Search

Abundance and diversity of natural enemies increases with higher landscape complexity. However, more species can also increase negative interactions such as intraguild predation (IGP), which could be detrimental to pest control. Direct observations of these trophic interactions are still lacking. In the present study, we employed DNA-based gut content analyses of coccinellid beetles to assess IGP (direct and coincidental) and aphid consumption. Species-specific and group-specific primer pairs were used to unveil the interactions of the most abundant coccinellid species, three cereal aphids and their associated parasitoids. In order to determine whether the landscape complexity promotes these interactions, we used replicated wheat fields in two contrasting landscape contexts over the season in central Chile. With higher abundance of coccinellids, we observed greater aphid consumption in complex contexts. The consumption of parasitized aphids was mostly detected early in complex contexts, suggesting a detrimental effect on the parasitoid population. Following molecular analysis, we can state that the aphids are important feeding resources for the coccinellid assemblage and are actively foraging on this important pest. Finally, this study demonstrates that direct IGP is a common interaction in this system, independently of the landscape context during the complete season. Nevertheless, the native Eriopis chilensis was found to be the most frequently consumed intraguild prey. In contrast with expected predictions, we found little evidence that the landscape context increased negative interactions, such as IGP and IGP-C and in turn that these decrease the control of Sitobion avenae. [ABSTRACT FROM AUTHOR]

Abstract: The “habitat heterogeneity hypothesis” predicts positive effects of structural complexity on species coexistence. Increasing habitat heterogeneity can change the diversity (number of species, abundances) and the functional roles of communities. The latter, however, is not well understood as species and individuals may respond very differently and dynamically to a changing environment. Here, we experimentally test how habitat heterogeneity affects generalist arthropod predators, including epigaeic spiders, carabid and staphylinid beetles, under natural conditions by assessing their diversity and directly measuring their trophic interactions (which provide a proxy for their functional roles). The experiment was conducted in spring barley fields in Southern Sweden where habitat heterogeneity was manipulated by increasing within‐field plant diversity. Increased habitat heterogeneity triggered rapid changes in the feeding behaviour of generalist predators characterized by lower trophic specialization at both network (H2’, degree of interaction specialization in the entire network) and species level (d’, degree of interaction specialization at the species level). We presume that this is because spatial separation resulted in relaxed competition and allowed an increased overlap in resources used among predator species. Predators collected from heterogenous habitats also showed greater individual‐level dietary variability which might be ascribed to relaxed intraspecific competition. Our results provide conclusive evidence that habitat heterogeneity can induce rapid behavioural responses independent of changes in diversity, potentially promoting the stability of ecosystem functions. A plain language summary is available for this article. [ABSTRACT FROM AUTHOR]

Molecular techniques have become an important tool to empirically assess feeding interactions. The increased usage of next-generation sequencing approaches has stressed the need of fast DNA extraction that does not compromise DNA quality. Dietary samples here pose a particular challenge, as these demand high-quality DNA extraction procedures for obtaining the minute quantities of short-fragmented food DNA. Automatic high-throughput procedures significantly decrease time and costs and allow for standardization of extracting total DNA. However, these approaches have not yet been evaluated for dietary samples. We tested the efficiency of an automatic DNA extraction platform and a traditional CTAB protocol, employing a variety of dietary samples including invertebrate whole-body extracts as well as invertebrate and vertebrate gut content samples and feces. Extraction efficacy was quantified using the proportions of successful PCR amplifications of both total and prey DNA, and cost was estimated in terms of time and material expense. For extraction of total DNA, the automated platform performed better for both invertebrate and vertebrate samples. This was also true for prey detection in vertebrate samples. For the dietary analysis in invertebrates, there is still room for improvement when using the high-throughput system for optimal DNA yields. Overall, the automated DNA extraction system turned out as a promising alternative to labor-intensive, low-throughput manual extraction methods such as CTAB. It is opening up the opportunity for an extensive use of this cost-efficient and innovative methodology at low contamination risk also in trophic ecology. [ABSTRACT FROM AUTHOR]

