Characteristics of higher plant terpenoids that result in mediation of numerous kinds of ecological interactions are discussed as a framework for this Symposium on Chemical Ecology of Terpenoids. However, the role of terpenoid mixtures, either constitutive or induced, their intraspecific qualitative and quantitative compositional variation, and their dosage-dependent effects are emphasized in subsequent discussions. It is suggested that little previous attention to these characteristics may have contributed to terpenoids having been misrepresented in some chemical defense theories. Selected phytocentric examples of terpenoid interactions are presented: (1) defense against generalist and specialist insect and mammalian herbivores, (2) defense against insect-vectored fungi and potentially pathogenic endophytic fungi, (3) attraction of entomophages and pollinators, (4) allelopathic effects that inhibit seed germination and soil bacteria, and (5) interaction with reactive troposphere gases. The results are integrated by discussing how these terpenoids may be contributing factors in determining some properties of terrestrial plant communities and ecosystems. A terrestrial phytocentric approach is necessitated due to the magnitude and scope of terpenoid interactions. This presentation has a more broadly based ecological perspective than the several excellent recent reviews of the ecological chemistry of terpenoids.

Higher plant terpenoids:a phytocentric overview of their ecological roles

http://www.dartmouth.edu/~mpayres/pubs/gepidem.PDF

Assessing the consequences of global change for forest disturbance from herbivores and pathogens.

Contents

 Summary 657

I. Introduction 658
II. Identification and functional characterization of  terpenoid pathway genes 658
III. Insect interactions with conifers 667
IV. Conclusions and outlook 670

 Acknowledgements 671


 References 671



Summary
Insects select their hosts, but trees cannot select which herbivores will feed upon them. Thus, as long-lived stationary organisms, conifers must resist the onslaught of varying and multiple attackers over their lifetime. Arguably, the greatest threats to conifers are herbivorous insects and their associated pathogens. Insects such as bark beetles, stem- and wood-boring insects, shoot-feeding weevils, and foliage-feeding budworms and sawflies are among the most devastating pests of conifer forests. Conifer trees produce a great diversity of compounds, such as an enormous array of terpenoids and phenolics, that may impart resistance to a variety of herbivores and microorganisms. Insects have evolved to specialize in resistance to these chemicals – choosing, feeding upon, and colonizing hosts they perceive to be best suited to reproduction. This review focuses on the plant–insect interactions mediated by conifer-produced terpenoids. To understand the role of terpenoids in conifer–insect interactions, we must understand how conifers produce the wide diversity of terpenoids, as well as understand how these specific compounds affect insect behaviour and physiology. This review examines what chemicals are produced, the genes and proteins involved in their biosynthesis, how they work, and how they are regulated. It also examines how insects and their associated pathogens interact with, elicit, and are affected by conifer-produced terpenoids.

/pdf/genes-enzymes-and-chemicals-of-terpenoid-diversity-in-the-156bm97ppc.pdf

Genes, enzymes and chemicals of terpenoid diversity in the constitutive and induced defence of conifers against insects and pathogens.

Each perennial woody plant is a highly integrated system of competing carbohydrate sinks (utilization sites). Internal competition for carbohydrates is shown by changes in rates of carbohydrate movement from sources to sinks and reversals in direction of carbohydrate transport as the relative sink strengths of various organs change. Most carbohydrates are produced in foliage leaves but some are synthesized in cotyledons, hypocotyls, buds, twigs, stems, flowers, fruits, and strobili. Although the bulk of the carbohydrate pool moves to sinks through the phloem, some carbohydrates are obtained by sinks from the xylem sap. Sugars are actively accumulated in the phloem and move passively to sinks along a concentration gradient. The dry weight of a mature woody plant represents only a small proportion of the photosynthate it produced. This discrepancy results not only from consumption of plant tissues by herbivores and shedding of plant parts, but also from depletion of carbohydrates by respiration, leaching, exudation, secretion, translocation to other plants through root grafts and mycorrhizae and losses to parasites. Large spatial and temporal variations occur in the use of reserve- and currently produced carbohydrates in metabolism and growth of shoots, stems, roots, and reproductive structures. A portion of the carbohydrate pool is diverted for production of chemicals involved in defense against fungi, herbivores, and competing plants. Woody plants accumulate carbohydrates during periods of excess production and deplete carbohydrates when the rate of utilization exceeds the rate of production. Stored carbohydrates play an important role in metabolism, growth, defense, cold hardiness, and postponement or prevention of plant mortality.

Carbohydrate sources and sinks in woody plants

Climate change is expected to drive increased tree mortality through drought, heat stress, and insect attacks, with manifold impacts on forest ecosystems. Yet, climate-induced tree mortality and biotic disturbance agents are largely absent from process-based ecosystem models. Using data sets from the western USA and associated studies, we present a framework for determining the relative contribution of drought stress, insect attack, and their interactions, which is critical for modeling mortality in future climates. We outline a simple approach that identifies the mechanisms associated with two guilds of insects - bark beetles and defoliators - which are responsible for substantial tree mortality. We then discuss cross-biome patterns of insect-driven tree mortality and draw upon available evidence contrasting the prevalence of insect outbreaks in temperate and tropical regions. We conclude with an overview of tools and promising avenues to address major challenges. Ultimately, a multitrophic approach that captures tree physiology, insect populations, and tree-insect interactions will better inform projections of forest ecosystem responses to climate change.

