Aphid deterrence by glucose esters in glandular trichome exudate of the wild tomato,Lycopersicon pennellii

Settling of the potato aphid,Macrosiphum euphorbiae, on feeding membranes was deterred by methanolic leaf rinses ofLycopersicon pennellii, or of its F₁ with tomato,L. esculentum. The active compounds in theL. pennellii rinsates were identified as 2,3,4-tri-O-acylglucoses bearing short to medium chain length fatty acids. These compounds are localized in the glandular exudate of the type IV trichomes and may accumulate to levels in excess of 400 g/cm². In choice assays, purified glucose esters fromL. pennellii reduced aphid settling at concentrations as low as 25 g/cm²; at concentrations of 150 g/cm² or more, all aphids avoided treated areas. Glucose esters were also active in deterring aphid settling in no-choice assays. At 100 g/ cm², these esters resulted in increased levels of mortality after 48 hr.     

Leaf surface chemicals fromNicotiana affecting germination ofPeronospora tabacina (adam) sporangia

A bioassay was used to evaluate the effects of cuticular leaf components, isolated fromN. tabacum, N. glutinosa (accessions 24 and 24a), and 23other Nicotiana species, on germinationof P. tabacina (blue mold). The leaf surface compounds included- and-4,8,13,-duvatriene-l,3-diols (DVT-diols), (13-E)-labda-13-ene-8-,15-diol (labdenediol), (12-Z)-labda-12,14-diene-8-ol (cis-abienol), (13-R)-labda-8,14-diene-13-ol (manool), 2-hydroxymanool, a mixture of (13-R)-labda-14-ene-8,13-diol (sclareol), and (13-S)-labda-14-ene-8,13-diol (episclareol), and various glucose and/or sucrose ester isolates. The above in acetone were applied onto leaf disks of the blue moldsusceptibleN. tabacum cv. TI 1406, which was then inoculated with blue mold sporangia. Estimated IC₅₀ values (inhibitory concentration) were 3.0g/cm² for-DVT-diol, 2.9/cm² for-DVT-diol, 0.4g/cm² for labdenediol and 4.7g/cm² for the sclareol mixture. Manool, 2-hydroxymanool, andcis-abienol at application rates up to 30g/cm² had little or no effect on sporangium germination. Glucose and/or sucrose ester isolates from the cuticular leaf extracts of 23Nicotiana species and three different fractions fromN. bigelovii were also evaluated for antimicrobial activity at a concentration of 30g/cm². Germination was inhibited by >20% when exposed to sugar esters isolated fromN. acuminata, N. benthamiana, N. attenuata, N. clevelandii, andN. miersii, and accessions 10 and 12 ofN. bigelovii. These results imply that a number of compounds may influence resistance to blue mold in tobacco.     

Fate of quinolizidine alkaloids through three trophic levels:Laburnum anagyroides (Leguminosae) and associated organisms

The quinolizidine alkaloids (QA) of golden rain,Laburnum anagyroides, and those of phytophagous insects associated with the plant, as well as of parasitoids of the latter, were analyzed by capillary GLC and GLC-MS. The alkaloid content in samples of vegetative plant parts was high at the beginning of the season, then decreased, while that of reproductive organs was high throughout flowering, pod formation, and maturation. The analyses showed that the QA of the plant passed through two higher trophic levels (herbivorous insects and their parasitoids) and that the alkaloid pattern changed little during the passage. The alkaloids were present in two phytophagous insect species associated with golden rain: the predispersal seed predator,Bruchidius villosus [5–13g/g fresh weight (fw)], andAphis cytisorum (182–1012g/g fw), an aphid that feeds on shoots, leaves, and inflorescences. Braconid and chalcidoid parasitoids emerging from the bruchid host also contained alkaloids (1.3–3g/g fw), as did three foraging ant species,Lasius niger, Formica rufibarbis, andF. cunicularia (45g/g fw), that visited the aphid colonies or honeydew-covered leaves of aphid-infested plants. The hypothesis that developing bruchid larvae and/or the plant manipulate QA supply to infested seeds was not supported, because QA content of leftover endosperm in seeds after bruchid development was similar to that of uninfested seeds. The frass of developing bruchid larvae was rich in QA (31g/ g dry weight). While aphids sequestered, the bruchid larvae took up and eliminated QA with the frass without chemical transformation.     

