virescens (F.) on treated substrates in the laboratory. Doses of the aqueous extract equivalent to as little as 0.8 mg of leaves/cm2 of oviposition substrate were effective in reducing egg deposition. There was no significant difference in the mean number of landings on extract-treated and untreated surfaces. When either the antennae, proboscis, or the metathoracic legs were removed from female moths, there was no significant effect on oviposition on paper towels treated with elderberry leaf-water extract in laboratory bioassays, but in field cages, moths without these appendages deposited significantly fewer eggs on treated leaves of tobacco plants, a preferred host. There was no evidence that elderberry leaf-water extract affected mating byH. virescens.Lepidoptera: Noctuidae.Mention of a commercial or proprietary product does not constitute an endorsement by the USDA.     

The Involvement of Volatile Infochemicals from Spider Mites and from Food-Plants in Prey Location of the Generalist Predatory Mite <Emphasis Type="Italic">Neoseiulus californicus</Emphasis>

We investigated volatile infochemicals possibly involved in location of the generalist predatory mite Neoseiulus californicus to plants infested with spider mites in a Y-tube olfactometer. The predators significantly preferred volatiles from lima bean leaves infested with Tetranychus urticae to uninfested lima bean leaves. Likewise, they were attracted to volatiles from artificially damaged lima bean leaves and those from T. urticae plus their visible products. Significantly more predators chose infested lima bean leaves from which T. urticae plus their visible products had been removed than artificially damaged leaves, T. urticae, and their visible products. These results suggest that N. californicus is capable of exploiting a variety of volatile infochemicals originating from their prey, from the prey-foodplants themselves, and from the complex of the prey and the host plants (e.g., herbivore-induced volatiles). We also investigated predator response to some of the synthetic samples identified as volatile components emitted from T. urticae-infested lima bean leaves and/or artificially damaged lima bean leaves. The predators were attracted to each of the five synthetic volatile components: linalool, methyl salicylate, (Z)-3-hexen-1-ol, (E)-2-hexenal, and (Z)-3-hexenyl acetate. The role of each volatile compound in prey-searching behavior is discussed.     

Induction of Direct and Indirect Plant Responses by Jasmonic Acid, Low Spider Mite Densities, or a Combination of Jasmonic Acid Treatment and Spider Mite Infestation

Jasmonic acid (JA) and the octadecanoid pathway are involved in both induced direct and induced indirect plant responses. In this study, the herbivorous mite, Tetranychus urticae, and its predator, Phytoseiulus persimilis, were given a choice between Lima bean plants induced by JA or spider mites and uninduced control plants. Infestation densities resulting in the induction of predator attractants were much lower than thus far assumed, i.e., predatory mites were significantly attracted to plants that were infested for 2 days with only one or four spider mites per plant. Phytoseiulus persimilis showed a density-dependent response to volatiles from plants that were infested with different numbers of spider mites. Similarly, treating plants with increasing concentrations of JA also led to increased attraction of P. persimilis. Moreover, the duration of spider mite infestation was positively correlated with the proportion of predators that were attracted to mite-infested plants. A pretreatment of the plants with JA followed by a spider mite infestation enhanced the attraction of P. persimilis to plant volatiles compared to attraction to volatiles from plants that were only infested with spider mites and did not receive a pretreatment with JA. The herbivore, T. urticae preferred leaf tissue that previously had been infested with conspecifics to uninfested leaf tissue. In the case of choice tests with JA-induced and control leaf tissue, spider mites slightly preferred control leaf tissue. When spider mites were given a choice between leaf discs induced by JA and leaf discs damaged by spider mite feeding, they preferred the latter. The presence of herbivore induced chemicals and/or spider mite products enhanced settlement of the mites, whereas treatment with JA seemed to impede settlement.     

Vitamin a deficiency modifies response of predatory miteAmblyseius potentillae to volatile kairomone of two-spotted spider mite,Tetranychus urticae

A volatile kairomone of the two-spotted spider mite,Tetranychus urticae, elicits a searching response of the phytoseiid predatorAmblyseius potentillae, only when the predator is reared on a carotenoid-free diet. However, after addition of crystalline -carotene or vitamin A acetate to the predator's rearing diet this searching response was absent. Because vitamin A and -carotene are indispensable nutrients for diapause induction, the carotenoid-deficient predators increase their fitness by searching for two-spotted spider mites, when other spider mites are unavailable. Two-spotted spider mites, among others, contain the carotenoids required for diapause induction, but are an inferior prey due to the dense webbing they produce. When the predators have carotenoids at their disposal, they do better by searching for other spider mites that are more profitable in terms of reproductive success. Such a prey is the European red spide mite,Panonychus ulmi. The volatile kairomone of this prey elicits a searching response of the predator whether it has a carotenoid deficiency or not.     