Successful biological control of agricultural pests is dependent on a thorough understanding of the underlying trophic interactions between predators and prey. Studying trophic interactions can be challenging, particularly when generalist predators that frequently use multiple prey and interact with both pest and alternative prey are considered. In this context, diagnostic PCR proved to be a suitable approach, however at present, prey-specific PCR primers necessary for assessing such interactions across trophic levels are missing. Here we present a new set of 45 primers designed to target a wide range of invertebrate taxa common to temperate cereal crops: cereal aphids, their natural enemies such as carabid beetles, ladybeetles, lacewings, and spiders, and potential alternative prey groups (earthworms, springtails, and dipterans). These primers were combined in three 'ready to use' multiplex PCR assays for quick and cost-effective analyses of large numbers of predator samples. The assays were tested on 560 carabids collected in barley fields in Sweden. Results from this screening suggest that aphids constitute a major food source for carabids in cereal crops (overall DNA detection rate: 51 %), whereas alternative extraguild and intraguild prey appear to be less frequently preyed upon when aphids are present (11 % for springtails and 12 % for earthworms; 1 % for spiders and 4 % for carabids). In summary, the newly developed molecular assays proved reliable and effective in assessing previously cryptic predator-prey trophic interactions, specifically with focus on biological control of aphids. The diagnostic PCR assays will be applicable manifold as the targeted invertebrates are common to many agricultural systems of the temperate region. [ABSTRACT FROM AUTHOR]

Belowground herbivores impact plant performance, thereby inducing changes in plant community composition, which potentially leads to cascading effects onto higher trophic levels and ecosystem processes and productivity. Among soil-living insects, external root-chewing generalist herbivores have the strongest impact on plants. However, the lack of knowledge on their feeding behaviour under field conditions considerably hampers achieving a comprehensive understanding of how they affect plant communities. Here, we address this gap of knowledge by investigating the feeding behaviour of Agriotes click beetle larvae, which are common generalist external root-chewers in temperate grassland soils. Utilizing diagnostic multiplex PCR to assess the larval diet, we examined the seasonal patterns in feeding activity, putative preferences for specific plant taxa, and whether species identity and larval instar affect food choices of the herbivores. Contrary to our hypothesis, most of the larvae were feeding-active throughout the entire vegetation period, indicating that the grassland plants are subjected to constant belowground feeding pressure. Feeding was selective, with members of Plantaginaceae and Asteraceae being preferred; Apiaceae were avoided. Poaceae, although assumed to be most preferred, had an intermediate position. The food preferences exhibited seasonal changes, indicating a fluctuation in plant traits important for wireworm feeding choice. Species- and instar-specific differences in dietary choice of the Agriotes larvae were small, suggesting that species and larval instars occupy the same trophic niche. According to the current findings, the food choice of these larvae is primarily driven by plant identity, exhibiting seasonal changes. This needs to be considered when analysing soil herbivore-plant interactions. [ABSTRACT FROM AUTHOR]

Agriotes wireworms (Coleoptera: Elateridae) are abundant soil-dwelling herbivores which can inflict considerable damage to field crops. In Europe up to 40 species occur, differing in their ecology and pest status. Their distribution in the larval stage, however, has rarely been assessed because of the considerable effort in collecting wireworms and the difficulties in identifying them to species-level. Here, we examined the occurrence of Agriotes wireworms in Austrian agricultural land with regard to their association with climatic and soil parameters. Using a molecular identification system, 1348 field-collected larvae from 85 sites were identified to species-level. Three species, Agriotes obscurus, Agriotes brevis, Agriotes ustulatus, and two that could not be discerned molecularly ( Agriotes lineatus and Agriotes proximus), were assigned to two ecological groups: (i) A. brevis/A. ustulatus, found in areas with a warmer, drier climate and alkaline soils, and (ii) A. obscurus/A. lineatus/proximus which occur mainly at higher altitude characterised by lower temperatures, higher precipitation and acidic, humus-rich soils. Agriotes sputator was abundant throughout Austria, confirming its euryoecious nature. Only one larva of Agriotes litigiosus was found, prohibiting further analysis. These data contribute to a characterisation of species-specific traits in Agriotes larvae in agricultural land, an important prerequisite to develop efficient control strategies for these wireworms. [ABSTRACT FROM AUTHOR]

