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Plant species which produce essential oils are important in the healthcare of rural Guatemalans. Steam distilled essential oils from 22 medicinal plant species were analyzed for activity against tongue, skin, and stomach cancer cell lines using a neutral red assay, Vero C1008 cells to assess cytotoxicity, and [3H]-thymidine incorporation assay to assess inhibition of cancer cell proliferation. IC50, CC50, and therapeutic indices were determined. IC50 values indicated that all oils showed inhibitory activity against one or more cancer cell lines. Highly inhibitory IC50 values (0.10 μL/mL or less) indicated that Citrus aurantiifolia (Christm.) Swingle (Rutaceae) oil was significantly inhibitory to all three cancer cell lines, Origanum vulgare L. (Lamiaceae) and Teloxys ambrosioides (L.) W. A. Weber (Chenopodiaceae) oils were highly inhibitory to two cell lines, and Lippia graveolens Kunth (Verbenaceae) oil was highly inhibitory to one cell line. TI values equal to or greater than one showed significantly higher cytotoxicity to cancer cells compared to the Vero cell line for Ruta chalepensis L. (Rutaceae), Citrus limetta Risso (Rutaceae), C. aurantium L. (Rutaceae), Rosmarinus officinalis L. (Lamiaceae), and O. vulgare. Essential oils from L. graveolens, O. vulgare, and T. ambrosioides yielded high percentages (>96%) of decreased cell proliferation at low oil concentration (0.05 μL/mL). Results indicate that essential oils were more toxic to cancer cells than to cells from an established cell line, and such oils can be highly suppressive to DNA synthesis and cancer cell growth. Key words: Essential oils, medicinal plants, IC50, anticancer activity, Guatemala.

Thirty-one medicinal plant species from Hawaii, Morocco, and the Sonoran Desert, USA have been shown in past studies to be highly inhibitory to pathogenic bacteria, fungi, and certain cancer cell lines. However, none were tested for antiviral activity.Acetone and methanol extracts from these species were bio-assayed for antiviral activity against herpes simplex virus types 1 and 2, and for cytotoxicity to the Vero C1008 cell line.Extracts from these species were tested in vitro for antiviral activity using an immunoperoxidase mini-plaque reduction assay to detect viral structural protein synthesis. A 50% inhibitory concentration (IC(50)) was computed. Sulforhodamine B and neutral red assays were used to qualitatively and quantitatively assess the cytotoxicity of extracts to C1008 cells, and to compute a 50% cytotoxic concentration (CC(50)) using a dose response curve.Eight of the 31 plant species assayed showed significant antiviral activity against HSV 1 and HSV 2 viruses. The acetone extract of Kalanchoe pinnata Pers. (Crassulaceae) produced an IC(50) of 0.025 mg/mL and a CC(50) of 1.25 mg/mL yielding a therapeutic index of 50. Additionally, this extract reduced plaque numbers to zero or near zero at a concentration of 0.1 mg/mL when added 30 min before or 30 min after virus infection.The mechanism of inhibition against HSV 1 and HSV 2 viruses is now being investigated, along with fractionation of the acetone extract in search of the active compound or compounds.

Concept inventories are often used to assess current student understanding although conceptual change models are problematic. Due to controversies with conceptual change models and the realities of student assessment, it is important that concept inventories are evaluated using a variety of theoretical models to improve quality. This study used a modified item response theory model to determine university nonmajor biology students’ levels of understanding of natural selection (n = 1,192). Using Conceptual Inventory of Natural Selection, we have reported how we applied Bock’s modified nominal item response theory model and the distracter test item analysis. We found that the use of this model can define student levels of understanding and identify problematic distracters.

The lack of solubility and the high degree of volatility of essential oils present significant problems to determining the biological effects of these oils. The activity of 10 essential oils and 4 essential oil blends against a Gram-positive bacterium, Staphylococcus aureus., and a yeast, Candida albicans., was compared using a dilution assay and two diffusion methods. The tube dilution assay, using a 0.2% agar solution to provide a stable homogeneous dispersion of oils, was used to measure minimum inhibitory concentrations (MICs). The relative merits of using p.-iodonitro tetrazolium dye (INT) or optical density (OD) in measuring MIC of essential oils also were evaluated. All 14 oils were active against both microorganisms. Thyme, mountain savory, and Turkish oregano were the most active oils against S. aureus. with MICs of 0.31–0.42 µl/ml. Thyme, Turkish oregano, and mountain savory also were the most active against C. albicans. with MICs of 0.31–0.42 µl/ml. The MIC values as determined by INT o...