Chemical constituents and inhibitory activities of essential oils fromCyperus brevifolius andC. kyllingia

Cyperus brevifolius andC. kyllingia are two common weeds in Hawaii. The underground parts, including the rhizomes and roots, contain allelopathic essential oils, which may contribute to the aggressive spread of these weeds in grasslands and lawns. Although morphologically similar,C. kyllingia contains more essential oils thanC. brevifolius. Also, the former is rich in terpenes, including -cyperone, -selinene, and -humulene, while the latter is rich in C₁₇ to C₂₅ n-paraffins. These chemical differences agree with their inhibitory activities against indicator species and the general observation thatC. kyllingia is the more prevalent weed of the two.On leave from the Department of Agricultural Chemistry, Kinki University, Osaka, Japan.     

Effects ofneo-clerodane diterpenes fromTeucrium on feeding behavior of colorado potato beetle larvae

Treatment of potato leaf disks with fourneo-clerodane diterpenes fromTeucrium (eriocephalin, teucrin-A, teucvin, and teuscorolide) significantly reduced feeding by larvae ofLeptinotarsa decemlineata (Colorado potato beetle). Choice and no-choice tests suggest that teuscorolide acts as a feeding deterrent, whereas the antifeedant activity of teucrin-A, teucvin, and eriocephalin is likely associated with a toxic mode of action. Nutritional tests, antifeedant simulation assays, and posttreatment studies confirmed that teucrin-A can be categorized by its mode of action as a toxin, rather than as a feeding deterrent.     

Antifungal activity of volatile fractions of essential oils from four aromatic wild plants in israel

Essential oils were extracted fromMajorana syriaca, Satureja thymbra, Micromeria fruticosa, andSalvia triloba, and their volatile fractions were tested for their antifungal activity against the soil-borne pathogensFusarium oxysporum andMacrophomina phaseolina and the foliar pathogensBotrytis cinerea andExserohilum turcicum. Results showed a fungistatic effect of 1, 2.5, and 5l of the various essential oils on fungal mycelium growth. The most significant effect was exerted by essential oils extracted fromM. syriaca, which inhibited the growth ofB. cinerea by 44% and of all the other fungi tested by 100%.Contribution from the Agricultural Research Organization, the Volcani Center, Bet Dagan, Israel. No. 3555-E, 1992 series.     

Effect of some leaf essential oil phenotypes from coastal redwood on growth of its predominant endophytic fungus,Pleuroplaconema sp.

Experiments were performed to assess the effect of four foliar essential oil phenotypes from a coastal redwood (Sequoia sempervirens) population on isolates ofPleuroplaconema sp., its ubiquitous endophytic fungus. Isolates were exposed to essential oils extracted from their trees of origin and from other trees. The hypotheses tested were: (1) redwood leaf essential oils extracted from distinct trees would have a differential effect onPleuroplaconema sp. growth, and (2) growth of isolates from a particular tree would be differentially affected when exposed to essential oil phenotypes different from that of their tree of origin. The essential oil phenotypes were differentially inhibitory, but the pattern of inhibition did not support the second hypothesis.Pleuroplaconema sp. showed low average tolerance to all of the essential oils; two phenotypes reduced growth 70–80% and the other two 50–60% at the dose tested. The overall growth response of individual isolates to all treatments suggests that more than one fungus genotype per tree was represented in the experiment. The variability in tolerance of individual isolates to the essential oils was low for three phenotypes. The low tolerance ofPleuroplaconema sp. to redwood essential oils, in spite of its predominance and specialization in this conifer, is discussed considering: (1) the possible pathogenic ancestry of this fungus, and (2) that essential oil phenotypes may be important in controlling the activity ofPleuroplaconema sp. after it colonizes the leaf.     

Fumigant toxicity of essential oils against four major stored-product insects

The fumigant toxicity of 28 essential oils extracted from various spice and herb plants and some of their major constituents were assessed for adult coleopteransRhyzopertha dominica, Oryzaephilus surinamensis, Tribolium castaneum, andSitophilus oryzae. Three groups of active materials were distinguished: (1) The compounds terpinen 4-ol, 1,8-cineole, and the essential oils of three-lobed sage, sage, bay laurel, rosemary, and lavender were most active againstR. dominica; (2) The compounds linalool,-terpineol, and carvacrol and the essential oils of oregano, basil, Syrian marjoram, and thyme were most active againstO. surinamensis; and (3) the compound 1,8-cineole and the essential oils anise and peppermint were active againstT. castaneum.     