Plant roots represent an important food source for soil-dwelling animals, but tracking herbivore food choices below-ground is difficult. Here, we present an optimized PCR assay for the detection of plant DNA in the guts of invertebrates, using general plant primers targeting the trn T- F chloroplast DNA region. Based on this assay, we assessed the influence of plant identity on the detectability of ingested plant DNA in Agriotes click beetle larvae. Six different plant species were fed to the insects, comprising a grass, a legume and four nonlegume forbs. Moreover, we examined whether it is possible to amplify DNA of decaying plants and if DNA of decayed plant food is detectable in the guts of the larvae. DNA of the ingested roots could be detected in the guts of the larvae for up to 72-h post-feeding, the maximum digestion time tested. When fed with living plants, DNA detection rates differed significantly between the plant species. This may be ascribed to differences in the amount of plant tissue consumed, root palatability, root morphology and/or secondary plant components. These findings indicate that plant identity can affect post-feeding DNA detection success, which needs to be considered for the interpretation of molecularly derived feeding rates on plants. Amplification of plant DNA from decaying plants was possible as long as any tissue could be retrieved from the soil. The consumption of decaying plant tissue could also be verified by our assay, but the insects seemed to prefer fresh roots over decaying plant material. [ABSTRACT FROM AUTHOR]

Abstract: Although a significant proportion of plant tissue is located in roots and other below-ground parts of plants, little is known on the dietary choices of root-feeding insects. This is caused by a lack of adequate methodology which would allow tracking below-ground trophic interactions between insects and plants. Here, we present a DNA-based approach to examine this relationship. Feeding experiments were established where either wheat (Triticum aestivum) or maize (Zea mays) was fed to Agriotes larvae (Coleoptera: Elateridae), allowing them to digest for up to 72 h. Due to the very small amount of plant tissue ingested (max = 6.76 mg), DNA extraction procedures and the sensitivity of polymerase chain reaction (PCR) had to be optimized. Whole-body DNA extracts of larvae were tested for the presence of both rbcL and trnL plastid DNA using universal primers. Moreover, based on cpDNA sequences encoding chloroplast tRNA for leucine (trnL), specific primers for maize and wheat were developed. With both, general and specific primers, plant DNA was detectable in the guts of Agriotes larvae for up to 72 h post-feeding, the maximum time of digestion in these experiments. No significant effect of time since feeding on plant DNA detection success was observed, except for the specific primers in maize-fed larvae. Here, plant DNA detection was negatively correlated with the duration of digestion. Both, meal size and initial mass of the individual larvae did not affect the rate of larvae testing positive for plant DNA. The outcomes of this study represent a first step towards a specific analysis of the dietary choices of soil-living herbivores to further increase our understanding of animal–plant feeding interactions in the soil. [ABSTRACT FROM AUTHOR]

Plant identification is challenging when no morphologically assignable parts are available. There is a lack of broadly applicable methods for identifying plants in this situation, for example when roots grow in mixture and for decayed or semidigested plant material. These difficulties have also impeded the progress made in ecological disciplines such as soil- and trophic ecology. Here, a PCR-based approach is presented which allows identifying a variety of plant taxa commonly occurring in Central European agricultural land. Based on the trnT-F cpDNA region, PCR assays were developed to identify two plant families (Poaceae and Apiaceae), the genera Trifolium and Plantago, and nine plant species: Achillea millefolium, Fagopyrum esculentum, Lolium perenne, Lupinus angustifolius, Phaseolus coccineus, Sinapis alba, Taraxacum officinale, Triticum aestivum, and Zea mays. These assays allowed identification of plants based on size-specific amplicons ranging from 116 bp to 381 bp. Their specificity and sensitivity was consistently high, enabling the detection of small amounts of plant DNA, for example, in decaying plant material and in the intestine or faeces of herbivores. To increase the efficacy of identifying plant species from large number of samples, specific primers were combined in multiplex PCRs, allowing screening for multiple species within a single reaction. The molecular assays outlined here will be applicable manifold, such as for root- and leaf litter identification, botanical trace evidence, and the analysis of herbivory. [ABSTRACT FROM AUTHOR]