This study evaluates the potential benefits of using ecology-based theories of plant chemical defense when screening plants for pharmaceutical activity. Extracts from 63 Sonoran Desert plant species representing 26 families were screened in microtiter/optical density–based assays against a cervix epithelial carcinoma cell line (HeLa) and mouse fibroblast cells (3T3). In HeLa cytotoxicity assays, 34 of 63 species (54%) showed significant inhibitory effects. Nine of these active extracts were significantly less toxic to a noncancerous mouse fibroblast cell line (3T3) and, thus, showed potentially cancer specific activity. Using the plant apparency/predictability hypothesis as a theoretical basis, this study used plant growth habit (e.g., annual, herbaceous perennial, woody perennial, evergreen) as an indicator of plant predictability, and hence likelihood of having well-established chemical defenses. This approach led to predictions that may be useful in locating plant species that produce biologically acti...

Essential oils are prevalent in many medicinal plants used for oral hygiene and treatment of diseases.Medicinal plant species were extracted to determine the essential oil content. Those producing sufficient oil were screened for activity against Staphylococcus aureus, Escherichia coli, Streptococcus mutans, Lactobacillus acidophilus, and Candida albicans.Plant samples were collected, frozen, and essential oils were extracted by steam distillation. Minimum inhibitory concentrations (MIC) were determined using a tube dilution assay for those species yielding sufficient oil.Fifty-nine of the 141 plant species produced sufficient oil for collection and 12 species not previously reported to produce essential oils were identified. Essential oil extracts from 32 species exhibited activity against one or more microbes. Oils from eight species were highly inhibitory to S. mutans, four species were highly inhibitory to C. albicans, and 19 species yielded MIC values less than the reference drugs.RESULTS suggest that 11 species were highly inhibitory to the microbes tested and merit further investigation. Oils from Cinnamomum zeylanicum Blume (Lauraceae), Citrus aurantiifolia (Christm.) Swingle (Rutaceae), Lippia graveolens Kunth (Verbenaceae), and Origanum vulgare L. (Lamiaceae) yielded highly significant or moderate activity against all microbes and have potential as antimicrobial agents.Teas prepared by decoction or infusion are known methods for extracting essential oils. Oils from 11 species were highly active against the microbes tested and merit investigation as to their potential for addressing health-related issues and in oral hygiene.

The feedbacks between plant and soil processes play an important role in driving forest succession. One poorly understood feedback mechanism is the interaction between plant secondary chemicals and soil microbes. In the Alaskan taiga, changes in nutrient cycling caused by balsam poplar (Populus balsamifera) secondary chemicals may affect the transition from alder (Alnus tenuifolia) to balsam poplar on river floodplains. We examined the effects of four poplar condensed tannin fractions on N cycling in alder and poplar soils. Tannins were added to forest floor samples from both poplar and alder sites. Samples were incubated for 1 month in the laboratory with soil respiration rates measured over the course of the incubation. At the end of the incubation we measured both net and gross nitrogen mineralization and nitrification, microbial biomass C and N, and the activity of various exoenzymes. In all soils, tannin additions reduced N availability, however, the mechanisms differed depending on the molecular weight of the tannin and the native soil microbial community. Low molecular weight tannin fractions served as a labile C source in poplar Oi, poplar Oe, and alder Oe horizons but were toxic to microbes in alder Oi. High molecular weight tannin fractions appeared to act primarily by binding extracellular substrates and thus limiting C and N mineralization, with the strongest effects observed in the alder soils.

The vegetation mosaic of the Alaskan taiga is produced by patterns of disturbance coupled to well-defined successional patterns. In primary succession on river floodplains, one of the critical transitions in succession is that from thinleaf alder (Alnus tenuifolia) to balsam poplar (Populus balsamifera). This is the shift from a N2-fixing shrub to a deciduous tree. Through this transition there are major changes in N cycling including a decrease in N2-fixation, mineralization, and nitrification. Most models of plant effects on soil processes assume that these changes are caused by shifts in litter quality and C/N ratio. This paper reviews several studies examining the effects of balsam poplar secondary chemicals on soil nutrient cycling. Balsam poplar tannins inhibited both N2-fixation in alder, and decomposition and N-mineralization in alder soils. Other poplar compounds, including low-molecular-weight phenolics, were microbial substrates and increased microbial growth and immobilization, thereby reducing net soil N availability. Thus, substantial changes in soil N cycling through succession appear to have been mediated by balsam poplar secondary chemicals.

