Plant Quantity Affects Development and Survival of a Gregarious Insect Herbivore and Its Endoparasitoid Wasp

Virtually all studies of plant-herbivore-natural enemy interactions focus on plant quality as the major constraint on development and survival. However, for many gregarious feeding insect herbivores that feed on small or ephemeral plants, the quantity of resources is much more limiting, yet this area has received virtually no attention. Here, in both lab and semi-field experiments using tents containing variably sized clusters of food plants, we studied the effects of periodic food deprivation in a tri-trophic system where quantitative constraints are profoundly important on insect performance. The large cabbage white Pieris brassicae, is a specialist herbivore of relatively small wild brassicaceous plants that grow in variable densities, with black mustard (Brassica nigra) being one of the most important. Larvae of P. brassicae are in turn attacked by a specialist endoparasitoid wasp, Cotesia glomerata. Increasing the length of food deprivation of newly molted final instar caterpillars significantly decreased herbivore and parasitoid survival and biomass, but shortened their development time. Moreover, the ability of caterpillars to recover when provided with food again was correlated with the length of the food deprivation period. In outdoor tents with natural vegetation, we created conditions similar to those faced by P. brassicae in nature by manipulating plant density. Low densities of B. nigra lead to potential starvation of P. brassicae broods and their parasitoids, replicating nutritional conditions of the lab experiments. The ability of both unparasitized and parasitized caterpillars to find corner plants was similar but decreased with central plant density. Survival of both the herbivore and parasitoid increased with plant density and was higher for unparasitized than for parasitized caterpillars. Our results, in comparison with previous studies, reveal that quantitative constraints are far more important that qualitative constraints on the performance of gregarious insect herbivores and their gregarious parasitoids in nature.     

To Smell you Better: Prior Food Deprivation Increases Herbivore Insect Responsiveness to Host Plant Odor Cues

Hunger plays a crucial role in insect feeding behavior, however food deprivation is rarely considered when insect responses to plant host and related chemical stimuli are investigated. Here we assessed, by means of experiments with Y-tube olfactometer, the effect of food deprivation time on the response of a specialist (Xanthogaleruca luteola) and a generalist (Diabrotica speciosa) herbivore beetle species (Coleoptera: Chrysomelidae) to odor cues of their respective host plants. Increasing food deprivation periods enhanced responses to host plant odor in both species, with insects remaining for longer in the olfactometer arm carrying plant odor than in the control, moving less frequently between olfactometer arms, and being more efficient in moving towards the plant odor as their first choice. These trends were less significant in the generalist species, which also required a longer fasting threshold (48 h) in comparison with the specialist (8 h). Our results, showing that prior food deprivation time can influence insect herbivore responsiveness to plant stimuli and that those effects may vary between species, highlight the risk of neglecting this factor in studies involving insect responses to host or chemical stimuli.     

An Insect Herbivore Microbiome with High Plant Biomass-Degrading Capacity

Herbivores can gain indirect access to recalcitrant carbon present in plant cell walls through symbiotic associations with lignocellulolytic microbes. A paradigmatic example is the leaf-cutter ant (Tribe: Attini), which uses fresh leaves to cultivate a fungus for food in specialized gardens. Using a combination of sugar composition analyses, metagenomics, and whole-genome sequencing, we reveal that the fungus garden microbiome of leaf-cutter ants is composed of a diverse community of bacteria with high plant biomass-degrading capacity. Comparison of this microbiome''s predicted carbohydrate-degrading enzyme profile with other metagenomes shows closest similarity to the bovine rumen, indicating evolutionary convergence of plant biomass degrading potential between two important herbivorous animals. Genomic and physiological characterization of two dominant bacteria in the fungus garden microbiome provides evidence of their capacity to degrade cellulose. Given the recent interest in cellulosic biofuels, understanding how large-scale and rapid plant biomass degradation occurs in a highly evolved insect herbivore is of particular relevance for bioenergy.     

