Allelopathic effects of giant foxtail on germination and radicle elongation of loblolly pine seed

Water extracts of giant foxtail grass inhibited germination and radicle elongation of loblolly pine seed in a laboratory test. Most of the toxic effects came from extracts of dried foxtail tops, with lesser amounts from fresh tops and roots. Soil texture affected the phytotoxicity of the extracts. Eight chemical compounds known to be phytotoxins inSetaria were identified in extracts of foxtail leaves but could not be found in soil samples under the leaves.     

Response of total tannins and phenolics in loblolly pine foliage exposed to ozone and acid rain

Tannin and total phenolic levels in the foliage of loblolly pine (Pinus taeda L.) were examined in order to evaluate the effect of atmospheric pollution on secondary plant metabolism. The trees were exposed to four ozone concentrations and three levels of simulated acid rain. Tannin concentration (quantity per gram) and content (quantity per fascicle) were increased in foliage exposed to high concentrations of ozone in both ozone-sensitive and ozone-tolerant families. No effect of acid rain on tannins was observed. Neither total phenolic concentration nor content was significantly affected by any treatment, indicating that the ozone-related increase in foliar tannins was due to changes in allocation within the phenolic group rather than to increases in total phenolics. The change in allocation of resources in the production of secondary metabolites may have implications in herbivore defense, as well as for the overall energy balance of the plant.AAES Journal no. 9-902690P.     

Variation in methylglucosinolate and insect damage toCleome serrulata (Capparaceae) along a natural soil moisture gradient

We tested the hypothesis that plant loss to insects, and thus the relative fitness of an annual, was inversely related to spatial variation in the concentration of its characteristic secondary compound, methylglucosinolate, a mustard oil precursor. We found that methylyglucosinolate concentrations decreased significantly and linearly from the dry to the wet end along short soil moisture gradients in dry shortgrass prairie. Both leaf damage and capsule predation increased from the dry to the wet end. Thus, the glucosinolate appears to function defensively. Plant growth and flower production were favored at the wet end of the gradient; yet plants in the wet portion of the gradient were also more vulnerable to significant insect damage. The net result was that seed production by individual plants after predation was actually greater in the drier, harsher half of the gradient. The outcome strongly suggests that environmentally related variation in secondary compound concentration along environmental gradients can mediate and influence host-plant population abundance and distribution.     

Effects of nitrogen fertilization on secondary chemistry and ectomycorrhizal state of Scots pine seedlings and on growth of grey pine aphid

Effects of nitrogen availability on secondary compounds, mycorrhizal infection, and aphid growth of 1-year-old Scots pine (Pinus sylvestris L.) seedlings were studied during one growing season. Seedlings were fertilized with nutrient solutions containing low, optimum, and two elevated (2 × and 4 × optimum) levels of NH₄NO₃. At the end of growing season foliar nitrogen concentration, needle biomass, needle length, water contents of needles, root collar diameter, and number of buds increased with enhanced nitrogen availability. Addition of nitrogen did not have effect on concentrations of monoterpenes in growing needles, but in mature needles significantly decreased concentrations of some individual and total monoterpenes were detected. In growing needles the concentrations of some individual resin acids decreased, and in mature needles concentrations of some individual and total resin acids increased with increased nitrogen fertilization. Higher numbers of resin ducts were found in mature needles with nitrogen fertilization. Nitrogen fertilization decreased total phenolic concentrations in growing and mature needles of the current year, but in needles of the previous year no significant differences occurred. Mycorrhizal infection was highest at medium (optimum and 2 × optimum) nitrogen fertilization levels. The relative growth rate (RGR) of grey pine aphid [Schizolachnus pineti (F.)] responded positively to the increase in foliar nitrogen content. However, the increase in aphid performance between optimum and the highest fertilization level was slight. This may indicate a deterring effect of resin acids on aphids. The results indicate that carbon/nutrient balance hypothesis fails to predict directly the effects of nitrogen availability on concentrations of carbon-based defensive compounds in mature foliage. Altered nitrogen supply affects allocation to secondary metabolites differently, depending on the developmental state of the plant and the biosynthesis pathway, cost of synthesis, and storage of compounds.     