Monoterpenes, sesquiterpenes, and phenolic and flavonoid glycosides typical of the current year's foliage of Douglas fir (Pseudotsuga menziesii) were bioassayed using agar diets to determine the effect of these compounds on natural and colony populations of western spruce budworm (Choristoneura occidentalis). Several terpenes adversely affected budworm larval growth, supporting previous field and laboratory studies. However, larvae collected from a population in southeastern Idaho were significantly more tolerant of the monoterpenes than those from a Montana population. For the Montana population, agar diet studies showed that camphene, myrcene, terpinolene, bornyl acetate, and tricyclene adversely affected larval growth rate and pupal weight. For the Idaho population, agar diet studies showed that only terpinolene and bornyl acetate adversely affected larval growth and pupal weights. For both populations bornyl acetate was the most toxic, and this compound in addition to other monoterpenes represent defensive mechanisms in the current year's growth of Douglas fir. Sesquiterpene and phenolic-flavonoid glycoside fractions extracted from Douglas fir current year's growth also were bioassayed using agar diets. The sesquiterpene fraction showed a significant negative effect on budworm larval growth, but phenolics and flavonoid glycosides had no effect. Sesquiterpenes, in combination with tricyclene, camphene, myrcene, limonene, terpinolene, and the acetate fraction appear to represent an effective mixture of defensive compounds against the budworm.

The transition from alder (Alnus tenuifolia) to balsam poplar (Populus balsamifera) is a critical turning point in primary succession on river floodplains in interior Alaska. Associated with the change in plant species are large changes in N cycling. N-fixation and nitrification decrease and the system becomes N-limited, with NH4+ dominating the inorganic N pool. Balsam poplar leaves contain large quantities of tannins and low molecular weight phenolic compounds. We evaluated the effect of these compounds on microbial respiration and N cycling in laboratory assays on soils from an alder-dominated site. Plant compounds were purified and applied to silica gel as an inert carrier. Both tannins and phenolics caused net N-immobilization over a 30-day assay. However, tannins inhibited respiration while phenolics stimulated it. There were no specific effects on nitrification. Thus, tannins acted as a general microbial inhibitor, while phenolics acted as a growth substrate. By inhibiting mineralization while stimulating immobilization, poplar secondary compounds may reduce soil N-availability during the transition betwen alder and poplar stages in succession. Keywords: respiration, mineralization, tannins, secondary chemicals, succession, plant–microbe interactions.

Four oleanne triterpene saponins, 3beta,16beta, 23-trihydroxy-keton-13beta,28-epoxyolean-9(11)-en-3-yl -[beta-D-glucopranosyl(1-->2)]-[beta-D-glucopyranosyl(1-->3)]-beta -D-fucopyranoside [1] (clinopodiside D), 16beta-propionyl-3beta,23-dihydroxyoleana-11-21-dien-3 -yl-[beta-D-glucopyranosyl(1-->2)]-[beta-D-glucopranosyl(1-->3)]-b eta-D-fucopyranoside [2] (clinipodiside E), 3beta,16beta,21alpha,23,28-pentahydroxy-11-methoxyolean++ +-12-en-3-yl-[beta-D-glucopyranolyl(1-->2)]-[beta-D-glucopyranosyl (1-->3)]-beta-D-fucopyranoside [3] (clinopodiside F), and 3beta,16beta,21beta,23,28-pentahydroxyoleana-11,13(18) -dien-3-yl-[beta-D-glucopyranosyl(1-->2)]-[beta-D-glucopyranosyl(1 -->3)]-beta-D-fucopyranoside [4] (clinopodiside G), were isolated and purified from the plant Clinopodium chinensis. Their structures were elucidated on the basis of interpretation of nmr and ms data and from chemical evidence. The results are of potential interest for medicinal reasons.