Host Feeding by an Herbivore Improves the Performance of Offspring

Herbivores have developed diverse strategies to manipulate host plants for their own benefits. The gall induction by the maize orange leafhopper Cicadulina bipunctata is different from that by other gall-inducing insects in that the galls are induced not on feeding sites but appear on distant, newly developing leaves. In addition, adult C. bipunctata are highly mobile and seldom feed on gall tissue that they have induced. These mean that the gall induction by C. bipunctata is unlikely to contribute to the fitness of the inducer itself. The objective of this study was to determine whether manipulation of the host plant by this leafhopper has a subsequent benefit to offspring. Adults feeding on maize seedlings caused a partial change in the glucose content and a remarkable change in the accumulation of free amino acids in the gall tissue. Increases in emergence and developmental rates were observed in nymphs feeding on gall tissue induced by prior adult feeding. Such improvements were not evident in nymphs feeding on a C. bipunctata-resistant variety, which rarely displays galls after C. bipunctata feeding, nor on maize seedlings previously foraged by another leafhopper, Psammotettix striatus. The results indicate that gall tissue induced by adult C. bipunctata contribute to better performance of its offspring through improvement of the nutritional components of host plants.     

Asynchrony between Host Plant and Insects-Defoliator within a Tritrophic System: The Role of Herbivore Innate Immunity

The effects of asynchrony in the phenology of spring-feeding insect-defoliators and their host plants on insects’ fitness, as well as the importance of this effect for the population dynamics of outbreaking species of insects, is a widespread and well-documented phenomenon. However, the spreading of this phenomenon through the food chain, and especially those mechanisms operating this spreading, are still unclear. In this paper, we study the effect of seasonally declined leafquality (estimated in terms of phenolics and nitrogen content) on herbivore fitness, immune parameters and resistance against pathogen by using the silver birch Betula pendula—gypsy moth Lymantria dispar—nucleopolyhedrovirus as the tritrophic system. We show that a phenological mismatch induced by the delay in the emergence of gypsy moth larvae and following feeding on mature leaves has negative effects on the female pupal weight, on the rate of larval development and on the activity of phenoloxidase in the plasma of haemolymph. In addition, the larval susceptibility to exogenous nucleopolyhydrovirus infection as well as covert virus activation were both enhanced due to the phenological mismatch. The observed effects of phenological mismatch on insect-baculovirus interaction may partially explain the strong and fast fluctuations in the population dynamics of the gypsy moth that is often observed in the studied part of the defoliator area. This study also reveals some indirect mechanisms of effect related to host plant quality, which operate through the insect innate immune status and affect resistance to both exogenous and endogenous virus.     

Understanding and Manipulating Plant Attributes to Enhance Biological Control

This paper demonstrates the necessity to consider plants as an essential and interactive component of biological control practices. Plants not only possess direct chemical and morphological defenses against herbivores but also benefit from indirect defenses provided by parasitoids and predators, which use herbivores as hosts or prey. Plants play an active role in the interplay between entomophagous arthropods and herbivores and actually mediate many of the interactions, thereby influencing the intensity of protection received. Herein, we review how plant attributes influence natural enemy efficiency by providing shelter, mediating host/prey accessibility, providing host/prey finding cues, influencing host/prey suitability, mediating host/prey availability, and providing supplemental food sources for natural enemies. In light of this crucial role, we suggest ways of manipulating morphological and chemical attributes of crop plants for a more sustainable and balanced control of insect pests in agro-ecosystems.     

Plant Host Finding by Parasitic Plants: A New Perspective on Plant to Plant Communication

