Predation risk affects diapause induction in the spider mite Tetranychus urticae

Whenever diapause induction triggers movement into another microhabitat or the development of protective morphological structures, this may also alter predation risk. If the risk of being eaten is lower in the diapause phase, then there may be selection favouring diapause induction in response to predators or their cues. In this article, we studied the effect of the predatory mite Typhlodromus pyri on diapause induction in the spider mite Tetranychus urticae. We used a Greek strain because under long-night photoperiods and low temperature only part of the population enters diapause, thereby leaving room for the impact of another factor. In spider mite groups under predation, the percentage diapause induction increased whenever night-lengths were such that diapause was induced (13–16 h of night). Given this diapause induction in response to predation risk, the question arises whether entering diapause helps spider mites to escape from predation and contribute more offspring to the spring generation next year.     

Functional analysis of NLP genes from Botrytis elliptica

We functionally analysed two Nep1-like protein (NLP) genes from Botrytis elliptica (a specialized pathogen of lily), encoding proteins homologous to the necrosis and ethylene-inducing protein (NEP1) from Fusarium oxysporum. Single gene replacement mutants were made for BeNEP1 and BeNEP2 , providing the first example of transformation and successful targeted mutagenesis in this fungus. The virulence of both mutants on lily leaves was not affected. BeNEP1 and BeNEP2 were individually expressed in the yeast Pichia pastoris , and the necrosis-inducing activity was tested by infiltration of both proteins into leaves of several monocots and eudicots. Necrotic symptoms developed on the eudicots tobacco, Nicotiana benthamiana and Arabidopsis thaliana , and cell death was induced in tomato cell suspensions. No necrotic symptoms developed on leaves of the monocots rice, maize and lily. These results support the hypothesis that the necrosis-inducing activity of NLPs is limited to eudicots. We conclude that NLPs are not essential virulence factors and they do not function as host-selective toxins for B. elliptica .     

Pathogen profile update: Fusarium oxysporum

Taxonomy: Kingdom Fungi; Phylum Ascomycota; Class Sordariomycetes; Order Hypocreales; Family Nectriaceae; genus Fusarium .
Host range: Very broad at the species level. More than 120 different formae speciales have been identified based on specificity to host species belonging to a wide range of plant families.
Disease symptoms: Initial symptoms of vascular wilt include vein clearing and leaf epinasty, followed by stunting, yellowing of the lower leaves, progressive wilting, defoliation and, finally, death of the plant. On fungal colonization, the vascular tissue turns brown, which is clearly visible in cross-sections of the stem. Some formae speciales are not primarily vascular pathogens, but cause foot and root rot or bulb rot.
Economic importance: Can cause severe losses in many vegetables and flowers, field crops, such as cotton, and plantation crops, such as banana, date palm and oil palm.
Control: Use of resistant varieties is the only practical measure for controlling the disease in the field. In glasshouses, soil sterilization can be performed.
Useful websites: http://www.broad.mit.edu/annotation/genome/fusarium_group/MultiHome.html ; http://www.fgsc.net/Fusarium/fushome.htm ; http://www.phi-base.org/query.php     

Seasonal changes on two different spatial scales： response of aquatic invertebrates to water body and microhabitat

Knowledge about the spatial and temporal scales of both habitat use and the functional significance of different adaptations is essential for an understanding of the population dynamics of invertebrate assemblages. This fundamental knowledge is not only interesting from an academic point of view, but is sorely lacking and needed in the field of restoration ecology. Many species are threatened due to degradation. Knowing what environmental conditions are needed dtLring the life cycle of these species is important in the design of restoration measures which aim to lift existing bottlenecks for threatened species. To assess the relative importance of water type and microhabitat in structuring the invertebrate assemblage during different seasons, invertebrates were sampled in three water bodies differing in trophic level and acidity. Different parts within a water body （microhabitats） were sampled separately and each water body was sampled in all four seasons. Results show that water body is an important factor structuring the invertebrate assemblage early in the season, whereas microhabitat became more important later in the season. Structural complexity of microhabitats was related to the type of locomotion employed by invertebrates. Seasonal differences could be related to population dynamics （reproduction, mortality）. Moreover, fluctuations in resource availability were expected to differ between the water bodies, with highest fluctuations in the eutrophic water body and with fluctuations becoming less predictable later in the season. This was confirmed by the data： species synchronization to pulses in food availability was strongest in the eutrophic water body. Moreover, synchronization was strongest in summer, while in autumn waters were invaded by dispersive species. Based on these results a synthesis is presented on the functioning of the different waters during the different seasons.     