Monoterpene accumulation during maturation of the current year's growth of Douglas-fir, Rocky Mountain variety, is characterized by a two-phase response. Beginning at or near budbreak, α-pinene and a tricyclene-(1)-camphene-bornyl acetate biogenetic group accumulate 3–10-fold. This is followed by another lesser increase later in the season of the minor components (E-) ocimene, citronellal, and borneol. In contrast, levels of β-pinene, myrcene, and terpinolene, and the sesquiterpenes γ-cadinene, α-bisabolene, and an oxygenated sesquiterpene, did not vary significantly during needle maturation. These increases occur first in the lower canopy and proceed upward toward the mid- and upper-canopy levels shortly thereafter. Implications of these observations with respect to metabolism, host-insect interactions, and silviculture management are discussed.

We conducted a field experiment to assess interrelationships between leaf- tissue secondary chemistry, avian predation, and the abundance and diversity of arthropods occurring on sagebrush (Artemisia tridentata) in central Oregon. Arthropods were removed from individual shrubs, some of which were then caged to exclude birds. Secondary chem- istry and arthropods were sampled at intervals up to 56 wk following the defaunation/ caging treatment. Recovery rates differed among arthropod taxa and functional groups. Several sap- sucking homopterans and hemipterans reached control levels within 2-4 wk of the treat- ment, whereas abundances ofparasitoids and predators recovered to match control numbers only 6 wk after defaunation. Abundances of several herbivorous leaf-chewing taxa (pri- marily lepidopteran larvae) remained significantly depressed even 56 wk after the treatment. Fungivores (oribatid mites) reached greater abundances on defaunated than on control shrubs by the end of the experiment. There were also significant changes in the concen- trations or frequency of occurrence of several chemical compounds following the defauna- tion treatment. Several hydrocarbons, sesquiterpenes, and monoterpenes that were present in most shrubs exhibited sharply reduced concentrations in leaf tissues within 4 wk of the treatment, whereas some alcohols and ketones (linalool, borneol, thujone), which occurred at relatively low frequencies among control plants, increased dramatically in their fre- quencies of occurrence following arthropod removal. Both changes persisted for the du- ration of the experiment. We found several significant associations between the abundance or occurrence of arthropod taxa or groups and concentrations or frequencies of secondary compounds, but these were most prevalent among the leaf-chewing lepidopterans. We suggest that the shrubs responded to the removal of herbivorous, leaf-chewing arthropods by altering chemical allocation patterns; the changes in chemistry persisted for over a year because recolonization of the defaunated plants by these herbivores was slow. Effects of the caging treatment were much less obvious. The recovery of the diversity of arthropods known to constitute prey for birds in this system was slower on shrubs

The regulation of natural populations was debated intensively during the 1950s and 1960s, and continues to be an important topic of investigation. Although several treatises on this subject could be cited, one of the most important to the area of plant-herbivore-pathogen interactions was published by Hairston, Smith, and Slobodkin.1 In this stimulating paper the authors put forward three tenants, the third of which states that “Herbivores are seldom food-limited, appear most often to be predator-limited, and therefore are not likely to compete for common resources.” Contributing to this conclusion is the disparity between plants and herbivores in mobility, generation times, and the ability of insects and pathogens to adapt to host trees. Generation times of the myriad of insect herbivores that use woody plants are short, and the insects are highly mobile and depend upon host plants for most life processes.2 Alternatively, woody perennials are long-lived, immobile, and seemingly at the mercy of their natural enemies. This explicit yet sweeping scenario provided a major impetus toward investigations that have led to our current knowledge of plant-herbivore-pathogen interactions at the population, community, and ecosystem levels. Five years later a seminal paper by Ehrlich and Raven3 enhanced the field of plant-herbivore interactions and chemical ecology with a provocative discussion of the coevolution between butterflies and host plants. Now the field has advanced to investigations at the tritrophic level; and the linking thread among tritrophic interactions is to a large extent the natural products produced by plants.4

Three new triterpenoid saponins were isolated from the roots of Gypsophila oldhamiana. Their structures were elucidated, using a combination of homonuclear and heteronuclear 2D nmr and fabms, as 3-0-beta-D-galactopyranosyl-(1-->2)-[beta-D-xylopyranolyl-(1-->3)] -beta-D-glucuronopyranosyl quillaic acid methyl ester [1], 3-0-beta-D-galactopyranosyl-(1-->2)-[beta-D-xylopyranosyl-(1-->3)]-beta- D-glucuronopyranosyl gypsogenin methyl ester [2], and 3-0-beta-D-galactopyranolsyl-(1-->2)-[beta-D-xylopyranosyl-(1-->3) ]-beta-D-glucuronopyranosyl quillaic acid 28-[0-beta-D-fucopyranosyl(1-->4)-beta-D-glucopyranosyl(1-->3)]-alpha-L- rhamnopyranosyl] ester.