Plants release airborne chemicals that can convey ecologically relevant information to other organisms. These plant volatiles are known to mediate a large array of, often complex, interactions between plants and insects. It has been suggested that plant volatiles may have similar importance in mediating interactions among plant species, but there are few well-documented examples of plant-to-plant communication via volatiles, and the ecological significance of such interactions has been much debated. To date, nearly all studies of volatile-mediated interactions among plant species have focused on the reception of herbivore-induced volatiles by neighboring plants. We recently documented volatile effects in another system, demonstrating that the parasitic plant Cuscuta pentagona uses volatile cues to locate its hosts. This finding may broaden the discussion regarding plant-to-plant communication, and suggests that new classes of volatile-meditated interactions among plant species await discovery.Key Words: chemical communication, Cuscuta pentagona, host fiding, host selection, plant-plant communication, plant volatiles, parasitic plantsFor nearly 25 years, the ecological importance of plant-to-plant communication through volatiles has remained an open and much debated question. Plants exchange gases with the atmosphere and, in so doing, release plumes of volatile chemicals that can convey ecologically important information to other organisms. The potential ecological significance of these volatile cues is demonstrated by the large and growing array of interactions between plants and arthropods known to be mediated by plant volatiles. Volatiles serve as foraging cues both for insects that are beneficial to plants, such as pollinators,¹ and those that are harmful such as herbivores.^2,3 Because the volatile blends released by plants exhibit variation in response to environmental stimuli, volatiles can convey detailed information about the status of the emitting plant. Predatory and parasitic insects that feed on herbivorous insects respond preferentially to plant volatiles that are induced by insect feeding,⁴ while female herbivores use such cues to avoid laying their eggs on already-infested plants.^3,5 Moreover, the volatile blends released in response to herbivory can differ between individual herbivore species, providing highly specific cues to specialist parasitoids.⁶ Thus, plant volatiles are known to mediate complex interactions among plants and insects across multiple trophic levels.It has long been speculated that plant volatiles might have similar significance for interactions among plant species, yet there are few well-documented examples of communication between plants by way of volatile signals. Essentially all previous work on plant-to-plant communication has focused on the reception of herbivore-induced volatile signals by neighboring plants, which may use them as early warning signals to initiate their own direct and indirect defense responses. The first studies claiming to document such effects were published almost 25 years ago.^7,8 But issues with the experimental design of these early experiments and the availability of alternative explanations for their results led many ecologists to disregard the phenomenon.^9–11 Later, a number of studies demonstrated that direct and indirect plant defenses could be elicited by exposure to certain induced plant volatiles.^12–15 But many of these effects were demonstrated in airtight chambers with volatile concentrations far higher than those likely experienced in natural settings, again raising doubts about the ecological significance of plant-plant communication.^16–18 Still more recently, some researchers have provided evidence that more realistic volatile concentrations likely induce priming of the defenses of receiving plants, rather than the initiation of full scale responses,¹⁵ while others have documented volatile effects under natural conditions.^19–21 Thus, despite continuing caution about the interpretation of experiments in this area,^17,18 there is mounting evidence that plant herbivore-induced volatiles can serve as early warning signals to neighboring plants.We recently documented an entirely new class of volatile mediated interactions among plants: the role of plant volatiles in host location by parasitic plants that attach to above ground shoots of other plants. Plant parasites are important components of natural and agricultural ecosystems and play important roles in determining community structure and dynamics.^22,23 We are exploring the mechanisms of host-location and other interactions between parasitic plants in the genus Cuscuta (dodder) and their host plants. Dodder vines germinate from seeds containing limited energy reserves and, as the parasites have no roots and little photosynthetic ability, must quickly locate and attach to suitable hosts in order to survive (Fig. 1). Thus, there is presumably significant selection pressure for dodder vines to employ efficient strategies for host location, and host plant volatiles may be expected to provide relevant directional cues. Dodder seedlings exhibit a rotational growth habit (circumnutation) following germination and previous researchers have suggested that host-finding might involve random growth²⁴ or the exploitation of light cues.²⁵Open in a separate windowFigure 1Seedling of Cuscuta pentagona (A) foraging toward a 20-day-old tomato plant, (B) attaching to and beginning to grow from stems of tomato seedlings and (C) close up of C. pentagona attachment.Using a very simple experimental design, we explored the possibility that host-plant volatiles might mediate host-location by seedlings of C. pentagona. We placed a germinated seedling in a vial of water located at the center of a dry filter paper disk. A host plant (a 20-day old tomato seedling) was placed near the edge of the disk and the dodder seedling was allowed to forage for four days. By the end of the experiment the seedling would lay horizontally on the disk and we traced its position on the filter paper in order to assess the directionality of growth relative to the host plant. This experiment was replicated 30 times and our results clearly indicated directional growth toward the tomato plant (80% of the tested seedlings grew into the disk half nearest the host) demonstrating that C. pentagona seedlings were perceiving some host-derived cue.We did not observe directed growth when we tested dodder seedling response to alternative targets including pots of moist soil, artificial plants, and vials of colored water intended to mimic possible light cues. In order to confirm a role for plant volatiles in host location by C. pentagona, we tested seedling response to host plant volatiles extracted from filtered air in a volatile collection system and then released from rubber septa in the absence of any other host-derived cues. Here we observed a directed growth response similar to that exhibited toward an intact tomato seedling, confirming that host plant volatiles do provide a cue used for host location by C. pentagona. In subsequent experiments we found directed growth toward impatiens and alfalfa plants, which are attractive hosts for C. pentagona and also toward wheat plants which are poor hosts, suggesting that the host-location mechanisms operate over a wide range of host species.Since discriminating between more and less desirable host species is likely to be important in natural settings, we next explored whether dodder seedlings could distinguish volatile signals from host and nonhost plants. Cuscuta pentagona seedlings exhibited directional growth toward tomato plants in preference to wheat plants and also to extracted volatiles from tomato in preference to those from wheat, demonstrating an ability to distinguish and choose among volatiles from more and less preferred hosts.When we tested seedling responses to individual compounds from the wheat and tomato blends, we found that three compounds from tomato, α-pinene, β-myrcene, and β-phellandrene elicited directed growth. β-myrcene was also present in the wheat blend. Unexpectedly, we also found that one compound present in the wheat blend, (Z)-3-hexenyl acetate, was repellent, providing a plausible explanation for the lower attractiveness of the wheat blend. It is interesting to note that (Z)-3-hexenyl acetate is also released by tomato in response to feeding by herbivores, and we have some data suggesting that C. pentagona seedlings may find tomato seedlings infested by Heliothis virescens caterpillars less attractive than un-attacked plants (unpublished data).The discovery that some parasitic plants exploit host plant volatiles for host location provides a new perspective on volatile mediated interactions among plant species, demonstrating that plant volatiles play a role in mediating ecologically significant interactions in at least one system other than the transfer of herbivore-induced warning signals. We think it is quite likely that plant volatiles will be found to play a role in host location by other parasitic plants and perhaps even by vining plants generally. Moreover, we think it is more likely than not that more classes of volatile mediated interactions among plants remain to be discovered given the potential availability of volatile cues and the fitness benefits to be derived by plants using such cues to gather information about the identity and condition of their neighbors.     