Effects of plant diversity and structural complexity on parasitoid behaviour in a field experiment

1. In natural ecosystems, plants containing hosts for parasitoids are often embedded within heterogeneous plant communities. These plant communities surrounding host‐infested plants may influence the host‐finding ability of parasitoids. 2. A release‐recapture‐approach was used to examine whether the diversity and structural complexity of the community surrounding a host‐infested plant influences the aggregation behaviour of the leaf‐miner parasitoid Dacnusa sibirica Telenga and naturally occurring local leaf‐miner parasitoids. Released and locally present parasitoids were collected on potted Jacobaea vulgaris Gaertn.plants infested with the generalist leaf‐miner Chromatomyia syngenesiae Hardy. The plants were placed in experimentally established plant communities differing in plant diversity (1–9 species) and habitat complexity (bare ground, mown vegetation, and tall vegetation). Additionally, parasitoids were reared out from host mines on the trap plants. 3. Plant diversity did not influence the mean number of recaptured D. sibirica or captures of other locally present parasitoids but the number of recaptured parasitoids was influenced by habitat complexity. No D. sibirica parasitoids were recaptured in the bare ground plots or plots with mown vegetation. The mean number of recaptured D. sibirica generally increased with increasing complexity of the plant community, whereas locally present parasitoids were captured more frequently in communities with more bare ground. There was a unimodal relationship between the number of reared out parasitoids and diversity of the surrounding vegetation with the highest density of emerged parasitoids at intermediate diversity levels. 4. The present study adds to the thus far limited body of literature examining the aggregation behaviour of parasitoids in the field and suggests that the preference of parasitoids to aggregate in complex versus simple vegetation is association specific and thus depends on the parasitoid species as well as the identity of the plant community.     

Influence of presence and spatial arrangement of belowground insects on host‐plant selection of aboveground insects: a field study

Abstract 1. Several studies have shown that above‐ and belowground insects can interact by influencing each others growth, development, and survival when they feed on the same host‐plant. In natural systems, however, insects can make choices on which plants to oviposit and feed. A field experiment was carried out to determine if root‐feeding insects can influence feeding and oviposition preferences and decisions of naturally colonising foliar‐feeding insects. 2. Using the wild cruciferous plant Brassica nigra and larvae of the cabbage root fly Delia radicum as the belowground root‐feeding insect, naturally colonising populations of foliar‐feeding insects were monitored over the course of a summer season. 3. Groups of root‐infested and root‐uninfested B. nigra plants were placed in a meadow during June, July, and August of 2006 for periods of 3 days. The root‐infested and the root‐uninfested plants were either dispersed evenly or placed in clusters. Once daily, all leaves of each plant were carefully inspected and insects were removed and collected for identification. 4. The flea beetles Phyllotreta spp. and the aphid Brevicoryne brassicae were significantly more abundant on root‐uninfested (control) than on root‐infested plants. However, for B. brassicae this was only apparent when the plants were placed in clusters. Host‐plant selection by the generalist aphid M. persicae and oviposition preference by the specialist butterfly P. rapae, however, were not significantly influenced by root herbivory. 5. The results of this study show that the presence of root‐feeding insects can affect feeding and oviposition preferences of foliar‐feeding insects, even under natural conditions where many other interactions occur simultaneously. The results suggest that root‐feeding insects play a role in the structuring of aboveground communities of insects, but these effects depend on the insect species as well as on the spatial distribution of the root‐feeding insects.     