Critical Zn concentration for essential oil yield and menthol concentration of Japanese mint

The effect of different concentrations of Zn nutrient application on Japanese mint (Mentha arvensis L.) was studied under glasshouse conditions. Zn application stimulated the dry matter production, essential oil concentration and menthol concentration of Japanese mint. Zn supplies of 0.05µg ml^–1 were required for maximum responses in dry matter yield and oil concentration. Significantly positive interrelationships were observed among fresh herb yield, dry matter yield and menthol concentration in the oil. Graphical analyses of Cate and Nelson model indicated the critical Zn concentration in leaves to be 28µg g^–1 on a dry matter basis and in the solution culture 0.0475µg ml^–1 on the basis of Zn concentration in leaves.     

Devil's-claw (Proboscidea louisianica), essential oil and its components

The potential allelopathic activity of devil's-claw [Proboscidea louisianica (Mill.) Thellung] essential oil and a few of the compounds it contains on the elongation of cotton (Gossypium hirsutum L.) and wheat (Triticum aestivum L.) radicles was studied using a Petri dish bioassay. Essential oil was collected by steam distillation using an all-glass-Teflon assembly. Ether extracts of the steam distillates from fresh devil's-claw were inhibitory to cotton and wheat radicle elongation. The following six components of devil's-claw essential oil identified by CGC-MS-DS were inhibitory to cotton and/or wheat at a concentration of 1 mM: vanillin, piperitenone, -cadinene,p-cymen-9-ol, -bisabolol, and phenethyl alcohol.     

The Response of Phytoseiulus persimilis to Spider Mite-Induced Volatiles from Gerbera: Influence of Starvation and Experience

When leaves of the ornamental crop Gerbera jamesonii are damaged by the spider mite Tetranychus urticae, they produce many volatile compounds in large quantities. Undamaged gerbera leaves produce only a few volatiles in very small quantities. In the headspace of spider mite-damaged gerbera leaves many terpenoids are present, comprising 65% of the volatile blend. In addition, a number of nitrogen containing compounds, such as oximes and nitriles, are produced.We studied the attraction of P. persimilis to the volatiles from spider mite-damaged gerbera leaves and how attraction is affected by starvation and previous experience. Phytoseiulus persimilis that were reared on spider mites (T. urticae) on Lima bean were not attracted to spider mite-induced volatiles from gerbera. Starvation did not influence the predator's response to these volatiles. In contrast, predators that were reared on spider mites on gerbera leaves were strongly attracted to volatiles from spider mite-infested gerbera. This was found also for predators that originated from a culture on spider mite-infested bean and were offered six days of experience with spider mites on gerbera leaves.     

Activation of soil respiration and shift of the microbial population balance in soil as a response to Lavandula stoechas essential oil

Lavandula stoechas, a native plant of Greece, is rich in essential oil and fenchone is its major constituent. We examined the effect of the essential oil and its main constituents on soil metabolism and microbial growth. Addition of the essential oil or fenchone to soil samples induced a remarkable increase in soil respiration. This was accompanied by an increase in the soil bacterial population of three orders of magnitude. This sizable population was not qualitatively similar to that of the control soil samples. One bacterial strain dominated soil samples treated with L. stoechas essential oil or fenchone. By use of the disk diffusion assay, we evaluated the capacity of three bacterial strains that we isolated from the soil samples, as well as Escherichia coli and Bacillus subtilis (reference strains), to grow in the presence of the essential oil and three of its main constituents (fenchone, cineol, -pinene). The substances tested did not inhibit the growth of the strain found to dominate the bacterial populations of treated soil samples; they severely inhibited B. subtilis. The other two isolated strains could also grow in liquid cultures in the presence of different quantities of essential oil or fenchone. Addition of fenchone at the end of the exponential phase increased the cell numbers of the strain that dominated the bacterial populations of treated soil samples, indicating use of the substrate added. On the basis of these results, we propose a scheme of successional stages during the decomposition process of the rich-in-essential-oil litter of aromatic plants that abound in the Mediterranean environment.     

A study on the extraction of essential oil of Persian black cumin using static supercritical CO2 extraction,and comparison with hydro-distillation extraction method

The essential oil of Persian black cumin was extracted using static supercritical CO₂ technique at different temperatures, extraction times, and number of extractions. The composition of extracted oil was measured by GC-MS analysis and 25 components were identified. It was found that the oil recovery was reduced by increasing the temperature. Maximum recovery was achieved at two-step extraction that was about 49%. Both dissolution rate and solubility limited the oil recovery at the tested extraction conditions. The oxygenate components have less dissolution rate than the terpenes. The application of experimental data for design of an efficient dynamic extraction system was discussed.