/pdf/tree-mortality-from-drought-insects-and-their-interactions-2bxzr4bm9u.pdf

Tree mortality from drought, insects, and their interactions in a changing climate

Agrilus bilineatus (Weber) is univoltine in Wisconsin. Adults were present from early June through mid-September; however, peak flight and oviposition occurred during the second half of June. Adults consumed significantly more oak foliage than foliage of hardwoods other than oak. Stressed oaks attracted significantly more adults than did uninjured controls, as measured by density of captured adults on sticky traps. Four larval instars were determined; instar IV was the overwintering stage. Fourth instar larvae generally overwintered in pupal cells in the outer bark or in sapwood if the bark was thin. Larvae, especially third and fourth instars, damaged oaks by girdling the conducting xylem and phloem. Attacked oaks had low root starch content relative to those unattacked. Tree death normally resulted after 2 or 3 years of borer infestation, yet tree death may occur in a single season. Initial attack usually began in the live crown and proceeded downward in succeeding years with no apparent reinfestation of previously killed areas. Mean adult longevity in days for adults fed red oak foliage was 28.1 at 20°, 37.8 at 24°, and 8.3 at 30 °C. Mean duration of the pupal stage in days was 11.7 at 24 °and 8.5 at 30 °C.

The biology and ecology of the twolined chestnut borer, agrilus bilineatus (coleoptera: buprestidae), on oaks, quercus spp., in wisconsin

The biology of the pine engraver, Ips pini (Say) (Coleoptera: Scolytidae), was investigated employing caged and exposed jack pine logs in central Wisconsin in 1957-59. The beetle overwintered only as mature adults in soil and litter. Spring flight normally occurred following a period of about 1 week, during which ambient temperatures averaged 16.7°C, with little or no rainfall. A single male was able to mate 1-6 females, and each female laid 4-5 eggs per day, or 146 eggs during its lifetime. Head capsule measurements revealed 3 larval instars. The complete cycle, including mating and oviposition, required 33-35 days. Mature adults may delay emergence an additional 6-11 days. Inter- and intra-specific competition for food and space was severe. Thanasimus dubius (F.) was the most abundant and efficient predator. No parasites were noted. The top surface of logs in light to moderate shade was most heavily infested. The seasonal history of the pine engraver closely approximated Canadian and other northern United States data.

Notes on the Biology of Ips pini in Central Wisconsin Jack Pine Forests

Two species of pine sawflies,Neodiprion rugifrons Midd. andN. swainei Midd., feed only on matured foliage of jack pine,Pinus banksiana Lamb., and leave juvenile or current-season foliage intact. This unique form of adaptation was studied from the viewpoint of the chemical ecology of this insect-host plant relationship. It was first determined that the differential larval feeding behavior reflects the presence of feeding deterrents. Two major biologically active substances were isolated and identified as 13-keto-8(14)-podocarpen-18-oic acid and dehydroabietic acid. These account for 63.5% and 24.6% of the total deterrency, respectively. The content of the former substance in current-year foliage decreases, as the foliage begins to mature, to the levels that become acceptable toN. swainei by August (60 days old) and to the second generationN. rugifrons by September (90 days old). The timing of their acceptance of juvenile foliage indicates the high levels of adaptation by these insects to allow oviposition for the on-coming adults and acceptable needles for the next generation of larvae. The level of dehydroabietic acid, on the other hand, does not change appreciably during the same time period: this indicates that the component does not play a significant role in the mechanism of differentiating juvenile from matured foliage by the sawfly larvae.

Mechanism of feeding discrimination between matured and juvenile foliage by two species of pine sawflies

Larvae of two pine sawflies, Neodiprion rugifrons Midd. and Neodiprion swainei Midd., consume only old foliage of jack pine, Pinus banksiana Lamb., and leave juvenile foliage intact early in the growing season. The chemical basis for this unique adaptation is a feeding deterrent chemical, 13-keto-8(14)-podocarpen-18-oic acid, which was isolated from juvenile foliage. The content of this deterrent chemical decreases as the foliage begins to mature until needles become acceptable to Neodiprion swainei larvae by August (60-day-old foliage) and to second-generation Neodiprion rugifrons by September (90-day-old foliage). The precise timing of larval acceptance of juvenile foliage indicates a highly specific relationship between these insects and their host tree based on the composition of chemicals in the foliage.

Chemical Basis for Feeding Adaptation of Pine Sawflies Neodiprion rugifrons and Neodiprion swainei.

Diterpene resin acids significantly affect consumption rates, feeding efficiencies, and growth rates of the larch sawfly,Pristiphora erichsonii (Hartig) when topically applied to their natural food, tamarackLarix laricina (DuRoi) K. Koch. Abietic acid, neoabietic acid, dehydroabietic acid, and isopimaric acid significantly reduced consumption rates, feeding efficiencies, and growth rates. Sandaracopimaric acid reduced growth and efficiency but did not influence consumption rate. Two-way analysis of variance indicates a significant interaction between chemical and concentration for growth rate, feeding efficiency, and consumption rate. This interaction indicates that increasing chemical concentrations do not influence the larch sawfly in a uniform manner, supporting the concept of concentration-dependent biological activity of allelochemics.

D. M. Benjamin

Papers

The biology and ecology of the twolined chestnut borer, agrilus bilineatus (coleoptera: buprestidae), on oaks, quercus spp., in wisconsin

Notes on the Biology of Ips pini in Central Wisconsin Jack Pine Forests

Mechanism of feeding discrimination between matured and juvenile foliage by two species of pine sawflies

Chemical Basis for Feeding Adaptation of Pine Sawflies Neodiprion rugifrons and Neodiprion swainei.

Influence of diterpene resin acids on feeding and growth of larch sawfly, Pristiphora erichsonii (Hartig)