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Aphid prey species consumed by the two studied ladybird species. Total number of hand-sampled ladybirds positively tested for aphids was 167 compared to 19 trap-sampled ladybirds (see S1 Data for more detail). https://doi.org/10.1371/journal.pone.0235054.g004
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Elucidating the diets of insect predators is important in basic and applied ecology, such as for improving the effectiveness of conservation biological control measures to promote natural enemies of crop pests. Here, we investigated the aphid diet of two common aphid predators in Central European agroecosystems, the native Coccinella septempunctata...
Contexts in source publication
Context 1
... C. septempunctata, Aphis spp. and S. avenae (cereal aphid) comprised a greater fraction in the diet (28.0% and 13.4%) compared to H. axyridis (16.5% and 2.4%, Fig 4). All other aphid taxa were only found in a few ladybird individuals. ...
Context 2
... of trap-sampled ladybirds positive for aphids were too low (a total of 19 individuals) for statistical comparison of ladybird prey. While hand-sampled ladybirds were positive for 18 aphid taxa, the 19 trap-sampled ladybirds were positive for 12 taxa, of which six were found in trap-sampled ladybirds exclusively (Fig 4). Thus, the most commonly consumed aphid taxa by hand-sampled ladybirds could also be found in trap-sampled individuals. ...
Context 3
... C. septempunctata, Aphis spp. and S. avenae (cereal aphid) comprised a greater fraction in the diet (28.0% and 13.4%) compared to H. axyridis (16.5% and 2.4%, Fig 4). All other aphid taxa were only found in a few ladybird individuals. ...
Context 4
... of trap-sampled ladybirds positive for aphids were too low (a total of 19 individuals) for statistical comparison of ladybird prey. While hand-sampled ladybirds were positive for 18 aphid taxa, the 19 trap-sampled ladybirds were positive for 12 taxa, of which six were found in trap-sampled ladybirds exclusively (Fig 4). Thus, the most commonly consumed aphid taxa by hand-sampled ladybirds could also be found in trap-sampled individuals. ...
Citations
... Second, primers can also be designed carefully with a comprehensive reference database to amplify only target taxa, excluding (or at least exhibiting bias against) the predator's DNA (Lafage et al., 2019;Ammann et al., 2020;Zeale et al., 2011;Figure 2). Such 'exclusion primers' can serendipitously occur among existing primers, for example those designed by Zeale et al., (2011) which have demonstrated exclusion of many taxa other than the bats they were designed to exclude (Berman & Inbar, 2021;Mitchell, Horsburgh, Dawson, Maher, & Arnold, 2021). ...
Dietary metabarcoding has vastly improved our ability to analyse the diets of animals, but it is hampered by a plethora of technical limitations including potentially reduced data output due to the disproportionate amplification of the DNA of the focal predator, here termed ‘the predator problem’. We review the various methods commonly used to overcome this problem, from deeper sequencing to exclusion of predator DNA during PCR, and how they may interfere with increasingly common multi-predator-taxon studies. We suggest that multi-primer approaches with an emphasis on achieving both depth and breadth of prey detections may overcome the issue to some extent, although multi-taxon studies require further consideration, as highlighted by an empirical example. We also review several alternative methods for reducing the prevalence of predator DNA that are conceptually promising but require additional empirical examination. The predator problem is a key constraint on molecular dietary analyses but, through this synthesis, we hope to guide researchers in overcoming this in an effective and pragmatic way.
... Forest edges are considered as an important habitat for many natural enemies (Ingrao et al. 2017;Schirmel et al. 2018;Bartual et al. 2019) in terms of facilitated movement of predators between habitats and as an important source of prey and shelter (reviewed by Holland et al. 2016). For example, stinging nettles (Urtica dioica), prevalently found along forest edges in the studied landscapes, are hosts of important alternative ladybird prey (Ammann et al. 2020) and were found to host ladybirds as well as hoverflies prior to crop colonisation (Alhmedi et al. 2009). ...
