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Intact soil food webs are pivotal to maintaining essential soil functions, such as carbon recycling, sequestering, and biomass production. Although the functional role of micro- (e.g., bacteria and fungi) and macrofauna (e.g., earthworms) is comparatively well established, the importance of the mesofauna community (e.g., abundance and diversity of Acari and Collembola) in maintaining soil functionality is less clear. We investigated this question in a six-month field experiment in arable soil by actively manipulating mesofauna abundance and biodiversity through the application of two legacy insecticides (lindane and methamidophos) at sufficiently high doses to reduce mesofauna abundance (well above previously registered application rates; 2.5 and 7.5 kg a.s./ha for lindane, and 0.6 and 3 kg a.s./ha for methamidophos) and measure the impact on organic matter degradation. Our results demonstrate that both insecticides had reduced Collembola and Acari abundances by up to 80% over the study's six-month duration. In addition, we observed less pronounced and more complex changes in mesofauna biodiversity over time. These included insecticide-dependent temporal fluctuations (both reduction and increase) for different estimates (indices) of local (alpha)-diversity over time and no lasting impact for most estimates after six months. Even at these exceptionally high field rates, Collembola and Acari diversity was observed to generally recover by six months. In contrast, considering organic matter breakdown, we found no evidence of a treatment-related effect. These results suggest that organic matter breakdown in arable soils is likely driven by other trophic levels (e.g., microorganisms or earthworms) with only a limited influence of the mesofauna community. We discuss these findings with regard to their implications for our current understanding of soil food web function and future European soil risk assessments. Integr Environ Assess Manag 2022;18:1423-1433. © 2021 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental ToxicologyChemistry (SETAC).

Clearly defined protection goals specifying what to protect, where and when, are required for designing scientifically sound risk assessments and effective risk management of chemicals. Environmental protection goals specified in EU legislation are defined in general terms, resulting in uncertainty in how to achieve them. In 2010, the European Food Safety Authority (EFSA) published a framework to identify more specific protection goals based on ecosystem services potentially affected by plant protection products. But how applicable is this framework to chemicals with different emission scenarios and receptor ecosystems? Four case studies used to address this question were: (i) oil refinery waste water exposure in estuarine environments; (ii) oil dispersant exposure in aquatic environments; (iii) down the drain chemicals exposure in a wide range of ecosystems (terrestrial and aquatic); (iv) persistent organic pollutant exposure in remote (pristine) Arctic environments. A four-step process was followed to identify ecosystems and services potentially impacted by chemical emissions and to define specific protection goals. Case studies demonstrated that, in principle, the ecosystem services concept and the EFSA framework can be applied to derive specific protection goals for a broad range of chemical exposure scenarios. By identifying key habitats and ecosystem services of concern, the approach offers the potential for greater spatial and temporal resolution, together with increased environmental relevance, in chemical risk assessments. With modifications including improved clarity on terminology/definitions and further development/refinement of the key concepts, we believe the principles of the EFSA framework could provide a methodical approach to the identification and prioritization of ecosystems, ecosystem services and the service providing units that are most at risk from chemical exposure.

In the EU, earthworm field studies are an important step in the risk assessment of plant protection products (PPP) on soil macrofauna. The minimum significant difference (MSD) is a metric which allows the assessment of the magnitude of statistically detectable effects. This paper aims to investigate the MSD values in such studies in order to assess whether their statistical robustness is compatible with desirable soil macrofauna protection goals. Earthworm biomass and abundance data from six standard earthworm field studies was analysed for MSD values, calculated through a t-statistic method. A comparison of MSD values resulting from replicates with four subsamples and from replicates with eight subsamples was also performed. Small to medium effects (0 to 70%) were more often detectable for both biological variables in more abundant groups, such as juvenile earthworms and overall earthworm communities. Adult earthworms grouped into single species or functional groups (anecic, endogeic) presented more variable MSD values. A decrease in MSD values was observed when increasing the number of subsamples per replicate from four to eight. Initial earthworm densities above 50 individuals/m2 generally resulted in MSD values up to 70% of the control mean value. These results indicate that the standard test design of current earthworm field studies provide a suitable degree of statistical power when earthworm density is sufficiently high, considering the magnitude of effects that are relevant at the earthworm community level. Furthermore, a decrease in the MSD values can be obtained through an increase in the number of soil samples per test replicate, an option to be considered to improve statistical robustness.

