Chemical Defenses Promote Persistence of the Aquatic Plant Micranthemum umbrosum

Five of the most common macrophytes from an aquaculture facility with high densities of the herbivorous Asian grass carp (Ctenopharyngodon idella) were commonly unpalatable to three generalist consumers—grass carp and the native North American crayfishes Procambarus spiculifer and P. acutus. The rooted vascular plant Micranthemum umbrosum comprised 89% of the total aboveground plant biomass and was unpalatable to all three consumers as fresh tissues, as homogenized pellets, and as crude extracts. Bioassay-guided fractionation of the crude extract from M. umbrosum led to four previously known compounds that each deterred feeding by at least one consumer: 3,4,5-trimethoxyallylbenzene (1) and three lignoids: β-apopicropodophyllin (2); (−)-(3S,4R,6S)-3-(3′,4′-methylenedioxy-α-hydroxybenzyl)-4-(3″,4″-dimethoxybenzyl)butyrolactone (3); and (−)-hibalactone (4). None of the remaining four macrophytes produced a chemically deterrent extract. A 16-mo manipulative experiment showed that the aboveground biomass of M. umbrosum was unchanged when consumers were absent, but the biomass of Ludwigia repens, a plant that grass carp preferentially consumed over M. umbrosum, increased over 300-fold. Thus, selective feeding by grass carp effectively eliminates most palatable plants from this community and promotes the persistence of the chemically defended M. umbrosum, suggesting that plant defenses play critical yet understudied roles in the structure of freshwater plant communities.     

Chemical Constituents of the Aquatic Plant Schoenoplectus lacustris: Evaluation of Phytotoxic Effects on the Green Alga Selenastrum capricornutum

Forty-nine secondary metabolites were isolated from aqueous and alcoholic extracts of the aquatic plant Shoenoplectus lacustris. All compounds were characterized based on spectroscopic data. Eleven free and glycosylated low-molecular polyphenols, 17 cinnamic acid and dihydrocinnamic acid derivatives, 11 flavonoids, and 10 C₁₃ nor-isoprenoids were identified. The structure of the new compound, 1-benzoyl-glycerol-2-α-l-arabinopyranoside, was elucidated by 2D NMR experiments (COSY, HSQC, HMBC, NOESY). To evaluate potential phytotoxic effects, all compounds were tested on the green alga Selenastrum capricornutum, a unicellular organism commonly used in tests of toxicity as a bioindicator of eutrophic sites. The most active compound was (−)-catechin, showing an inhibition similar to that of the algaecide CuSO₄.     

Chemical Defense in the Plant Bug Lopidea robiniae (Uhler)

Secretions from the metathoracic glands (MTG) of the black locust bug, Lopidea robiniae (Uhler) (Heteroptera: Miridae) contained six major compounds, including (E)-2-hexenal, (E)-2-hexen-1-ol, (E)-2-octenal, (E)-2-octen-1-ol (E)-2-heptenal, and (Z)-3-octen-1-ol. Males and females did not differ significantly in the relative compositions of identified compounds. In feeding trials, six bird species [robin (Turdus migratorious), blue jay (Cyanocitta cristata), brown thrasher (Toxostoma rufum), killdeer (Charadrius vociferus), starling (Sturnus vulgaris), and house wren (Troglodytes aedon)] demonstrated feeding aversions towards L. robiniae, implying that black locust bugs are chemically defended. Bugs discharged the liquid contents of their MTG when attacked, thereby producing a strong and distinct odor. Some birds immediately ejected bugs out of their mouth after biting them, suggesting that the MTG secretion was a deterrent.     

Sex pheromone components of the buck moth Hemileuca maia

The sex attractant pheromone blend of Hemileuca maia (Lepidoptera: Saturniidae) from the vicinity of Baton Rouge, Louisiana, has been identified. The major component of the blend is (E10,Z12)-hexadeca-10,12-dienal (E10,Z12–16:Ald), in combination with the minor components (E10,Z12)-hexadeca-10,12-dien-1-ol (E10,Z12–16:OH), and (E10,Z12)-hexadeca-10,12-dien-1-yl acetate (E10,Z12–16:Ac). Ratios of the compounds in extracts of female pheromone glands varied around a mean of 100:7.4:6.3. None of the three components were attractive to male moths when tested as single components. Several other compounds were tentatively identified from female pheromone gland extracts, including E10,E12–16:Ald, E10,E12–16:OH, and E10,E12–16:Ac, but addition of these components, either alone or in combination, at biologically relevant rates, did not significantly increase the attractiveness of lures. The saturated analogs, hexadecanal, hexadecanol, and hexadecyl acetate, also were identified in gland extracts, but had no apparent effect as pheromone components.     