Effect of fungal metabolite peramine and analogs on feeding and development of argentine stem weevil (Listronotus bonariensis)

Peramine, a pyrrolopyrazine alkaloid produced by the fungal endophyte of perennial ryegrassAcremonium lolii, deterred the feeding of both adults and larvae of the graminacious herbivore, the Argentine stem weevil (Listronotus bonariensis), at 0.1 g/g and 10 g/g, respectively. In a no-choice test fewer stem weevil larvae fed and developed on diet containing as little as 2 g/g peramine. The proportion of larvae which did not develop beyond the first instar was higher on diet containing peramine and appeared to be due to a higher proportion of larvae which did not feed. For larvae which fed on the peramine-containing diet, feeding scores and times to pupation were not significantly different from those of controls. A number of simple peramine analogues showed feeding-deterrent activity against adult weevils, indicating the importance of the pyrrolopyrazine ring system of peramine in determining feeding-deterrent activity.     

Role of the isoflavonoid coumestrol in the constitutive antixenosic properties of “Davis” soybeans against an oligophagous insect,the mexican bean beetle

The antixenosic properties of the isoflavonoid, coumestrol, were tested in dual-choice leaf disk bioassays with the Mexican bean beetle (Epilachna varivestis Mulsant).E. varivestis preferred the methanol-r,reated (solvent-control) disk when the coumestrol concentration was 1.8 or 0.9/leaf disk. No preference was observed between the coumestrol-treated and the solvent-control disks when the coumestrol concentration was higher, at 3.6, or lower, at 0.45g/leaf disk. Coumestrol alone clearly is not responsible for the significant constitutive antixenosic properties of Davis soybeans,Glycine max (L.) Merrill, because the amount of coumestrol in these plants is significantly less than the minimum concentration which was antixenosic in this study. However, it might contribute to a constitutive antixenosis in Davis involving a profile of allelochemicals. A computer-aided densitometer, adapted to measure the leaf disk area, increased the resolution of the leaf area 250 (X)-fold as compared to the standard LI-COR leaf area meter.     

Defensive secretions of three species ofAcilius (Coleoptera: Dytiscidae) and their seasonal variations as determined by high-pressure liquid chromatography

A rapid, sensitive, stable, and quantitative high-pressure liquid chromatographic technique was developed for the analysis of defensive secretions obtained from the pygidial and prothoracic glands of dytiscids. Methods were developed for both normal phase (Porasil) and reverse phase (Bondapak C₁₈) columns. The applicability of this technique was demonstrated when defensive compounds ofAcilius semiculcatus, A. sylvanus andA. mediatus were isolated, identified, and quantitated. No major differences were found in the composition of the defensive secretions between the three species. The seasonal defensive titer ofA. semisulcatus was determined from June through October 1977. The pygidial defensive agents (benzoic acid,p-hydroxybenzaldehyde, and methylp-hydroxybenzoate varied from 9.0 to 67.8 g and exhibited a maximum in July, and a steroid from the prothoracic gland varied from 7.1 to 33.2 g and was maximum in October.     

Isolation,characterization and activity of phytotoxic compounds from quackgrass [Agropyron repens (L.)Beauv.]

Previous experiments showed that legumes grown in the presence of living or herbicidally treated quackgrass residues or extracts exhibited reduced seedling root and shoot growth and decreased nodulation and nitrogen fixation. Aqueous extracts of quackgrass shoots were most inhibitory to plant growth. Upon sequential partitioning of an aqueous extract of quackgrass shoots, the ether extract possessed the most activity and caused 50% reductions in radicle elongation of eight crop and weed species at concentrations of less than 240 g/ml (small-seeded species) and 1000 g/ml (large-seeded species). Snapbeans (Phaseolus vulgaris L. Bush Blue Lake) grown aseptically in agar containing an ether extract at 100 and 200 g/ml exhibited severe root browning, lack of root hair formation, and a two- to three-fold reduction in root and shoot dry weights. The ether extract of quackgrass shoots had no inhibitory effect on the growth of fourRhizobium species in Petri dishes or two species in broth culture. Inhibitors present in the ether extract may influence the legumeRhizobium symbiosis indirectly by reducing legume root growth and root hair formation. The ether extract of quackgrass shoots was separated using high-pressure liquid, thin-layer, and liquid column chromatography in an attempt to isolate and identify the inhibitors responsible for the inhibition of seedling growth. Two closely related flavonoid inhibitors were isolated from the ether extract. One was identified as 5,7,4-trihydroxy-3,5-dimethoxyflavone (tricin). Both flavonoids caused 50% inhibition of radicle elongation in cress (Lepidium sativum L. Burpee curly) seeds at concentrations of less than 125 g/ml. Both flavonoids were found in ether extracts of quackgrass shoots and rhizomes, but the largest amounts of both compounds occurred in quackgrass shoots collected from the field.Journal article No. 11887 of the Michigan Agricultural Experiment Station.     

