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• Intraguild predation within beetle communities was analysed in cereal fields. • Organic fertilization increased non-pest prey and lowered intraguild predation. • Lower intraguild predation correlated with lower pest spread, but not density. • No effect of organic fertilization was found on pest density or consumption. • Fertilization effects may offset pest predation from lower predator interference. Intraguild predation is an extreme form of competition, that depends on resource availability, niche overlap, behaviour and diversity. However, despite modelling and mesocosm experiments, field studies are scarce, and we know nothing of its temporal dynamics within real-world food webs, particularly in the context of biological control. To address this, we added manure to cereal fields to increase decomposer prey, and analysed the diet of over 6000 predators over the entire cropping season during two consecutive years. Our results show that manure increased available prey temporarily and reduced intraguild predation. With this organic fertilization, a reduction in pest spread between tillers within fields correlated with lower intraguild predation, while pest density remained unchanged across treatments, making the net effect on biological control unclear. We hypothesize that the mechanism responsible for why lowering intraguild predation reduces pest spread are changes in predator behaviour, that allow predators to exert more pressure on pests. Conversely, the absence of an effect on pest density may be linked to other effects of fertilization, such as increased pest and plant growth counteracting any increase in predation pressure. The high temporal resolution of our data showed how dynamic IGP is throughout the season, which stresses the importance of studying food webs over time, to generate a mechanistic understanding of biological control. [ABSTRACT FROM AUTHOR]

Next‐generation sequencing (NGS) is increasingly used for diet analyses; however, it may not always describe diet samples well. A reason for this is that diet samples contain mixtures of food DNA in different amounts as well as consumer DNA which can reduce the food DNA characterized. Because of this, detections will depend on the relative amount and identity of each type of DNA. For such samples, diagnostic PCR will most likely give more reliable results, as detection probability is only marginally dependent on other copresent DNA. We investigated the reliability of each method to test (a) whether predatory beetle regurgitates, supposed to be low in consumer DNA, allow to retrieve prey sequences using general barcoding primers that co‐amplify the consumer DNA, and (b) to assess the sequencing depth or replication needed for NGS and diagnostic PCR to give stable results. When consumer DNA is co‐amplified, NGS is better suited to discover the range of possible prey, than for comparing co‐occurrences of diet species between samples, as retested samples were repeatedly different in prey detections with this approach. This shows that samples were incompletely described, as prey detected by diagnostic PCR frequently were missed by NGS. As the sequencing depth needed to reliably describe the diet in such samples becomes very high, the cost‐efficiency and reliability of diagnostic PCR make diagnostic PCR better suited for testing large sample‐sets. Especially if the targeted prey taxa are thought to be of ecological importance, as diagnostic PCR gave more nested and consistent results in repeated testing of the same sample. [ABSTRACT FROM AUTHOR]

The nucleotide variation in the cytochrome c oxidase subunit I (COI) gene makes it ideal for assigning sequences to species. However, this variability also makes it difficult to design truly universal primers. Here, we present the forward primer "Sauron‐S878," specifically designed to facilitate library preparation for metabarcoding. This primer is modified to improve the coverage of terrestrial species compared to the primer mCOIintF, optimized for aquatic systems, which raised the in silico coverage from 74.4% to 98.3% of available NCBI sequences (perfect match in 3′ region, up to three mismatches in remaining primer). When paired with the reverse primer "jgHCO2198" (fragment length ~313 bp), these primers amplified 98.4% of 255 tested DNA extracts from various taxa, which are better than many other common COI barcoding primers. Furthermore, a single‐tube protocol was developed, wherein these primers amplify the target gene, and attach MIDs and Illumina sequencing adapters in one reaction. This eliminates the need for re‐amplification or enzymatic ligation during library preparation while keeping the flexibility to modularly combine primers and MIDs. Using the single‐tube approach, three replicates of three mock samples were sequenced on a MiSeq platform with no adverse effects compared to commercial Nextera indexing kits. From this run, 75% of all included taxa could be recovered, with no considerable bias among taxonomic groups. Despite the fact that 98.4% of the extracts were confirmed to amplify in vitro, this number was lower than expected. A reason for this discrepancy was a clear link between the relative concentration of a specific DNA type in the template and the number of returned reads for this DNA. We would argue that such a bias may be especially problematic in metabarcoding where samples usually contain trace DNA in unknown amounts. However, how this affects the completeness of metabarcoding results has yet been poorly investigated. Here, we present the forward primer "Sauron‐S878," specifically designed to facilitate library preparation for metabarcoding. This primer exhibits little bias between taxonomic groups. Furthermore, when paired with the reverse primer "jgHCO2198," these primers can be used to attach MIDs and Illumina sequencing adapters in one reaction. [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]

Soil-dwelling insect pests may cause considerable damage to crops worldwide, and their belowground lifestyle makes them hard to control. Amongst the most promising control agents for subterranean pests are soilborne entomopathogenic fungi (EPF) such as Metarhizium brunneum. Albeit EPF can be highly pathogenic to their target pest species under laboratory conditions, their efficacy in the field is often limited due to adverse environmental conditions. Here, we test for the first time if the efficacy of EPF can be improved when they are augmented with trap crops. In a field experiment, the M. brunneum strain ART2825 was combined with a trap crops mixture of six plant species and evaluated for its control effect of wireworms (Coleoptera: Elateridae). When both were combined in the main crop, potato damage was lowered on average by 42.5% and wireworm abundance by 50.8%. Single application of trap crops or EPF lowered damage/pest abundance only by 29.9%/15.89% and 34.7%/4.77%, respectively. Importantly, the strength of the synergistic pest control effect between trap crops and EPF increased disproportionately with increasing wireworm abundance. However, DNA-based gut content analysis showed that wireworms' feeding preferences were not shifting toward the trap crops. Our findings demonstrate that combining trap crops with EPF improves the efficacy of the latter and leads to a synergistic control effect which magnifies with increasing wireworm abundance. Hence, the synergistic effect of EPF and trap crops might be a promising control strategy for soil-dwelling pests in general and significantly improve our abilities to manage soil pests environmentally friendly. [ABSTRACT FROM AUTHOR]