Defensive mechanisms of loblolly and shortleaf pine against attack by southern pine beetle,Dendroctonus frontalis Zimmermann,and its fungal associate,Ceratocystis minor (Hedgecock) Hunt

Loblolly and shortleaf pine growing on a single site in the North Carolina piedmont were examined to determine similarities and differences in their defensive mechanisms against the southern pine beetle,Dendroctonus frontalis Zimmermann, and its fungal associate,Ceratocystis minor (Hedgecock) Hunt. Both species responded to wounding and fungal inoculation by forming a hypersensitive lesion around the wound site. There were significantly less soluble sugars and more monoterpenes in the lesion tissue than in unwounded inner bark. The two species were similar in resin flow rate and inner bark soluble sugar content, but the loblolly pines had thicker bark, longer hypersensitive lesions, and a higher concentration of inner bark monoterpenes. Inner bark monoterpene composition was also significantly different between the two pine species. It is hypothesized that two different defensive strategies against southern pine beetle attack may be utilized.     

Oviposition and feeding preferences of the southern pine coneworm (Lepidoptera: Pyralidae) for different host-plant materials and observations on monoterpenes as an oviposition stimulant

Bioassays were conducted with first-stage larvae and newly emerged females of the southern pine coneworm,Dioryctria amatella (Hulst), to detect feeding and ovipositional preferences for different host-plant materials collected between April and August. Correlations between measures of insect preferences and estimates of wood parameters indicated that larvae preferred to feed on host-plant materials with high moisture contents, low wood densities, and low monoterpene contents. Female moths, however, did not necessarily select those plant materials preferred by larvae for feeding, but tended to oviposit more frequently on materials with high monoterpene contents. A synthetic mixture of monoterpenes similar in composition to those present in fusiform rust galls of slash pine (Pinus elliottii) Englem. var.elliottii) elicited mating and oviposition behavior.Mention of proprietary products does not necessarily imply endorsement by USDA.     

Influence of white pine watering regimes on feeding preferences of spring and fall adults of the white pine weevilPissodes strobi (Peck)

Spring and fall adults of the white pine weevil,Pissodes strobi (Peck), were exposed in no-choice and two-choice tests to bark from water-stressed and non-water-stressed white pine (Pinus strobus L.), which had also been exposed or not exposed to weevil attack. This experiment demonstrated that the weevils could discriminate between bark from water-stressed white pine and preferred bark from the nonstressed plants. The weevils also preferred bark from nonstressed plants that were previously exposed to weevil damage. Spring and fall adults displayed the same feeding preferences. No sex differences were found in feeding preferences. Less nitrogen, phosphorus, and potassium were found in bark from the nonstressed plants, and the potassium level was higher in damaged plants. We expect that the biological performance of the weevil should be favored by vigorously growing plants rather than by stressed plants.     

Frontalin in the male mountain pine beetle

Frontalin andexo-brevicomin were identified by GC-MS in air drawn over maleDendroclonus ponderosae Hopk. (MPB) from Oregon that had joined females for 1–2 days in the bark of lodgepole and ponderosa pine logs. Unfed males releasedexo- andendo-brevicomin but not frontalin. These three compounds were not detected in either unfed or fed females. Arrestment of males bytrans-verbenol and terpenes in an olfactory walkway was reduced by the addition of racemic frontalin; production of attractant chirps also diminished. Racemic frontalin also strongly reduced the aggregation of MPB in lodgepole and ponderosa pine stands to sticky traps baited with the aggregation pheromonetrans-verbenol and host terpenes; however, the function of the natural enantiomer of frontalin in MPB is unknown.Research supported by NSF Grant PCN 79-21708. O.S.U. Agricultural Experiment Station Technical Paper No. 6219.     

Inhibition of Scots pine seedling establishment byEmpetrum hermaphroditum

Poor establishment and reduced seedling growth of Scots pine (Pinus silvestris L.) in northern Sweden is related to an allelopathic inhibition by the dwarf shrubEmpetrum hermaphroditum Hagerup. Indoor bioassays with green and brown leaves ofEmpetrum have strong negative effects on rooting ability, radicle elongation, and growth of Scots pine seedlings. Bioassays with soil samples show that phytotoxic substances leached fromEmpetrum foliage accumulate in the soil. Field experiments reveal that chemical inhibition byEmpetrum, causing high mortality and slow growth of pine seedlings, can be reduced by adding activated carbon to the soil.     