Attraction of Male European Tarnished Plant Bug, <Emphasis Type="Italic">Lygus rugulipennis</Emphasis> to Components of the Female Sex Pheromone in the Field

Previous work showed that females of the European tarnished plant bug, Lygus rugulipennis Poppius (Heteroptera: Miridae), produced three chemicals, hexyl butyrate, (E)-2-hexenyl butyrate, and (E)-4-oxo-2-hexenal, and that these were suspected to be components of the female sex pheromone. In field experiments, traps baited with blends of these chemicals dispensed from polyethylene vials and sachets failed to catch significant numbers of males. Here, we report more recent field experiments in which the chemicals were released from glass microcapillary tubes. A blend of hexyl butyrate and (E)-4-oxo-2-hexenal was significantly attractive to male L. rugulipennis. In addition, whereas the mixture of all three components attracted fewer L. rugulipennis males, this tertiary blend captured significantly greater numbers of males of the congeneric species Lygus pratensis than the binary mixture. The possible reasons for the success of the microcapillaries compared with other dispensers are discussed.     

Sex pheromone of the chokecherry leafroller moth,Sparganothis directana

(E)-9,11-Dodecadienyl acetate and (Z)-9,11-dodecadienyl acetate in conjunction with (E)-11-tetradecenyl acetate and (Z)-11-tetradecenyl acetate were found to comprise the sex pheromone ofSparganothis directana, based on chemical analysis, electroantennogram tests, and field trapping. (E)-9-Dodecenyl acetate and (Z)-9-dodecenyl acetate were also found in gland extracts but did not influence trap catches. The relative amounts of these compounds in the gland were 3521928 106, in the order named. Only (E)-9,1 1-dodecadienyl acetate, (E)-11-tetradecenyl acetate, and (Z)-11-tetradecenyl acetate were required for attraction of males to traps, dispensed in the relative amounts 501238, respectively.Lepidoptera: Tortricidae.Supported by National Science Foundation grant PCM 78-13241.     

Role of Ecological Variables in the Seasonal Variation of Flavonoid Content of Cistus ladanifer Exudate

The leaves and photosynthetic stems of Cistus ladanifer, a plant that colonizes arid lands, secrete an exudate that shows a large seasonal variation in its flavonoid content. The maximum secretion of flavonoids in the exudate is produced during summer, increasing approximately three-to fourfold with respect to the secretion measured in spring. Summer is the season in which the plant suffers the greatest stress from environmental physical variables such as UV irradiation, high temperatures, and hydric stress. Studies were conducted in plants from several locations, which were selected considering daily UV irradiation (open or shaded areas), annual precipitation, and annual average maximum and minimum temperatures. Additional studies to control UV irradiation, drought, and temperature separately were performed with C. ladanifer plants growing in a glasshouse and in a culture room. The UV irradiation was found to be the major inducer of the enhanced flavonoid secretion during summer, because no significant increase of flavonoid secretion during summer was observed when the C. ladanifer plants in the field were covered with a Plexiglas box (total UV absorption below 380 nm). These results support an ecophysiological role of the flavonoids in the exudate to protect the plant against the damaging effects of UV irradiation. The culture room experiments confirmed this point and also showed that the induction of flavonoid secretion by UV irradiation is synergistically augmented by drought. The glasshouse and culture room experiments showed drought and high temperatures (between 30° and 45°C) to correlate with the summer increase of the more methylated flavonoids (kaempferols and 7-methylated apigenins) in the exudate. Because these more methylated flavonoids have higher hydropathy than the less methylated, these results suggest that the secretion of more methylated flavonoids is part of the defense mechanism of the plant against the hydric stress of summer.     

Sex-Related Perception of Insect and Plant Volatiles in Lygocoris pabulinus

We recorded electroantennograms of male and female Lygocoris pabulinus antennae to 63 insect and plant volatiles. EAGs were between 100 and 500 V. Overall, male EAGs were about twice the size of female EAGs. In both sexes, largest EAGs were recorded to (E)-2-hexenyl butanoate and (E)-2-hexen-1-ol. Response profiles were similar in both sexes. However, male antennae were more sensitive to a number of esters, especially the butanoates and pentanoates. Female antennae were more sensitive to nine of the 19 plant volatiles, i.e., to hexan-1-ol, heptan-1-ol, 1-octen-3-ol, 2-heptanone, (R)-carvone, linalool, geraniol, nerol, and methyl salicylate. Sexual differences in responses suggest that males are more sensitive to insect-produced pheromone-type compounds, whereas females are more sensitive to plant compounds for their orientation towards oviposition sites.     