Influence of tobacco leaf surface chemicals on germination ofPeronospora tabacina adam sporangia

Chromatographic procedures were utilized to isolate and purify components of tobacco cuticular extracts and leaf surface chemicals.In vitro microbial bioassays determined the influence of these leaf surface compounds on germination and germ tube morphology ofP. tabacina sporangia, the tobacco blue mold pathogen, and to a lesser extentAlternaria alternata, the tobacco brown spot pathogen. Exposure to 10 g/cm² of - and -duvatrienemonols, sucrose esters, or hydrocarbons did not inhibit germination, whereas germination was significantly decreased bycis-abienol.cis-Abienol did not inhibit sporangial germination when combined with sucrose esters or hydrocarbons at a combined 10 g/cm². Germination of sporangia was completely inhibited by - and -duvatrienediols. In contrast to a previous report, -DVT-diol was more inhibitory than the isomer. Toxic effects of the DVT-diols were not altered by pH. Diluting the DVT-diols to less than 0.1 g/cm² resulted in a small but significant stimulation of germination. Previously, the DVT-diols had been identified only as inhibitory toP. tabacina. None of the leaf surface chemicals affected germination ofA. alternata conidia.Present Address: Department of Forestry, Biltmore Hall, North Carolina State University, P.O. Box 8002, Raleigh, North Carolina 27695-8002.     

Synergistic Sex Pheromone Components of White-Spotted Tussock Moth, Orgyia thyellina

In 1996, the exotic white-spotted tussock moth (WSTM), Orgyia thyellina (Lepidoptera: Lymantriidae), was discovered in Auckland, New Zealand. Because establishment of WSTM would threaten New Zealand's orchard industry and international trade, eradication of WSTM with microbial insecticide was initiated. To monitor and complement eradication of WSTM by capture of male moths in pheromone-baited traps, pheromone components of female WSTM needed to be identified. Coupled gas chromatographic–electroantennographic detection analysis of pheromone gland extract revealed several compounds that elicited responses from male moth antennae. Mass spectra of the two most EAD-active compounds suggested, and comparative GC-MS of authentic standards confirmed, that they were (Z)-6-heneicosen-11-one (Z6–11-one) and (Z)-6-heneicosen-9-one, the latter termed here thyellinone. In field experiments in Japan, Z6–11-one plus thyellinone at a 100:5 ratio attracted WSTM males, whereas either ketone alone failed to attract a single male moth. Addition of further candidate pheromone components did not enhance attractiveness of the binary blend. Through the 1997–1998 summer, 45,000 commercial trap lures baited with 2000 g of Z6–11-one and 100 g of thyellinone were deployed in Auckland towards eradication of the residual WSTM population.Dedicated to my dear mother in honor of her 75th birthday     

Evaluation of Synergism in the Feeding Deterrence of Some Furanocoumarins on Spodoptera littoralis

