This review examines the direct effects of climate change on insect herbivores. Temperature is identified as the dominant abiotic factor directly affecting herbivorous insects. There is little evidence of any direct effects of CO2 or UVB. Direct impacts of precipitation have been largely neglected in current research on climate change. Temperature directly affects development, survival, range and abundance. Species with a large geographical range will tend to be less affected. The main effect of temperature in temperate regions is to influence winter survival; at more northerly latitudes, higher temperatures extend the summer season, increasing the available thermal budget for growth and reproduction. Photoperiod is the dominant cue for the seasonal synchrony of temperate insects, but their thermal requirements may differ at different times of year. Interactions between photoperiod and temperature determine phenology; the two factors do not necessarily operate in tandem. Insect herbivores show a number of distinct life-history strategies to exploit plants with different growth forms and strategies, which will be differentially affected by climate warming. There are still many challenges facing biologists in predicting and monitoring the impacts of climate change. Future research needs to consider insect herbivore phenotypic and genotypic flexibility, their responses to global change parameters operating in concert, and awareness that some patterns may only become apparent in the longer term.

http://www.discoverlife.org/pa/or/polistes/pr/2010nsf_macro/references/Bale_et_al2002.pdf

Herbivory in global climate change research: direct effects of rising temperature on insect herbivores

Food webs in nature have multiple, reticulate connections between a diversity of consumers and resources. Such complexity affects web dynamics: it first spreads the direct effects of consumption and productivity throughout the web rather than focusing them at particular "trophic levels." Second, consumer densities are often donor controlled with food from across the trophic spectrum, the herbivore and detrital channels, other habitats, life-history omnivory, and even trophic mutualism. Although consumers usually do not affect these resources, increased numbers often allow consumers to depress other resources to levels lower than if donor-controlled resources were absent. We propose that such donor-controlled and "multichannel" omnivory is a general feature of consumer control and central to food web dynamics. This observation is contrary to the normal practice of inferring dynamics by simplifying webs into a few linear "trophic levels," as per "green world" theories. Such theories do not accommodate commo...

Food Web Complexity and Community Dynamics

Half of all insect species are dependent on living plant tissues, consuming about 10% of plant annual production in natural habitats and an even greater percentage in agricultural systems, despite sophisticated control measures. Plants are generally remarkably well-protected against insect attack, with the result that most insects are highly specialized feeders. The mechanisms underlying plant resistance to invading herbivores on the one side, and insect food specialization on the other, are the main subjects of this book. For insects these include food-plant selection and the complex sensory processes involved, with their implications for learning and nutritional physiology, as well as the endocrinological spects of life cycle synchronization with host plant phenology. In the case of plants exposed to insect herbivores, they include the activation of defence systems in order to minimize damage, as well as the emission of chemical signals that may attract natural enemies of the invading herbivores and maybe exploited by neighbouring plants that mount defences as well.

Insect-plant biology

Insect guts present distinctive environments for microbial colonization, and bacteria in the gut potentially provide many beneficial services to their hosts. Insects display a wide range in degree of dependence on gut bacteria for basic functions. Most insect guts contain relatively few microbial species as compared to mammalian guts, but some insects harbor large gut communities of specialized bacteria. Others are colonized only opportunistically and sparsely by bacteria common in other environments. Insect digestive tracts vary extensively in morphology and physicochemical properties, factors that greatly influence microbial community structure. One obstacle to the evolution of intimate associations with gut microorganisms is the lack of dependable transmission routes between host individuals. Here, social insects, such as termites, ants, and bees, are exceptions: social interactions provide opportunities for transfer of gut bacteria, and some of the most distinctive and consistent gut communities, with specialized beneficial functions in nutrition and protection, have been found in social insect species. Still, gut bacteria of other insects have also been shown to contribute to nutrition, protection from parasites and pathogens, modulation of immune responses, and communication. The extent of these roles is still unclear and awaits further studies.

The gut microbiota of insects - diversity in structure and function.

That major flows of energy occur along detrital pathways in all ecosystems is a recent recognition. In freshwater ecosystems, detritus or dead organic matter (217) has two possible sources: autochthonous detritus generated within the ecosystem and allochthonous detritus generated externally. This review is concerned with the breakdown of vascular plant detritus whether autochthonous, from aquatic vascular plants, or allochthonous, derived from riparian trees and herbs. The importance to the energetics of streams of vascular plant material from riparian vegetation was recognized in early studies by Nelson & Scott (184), Egglishaw (85), and Minshall (175). Organic matter budgets for various streams have provided quantitative data to support these early observations (96, 132, 182, 254). However, many low-order streams that lack canopies of riparian vegetation may be dominated by autochthonous primary production of nonvascular plant origin. (72, 176). Theoretical models (256) predict increasing importance of autochthonous production by periphyton and aquatic vascular plants for middle-order streams but less importance of these sources in very large streams, mainly due to light limitation. The relative dominance of allochthonous vs autochthonous sources has been shown to vary between stream systems and with local conditions within streams (72, 178). While vascular plant leaves have received most attention in stream research, there is growing recognition that wood is also important. The direct contribution of wood to stream energy budgets is minimal because wood is resistant to breakdown (e.g. 8, 251). However, woody debris is indirectly important because it creates habitat for aquatic organisms (5), promotes