Production and Predator-Induced Release of Volatile Chemicals by the Plant Bug Lygus hesperus

Both sexes of adult western tarnished plant bug, Lygus hesperus Knight (Heteroptera: Miridae), released three volatile chemicals in relatively large amounts when attacked by ants (Pogonomyrmex rugosus and Solenopsis xyloni) or when grabbed by forceps, as determined by solid-phase microextraction (SPME) and gas chromatography–mass spectrometry (GC–MS). The relative amounts of the volatile compounds, hexyl butyrate, (E)-4-oxo-2-hexenal, and (E)-2-hexenyl butyrate, absorbed by SPME as a percentage of the largest were 100%, 44%, and 4%, respectively, from females, and 83%, 37%, and 3% from males. Both ant species were repelled by the defensive discharges (confirmed by SPME) when the ants attacked L. hesperus adults. Sexually mature L. hesperus were individually extracted in pentane to quantify the mean amounts of hexyl butyrate (14.9 μg/female; 10.3 μg/male), (E)-4-oxo-2-hexenal (2.7 μg/female; 3.1 μg/male), and (E)-2-hexenyl butyrate (1.2 μg/female; 0.6 μg/male). (E)-4-Oxo-2-hexenal was unstable in solvent when in contact with a macerated adult, but relatively stable when the solution was decanted within minutes. The production of the three major volatile components began soon after the emergence of the adult and amounts increased for about 5–10 d with little or no increase thereafter. Minor additional constituents were cross-correlated in many cases with the three major ones. A cost of defensive secretion is suggested for females but not for males, because heavier females produced more volatile compounds than lighter females. The initial discharge percentage, defined as the proportion of volatile compounds initially present that is discharged to defend against predation was estimated at about 50% in males and 70% in females. Newly eclosed adults did not produce volatile chemicals until 2 d after molting.     

Investigation of Long-Range Female Sex Pheromone of the European Tarnished Plant Bug, Lygus rugulipennis: Chemical, Electrophysiological, and Field Studies

The European tarnished plant bug, Lygus rugulipennis, is an important pest of agricultural and horticultural crops throughout Europe. Adult male L. rugulipennis were previously shown to be attracted to traps baited with live virgin females, which suggests the females produce a sex pheromone. Volatiles produced by virgin female L. rugulipennis were shown to contain three components, hexyl butyrate, (E)-2-hexenyl butyrate, and (E)-4-oxo-2-hexenal which elicited electroantennographic (EAG) responses from males in analyses by linked gas chromatography-electroantennography (GC-EAG). They were produced in 1.5:1:0.08 ratio, respectively, by single females. Collections from 1, 2, or 4 virgin females showed the proportions of hexyl butyrate and (E)-4-oxo-2-hexenal to increase relative to that of (E)-2-hexenyl butyrate with increasing number of females. Although these compounds were found in body extracts of both male and female L. rugulipennis, they were not detected in volatiles released by virgin males. EAG dose-response studies showed that both males and females responded to these chemicals with minimal differences in sensitivity between the sexes or to the three components, except that males were more responsive than females to (E)-4-oxo-2-hexenal at the two highest doses tested. Release rates of the compounds from rubber septa, polyethylene vials, and polyethylene sachets were measured under laboratory conditions. Four field tests were carried out using sticky traps baited with all possible binary and tertiary combinations of the three chemicals using different combinations of dispensing systems. Catches of male L. rugulipennis in baited traps were similar to those in unbaited traps. Significantly fewer females were caught on traps baited with blends containing hexyl butyrate than on traps without hexyl butyrate or unbaited traps in one test and overall. The roles of the three compounds and possible reasons for their failure to attract males are discussed.     

Influence of Induced Plant Defenses in Cotton and Tomato on the Efficacy of Baculoviruses on Noctuid Larvae

Constitutive phenolase activity of plants has a profound ability to modulate disease in insects caused by baculoviruses. We investigated the influence of damage-induced plant phenolic oxidases in cotton and tomato on mortality caused by two different baculoviruses in their respective hosts, Heliothis virescens (L.) and Helicoverpa zea (Boddie). For both plant species, peroxidase (POD) and phenolic levels were predictive of larval mortality caused by baculoviruses. The higher the POD activity, the lower the mortality in both hosts. Different classes of phenolics (e.g., monohydroxyphenolics vs. catecholic phenolics) in combination with POD activity had different effects on the severity of viral disease depending upon mixture, which implies that viral efficacy is predictable only if total chemical content of the plants is specified. Inhibition of baculoviral disease by plant phenolase activity has potential implications for the compatibility of baculoviruses with induced resistance in IPM programs.     