The Root Herbivore History of the Soil Affects the Productivity of a Grassland Plant Community and Determines Plant Response to New Root Herbivore Attack

Insect root herbivores can alter plant community structure by affecting the competitive ability of single plants. However, their effects can be modified by the soil environment. Root herbivory itself may induce changes in the soil biota community, and it has recently been shown that these changes can affect plant growth in a subsequent season or plant generation. However, so far it is not known whether these root herbivore history effects (i) are detectable at the plant community level and/or (ii) also determine plant species and plant community responses to new root herbivore attack. The present greenhouse study determined root herbivore history effects of click beetle larvae (Elateridae, Coleoptera, genus Agriotes) in a model grassland plant community consisting of six common species (Achillea millefolium, Plantago lanceolata, Taraxacum officinale, Holcus lanatus, Poa pratensis, Trifolium repens). Root herbivore history effects were generated in a first phase of the experiment by growing the plant community in soil with or without Agriotes larvae, and investigated in a second phase by growing it again in the soils that were either Agriotes trained or not. The root herbivore history of the soil affected plant community productivity (but not composition), with communities growing in root herbivore trained soil producing more biomass than those growing in untrained soil. Additionally, it influenced the response of certain plant species to new root herbivore attack. Effects may partly be explained by herbivore-induced shifts in the community of arbuscular mycorrhizal fungi. The root herbivore history of the soil proved to be a stronger driver of plant growth on the community level than an actual root herbivore attack which did not affect plant community parameters. History effects have to be taken into account when predicting the impact of root herbivores on grasslands.     