The phagodepression activity of five furanocoumarins (FC), bergapten, xanthotoxin, psoralen, imperatorin, and angelicin, has been studied against larvae of Egyptian cotton leafworm Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae) using a leaf-disk choice bioassay. The dose range used was 0–10 g/cm² for linear furocoumarins and 0–30 g/cm² for angelicin, the angular furanocoumarin. Dose–feeding deterrency activity correlations were governed by various sigmoidal functions, except in the case of imperatorin and bergapten, which had dose–response curves showing irregular traces with two maxima. All five FCs induced various degrees of phagodepression in S. littoralis; at 3 g/cm², the relative feeding deterrence was bergapten = xanthotoxin > psoralen = imperatorin = angelicin. Structure–activity correlations indicated that a methoxy group on C-5 or C-8 enhanced the activity. Comparison of experimental feeding deterrence of binary mixtures of imperatorin with xanthotoxin, bergapten, or psoralen at various relative concentrations with the calculated additive activity of each combination indicated that a proportion of 40% or more of imperatorin may exert a greater antifeedant effect on S. littoralis than the sum of individual compounds. The effect of angelicin also was examined in combination with psoralen, both of which are present in Psoralea plants. Their mixtures yielded a clear synergistic effect in the 20–80% angelicin range (coactivity coefficient = 124–133). By contrast, the effect of angelicin on xanthotoxin was only additive. In the dose–response curves of imperatorin/bergapten combinations, synergism was found at >60% imperatorin relative concentration and 1 g/cm², whereas lower proportions led to antagonism. The threshold between the two opposing effects was found to depend on the total FC concentration employed. Some natural systems contain FCs in the range of synergistic proportions recorded here and, thus, may have been produced by the host to increase its defensive effect at a lower metabolic cost.     

Behavioral response of male white peach scale to the sex pheromone, (R,Z)-3,9,-dimethyl-6-isopropenyl-3,9-decadien-1-ol propionate and corresponding alcohol

Males of the white peach scale,Pseudaulacaspis pentagona (Tar-gioni-Tozzetti), in Florida differ from this scale in France in their responses to putative pheromonal chemicals presented in a laboratory bioassay. Males from Florida were attracted to, and exhibited sexual (coputatory) behaviors at, the locus of evaporation of (R,Z)-3,9-dimethyl-6-isopropenyl-3,9-deca-dien-1-ol propionate (P) (previously identified from effluvia of Florida females). Addition of the corresponding primary alcohol (A) to the propionate did not alter the attraction of Florida males to the synthetic P and did not alter their sexual responses from those exhibited by males exposed to P alone. In contrast, the effluvia from French scales has been reported to contain P and A, and the alcohol has been reported in laboratory studies to be required to release sexual behavior in French males. This suggests that the conspecific status of the scale in Florida and France should be reexamined. Field trap baits with 2.5 g of a 1 1 mixture of P and A captured significantly fewer Florida males than traps baited with 1.25 g of P alone, but traps similarly baited with 0.125 g of each material captured the same number of insects as traps baited with 0.125 g of P alone.Mention of a commerical or proprietary product in this paper does not constitute an endorsement of that product by the USDA.     

Effect of diacetyl piquerol on H+-ATPase activity of microsomes fromIpomoea purpurea

The effect of an allelopathic compound, diacetyl-piquerol on the H⁺ -ATPase activity of the microsomal fraction from the radicles of a common weedIpomoea purpurea was studied. The diacetyl-piquerol inhibited the germination and radicle growth fromI. purpurea; the radicle growth was increasingly inhibited (10% to 100%) as piquerol concentrations were raised (10 M to 1000 M). The H⁺-ATPase activity was inhibited (48%) by 500 M diacetyl-piquerol, and this inhibition was higher in plasma membrane ATPase (67.2%) than in tonoplast membrane ATPase (31.4%). Additional studies of the precise physiological mechanisms of interference caused by allelopathic compounds are needed.This study was sponsored by Project PCECCCNA-050954 of Consejo Nacional de Ciencia y Tecnología (CONACyT).     

Synergism of Polygodial and trans-Cinnamic Acid on Inhibition of Root Elongation in Lettuce Seedling Growth Bioassays

A bicyclic sesquiterpene dialdehyde, polygodial did not inhibit root elongation up to a concentration of 12.5 g/ml in a lettuce seedling assay: trans-Cinnamic acid inhibited the elongation by 50% at 1.2 g/ml (8.1 M). The inhibitory activity of trans-cinnamic acid was enhanced 17-fold when used in combination with 6.25 g/ml (26.5 M) of polygodial. A decrease in the pH of the medium was observed during normal seedling growth, indicating transport of protons from the cells by a plasma membrane H⁺-ATPase. The inhibitory effect of trans-cinnamic acid on the elongation was reduced to some extent in 2 mM phosphate buffer (pH 7.0) during seedling growth. Although polygodial did not inhibit the activity of H⁺-ATPase in the plasma membrane fraction of roots in normally growing seedlings, a decrease in activity was found in the fraction obtained from seedlings incubated with 20 g/ml of polygodial. These results suggest that polygodial functions synergistically with trans-cinnamic acid in the inhibition of root elongation via restriction of proton transport from the cytoplasm of germinated cells.     