Field bioassay ofexo- andendo-brevicomin withDendroctonus ponderosae in lodgepole pine

Bothexo- andendo-brevicomin reduced the response of flyingDendroctonus ponderosae (Coleoptera: Scolytidae) to an attractant composed oftrans-verbenol and terpenes or oftrans- andcis-verbenol and terpenes in a stand ofPinus contorta var.murrayana. These data suggest that racemicexo- andendo-brevicomin may interrupt aggregation in populations of mountain pine beetle colonizing lodgepole pine; functions of the natural chiral compounds are unknown.Research supported by NSF grants DEB 77-11367 and PCN 79-21708 and the O.S.U. School of Forestry. O.S.U. Agric. Exp. Sta. Tech. Paper No. 5713.     

Weak responses of pine sawfly larvae to high needle flavonoid concentrations in scots pine

Responses of sawfly larvae (Hymenoptera, Diprionidae) to the flavonoid taxifolin glucoside in their host plant were studied in a laboratory experiment. Larvae ofNeodiprion sertifer andDiprion pini were raised from egg hatch to cocoon spinning on two Scots pine (Pinus sylvestris) chemotypes, one without needle taxifolin glucoside (–) and the other containing 2–4% taxifolin glucoside (+). The (+) chemotype had somewhat lower concentrations of needle terpenoids (resin acids) than the (–) chemotype. Current-year needles had higher taxifolin glucoside concentrations than mature needles. There were no differences in survival or body size betweenN. sertifer larvae that fed on the (+) chemotype and those that fed on the (–) chemotype. FemaleD. pini larvae raised on (+) needles developed 6% more slowly than larvae fed (–) needles. The results from this study are contrary to earlier findings showing that flavonoid glucosides have strong negative effects on insect performance. Possible explanations for the different outcomes are discussed.     

Pheromone-dependent species recognition mechanisms betweenNeodiprion pinetum andDiprion similis on white pine

The sex pheromones ofNeodiprion pinetum (Norton) andDiprion similis (Hartig) consist of two isomers, 2S,3S,7S and 2S,3R,7R, in either the acetate orpropionate forms of 3,7-dimethylpentadecan-2-ol, respectively. The 2S,3S,7S acetate isomer is utilized byN. pinetum as the major pheromone component and the 2S,3R,7R acetate as a Synergist. ConverselyD. similis utilizes 2S,3R,7R as propionate the major pheromone component and 2S,3S,7S propionate as a Synergist. This was confirmed in the field in both Michigan and Wisconsin. Capillary gas-liquid chromatographie analyses revealed that these two isomers are present in the natural pheromones of both species at the ratios close to those predicted by artificial blending of the two optical isomers.     

Volatiles Associated with Preferred and Nonpreferred Hosts of the Nantucket Pine Tip Moth, Rhyacionia frustrana

Ovipositing female Nantucket pine tip moth, Rhyacionia frustrana, prefer loblolly pine, Pinus taeda L., to slash pine, Pinus elliottii Engelm, except during the first spring following planting of seedlings. Host discrimination by R. frustrana increases as seedlings develop, suggesting that changes in the chemical composition of seedlings may mediate the moth's host preferences. Volatile compounds from slash and loblolly pine seedlings were collected using solid-phase microextraction (SPME) during the first year following planting. Four collection periods coincided with adult emergence and oviposition during each of four annual generations of R. frustrana in the Georgia Coastal Plain. Infestation of slash pine peaked during the second tip moth generation and was similar to the loblolly pine infestation level. By the fourth tip moth generation, slash pine infestation levels had declined and diverged considerably from those of loblolly pine. Significant differences in relative quantities of beta-pinene, alpha-phellandrene, limonene, beta-phellandrene, bornyl acetate, beta-caryophyllene, and an unidentified sesquiterpene occurred between slash and loblolly pine during the fourth generation. However, no strong correlation was observed between any individual compound and host damage that could readily explain the temporal changes in R. frustrana host preference. Gas chromatographic-electroantennographic detection (GC-EAD) analyses of standards identified 19 different seedling-associated compounds that elicited antennal responses from R. frustrana females, indicating that a blend of terpenoids may mediate host discrimination.     