Phytohormones Related to Host Plant Manipulation by a Gall-Inducing Leafhopper

The maize orange leafhopper Cicadulina bipunctata (Hemiptera: Cicadellidae) induces galls characterized by growth stunting and severe swelling of leaf veins on various plants of Poaceae. Previous studies revealed that galls are induced not on feeding site but on distant, newly extended leaves during the feeding, and strongly suggested that some chemicals injected by the leafhopper affect at the leaf primordia. To approach the mechanism underlying gall induction by C. bipunctata, we examined physiological response of plants to feeding by the leafhopper. We performed high-throughput and comprehensive plant hormone analyses using LC-ESI-MS/MS. Galled maize leaves contained higher contents of abscisic acid (ABA) and trans-Zeatin (tZ) and lower contents of gibberellins (GA₁ and GA₄) than ungalled maize leaves. Leafhopper treatment significantly increased ABA and tZ contents and decreased GA₁ and GA₄ contents in extending leaves. After the removal of leafhoppers, contents of tZ and gibberellins in extending leaves soon became similar to the control values. ABA content was gradually decreased after the removal of leafhoppers. Such hormonal changes were not observed in leafhopper treatment on leaves of resistant maize variety. Water contents of galled leaves were significantly lower than control leaves, suggesting water stress of galled leaves and possible reason of the increase in ABA content. These results imply that ABA, tZ, and gibberellins are related to gall induction by the leafhopper on susceptible variety of maize.     

An Exploration of Hypotheses that Explain Herbivore and Pathogen Attack in Restored Plant Communities

Many hypotheses address the associations of plant community composition with natural enemies, including: (i) plant species diversity may reduce enemy attack, (ii) attack may increase as host abundance increases, (iii) enemy spillover may lead to increased attack on one host species due to transmission from another host species, or enemy dilution may lead to reduced attack on a host that would otherwise have more attack, (iv) physical characteristics of the plant community may influence attack, and (v) plant vigor may affect attack. Restoration experiments with replicated plant communities provide an exceptional opportunity to explore these hypotheses. To explore the relative predictive strengths of these related hypotheses and to investigate the potential effect of several restoration site preparation techniques, we surveyed arthropod herbivore and fungal pathogen attack on the six most common native plant species in a restoration experiment. Multi-model inference revealed a weak but consistent negative correlation with pathogen attack and host diversity across the plant community, and no correlation between herbivory and host diversity. Our analyses also revealed host species-specific relationships between attack and abundance of the target host species, other native plant species, introduced plant species, and physical community characteristics. We found no relationship between enemy attack and plant vigor. We found minimal differences in plant community composition among several diverse site preparation techniques, and limited effects of site preparation techniques on attack. The strongest associations of community characteristics with attack varied among plant species with no community-wide patterns, suggesting that no single hypothesis successfully predicts the dominant community-wide trends in enemy attack.     

Host Preference and Progeny Sex Ratio in a Solitary Koinobiont Mealybug Endoparasitoid, Anagyrus Pseudococci (Girault), in Response to its Host Stage

Anagyrus pseudococci (Girault) , a koinobiont endoparasitoid , is a potential biological control agent of the citrus mealybug Planococcus citri (Risso) . This paper examines the effect of host stage of the mealybugs on the parasitoid preference , development , survival and sex ratio of the offspring . Host susceptibility and preference tests showed that the parasitoid had a significant preference for the older host instars . Percentage parasitization increased 4.8 - fold in the adult stage , compared with the second - instar host , although the parasitoid developed and emerged successfully from all stages . Mean developmental time for male parasitoids was faster than for the females . There was some evidence of delayed development of males in young hosts . Higher percentage emergence of parasitoid was observed from older mealybugs . A. pseudococci exhibited maternal adjustment of sex ratio as a function of host size with an increased proportion of females with the increasing host size . Females maximized their fitness by adjusting offspring sex ratio in response to host size without evaluating the future host quality . This information is important for mass rearing of A. pseudococci and for evaluating it in a biological control programme for P. citri.     