Behavioral responses of malePeriplaneta americana to periplanone B,a synthetic component of the female sex pheromone

Bioassays were performed on malePeriplaneta americana L. using concentrations of (±)-periplanone B of 10^–9-10^–3 g and a serial dilution of natural female sex pheromone extract. Synthetic (±)-periplanone B stimulated the complete repertoire of behavior released by the extract: increased rate of locomotion, upwind orientation, and the wingraising component of courtship display. Quantitative behavioral comparisons of the activity of natural extracts prepared by this and other laboratories are possible by the standardization of the stimulus in terms of g of (±)-periplanone B applied per assay.     

Antifungal polyoxygenated fatty acids fromAeollanthus parvifolius

Two polyoxygenated fatty acids with antifungal activity have been isolated from aerial parts ofAeollanthus parvifolius (Labiatae) using bioassay-guided isolation procedures. Spectroscopic analysis was used to identify the compounds as (Z)-4,9-diacetoxy-6,7-epoxy-5-hydroxy-8-oxododeca-2-enoic acid and (Z)-4,6,7,9-tetraacetoxy-5-hydroxy-8-oxododeca-2-enoic acid. Both of these compounds inhibited spore germination ofCladosporium cucumerinum. Minimum inhibitory doses were 1 µg and 5 µg, respectively, but only the former inhibited germination ofAspergillus niger at a dose of 5 µg. Neither compound exhibited antibacterial activity. (Z)-4,9-Diacetoxy-6,7-epoxy-5-hydroxy-8-oxododeca-2-enoic acid reduced the hyphal growth ofPythium ultimum. The mode of action was not resolved but did not involve either the disruption of the cell wall membrane or the inhibition of extracellular enzymes. Application of (Z)-4,6,7,9-tetraacetoxy-5-hydroxy-8-oxododeca-2-enoic acid to seedling plants did not give any protection against fungal attack, and indeed the compound appeared to be phytotoxic.     

Responses of male codling moths (Laspeyresia pomonella) to codlemone and other alcohols in a wind tunnel

The primary pheromone (E,E)-8,10-dodecadien-1-ol (I, codle-mone), 11 further alcohols, and binary blends of both were evaluated for attractiveness as defined by the percentage ofL. pomonella males showing oriented upwind flight terminated by landing at the source within 10 min after release. Sources of I were attractive from 10^–5 g to 10¹ g, with approx. 70% males responding at 10^–3–10^–1 g. Most other alcohols also showed attractiveness, but the dose-response curves differed greatly with respect to the range of effective lure doses as well as the maximum response level reached at any dose. (E,E)-7,9-Undecadien-1-ol (III) revealed a dose-response curve similar in shape to I but shifted towards higher concentrations. (E,E)-8,10-Tridecadien-1-ol (II) and (E)-8,10-undecadien-1-ol (IV) exhibited threshold values of 10^–5 g (same as for I) and were effective over, respectively, seven and nine decades of source load, but they did not reach a response level of 40% at any test amount. (E)-9,11-Dodecadien-1-ol (VI) and the monoenes (E)-8-, (E)-10-, and (Z)-10-dodecen-1-ol (VIII-X) showed weak attractivity restricted to one to three test doses. Upwind approaches that broke off a few centimeters from the source were rarely seen in tests with I but frequently occurred with some of the analogs. When combined with 10^–3 g of I, all alcohol analogs showed inhibitory properties, although the amounts required to obtain a significant lowering of response differed by up to 10⁵-fold. This amount was the lowest (10^–4 g) for the positional isomer VI, and the highest (10¹ g) for undecan-1-ol (XI) and dodecan-1-ol (XII). With some mixtures, the presence of the inhibitor appeared to cause an alteration in landing behavior. No synergistic effects were seen in these tests. The results are briefly considered with respect to the sensory perception of the test stimuli and the involvement of minor components in the female pheromone blend.     