Context
Predatory insects contribute to the natural control of agricultural pests, but also use plant pollen or nectar as supplementary food resources. Resource maps have been proposed as an alternative to land cover maps for prediction of beneficial insects.
Objectives
We aimed at predicting the abundance of crop pest predating insects and the pest control service they provide with both, detailed flower resource maps and land cover maps.
Methods
We selected 19 landscapes of 500 m radius and mapped them with both approaches. In the centres of the landscapes, aphid predators – hoverflies (Diptera: Syrphidae), ladybeetles (Coleoptera: Coccinellidae) and lacewings (Neuroptera: Chrysopidae) – were surveyed in experimentally established faba bean phytometers ( Vicia faba L. Var. Sutton Dwarf) and their control of introduced black bean aphids ( Aphis fabae Scop.) was recorded.
Results
Landscapes with higher proportions of forest edge as derived from land cover maps supported higher abundance of aphid predators, and high densities of aphid predators reduced aphid infestation on faba bean. Floral resource maps did not significantly predict predator abundance or aphid control services.
Conclusions
Land cover maps allowed to relate landscape composition with predator abundance, showing positive effects of forest edges. Floral resource maps may have failed to better predict predators because other resources such as overwintering sites or alternative prey potentially play a more important role than floral resources. More research is needed to further improve our understanding of resource requirements beyond floral resource estimations and our understanding of their role for aphid predators at the landscape scale.
... All rights reserved increasingly common and accurate method for the identification of species consumed by a given animal (Pompanon et al. 2012;Clare 2014). Metabarcoding has been used to study the diet of vertebrates (e.g., bats (Hemprich-Bennett et al. 2021), pigs (Robeson et al. 2018), penguins (Cavallo et al. 2018)) and invertebrates (e.g., beetles (Ammann et al. 2020), spiders (Lafage et al. 2019), dragonflies (Kaunisto et al. 2017)), including carnivores (Deagle et al. 2009;Birkhofer et al. 2017;Galan et al. 2018), herbivores (Soininen et al. 2009;Kartzinel et al. 2015), omnivores (Barba et al. 2014;Robeson et al. 2018), sanguivores (Schnell et al. 2012) and coprophagous species (Drinkwater et al. 2021), but rarely in an ecological network context. ...
The construction of increasingly detailed species-interaction networks is extending the potential applications of network ecology, providing an opportunity to understand complex eco-evolutionary interactions, ecosystem service provision and the impacts of environmental change on ecosystem functioning. Dietary metabarcoding is a rapidly growing tool increasingly used to construct ecological networks of trophic interactions, enabling the determination of individual animal diets including difficult-to-distinguish prey taxa and even for species where traditional dietary analyses are unsuitable (e.g., fluid feeders and small invertebrates).
Several challenges, however, surround the use of dietary metabarcoding, especially when metabarcoding-based interactions are merged with observation-based species interaction data.
We describe the difficulties surrounding the quantification of species interactions, sampling perspective discrepancy (i.e., zoocentric vs. phytocentric sampling), experimental biases, reference database omissions and assumptions regarding direct and indirect consumption events.
These problems are not, however, insurmountable. Effective experimental design and data curation with appropriate attention paid to these problems renders the incorporation of dietary metabarcoding into ecological network analysis a powerful tool for the construction of highly resolved networks. Throughout, we discuss how these problems should be addressed when merging data to construct ecological networks.
... As insecticides decline in use due to increased resistance, regulation and detrimental environmental effects, alternative and integrated pest management is increasingly pertinent (Fountain et al., 2007;Loetti & Bellocq, 2017;MacFadyen et al., 2009;Pekár, 2013;Whitehorn et al., 2012). Specialist predators and parasitoids offer effective biocontrol, but given their dependence on a narrow niche of host/prey taxa, pest populations can reach large sizes before these biocontrol agents intervene (Ammann et al., 2020;Jordan et al., 2020;Levie et al., 2005;Sunderland et al., 1997). Polyphagous generalist predators such as spiders, which are abundant in arable fields (Nyffeler & Sunderland, 2003), can be effective conservation biocontrol agents of crop pests, even when they first emerge or arrive (Alderweireldt, 1994;Boreau De Roincé et al., 2013;Chapman et al., 2013;Juen et al., 2002;Korenko et al., 2010;Riechert & Lockley, 1984;Symondson et al., 2002). ...