Two new triterpenoid saponins, 3 beta,16 beta,23-trihydroxy-13,28-epoxyolean- 11-en-3-yl-[beta-D-glucopyranosyl(1-->4)-beta-D-glucopyranosyl(1-->3)]- [beta-D-glucopyranosyl(1-->2)]-beta-D-fucopyranoside[1](clinopodiside B) and 28-O-beta-D-glucopyranosyl-3 beta,23-dihydroxyoleana-12,21-dien-3-yl-beta-D-glucopyranosy l-(1-->3)-beta-D- fucopyranoside [3] (clinopodiside C), together with three known saikosaponins, buddlejasaponins IV, IVa, and IVb, have been isolated from the plant, Clinopodium chinensis, and characterized using chemical evidence and spectroscopic methods, in particular 2D nmr spectroscopy.

The current year's growth of Douglas fir contains galactose, unusual in that this carbohydrate makes up 78.7% of the total carbohydrate fraction. An agar diet study was undertaken to determine the effects of galactose, other carbohydrates, and terpenes on western spruce budworm larval mortality, growth rate, and adult biomas production. All concentrations of the carbohydrates and terpenes tested, as well as other mineral elements not tested, were typical of the current year's foliage of Douglas fir. In experiment I, the diet containing 5.61% total carbohydrate did not significantly affect larval mortality when compared to the control diet. However, diets containing 9.45% and 15% total carbohydrate concentrations significantly increased larval mortality 64% and 96.1%, respectively, when compared to the control. Also in experiment I, terpenes alone (78.9% morality) and terpenes in combination with 9.45% and 15% total carbohydrates significantly increased larval mortality (97.2% and 100%, respectively) when compared to mortality on the control diet (44%). To determine which carbohydrate was causing the adverse effect, 6% glucose, 6% fructose, and 6% galactose were placed individually and in combination with terpenes in diets in experiment II. The 6% galactose diet significantly increased larval mortality and reduced growth rate when compared to the control, glucose, and fructose diets. Glucose resulted in 16% less larval mortality, significantly enhanced female larval growth rate and pupal weight, but did not affect male larval growth rate and pupal weight, when compared to the control. Fructose resulted in a significant decrease in larval mortality and a general trend of enhanced female and male larval growth rate and pupal weight. Larval mortality on terpenes alone was not significantly different from the control, but terpenes with 6% galactose increased larval mortality and decreased female and male growth rate and pupal weight significantly when compared to glucose-terpene and fructose-terpene diets. No significant interactions were found between carbohydrates and terpenes in either experiment.

The correlation between total phenolics and tannin content within a species is often considered to be suitably strong to allow researchers to assume, with some degree of confidence, that levels of one will approximately parallel the other. However, the manipulation of resource availability could lead to disproportionate changes in total phenolics and tannins and/or in the specific monomers of which these fractions are composed, thus altering the correlation between these components. In order to test this hypothesis, we examined the correlation between foliar levels of total phenolics (as measured by the ferric chloride assay) and tannins (as measured by an astringency assay) in Douglas-fir (Pseudotsuga menziesii Mirb. Franco) before and after the manipulation of nitrogen and water availability. Prior to manipulation of resources, the correlation between total phenolics and tannins was strong and highly significant (r2=0.869;P < 0.001). This correlation was considerably weaker and not statistically significant following resource manipulation (r2 = 0.392; 0.20