Defense Secretion of Prorhinotermes simplex: Toxicity to Insecticide Susceptible and Resistant House Fly

(E)-1-Nitropentadec-1-ene (NPE), the main component of the defense secretion of Prorhinotermes simplex soldiers, is toxic to both insecticide-susceptible (S) as well as to insecticide-resistant (R) strains of the house fly, Musca domestica. The LD₅₀ is 11.7 g/female fly for the S strain and 9.7 g for the R strain. The same efficacy of NPE on R and S strains indicates a different mechanism of action compared to conventional chlorinated, organophosphorus, and pyrethroid insecticides. Termite nestmates are protected against NPE by a specific detoxification mechanism. 1-Nitropentadecane, the detoxification product of NPE is nearly nontoxic to house flies, and doses up to 160 g/fly caused only very low mortality.     

Caste-dependent pheromones in the head of the antTetramorium caespitum

The heads of maleT. caespitum contain 4-methyl-3-hexanol (1.7 g, only the erythro isomer(s) detected) and 4-methyl-3-hexanone (0.8 g). The heads of alate females contain 0.1 g of each compound, whereas only the alcohol (0.1 g) was found in the heads of workers. Both compounds act as attractants for the workers and their possible functions are discussed.'Chargé de Recherche du F.N.R.S.Chercheur qualifié du F.N.R.S.     

Evaluation of vetiver oil and seven insect-active essential oils against the Formosan subterranean termite

Repellency and toxicity of 8 essential oils (vetiver grass, cassia leaf, clove bud, cedarwood, Eucalyptus globules, Eucalyptus citrodora, lemongrass and geranium) were evaluated against the Formosan subterranean termite, Coptotermes formosanus Shiraki. Vetiver oil proved the most effective repellent because of its long-lasting activity. Clove bud was the most toxic, killing 100% of termites in 2 days at 50 g/cm². The tunneling response of termites to vetiver oil also was examined. Vetiver oil decreased termite tunneling activity at concentrations as low as 5 g/g sand. Tunneling and paper consumption were not observed when vetiver oil concentrations were higher than 25 g/g sand. Bioactivity of the 8 oils against termites and chemical volatility were inversely associated. Listed in decreasing order of volatility, the major constituents of the 8 oils were: eucalyptol, citronellal, citral, citronellol, cinnamaldehyde, eugenol, thujopsene, and both - and - vetivone. Vetiver oil is a promising novel termiticide with reduced environmental impact for use against subterranean termites.     

Sequestration of Host Plant Glucosinolates in the Defensive Hemolymph of the Sawfly Athalia rosae

Interactions between insects and glucosinolate-containing plant species have been investigated for a long time. Although the glucosinolate–myrosinase system is believed to act as a defense mechanism against generalist herbivores and fungi, several specialist insects use these secondary metabolites for host plant finding and acceptance and can handle them physiologically. However, sequestration of glucosinolates in specialist herbivores has been less well studied. Larvae of the turnip sawfly Athalia rosae feed on several glucosinolate-containing plant species. When larvae are disturbed by antagonists, they release one or more small droplets of hemolymph from their integument. This reflex bleeding is used as a defense mechanism. Specific glucosinolate analysis, by conversion to desulfoglucosinolates and analysis of these by high-performance liquid chromatography coupled to diode array UV spectroscopy and mass spectrometry, revealed that larvae incorporate and concentrate the plant's characteristic glucosinolates from their hosts. Extracts of larvae that were reared on Sinapis alba contained sinalbin, even when the larvae were first starved for 22 hr and, thus, had empty guts. Hemolymph was analyzed from larvae that were reared on either S. alba, Brassica nigra, or Barbarea stricta. Leaves were analyzed from the same plants the larvae had fed on. Sinalbin (from S. alba), sinigrin (B. nigra), or glucobarbarin and glucobrassicin (B. stricta) were present in leaves in concentrations less than 1 mol/g fresh weight, while the same glucosinolates could be detected in the larvae's hemolymph in concentrations between 10 and 31 mol/g fresh weight, except that glucobrassicin was present only as a trace. In larval feces, only trace amounts of glucosinolates (sinalbin and sinigrin) could be detected. The glucosinolates were likewise found in freshly emerged adults, showing that the sequestered phytochemicals were transferred through the pupal stage.