Influence of Ragweed (Ambrosia trifida) on Plant Parasitic Nematodes

The roots of ragweed Ambrosia trifida exude chemical compounds that have insecticidal activities. This paper reports a survey conducted in a soybean field infested with ragweed to determine if the ragweed affected the populations of plant parasitic nematodes. There was a strong indication that the ragweed decreased populations of plant parasitic nematodes in some cases.     

Sex pheromone components of the oblique-banded leafroller,Choristoneura rosaceana in the Okanagan Valley of British Columbia

(Z)-11-Tetradecen-1-yl acetate, (E)-11-tetradecen-1-yl acetate, and (Z)-11-tetradecen-1-ol were previously reported as the sex pheromone in New York strains of the oblique-banded leafroller,Choristoneura rosaceana (Harris), and (E)-11-tetradecen-1-ol was tentatively identified in female tip extracts. For Okanagan Valley strains ofC. rosaceana, an additional component, (Z)-11-tetradecenal, was identified from female tip extracts by split-less capillary gas-liquid chromatography and mass spectroscopy and was strongly stimulatory in electroantennogram studies. In field tests, 3 mg of 96.521.5 (Z)-11-tetradecen-1-yl acetate, (E)-11-tetradecen-1-yl acetate, and (Z)-11-tetradecen-1-ol (containing approx. 1%E isomer) was not as attractive as female-baited traps, and significant numbers of European leafrollerArchips rosanus L. were attracted. The above blend with 1% (Z)-11-tetradecenal added was significantly more attractive than traps baited with femaleC. rosaceana, butA. rosanus males were still attracted. Increased percentages of (Z)-11-tetradecenal up to 4% caused increased catches ofC. rosaceana and decreased catches ofA. rosanus. Low amounts of (E)-11-tetradecen-1-ol and (E)-11-tetradecenal male also contribute to increased specificity of the synthetic pheromone blend toC. rosaceana.Lepidoptera: Tortricidae.Contribution No. 638, Agriculture Canada, Research Station, Summerland, British Columbia, Canada.     

Identification, Synthesis, and Field Testing of the Sex Pheromone of the Citrus Leafminer, Phyllocnistis citrella

The citrus leafminer is an important vector of citrus canker in many of the major citrus production areas of the world. (7Z,11Z)-Hexadecadienal was reported as a sex attractant for this insect in the 1980s, based on trap catches during pheromone screening trials in Japan. However, attempts to reproduce this work in other areas of the world have not been successful. We report here that (7Z,11Z)-hexadecadienal is only one component of the pheromone, with the other critical component being the analogous trienal, (7Z,11Z,13E)-hexadecatrienal. Both compounds were identified in the effluvia from live female moths by coupled gas chromatography (GC)-electroantennography using nonpolar and polar GC columns, and the identifications were confirmed by comparisons of mass spectra with those of authentic standards. Stereoisomers of the two compounds, and a number of analogs, were synthesized to confirm the identifications. In field trials, neither compound alone was attractive to male moths, but blends of the two were highly attractive, with thousands of insects being caught per trial. Addition of the isomeric (7Z,11Z,13Z)-hexadecatrienal inhibited attraction to the two-component blend. Electronic Supplementary Material Supplementary material is available for this article at and accessible for authorized users. This paper and the preceding paper (Leal et al.) were submitted within a few days of each other. The editors and the authors agreed that they should be published in tandem.     

Optical isomers of 3,13-dimethylheptadecane: Sex pheromone components of the western false hemlock looper,Nepytia freemani (Lepidoptera: Geometridae)

(3S, 13R)-3, 13-Dimethylheptadecane [(3S, 13R)-3, 13-dime-17Hy] is the major pheromone component of the western false hemlock looper (WFHL),Nepytia freemani. In comparative gas chromotographic-electroantennographic detection (GC-EAD) analyses of stereoselectively synthesized isomers, 1 pg of (3S, 13R)-dime-17Hy elicited significantly stronger electrophysiological responses by male WFHL antennae than did 1 pg of separately injected (3R, 13R)-, (3R, 13S)- or (3S, 13S)-3, 13-dime-17Hy. In field experiments with individually tested stereoisomers. (3S, 13R)-3, 13-dime-17Hy was the only stereoisomer to attract males, but the four-stereoisomer blend was 3.6 times more attractive. Quaternary and all binary combinations of (3S, 13R)-3, 13-dime-17Hy with the other stereoisomers were equally attractive, suggesting that synergisytic behavioral activity in WFHL resided with either one of (3R, 13R)-, (3R, 13S)-, or (3S, 13S)-3, 13-dime-17Hy. Because optical isomers of (di)methylhydrocarbons do not separate on currently available columns, it remains unknown whether female WFHL also produce a four-stereoisomer pheromone blend. Substitutionality of pheromone stereoisomers without loss of behavioural activity has not previously been reported, but favorably compares with the concept of pheromone redundancy that was first suggested for the multiple pheromone component blend of the cabbage looper moth,Trichoplusia ni.     