Vascular plant breakdown in freshwater ecosystems

There is no correlation between protein-precipitating capacity and either total phenolic or proanthocyanidin content of extracts of mature foliage from six species of oaks: Quercus alba (white oak), Q. bicolor (swamp white oak), Q. macrocarpa (bur oak), Q. palustris (pin oak), Q. rubra (red oak), and Q. velutina (black oak). It is argued that studies which probe the role of tannins in the selection and utilization of food by herbivores should include a protein-precipitation assay, since such an assay provides a measure of the property of tannins which is presumed to contribute to their utility as defensive compounds. A convenient modification of the bovine serum albumin (BSA) precipitation assay, which measures the amount of protein precipitated when a plant extract is added to a BSA solution, is described. Advantages of this procedure recommend its routine adoption in studies of the role of tannins in plant-herbivore interactions.

/pdf/tannin-assays-in-ecological-studies-lack-of-correlation-1mk6kwa4t7.pdf

Tannin assays in ecological studies: Lack of correlation between phenolics, proanthocyanidins and protein-precipitating constituents in mature foliage of six oak species.

CONTENTS I. Intmduction . . . . . . . . . 11. Arthropod-fungal associations . . . . . . . (I) Arthropods associated with sporophores . . . . (2) Arthropods in habitats which include fungal mycelium . (3) Insects involved symbiotically with fungi . . . . 111. Nutritive characteristics of fungal tissue . . . . . (I) Caloric value . . . . . . . . (2) Elemental composition . . . . . . . (3) The macronutrients of fungi . . . . . . (4) The micronutrients of fungi . . . . . . (5) summary. . . . . . . . . . IV. Digestive and metabolic requirements imposed on mycophagous species by the special characteristics of fungal tissue. . . . . . . . (I) Fungal polysaccharides . . . . . . . . . . (2) Fungal sterols . . . . . . . . . . . . (3) Urea and ammonia . . . . . . . . . . . (4) Secondary metabolites . . . . . . . . . . (5) Summary. . . . . . . . . . . . . V. Acquired digestive enzymes: a windfall of mycophagy . . . . . (I) Enzymes active against plant cell-wall polysaccharides . . . . (2) Enzymes active against fungal constituents. . . . . . . (3) Enzymes active against phenolic substances . . . . . . (4) Requirements imposed by the exploitation of acquired digestive enzymes . (5) Acquired digestive enzymes: a closing comment . . . . . VI. summary . . . . . . . . . . . . . VII. Acknowledgement . . . . . . . . . . . . VIII. References . . . . . . . . . . . . . i

/pdf/biochemical-implications-of-insect-mycophagy-1t5swfued8.pdf

Biochemical implications of insect mycophagy

Despite the abundance and diversity of species that include living or dead plant tissue in their diets, the ability to digest cellulose is rare in insects and is restricted to a small number of orders and families. In this paper it is argued that cellulolytic capacity is uncommon in insects simply because it is a trait that is rarely advantageous to possess. Although there is a growing body of evidence for the occurrence of symbiont-independent cellulose digestion in cockroaches and in higher termites from the subfamily Nasutitermitinae, cellulose digestion in insects is usually mediated by microorganisms. It is proposed that non-cellulolytic omnivorous scavengers and detritivores may be preadapted to evolve symbiont-mediated cellulolytic mechanisms because of the prevalence of mutualistic associations between such species and the microorganisms that normally reside in their hindguts. A scenario is proposed for the evolution of symbiont-mediated cellulolytic capacity in roaches and lower termites. Finally, it is suggested that biochemical studies of insect cellulases might provide crucial insights that would greatly advance our understanding of the evolution of cellulose digestion in insects.

The evolution of cellulose digestion in insects

The midguts of adult workers of the higher termite species Macrotermes natalensis contain the entire set of digestive enzymes required for the digestion of native cellulose. The C(x)-cellulases and the beta-glucosidases are produced, at least in part, by the termite's own midgut epithelium and salivary glands. The C(1)-cellulases, on the other hand, are acquired by the termites when they feed on a fungus that grows in their nests. We propose that the involvement of acquired digestive enzymes could serve as the basis for a general strategy of resource utilization and further suggest that the acquisition of digestive enzymes may be a widespread phenomenon among mycophagous invertebrates.

https://science.sciencemag.org/content/sci/199/4336/1453.full.pdf

Cellulose Digestion in the Midgut of the Fungus-Growing Termite Macrotermes natalensis: The Role of Acquired Digestive Enzymes.

/pdf/cellulose-digestion-in-insects-2ebz0ntanq.pdf

Michael M. Martin

Papers

Tannin assays in ecological studies: Lack of correlation between phenolics, proanthocyanidins and protein-precipitating constituents in mature foliage of six oak species.

Biochemical implications of insect mycophagy

The evolution of cellulose digestion in insects

Cellulose Digestion in the Midgut of the Fungus-Growing Termite Macrotermes natalensis: The Role of Acquired Digestive Enzymes.

Cellulose digestion in insects