Behavior of the western pine beetle during host colonization

After living ponderosa pines were baited with either female-infested bolts or synthetic pheromones,Dendroctonus brevicomis were caught on sticky screens throughout trapping periods of 15–46 days; however, large numbers of beetles were trapped during only a small portion (5–10 days) of these trapping periods. The most attractive portions of trees attacked contained 3–6 beetles dm², in galleries ca. 2 cm long. Catch increased following addition of males to female-infested bolts, supporting the hypothesis that male-produced frontalin is an attractive pheromone of the western pine beetle. Catch at bolts removed from trees under attack was strongly dependent upon levels of boring activity. We found no evidence of interruption of the response to attractants during host colonization.Coleoptera: Scolytidae. Trade names and commercial enterprises or products are mentioned solely for information and do not constitute endorsement by the U.S. Department of Agriculture or University of California.     

Monoterpene metabolism in female mountain pine beetles,Dendroctonus ponderosae Hopkins,attacking ponderosa pine

Abdominal volatiles of female mountain pine beetles,Dendroctonus ponderosae Hopkins, fed in ponderosa pine,Pinus ponderosa Dougl. ex Laws, and in lodgepole pine,P. contorta var.latifolia Engelmann, were analyzed by gas chromatography and coupled gas chromatography-mass spectrometry and were found to comprise host oleoresin components and beetle-produced alliylic alcohols, aldehydes, and ketones derived from host monoterpenes. Neitherexo- andendo-brevicomin nor frontalin were detected. Three metabolic pathways are proposed to account for the distribution of beetle-produced monoterpene alcohols. The first pathway involves hydroxylation of monoterpene substrates on allylic methyl groups which areE to a methylene or vinyl group. This oxidation pathway is indiscriminate with respect to substrate and probably functions to detoxify monoterpenes. A second pathway, which hydroxylates theendo-cyclic methyleneE to a vinyl methyl group of bicyclic monoterpenes to give almost exclusively thetrans alcohol, is hypothesized to be involved in pheromone production. A third detoxification pathway involves anti-Markovnikov addition of water to theexo-cyclic double bond of -phellandrene to give predominantlytrans-2-p-menthen-7-ol.Coleoptera: Scolytidae.Research supported by the Natural Sciences and Engineering Research Council of Canada: Operating Grant A3881 and A3706; Strategic Grant G1039; and Science Council of British Columbia Grant 33 (RC-4).     

Trapping the western pine beetle at and near a source of synthetic attractive pheromone Effects of trap size and position

Western pine beetles were caught on unbaited sticky traps placed near a source ofexo-brevicomin, frontalin, and myrcene. Size of trap, distance and direction from the source of attractant, and height from the ground were varied. Significant differences in trap catch were observed in relation to each of the variables. Traps close to the source of attractant caught more beetles than traps farther from the source. Traps downwind of the source of attractant caught more beetles than did upwind traps. More males than females were trapped close to the source of attractant.Based in part on a thesis submitted by the senior author to the University of California, Berkeley, California, in partial fulfillment of the requirements for the degree Master of Science in entomology, December 1976. These studies were supported by the U.S. Forest Service and in part by the Rockefeller Foundation and a joint grant (NSF GB-34718/BMS 75-04223) from the U.S. National Science Foundation and the U.S. Environmental Protection Agency to the University of California. The findings, opinions, and recommendations are not necessarily those of the University of California or the funding agencies.Trade names and commercial enterprises or products are mentioned solely for information and do not constitute endorsement by the U.S. Department of Agriculture or University of California.     

Multivariate study of moose browsing in relation to phenol pattern in pine needles

Extracts of needles from Scots pine,Pinus sylvestris L., grown on fertile (A) or poor (B) soil, and from lodgepole pine,P. contorta Doug. (C), have been analyzed with HPLC and UV detection. By application of multivariate analysis, the phenol pattern was shown to vary between species and between habitats. Within groups A and B, moose food choice was highly correlated to phenol pattern. Concentrations of most of the analyzed compounds were internally correlated. Information related to pine growth rate could also be extracted from the phenolic pattern for A, B, and C. Moose food choice was not correlated to pine growth rate.     