Isolation, Identification and Field Tests of the Sex Pheromone of the Carambola Fruit Borer, Eucosma notanthes

Two components, (Z)-8-dodecenyl acetate (Z8-12:Ac) and (Z)-8-dodecenol (Z8-12:OH), were isolated from sex pheromone glands of the carambola fruit borer, Eucosma notanthes, and were identified by GC, and GC-MS, chemical derivatization, and comparison of retention times. The ratio of the alcohol to acetate in the sex pheromone extracts was 2.7. However, synthetic mixtures (1 mg) in ratios ranging from 0.5 to 1.5 were more effective than other blends in trapping male moths in field tests.     

The female sex pheromone of sugarcane stalk borer,Chilo auricilius identification of four components and field tests

Four pheromonal components have been detected in ovipositor washings and volatiles from female sugarcane stalk borers,Chilo auricilius Dudgeon (Lepidoptera: Pyralidae), using combined gas chromatography-electroantennography. The components have been identified as (I) (Z)-7-do-decenyl acetate, (II) (Z)-8-tridecenyl acetate, (III) (Z)-9-tetradecenyl acetate, and (IV) (Z)-10-pentadecenyl acetate by comparison of their gas chromatographic behavior with that of synthetic standards. In field tests carried out in northern India during 1982–1984, a combination of II, III, and IV in their naturally occurring ratio (841) was shown to provide a highly attractive synthetic source for trap use. (Z)-7-Dodecenyl acetate was found to reduce catches of maleC. auricilius, both when dispensed with the other three components and when released from dispensers surrounding a trap baited with the other three components.     

(2R,7S)-Diacetoxytridecane: Sex Pheromone of the Aphidophagous Gall Midge, Aphidoletes aphidimyza

In a recent study, evidence was presented that females of the aphidophagous midge Aphidoletes aphidimyza (Rondi) (Diptera: Cecidomyiidae) release a sex pheromone to attract mates. Our objectives were to identify and bioassay the pheromone. Coupled gas chromatographic-electroantennographic detection(GC-EAD) analyses of untreated and hydrogenated pheromone extract on three fused-silica columns (DB-5, DB-23, DB-210) revealed a single compound that elicited responses from male antennae. Retention index calculations of this candidate pheromone (CP) suggested that it was a di-acetate. Considering that most of the presently identified cecidomyiid pheromones consist of a 13-carbon chain with (at least) one acetate group in C2, we synthesized 2,6-, 2,7-, 2,8-, 2,9-, 2,10-, 2,11-, and 2,12-diacetoxytridecane. In GC analyses of these compounds, only 2,7-diacetoxytridecane cochomatographed with CP on all columns. In laboratory two-choice experiments with stereospecifically synthesized stereoisomers, only (2R,7S)-diacetoxytridecane elicited significant anemotatic responses by male A. aphidimyza. In trapping experiments in greenhouse compartments, only traps baited with (2R,7S)-diacetoxytridecane captured significant numbers of male A. aphidimyza, clearly revealing the absolute configuration of the pheromone. Failure of the stereoisomeric mixture (containing all four stereoisomers including the pheromone) to attract males is due to inhibitory characteristics of the (2R,7R)- and (2S,7R)-stereoisomers. The pheromone of zoophagous A. aphidimyza resembles those from phytophagous cecidomyiid midges, suggesting a common, diet-independent pathway for pheromone biosyntheses.     

Sex pheromone components of the blueberry leaftier mothCroesia curvalana kearfott (Lepidoptera: Tortricidae)

The GC-MS and GC-EAD analyses of sex-gland components and sex-gland-released volatiles have identified (E)- and (Z)-11-tetradecenal (9010) and (E)- and (Z)-11-tetradecenyl acetate (8515) as components of the sex pheromone chemical communication system ofCroesia curvalana (Kearfott). The aldehyde-to-acetate ratio of 91 was found in the gland-released components. This blend at a 0.1–1 g/day release rate from PVC lures was shown to be as effective as virgin females in the trapping of maleC. curvalana.