Structural and functional characterization of a novel, host penetration-related pectate lyase from the potato cyst nematode Globodera rostochiensis

The cell wall, a strong extraprotoplasmic layer surrounding plant cells that mainly consists of a variety of polysaccharides, constitutes a major barrier for potential parasites. Plant-parasitic nematodes are well equipped to overcome this barrier as they produce and secrete cell-wall-degrading enzymes. Expression profiling of various life stages of the potato cyst nematode Globodera rostochiensis revealed a novel pectate lyase gene ( Gr-pel2 , 759 bp). The Gr-PEL2 protein showed highest similarity to pectate lyases from the facultative plant-parasitic nematodes Bursaphelenchus mucronatus and B. xylophilus and the soil-inhabiting saprophytic Streptomyces and Frankia species (i.e. 40–42% identity and 58–60% similarity), whereas only a remote relatedness to the previously identified Gr-PEL1 was observed (i.e. 28% identity and 43% similarity). Transient expression of Gr-pel2 in leaves of Nicotiana benthamiana resulted in severe malformations of the infiltrated tissues, not relating to maceration and soft rot symptoms. Ca²⁺ is known to be essential for pectate lyase activity, and the most likely calcium-binding site was identified in the Gr-PEL2 protein by combining homology modelling of the three-dimensional structure, site-directed mutagenesis and transient expression in leaves. A highly charged cleft in Gr-PEL2, which is likely to be involved in substrate binding and which is also significantly more hydrophobic in Gr-PEL1, was shown to be essential for protein activity. Our results underline the broad spectrum of pectate lyases and cell-wall-degrading enzymes necessary for successful parasitism by cyst nematodes.     

Effects of contrasting omnivorous fish on submerged macrophyte biomass in temperate lakes: a mesocosm experiment

1. Freshwater fish can affect aquatic vegetation directly by consuming macrophytes or indirectly by changing water quality. However, most fish in the temperate climate zone have an omnivorous diet. The impact of fish as aquatic herbivores in temperate climates therefore remains unclear and depends on their dietary flexibility. 2. We tested the effects of a flexible omnivore and an herbivore on aquatic vegetation by comparing the effects of rudd (Scardinius erythrophthalmus, the most herbivorous fish in temperate climates) with grass carp (Ctenopharyngodon idella) in a mesocosm pond study. Exclosures distinguished herbivorous effects of fish on submerged macrophytes from indirect effects through changes in water quality, whereas stable isotope food‐web analysis provided information on fish diets. 3. We hypothesised that rudd, with its flexible diet and preference for animal food items, would only indirectly affect macrophytes, whereas grass carp, with its inflexible herbivorous diet, would directly affect macrophyte biomass. 4. Only grass carp significantly reduced macrophyte biomass through consumption. Rudd had no effect. Food‐web analysis indicated that rudd predominantly consumed animal prey, whereas grass carp included more plants in their diet, although they also consumed animal prey. Grass carp significantly affected water quality, resulting in lowered pH and increased N‐NH₄ concentrations, whereas more periphyton growth was observed in the presence of rudd. However, the indirect non‐herbivorous effects of both fish species had no effect on macrophyte biomass. 5. Both fish species should be considered as omnivores. Despite the fact that rudd is the most herbivorous fish in the western European climate zone, its effect on submerged macrophyte biomass is not substantial at natural densities and current temperatures.     

Rearing conditions determine offspring survival independent of egg quality: a cross-foster experiment with Oystercatchers Haematopus ostralegus

Variation in rearing conditions, due either to parental or to environmental quality, can result in offspring of different quality (e.g. body condition, immune function). However, evidence is accumulating that egg size and composition can also affect offspring quality. In Oystercatchers Haematopus ostralegus , high-quality rearing conditions result in a higher quantity as well as quality of offspring. This is thought to be caused by increased parental food provisioning to the chicks in high-quality environments. However, variation in egg quality between rearing conditions could also affect the quantity and quality of offspring. Determining the mechanism and ontogeny of quality differences is important in unravelling the causes of variation in reproductive success. To disentangle the effects of egg quality, and quality of the rearing conditions, on the future survival of offspring, we cross-fostered complete clutches between nests. When reared under conditions of similar environmental quality, chicks originating from eggs laid in low-quality environments survived as well as chicks originating from eggs laid in a high-quality environment. However, chicks reared in high-quality environments survived twice as long as chicks reared in low-quality environments, independent of the environmental quality in which the eggs were laid. This suggests that variation in the future survival of offspring is primarily caused by differences in environmental and/or parental quality, with no clear effect of egg quality (size).