This critical review examines the definition and implementation of environmental protection goals for chemicals in current European Union (EU) legislation, guidelines, and international agreements to which EU countries are party. The European chemical industry is highly regulated, and prospective environmental risk assessments (ERAs) are tailored for different classes of chemical, according to their specific hazards, uses, and environmental exposure profiles. However, environmental protection goals are often highly generic, requiring the prevention of "unacceptable" or "adverse" impacts on "biodiversity" and "ecosystems" or the "environment as a whole." This review aims to highlight working examples, challenges, solutions, and best practices for defining specific protection goals (SPGs), which are seen to be essential for refining and improving ERA. Specific protection goals hinge on discerning acceptable versus unacceptable adverse effects on the key attributes of relevant, sensitive ecological entities (ranging from organisms to ecosystems). Some isolated examples of SPGs for terrestrial and aquatic biota can be found in prospective ERA guidance for plant protection products (PPPs). However, SPGs are generally limited to environmental or nature legislation that requires environmental monitoring and retrospective ERA. This limitation is due mainly to the availability of baselines, which define acceptable versus unacceptable environmental effects on the key attributes of sentinel species, populations and/or communities, such as reproductive status, abundance, or diversity. Nevertheless, very few regulatory case examples exist in which SPGs incorporate effect magnitude, spatial extent, and temporal duration. We conclude that more holistic approaches are needed for defining SPGs, particularly with respect to protecting population sustainability, ecosystem function, and integrity, which are implicit in generic protection goals and explicit in the International Programme for Chemical Safety (IPCS) definition of "adverse effect." A possible solution, which the chemical industry is currently assessing, is wider application of the ecosystem services approach proposed by the European Food Safety Authority (EFSA) for the risk assessment of PPPs. Integr Environ Assess Manag 2017;13:17-37. © 2016 SETAC.

In the first step of earthworm risk assessment for plant protection products (PPPs), the risk is assessed by comparing the no-observed effect levels (NOELs) from laboratory reproduction tests with the predicted exposure of the PPP in soil, while applying a trigger value (assessment factor [AF]) to cover uncertainties. If this step indicates a potential risk, field studies are conducted. However, the predicted environmental concentration in soil, which can be calculated, for example, for different soil layers (ranging from 0-1 cm to 0-20 cm), and the AF determine the conservatism that is applied in this first step. In this review paper, the tier 1 earthworm risk assessment for PPPs is calibrated by comparing the NOEL in earthworm reproduction tests with effect levels on earthworm populations under realistic field conditions. A data set of 54 pairs of studies conducted in the laboratory and in the field with the same PPP was compiled, allowing a direct comparison of relevant endpoints. The results indicate that a tier 1 AF of 5 combined with a regulatory relevant soil layer of 0 to 5 cm provides a conservative tier 1 risk assessment. A risk was identified by the tier 1 risk assessment in the majority of the cases at application rates that were of low risk for natural earthworm populations under field conditions. Increasing the conservatism in the tier 1 risk assessment by reducing the depth of the regulatory relevant soil layer or by increasing the tier 1 AF would increase the number of false positives and trigger a large number of additional field studies. This increased conservatism, however, would not increase the margin of safety for earthworm populations. The analysis revealed that the risk assessment is conservative if an AF of 5 and a regulatory relevant soil layer of 0 to 5 cm is used. Integr Environ Assess Manag 2016;12:643-650. © 2015 SETAC.

Isothiocyanates (ITCs) hydrolyzed from glucosinolates (GSLs) in Brassicaceae tissue are toxic to soil organisms. In this study, the effect of aliphatic and aromatic ITCs from hydrated dry Brassicaceae shoot tissues on the mycelium and oospores of the pea root rot pathogen Aphanomyces euteiches was investigated. The profile and concentrations of GSLs in two test Brassicaceae species, Sinapis alba and Brassica juncea, and the ITCs from the dominant hydrolyzed parent GSLs were monitored. The concentrations of dominant ITCs and pathogen exposure time were evaluated in in vitro experiments. The greatest effect on the pathogen was observed from aliphatic ITCs hydrolyzed from B. juncea tissue, and the effect depended on the ITC concentration and exposure time. ITCs were more effectively hydrolyzed from B. juncea GSLs than from S. alba GSLs; i.e., the ITC/GSL ratio was higher in B. juncea than in S. alba tissue, giving a different release pattern. The release of phenylethyl isothiocyanate, which was common to both species, followed a pattern similar to that of the dominant ITC in each crop species. This suggests that traits other than GSL content, e.g., plant cell structure, may affect the release of ITCs and should therefore influence the choice of species used for biofiimigation purposes.