Terpenes of ponderosa pine and feeding preferences by pocket gophers

Yield and composition of essential oils were compared in foliage, stems, and roots of ponderosa pine seedlings, and preferences for the trees by pocket gophers were determined. Test seedlings represented nine widely separated provenances in the western United States. Seed source of the trees influenced gopher feeding preferences and resulted in varied tree damage. The damage ranged from 0 to 31%, suggesting that some sources might possess sufficient natural resistance to give trees practical protection from gophers in the field. There were no morphological differences among sources to explain differential tree damage. All sources contained essential oils in all tissues examined, but oil yield varied among and within tissue types. Oils were predominantly (76–97%) composed of monoterpene hydrocarbons. Oil composition varied by source, and different tissue types varied greatly in the yield and composition of their oils. Neither yield nor constituents of foliage oils were significantly correlated with gopher damage (or preference). In contrast, some components of stem and root oils were strongly related to preference. Results of correlation and discriminant analyses showed that some oil constituents could serve as indicators of resistance (or susceptibility) to gopher damage. Such important chemical variables, when verified, could be used in selections for ponderosa pine resistant to gophers.The authors thank Dr. K. Hungerford, University of Idaho, for supervising the gopher preference test under a cooperative-aid agreement with the U.S.D.A. Forest Service.     

Attraction of pinyon pine bark beetle,Ips hoppingi,to conspecific andI. confusus pheromones (Coleoptera: Scolytidae)

Females of a pinyon pine bark beetle,Ips hoppingi Lanier, were less attracted by the aggregation pheromone produced by conspecific males than by the pheromone produced by the neighboring sibling species,I. confusus (LeConte). Cross-attraction was elicited by males infesting the regional pinyon pine hosts (P. discolor andP. edulis) of eitherIps species in south-eastern Arizona. Pheromonal specificity has not accompanied speciation in this species pair.     

Effects of biotic and abiotic stress on induced accumulation of terpenes and phenolics in red pines inoculated with bark beetle-vectored fungus

This study characterized the chemical response of healthy red pine to artificial inoculation with the bark beetle-vectored fungusLeptographium terebrantis. In addition, we sought to determine whether stress altered this induced response and to understand the implications of these interactions to the study of decline diseases. Twenty-five-year-old trees responded to mechanical wounding or inoculation withL. terebrantis by producing resinous reaction lesions in the phloem. Aseptically wounded and wound-inoculated phloem contained higher concentrations of phenolics than did constitutive tissue. Trees inoculated withL. terebrantis also contained higher concentrations of six monoterpenes,-pinene,-pinene, 3-carene, limonene, camphene, and myrcene, and higher total monoterpenes than did trees that were mechanically wounded or left unwounded. Concentrations of these monoterpenes increased with time after inoculation. Total phenolic concentrations in unwounded stem tissue did not differ between healthy and root-diseased trees. Likewise, constitutive monoterpene concentrations in stem phloem were similar between healthy and root-diseased trees. However, when stem phloem tissue was challenged with fungal inoculations, reaction tissue from root-diseased trees contained lower concentrations of-pinene, the predominant monoterpene in red pine, than did reaction tissue from healthy trees. Seedlings stressed by exposure to low light levels exhibited less extensive induced chemical changes when challenge inoculated withL. terebrantis than did seedlings growing under higher light. Stem phloem tissue in these seedlings contained lower concentrations of-pinene than did nonstressed seedlings also challenge inoculated withL. terebrantis. It is hypothesized that monoterpenes and phenolics play a role in the defensive response of red pine against insect-fungal attack, that stress may predispose red pine to attack by insect-fungal complexes, and that such interactions are involved in red pine decline disease. Implications to plant defense theory and interactions among multiple stress agents in forest decline are discussed.To whom correspondence should be addressed at USDA Forest Service, 2500 Shreveport Hwy., Pineville, Louisiana 71360.