• Landscape had a lower effect on aphids and their parasitoids than fertilisation. • Fertilisation affected plants positively. • Fertilisation affected aphids and primary parasitism rate negatively. • Fertilisation had no effect on secondary parasitism rate. • H 2 ' and generality between parasitoids are affected by landscape and fertilisation. Agricultural intensification can impact agrobiodiversity in several ways such as in terms of population densities, community composition and food web interactions across all trophic levels. This effect can be investigated at two scales: field-scale and landscape scale. Here it was assessed how the impact of fertilisation (within field) and landscape complexity (within landscape) impact cereal aphid-primary parasitoid-secondary parasitoid systems in winter wheat in Germany. A newly developed molecular technique was used to quantify species-specific linkages between aphids, primary parasitoids and secondary parasitoids sampled in fertilised and unfertilised plots in either simple or complex structured landscapes. The results show a stronger effect of fertilisation than landscape complexity on the groups: fertilisation positively affected the crop plants while it negatively affected both the density of the cereal aphid Sitobion avenae and its primary parasitism rates whereas no effect on the level of secondary parasitism rates was observed. Landscape complexity had no effect on plants, aphids, as well as on primary parasitism rate. In case of secondary parasitism rate there was an effect in interaction with sampling date. Field identity accounted for the strongest effect on parasitoid community composition (10.6% of the variance) from all tested variables, while fertilisation and landscape complexity had almost no effect (1.1% and no effect). Nevertheless, a weak cascading effect of both environmental factors could be observed as the primary-secondary parasitoid network structure responded to both. However, these observed effects on food webs strongly depended on species identity, highlighting the need of species-level food web assessment. [ABSTRACT FROM AUTHOR]

Abstract: The rapidly growing field of molecular diet analysis is becoming increasingly popular among ecologists, especially when investigating methodologically challenging groups, such as invertebrate generalist predators. Prey DNA detection success is known to be affected by multiple factors; however, the type of dietary sample has rarely been considered. Here, we address this knowledge gap by comparing prey DNA detection success from three types of dietary samples. In a controlled feeding experiment, using the carabid beetle Pterostichus melanarius as a model predator, we collected regurgitates, faeces and whole consumers (including their gut contents) at different time points postfeeding. All dietary samples were analysed using multiplex PCR, targeting three different length DNA fragments (128, 332 and 612 bp). Our results show that both the type of dietary sample and the size of the DNA fragment contribute to a significant part of the variation found in the detectability of prey DNA. Specifically, we observed that in both regurgitates and whole consumers, prey DNA was detectable significantly longer for all fragment sizes than for faeces. Based on these observations, we conclude that prey DNA detected from regurgitates and whole consumers DNA extracts are comparable, whereas prey DNA detected from faeces, though still sufficiently reliable for ecological studies, will not be directly comparable to the former. Therefore, regurgitates and faeces constitute a useful, nonlethal source for dietary information that could be applied to field studies in situations when invertebrate predators should not be killed. [ABSTRACT FROM AUTHOR]

Abstract: Facultative bacterial endosymbionts can protect their aphid hosts from natural enemies such as hymenopteran parasitoids. As such, they have the capability to modulate interactions between aphids, parasitoids and hyperparasitoids. However, the magnitude of these effects in natural aphid populations and their associated parasitoid communities is currently unknown. Moreover, environmental factors such as plant fertilization and landscape complexity are known to affect aphid–parasitoid interactions but it remains unclear how such environmental factors affect the interplay between aphids, parasitoids and endosymbionts. Here, we tested whether facultative endosymbionts confer protection to parasitoids in natural populations of the English grain aphid, Sitobion avenae, and if this is affected by plant fertilization and landscape complexity. Furthermore, we examined whether the effects of facultative endosymbionts can cascade up to the hyperparasitoid level and increase primary‐hyperparasitoid food web specialization. Living aphids and mummies were collected in fertilized and unfertilized plots within 13 wheat fields in Central Germany. We assessed the occurrence of primary parasitoid, hyperparasitoid and endosymbiont species in aphids and mummies using a newly established molecular approach. Facultative endosymbiont infection rates were high across fields (~80%), independent of whether aphids were parasitized or unparasitized. Aphid mummies exhibited a significantly lower share of facultative endosymbiont infection (~38%). These findings suggest that facultative endosymbionts do not affect parasitoid oviposition behaviour, but decrease parasitoid survival in the host. Facultative endosymbiont infection rates were lower in mummies collected from fertilized compared to unfertilized plants, indicating that plant fertilization boosts the facultative endosymbiont protective effect. Furthermore, we found strong evidence for species‐specific and negative cascading effects of facultative endosymbionts on primary and hyperparasitoids, respectively. Facultative endosymbionts impacted parasitoid assemblages and increased the specialization of primary‐hyperparasitoid food webs: these effects were independent from and much stronger than other environmental factors. The current findings strongly suggest that facultative endosymbionts act as a driving force in aphid–parasitoid–hyperparasitoid networks: they shape insect community composition at different trophic levels and modulate, directly and indirectly, the interactions between aphids, parasitoids and their environment. [ABSTRACT FROM AUTHOR]