Spiders are among the dominant invertebrate predators in agricultural systems and are significant regulators of insect pests. The precise dynamics of biocontrol of pests in the field are, however, poorly understood. This study investigates how density-independent prey choice, taxonomy, life stage, sex, and web characteristics affect spider diet and biocontrol. We collected spiders in four genera of Linyphiidae (i.e., Bathyphantes, Erigone, Tenuiphantes, and Microlinyphia), and individuals from the Lycosidae genus Pardosa, and their proximate prey communities from barley fields in Wales, UK between April and September 2018. We analyzed the gut contents of 300 individual spiders using DNA metabarcoding. From the 300 spiders screened, 89 prey taxa were identified from 45 families, including a wide range of pests and predators. Thrips were the dominant prey, present in over a third of the spiders sampled , but a type IV functional response appears to reduce their predation at peak abundances. Spider diets significantly differed based on web characteristics, but this depended on the genus and sex of the spider and it was not the principal separating factor in the trophic niches of linyphiids and lycosids. Diets significantly differed between spider genera and life stages, reflected in different propensities for intragu-ild predation and pest predation. Adult spiders predated a greater diversity of other predators, and juveniles predated a greater diversity of pests. Overall, Tenuiphantes spp. and Bathyphantes spp. exhibited the greatest individual potential for biocontrol of the greatest diversity of pest genera. The greater trophic niche complementarity of Pardosa spp. and Erigone spp., however, suggests that their complementary predation of different pests might be of greater overall benefit to biocontrol. Sustainable agriculture should aim to optimize conditions throughout the cropping cycle for effective biocontrol, prioritizing provision for a diversity of spiders which predate a complementary diversity of pest species.
... If so, this approach would considerably reduce the associated sequencing costs of this analysis. (Ammann et al., 2020;Cuff et al., 2021;Dušátková et al., 2020;King et al., 2015;Krehenwinkel et al., 2017). Therefore, we chose the COI gene for the identification of prey remains in the spider's gut. ...
As one of the most abundant predators of insects in terrestrial ecosystems, spiders have long received much attention from agricultural scientists and ecologists. Do spiders have a certain controlling effect on the main insect pests of concern in farmland ecosystems? Answering this question requires us to fully understand the prey spectrum of spiders. Next‐generation sequencing (NGS) has been successfully employed to analyze spider prey spectra. However, the high sequencing costs make it difficult to analyze the prey spectrum of various spider species with large samples in a given farmland ecosystem. We performed a comparative analysis of the prey spectra of Ovia alboannulata (Araneae, Lycosidae) using NGS with individual and mixed DNA samples to demonstrate which treatment was better for determining the spider prey spectra in the field. We collected spider individuals from tea plantations, and two treatments were then carried out: (1) The DNA was extracted from the spiders individually and then sequenced separately (DESISS) and (2) the DNA was extracted from the spiders individually and then mixed and sequenced (DESIMS). The results showed that the number of prey families obtained by the DESISS treatment was approximately twice that obtained by the DESIMS treatment. Therefore, the DESIMS treatment greatly underestimated the prey composition of the spiders, although its sequencing costs were obviously lower. However, the relative abundance of prey sequences detected in the two treatments was slightly different only at the family level. Therefore, we concluded that if our purpose were to obtain the most accurate prey spectrum of the spiders, the DESISS treatment would be the best choice. However, if our purpose were to obtain only the relative abundance of prey sequences of the spiders, the DESIMS treatment would also be an option. The present study provides an important reference for choosing applicable methods to analyze the prey spectra and food web compositions of animal in ecosystems. Individual DNA sample sequencing obtains the accurate prey spectrum of spiders. Mixed DNA sample sequencing underestimates the prey spectrum of spiders. Individual and mixed DNA sample sequencing obtains almost the same relative abundance of prey sequences of spiders.