Drosophila suzukii (Diptera: Drosophilidae) is a highly polyphagous invasive pest threatening fruit production in the Americas and Europe. The current knowledge of its host plants is mainly based on oviposition and larval development in fruits, while little is known on the diet of the adult flies. This information is important for developing effective control strategies. Here, we examine DNA-based techniques to determine food plants of D. suzukii. Adult flies were fed with raspberries (Rubus idaeus) and allowed to digest up to 72 h after feeding. Raspberry DNA was detected by diagnostic PCR for up to 48 h post-feeding with a significant negative effect of time on DNA detection success but no significant differences between male and female flies in detection probabilities. As D. suzukii walks on plants, its body surface can get contaminated with DNA. With a bleaching experiment, we succeeded to remove contaminating external plant DNA, while the DNA in the gut content stayed unaffected. Finally, field-collected flies were subjected to a next-generation sequencing approach, demonstrating that plant DNA from different host plants can be efficiently detected in both bleached and non-bleached specimens. In order to safeguard against erroneous host plant detections, we recommend bleaching flies before they are subjected to DNA extraction. The current findings encourage the use of DNA-based gut content analysis in D. suzukii to obtain a better understanding of its feeding ecology which is a prerequisite for developing successful control strategies. [ABSTRACT FROM AUTHOR]

1. Studies of the impact of predator diversity on biological pest control have shown idiosyncratic results. This is often assumed to be as a result of differences among systems in the importance of predator-predator interactions such as facilitation and intraguild predation. The frequency of such interactions may be altered by prey availability and structural complexity. A direct assessment of interactions among predators is needed for a better understanding of the mechanisms affecting prey abundance by complex predator communities. 2. In a field cage experiment, the effect of increased predator diversity (single species vs. three-species assemblage) and the presence of weeds (providing structural complexity) on the biological control of cereal aphids were tested and the mechanisms involved were investigated using molecular gut content analysis. 3. The impact of the three-predator species assemblages of aphid populations was found to be similar to those of the single-predator species treatments, and the presence or absence of weeds did not alter the patterns observed. This suggests that both predator facilitation and intraguild predation were absent or weak in this system, or that these interactions had counteracting effects on prey suppression. Molecular gut content analysis of predators provided little evidence for the latter hypothesis: predator facilitation was not detected and intraguild predation occurred at a low frequency. 4. The present study suggests additive effects of predators and, therefore, that predator diversity per se neither strengthens nor weakens the biological control of aphids in this system. [ABSTRACT FROM AUTHOR]

Plant identity and diversity influence herbivore communities in many different ways. While it is well known how they affect the feeding preferences of aboveground herbivores, this information is lacking for soil ecosystems, where examining plant-herbivore trophic interactions is difficult. We performed a mesocosm experiment assessing how plant identity and diversity affect the food choice of Agriotes larvae, which are soil-living generalist herbivores. We offered four plant species, (maize, a grass, a legume, and a forb) at varying combinations and diversity levels to these larvae, and analyzed their feeding behavior using stable isotopes. We hypothesized that (1) their food choice is driven by preference for certain plant species rather than by root abundance and that (2) the preference for specific plants changes with increasing plant diversity. We found that larvae preferred the grass and legume but avoided maize and the forb. Whether a plant was preferred or avoided was independent of diversity, but the extent of avoidance or preference changed with increasing plant diversity. Our findings reveal that the dietary choice of soil-living generalist herbivores is determined by plant-specific traits rather than root abundance. Our data also suggest that soil herbivore feeding preferences are modulated by plant diversity. [ABSTRACT FROM AUTHOR]

Elacytarabine is a novel cytotoxic nucleoside analogue, independent of nucleoside transporters (e.g. human Equilibrative Nucleoside Transporter 1 [ hENT1]) for cell uptake, and mechanisms of action similar to those of cytarabine. This Phase II study assessed the efficacy and safety of elacytarabine in patients with advanced stage acute myeloid leukaemia ( AML). Patients received 2000 mg/m2 per d continuously i.v. during days 1-5 every 3 weeks. Patients were matched by six risk factors with historical controls; remission rate (assessed after 1 or 2 cycles) and 6-month survival were compared. Sixty-one patients, median age 58 years, were enrolled; 52% had five or six risk factors. The remission rate was 18% (95% confidence interval: 9-30%) vs. 4% in controls ( P < 0·0001), 6-month survival rate was 43%, median overall survival was 5·3 months (vs. 1·5 months); 10 patients (16%) were referred for stem cell transplantation after treatment. Side effects were predictable and manageable. The most common grade 3/4 non-haematological adverse events were febrile neutropenia, hypokalemia, fatigue, hyponatraemia, dyspnoea and pyrexia. Thirty-day all-cause mortality, after start of treatment, was 13% vs. 25% in controls. Elacytarabine has monotherapy activity in patients with advanced AML. This study provides proof-of-concept that lipid esterification of nucleoside analogues is clinically relevant. [ABSTRACT FROM AUTHOR]