The 13C and 1H resonances of the alkaloids, obscurinervine (1) and obscurinervidine (2), are assigned using high-field NMR experiments and computerized data analysis procedures. A 2D INADEQUATE analysis of 26 mg of 2 was performed with a high-sensitivity carbon probe and the data interpreted using the spectral analysis program, CCBOND, to provide unambiguous 13C assignments. Although all signals are visually undetectable, CCBOND determined 20 of the 22 carbon–carbon bonds present. Corresponding 1H chemical shift assignments are made from HETCOR data. Proton–proton couplings are determined from DQF-COSY data using the new analysis program, HHCORR. Since HHCORR models signals as AB spin systems, the determined coupling constants are fairly independent of higher order effects, linewidths and digital resolution. Also a significant sensitivity improvement over visual interpretation of DQF-COSY data is observed. The obtained coupling constants are interpreted through the Karplus relationship to provide conformational details. These novel software analysis techniques allow accurate and more routine analysis of INADEQUATE and DQF-COSY data providing non-specialists access to these powerful experiments. Absolute stereochemistry of 2 is determined by a comparison with the ORD curve of(–)-O-methylaspidolimine. Stereospecific 1H assignments are obtained from proton–proton couplings and molecular mechanics simulations. The 13C and 1H chemical shift assignments for the related alkaloid, obscurinervine 1, are determined from CCBOND processed 2D INADEQUATE, HHCORR processed DQF-COSY, and HETCOR data. Differences in the rigidity of 1 and 2 in dimethyl sulfoxide (DMSO) are quantified by variable-temperature 1H NMR spectroscopy. Complete conformations of all ring systems are obtained from molecular mechanics using dihedral angles derived from proton–proton couplings as a check on the quality of the model. All conformational conclusions are independently supported by the X-ray structure of 1.

We concur with Wagner et al (1995), that ungulate browsing has an import effect on growth form, productivity, and survival of willows in northern Yellowstone National Park (hereafter YNP). We concur with Wagner et al. (1995) that elevation, precipitation, willow height, aboveground biomass production, and concentrations of secondary compounds covary in willow shoots on Yellowstone's northern ungulate winter range. We do not imply cause and effect between the climate change in northern YNP this century and the willow decline, nor do we reject the overabundant elk hypothesis (Singer et al. 1994). We present the case for a more complex, multi-causal situation, where interactions between elk abundance, climate change, fire, mammalian predators, and beaver abundance, might all influence the status and recruitment of willows. Singer et al. (1994) was intended as a paper to suggest a set of hypotheses that might explain the willow decline in YNP. We use cautionary phrases like may, likely, proposed, apparently, speculate, and circumstantial 27 times in Singer et al. (1995). We disagree with Wagner et al. (1995) that elk densities in the area are inversely correlated with elevation (Coughenour and Singer 1995) and elk consume mostly a grass-sedge diet (86% of the elk diet) and few willows (

Pine needles from ponderosa pine (Pinus ponderosa Lawson) consumed by cows during winter can cause abortions. Our study determined the nutritional impact of pine needles given to steers intraruminally. In Trial 1, 12 steers were given either grass hay alone (CONT), 15% pine needles (15PN), or 30% pine needles (30PN) substituted for hay, as fed basis. In Trial 2, a 4 X 4 Latin square design was used with 4 steers. Treatments were: (1) control-grass hay alone (CONT); (2) grass hay plus 454 g/day of cottonseed meal (CSM); (3) pine needles substituted for 40% (as fed basis) of the hay (PN); and (4) pine needles (40%) plus 454 g/day of CSM (PNCSM). In Trial 1, dry matter intake (DMI), fecal N, and DM digestibility were not affected by either 15PN or 30PN. N intake and N digestibility were reduced (P < 0.07) by 30PN. Fluid dilution rate (FDR) and fluid outflow rate (FOR) were depressed (P = 0.10) by 30PN. Total VFA and ruminal ammonia-N also were depressed by 30PN. In Trial 2, the PN treatment adversely affected DMI, N intake, and all digestibility coefficients, and elevated fecal N. FDR, FOR, and turnover time (TOT) were reduced by 40% PN. Total VFA were increased by PN, while ammonia-N concentrations were reduced. Cottonseed meal had few effects on rumen variables, and there were no CSM X PN interactions. We conclude that pine needles severely affect cattle nutrition, particularly N intake and digestibility and fluid rate of passage. Cottonseed meal, at 1 kg/day, does not ameliorate the adverse effects of pine needles. Fifteen to 30% pine needles in cattle diets appears to be the threshold level for toxic effects on ruminal fermentation.