... This way we reduced the amount of PCR inhibitors present in the tissue of coleopterans. 31 The abdomens were then inserted into 200 μL tissue lysis buffer and squashed by a sterile pestle. After the addition of 20 μL of Proteinase K solution, samples were incubated overnight at 55°C. ...
... Before performing PCR diagnostics, the PCR mixture was optimized for amplification of the psyllid COI gene fragment in all types of predators, as DNA extracted from coccinellid beetles had PCR inhibitors. 31 The reaction volume was 15 μL; it consisted of 0.2 μL HiFi Polymerase (PCR Biosystems Ltd, London, UK), 3 μL of 5× HiFi buffer, 0.5 μL Forward and Reverse primer (10 μM each), 8.8 μL water and 2 μL DNA. PCR conditions were as follows: initial denaturation at 95°C for 5 min; 40 cycles of 95°C for 30 s, 58°C for 30 s, 72°C for 45 s; and a final extension at 72°C for 5 min. ...
BACKGROUND
Modern pest control management systems are based on the support of naturally occurring arthropod predators, as it has been shown that such predators offer an important ecosystem service. However, most naturally occurring arthropod predators are generalists (euryphagous). Their role in the biological control of specific pests has been recognized but remains poorly studied. Here, we focused on the naturally occurring arthropod predators of psyllids – the main insect pest of pear trees. We investigated the abundance of psyllids and all their potential enemies in an abandoned pear orchard on a weekly basis from early spring to early summer. In addition, employing PCR diagnostics and specific primers, we investigated the predation rate on psyllids in all predators collected.
RESULTS
We found four predatory groups: spiders were the most abundant (60%, N = 756), followed by coccinellid beetles, anthocorid bugs, and cantharid beetles. Anthocorids and spiders had the highest predation rates among the predatory groups. Among spiders, more than 50% of foliage dwelling spiders (belonging to the genera Philodromus and Clubiona; N = 206) were positive for psyllids and showed a numerical response to the abundance of psyllids.
CONCLUSION
We conclude that foliage‐dwelling spiders are, out of the four groups, the most important natural enemies of psyllids on pear trees during spring in Central Europe, as they outnumber specialised Anthocoris bugs.
... Multi-year ecologically based studies combined with molecular, genetic, and demographic modeling techniques to quantify population and food web dynamics and movement within landscapes in Asia would provide a better understanding of the mechanisms underlying coexistence of predatory coccinellids Thomas et al. 2013;Heimoana et al. 2017;Brown and Roy 2018;Sethuraman et al. 2018Sethuraman et al. , 2020Ammann et al. 2020). This type of detailed knowledge of the native coccinellid community in Asia is critical to determine the potential effects of the invasive populations (biotypes) of H. axyridis from Europe that are spreading in Eurasia. ...
Over the past 30 yr, multiple species of predatory Coccinellidae, prominently Coccinella septempunctata L. and
Harmonia axyridis (Pallas) have spread to new continents, influencing biodiversity and biological control. Here
we review the mechanisms underlying these ecological interactions, focusing on multi-year field studies of
native and non-native coccinellids and those using molecular and quantitative ecological methods. Field data
from Asia show that H. axyridis, C. septempunctata, and Propylea japonica (Thunberg) are regularly among the
most abundant predatory species but their rank varies by habitat. Studies of these species in their native Asian
range, primarily related to their range in mainland China, document different patterns of seasonal abundance,
species specific associations with prey, and habitat separation. Intraguild predation is well documented both
in Asia and in newly invaded areas, and H. axyridis benefits most from this interaction. Harmonia axyridis also
seems to rely more on cannibalism in times of prey scarcity than other species, and relatively sparse data indicate
a lower predation pressure on it from natural enemies of coccinellids. Declines in the abundance of native
coccinellids following the spread and increase of non-native species, documented in several multi-year studies
on several continents, is a major concern for native biodiversity and the persistence of native coccinellid species.
We suggest that future studies focus more attention on the community ecology of these invasive species
in their native habitats.