植食性昆虫诱导的挥发物及其在植物通讯中的作用

正常健康植株的挥发物代谢维持在基底水平,当遭到昆虫取食时,植物释放出特定的挥发物,用来招引害虫的天敌,还能诱导邻近植株产生防御反应.文章就此问题的研究进展作了介绍.     

Practical Applications of Manipulating Plant Architecture by Regulating Gibberellin Metabolism

The international trade in floriculture is estimated to be worth about US$150 billion, with the global demand for ornamentals steadily increasing. Consumer choice is influenced by factors such as plant architecture and flower colour. Conventional breeding has been responsible for the introduction of novel traits into ornamental plants and has played an important role in the development of new cultivars. However, a restricted gene pool and failure of distant crosses have led to the exploitation of somatic cell techniques, particularly genetic transformation, to generate plants with desirable traits. Gibberellins (GAs) are endogenous plant hormones that control key aspects of growth and development. Chemical growth regulators that modify GA biosynthesis are used extensively in horticulture to control plant stature, increasing production costs, manpower, and environmental risks. An alternative strategy involves genetic manipulation of GA metabolism to induce phenotypic changes, particularly alteration of stature. Because ornamentals are not used for human consumption, genetic manipulation approaches with these plants may be more acceptable in the immediate future to the general public, in certain parts of the world, than genetically manipulated food crops.     

Evolution of Territoriality by Herbivores in Response to Host Plant Defenses

Plants may play an active role in the evolution of territorialityand associated animal behaviors such as spacing and cannibalism.I hypothesize that these behaviors have in part evolved in directresponse to plant defenses that would otherwise diminish individualsuccess. These defenses limit resource availability and concentrateherbivores at specific sites where they then suffer from inducedplant defenses, increased predation and competition. Plant traitsthat enhance the negative effects of competition and increasedpredation must be included in the suite of plant defenses againstherbivory. In a specific example with Pemphigus gall aphids, plant defensesresult in a strong selection pressure favoring territorial behavior.The negative effects of competition give territorial individualsa 2.3-fold advantage over non-territorial individuals. Induceddefenses (i.e., density dependent leaf abscission) can be justas important as competition as a selection pressure for territorialbehavior. With the addition of induced plant defenses territorialindividuals realize a 4.4-fold advantage. Furthermore, roughapproximations suggest that in the absence of territorial behaviorpredation would increase by 52%. The same traits which promote territoriality also encouragecannibalism, a surprisingly common herbivore behavior. To theextent cannibalism reduces the herbivore population, plant traitswhich promote this behavior may realize a selective advantage. Viewing plants as dynamic rather than passive in their interactionswith pests may lead to a better understanding of animal behaviors.     

Solar Ultraviolet-B Radiation Affects Seedling Emergence,DNA Integrity,Plant Morphology,Growth Rate,and Attractiveness to Herbivore Insects in Datura ferox

To study functional relationships between the effects of solar ultraviolet-B radiation (UV-B) on different aspects of the physiology of a wild plant, we carried out exclusion experiments in the field with the summer annual Datura ferox L. Solar UV-B incident over Buenos Aires reduced daytime seedling emergence, inhibited stem elongation and leaf expansion, and tended to reduce biomass accumulation during early growth. However, UV-B had no effect on calculated net assimilation rate. Using a monoclonal antibody specific to the cyclobutane-pyrimidine dimer (CPD), we found that plants receiving full sunlight had more CPDs per unit of DNA than plants shielded from solar UV-B, but the positive correlation between UV-B and CPD burden tended to level off at high (near solar) UV-B levels. At our field site, Datura plants were consumed by leaf beetles (Coleoptera), and the proportion of plants attacked by insects declined with the amount of UV-B received during growth. Field experiments showed that plant exposure to solar UV-B reduced the likelihood of leaf beetle attack by one-half. Our results highlight the complexities associated with scaling plant responses to solar UV-B, because they show: (a) a lack of correspondence between UV-B effects on net assimilation rate and whole-plant growth rate, (b) nonlinear UV-B dose-response curves, and (c) UV-B effects of plant attractiveness to natural herbivores.     