An agar diet study using western spruce budworm populations from Idaho and New Mexico was carried out to determine the effects of varying concentrations of nitrogen, beta-pinene, and bornyl acetate on larval growth and survival. Increased availability of nitrogen resulted in increased larval growth rate and survival to the adult stage. Larval growth rates from the Idaho population were higher on the high-nitrogen diet than were growth rates from the New Mexico population. The high level of beta-pinene improved larval growth at the high-nitrogen concentration. Bornyl acetate significantly reduced larval growth at both the low and high levels of nitrogen although the effect was greatest with the high-nitrogen diet. High bornyl acetate concentrations also significantly reduced survival to the adult stage. At high-nitrogen levels, a high concentration of bornyl acetate reduced larval growth rates and adult survival to a level similar to that occurring at the low nitrogen and low bornyl acetate concentrations.

Measurements of foliage quality, physiological, and phenological condition of sample trees were used as independent variables in multiple correlation analyses to determine their effect on female and male spruce budworm larval dry weights. Female budworm from trees high in foliar concentrations of beta-pinene, myrcene and total nitrogen weighed less than those from trees lacking these characteristics. Male budworm from trees high in foliar concentrations of alpha-pinene, myrcene, terpinolene, citronellyl acetate, and bornyl acetate weighted less than those from trees lacking these characteristics. Additionally, relatively vigorous and productive trees tended to be less susceptible (as evidenced by reduced larval weight) to budworm of either sex.

The relationships between seral stage and nutrient and organic composition of five plant species used as forage by Sitka black-tailed deer were investigated in hemlock–spruce forest in southeastern Alaska. One shrub, three forbs, and one conifer species were collected during May, July, and October to ascertain differences among seral stands in seasonal patterns of nutrient levels, in vitro dry matter digestibility, astringency, and the concentrations of phenolics, terpenes, total nonstructural carbohydrates, and cyanide. In the shrub and forbs, concentrations of N, P, and K tended to be higher in leaves from forested than from open clear-cut areas, and higher in May than in July and October. These nutrients tended to covary in an opposite manner to Ca, Mg, and Na and in a similar manner to the trace elements Cu, Zn, Mn, and Fe, although these patterns were inconsistent. In these species there was also a general pattern of higher levels of total nonstructural carbohydrates, astringency, and phenolics in the three young open stands than in the shaded forest understories of the two oldest stands. Dry matter digestibility did not differ across stands but did vary seasonally. The among-stand differences in foliage chemical composition may have resulted from differences in the availability of light. While seral stage affected both the inorganic and organic quality of understory forage species, the combined results suggest that the impact on N economy of deer is greater than that on their energy economy.

Data collected on natural populations of Asarum caudatum in western Washington indicated that populations were polymorphic for growth rate, seed production, and palatability to a native slug. However, in habitats where slugs were not as abundant, populations of wild ginger were dominated by individuals allocating more energy to growth rate and seed production, and less to the production of an antiherbivore mechanism. On the basis of these data, I postulated that in the absence of grazing pressure, palatable, faster growing individuals would be at a competitive advantage over slower growing individuals that devote more energy to an antiherbivore mechanism. Under grazing pressure, however, fitness of the unpalatable individuals would be increased since smaller amounts of photosynthetic tissue would be consumed. See full-text article at JSTOR

Theoretical considerations and evidence from the literature suggest that early successional plant species should make a lesser commitment of resources to defense against herbivores, and should then provide better food sources for generalized herbivores than later successional and climax plants. Commitment to defense by plants is estimated by determining short-term palatabilities to two slug species; one native to western Washington, Ariolimax columbianus, and one introduced from Europe, Arion ater. Results of tests with 100 plant species of three growth forms and from different seral stages indicated that early successional annuals were significantly more palatable than early successional perennials which were sig- nificantly more palatable than later successional species. No correlation was found between palatability and evolutionary association of the herbivores with the plant species.

The diversity of chemical identity and mode of action of toxic substances present in plants is suggested to be partially the result of generalist herbivore grazing pressure, while convergence in digestibility-reducing substances and their method of function is due primarily to specialist herbivore. Analysis of alkaloid patterns from herbaceous and woody perennials show that most species differ in their alkaloid composition and many sympatric species and subspecies show unique patterns. The high degree of functional convergence in digestibility-reducing substances is supported by convergent patterns in tannins among woody perennials.