寄主大豆对根结瘤的控制

我国９个大豆（ＧｌｙｃｉｎｅｍａｘＬ．Ｍｅｒｒ．）品种感染根瘤菌ＵＳＤＡ１１０后,产生不同的结瘤数,低者在２０个以下．高者在６０个以上。赤豆、绿赤豆也可被感染结瘤,而豇豆、扁豆则不能。超结瘤大豆ｎｔｓ３８２作为接穗时能诱导我国大豆原结瘤数有４５个的开育１０号、原结瘤数有１２个的大黄分别发生高结瘤。ｎｔｓ３８２作为砧木时,则不能表现超结瘤．表明超结瘤因子能传给我国大豆,反之存在于我国大豆中的限制超结瘤的因子也能传给ｎｔｓ３８２。ｎｔｓ３８２于ＮＯ３－环境中仍表现超结瘤的特点也能导入开育１０号、大黄及赤豆根部,并使之在ＮＯ３－环境中结瘤。在ＮＯ３－环境中不能结瘤的开育１０号作为接穗,ｎｔｓ３８２作为砧木的嫁接植株,于子叶生长阶段接受ＮＯ３－时,仍能结瘤,于真对生长时接受ＮＯ３－时．则不能结瘤,表明限制结瘤因子于真叶细胞中被诱导形成。     

Plant Exclusion of a Herbivore; Crayfish Population Decline caused by an Invading Waterweed

The population of the crayfish Astacus astacus was recorded in Lake Steinsfjorden (southeast Norway) over the period 1979–1996 by studies of total catch effort (baited traps) and catch per unit effort over the season. Over the years 1979–1987, total population of exploitable crayfish (>9.5 cm) was 194,000 (±62,000 SD), and the catches were evenly distributed over the shallow areas. After 1987 there was a sudden decrease in population size, reaching a level of 92,000 (±22,000 SD) for the 10 years that followed. From 1977 onwards the Canadian pondweed Elodea canadensis invaded the lake and established dense covers over large parts of the shallow areas. The crayfish were gradually excluded from areas covered by Elodea, while the yield from remaining areas remained relatively constant. Direct observation by test-fishing and diving confirmed the virtual absence of crayfish within the Elodea stands. Dense stands may directly interfere with movement of adult crayfish, and also strong fluctuations in O₂ and pH were recorded within the stands, probably acting as a stress factor. Although anoxia was not observed in this survey, it may occur during years of massive dieback of Elodea. Thus, while crayfish are able to feed on Elodea, they are unable to control the rapid growth over large areas of this invader, and somewhat paradoxically the herbivore is spatially excluded by its potential resource.     

Production of Plant Made Pharmaceuticals: From Plant Host to Functional Protein

In the last two decades plants have emerged as valuable alternatives to mammalian cells for the production of pharmaceuticals and their potential as expression systems was shown by the commercial availability and acceptance of several plant made therapeuticals in clinical trials. Plants have many advantages over yeast, insect and bacterial expression systems such as the potential to properly fold the expressed proteins and the synthesis of more human-like N-glycans on the proteins. However, several constraints, such as expression yields, downstream processing and structural authenticity, currently limit the widespread use of plant expression systems. In this review, the focus is on the current limitations of plant systems for the production of pharmaceuticals and the possibilities to overcome these obstacles. A comparison is made with insect cell and yeast expression systems. Furthermore, the importance of glycosylation, in particular N-glycosylation for the biological function(s) of therapeutics in the human body will be discussed in detail and an overview of the state of art in the humanization of the N-glycosylation pathway in plants is provided.