Host plant preferences for 34 insect herbivore species are reported. Most polyphagous herbivores feeding on annuals, herbaceous perennials, and woody perennials show distinct preferences for the least abundant plant species among their various host plants. In addition, some populations of widely distributed polyphagous species are much more specialized in their diet than host plant lists alone would suggest. The high level of polyphagy on annuals and herbaceous perennials is suggested to be strongly influenced by the unpredictability of the host plant that is, in turn, controlled by environmental variability. Oligophagous herbivores preferred the least abundant woody perennials on the study sites. Ten of the 22 monophagous herbivores preferred the rarest of all the plant species on the same sites.

Litter decomposition in terrestrial habitats is affected by many factors, including temperature, moisture, and nutrient and organic composition of litter. Among organic components, lignin is the primary controlling factor of decomposition rates of surface litter during the later phase of decomposition in most habitats and during the initial phase in warm, moist habitats (i.e., those with a high actual evapotranspiration, AET). In habitats with moderate AET's, we suggest that the decreased control by lignin over annual decomposition rates of surface litter is due, at least in part, to a significant periodic or seasonal influence of other carbonbased plant secondary metabolites over rates in the initial phase of decomposition. The influence of other secondary metabolites over decomposition rates should be a function of other correlates of AET: the phytochemical composition of the community and the persistence of various secondary metabolites in litter. As AET decreases from the highest extreme, we expect mo...

Leaf tissue preferences of monophagous, oligophagous, and polyphagous insect herbivores were determined using young and mature leaf tissue abundances and herbivore feeding observations. Larvae of monophagous and oligophagous herbivores preferred young leaf tissues while, overall, larvae of polyphagous species preferred mature leaves of their various host plants. Even though a species is often polyphagous over its geographical range, larvae from local populations may be very specialized in their diet. When this occurs these specialized larvae prefer the more nutritious and perhaps more toxic young leaves of some of their host plants. Resource abundance and plant chemistry are discussed as major factors influencing herbivore feeding patterns.

Forty plant species common in western Washington were investigated for the presence of allelopathic chemicals capable of influencing the distribution of subordinate species. Under laboratory conditions most species contained inhibitory volatile compounds and many contained effective water—soluble compounds. The results of up to 13 bioassays per species were compared with descriptions of the distribution of subordinate species under natural conditions. In several cases, notably Acer circinatum, Arbutus menziesii, and Rhododendron albiflorum, high inhibition values in laboratory experiments were associated with distinct changes in ground—cover composition beneath the canopy of these species. The ratio between inhibition values produced by volatile and water—soluble inhibitors was higher in species from arid regions than in those from humid regions. This finding supports Muller and Whittaker's hypothesis that allelopathic compounds are primarily waste products.

Tannin, cell wall, and nitrogen composition of green foliage and needle litter of similar-aged Douglas-fir (Pseudotsuga menziesii Mirb. Franco) from two stands differing in density and crown closure were compared. Trees in the closed-canopy stand had a lower basal area growth rate than those in the open-canopy stand. Stands did not differ in wood basal area/ha or forest floor C/N ratios, but the closed-canopy stand had a significantly larger accumulation of forest floor biomass and significantly higher levels of field-extractable nitrogen and nitrogen mineralization rates. Green foliage from trees in the closed-canopy stand had significantly lower nitrogen, astringency, and lignin contents, but higher cellulose concentration than trees in the open-canopy stand. These trends, inconsistent with the inverse relationship often observed between nitrogen and polyphenol contents of foliage, may result from differences in relative resource availability in the two stands. In contrast to green foliage, needle litter from the two stands had comparable contents of nitrogen, cellulose, and lignin, but astringency was significantly higher in litter from the closed-canopy stand. It is suggested that, within the constraints imposed by site conditions, evergreens may alter the tannin composition of senescing foliage, potentially affecting herbivory and decomposition differently.

Much research has been conducted in an attempt to fit the so-called plant secondary substances into the general framework of plant metabolism. Though some success has been achieved in this area, e.g., chlorogenic acid as a regulator of plant metabolic systems under stress21, most such studies have met with a conspicuous lack of success. Possible metabolic roles for the plant alkaloids as intermediate metabolites have probably received the greatest such attention and it was concluded at an early stage44 that, since a definitive metabolic role could not be assigned to alkaloids, they best be considered as plant waste products. More recent workers in the field of alkaloid biochemistry have concurred with this evaluation44,83 and the “waste product hypothesis” has been expanded, principally by Muller (1969, 1970), to include plant secondary substances in general.