Background: Plant diversity can influence numerous ecosystem processes, including plant–animal interactions, which, in turn, will affect plant growth and fitness. At present, little is known on how plant–animal interactions in forests respond to gradients in tree and herb-layer diversity. Aims: To quantify how invertebrate herbivory, pollination-dependent seed production and post-dispersal seed predation vary along a gradient of tree and herb diversity in a semi-natural temperate deciduous forest. Methods: Potted individuals of the understorey herbs Lathyrus vernus and Primula elatior were exposed in 40 forest plots along a natural gradient of tree and herb diversity for 3 months to record seed production and leaf damage caused by invertebrate herbivores. In half the plants, pollinators were experimentally excluded to test if seed production depended on insect pollination. In Lathyrus vernus linkages between below- and above-ground herbivory were tested by inoculating plants with root-feeding nematodes. To study seed predation, we measured seed removal from seed depots that were selectively accessible to different seed predator groups. Results: Herbivore damage decreased with increasing tree diversity in P. elatior. In L. vernus, above-ground herbivory was higher in nematode-treated plants than in control plants. Seed production in L. vernus, which strongly depended on insect pollination, showed a positive relationship with tree diversity. Seed predation was positively related to herb diversity in L. vernus, but only weakly so in P. elatior. While both vertebrates and invertebrates acted as seed predators of L. vernus, seeds of P. elatior were mainly predated by invertebrates. Conclusions: The fitness of understorey plants is linked to tree and herb diversity via changes in plant-invertebrate interactions. However, species-specific responses of study plants underline the importance of species identity effects in addition to effects of biodiversity per se.

This critical review examines the definition and implementation of environmental protection goals for chemicals in current European Union (EU) legislation, guidelines, and international agreements to which EU countries are party. The European chemical industry is highly regulated, and prospective environmental risk assessments (ERAs) are tailored for different classes of chemical, according to their specific hazards, uses, and environmental exposure profiles. However, environmental protection goals are often highly generic, requiring the prevention of "unacceptable" or "adverse" impacts on "biodiversity" and "ecosystems" or the "environment as a whole." This review aims to highlight working examples, challenges, solutions, and best practices for defining specific protection goals (SPGs), which are seen to be essential for refining and improving ERA. Specific protection goals hinge on discerning acceptable versus unacceptable adverse effects on the key attributes of relevant, sensitive ecological entities (ranging from organisms to ecosystems). Some isolated examples of SPGs for terrestrial and aquatic biota can be found in prospective ERA guidance for plant protection products (PPPs). However, SPGs are generally limited to environmental or nature legislation that requires environmental monitoring and retrospective ERA. This limitation is due mainly to the availability of baselines, which define acceptable versus unacceptable environmental effects on the key attributes of sentinel species, populations and/or communities, such as reproductive status, abundance, or diversity. Nevertheless, very few regulatory case examples exist in which SPGs incorporate effect magnitude, spatial extent, and temporal duration. We conclude that more holistic approaches are needed for defining SPGs, particularly with respect to protecting population sustainability, ecosystem function, and integrity, which are implicit in generic protection goals and explicit in the International Programme for Chemical Safety (IPCS) definition of "adverse effect." A possible solution, which the chemical industry is currently assessing, is wider application of the ecosystem services approach proposed by the European Food Safety Authority (EFSA) for the risk assessment of PPPs. Integr Environ Assess Manag 2017;13:17-37. © 2016 SETAC.

Within the regulatory framework for authorisation of plant protection products (PPPs) (EU Directive 91/414/1991/EEC replaced by Regulation (EC) 1107/2009), higher tier risk assessments and earthworm field tests are conducted in different countries across Europe. This paper describes dominant earthworm species for regulatory and biogeographical regions in agricultural landscapes across Europe and examines regional differences in earthworm communities and densities and their respective response to a toxic reference. For the assessment of earthworm abundance and species distribution, data of untreated control plots from 30 earthworm field studies were analysed; each conducted according to the ISO 11268–3 (1999) guideline by European Crop Protection Association member companies in the context of registration of PPPs. For the evaluation of the response to PPPs under different regional and climatic conditions, the effect on earthworm abundance was assessed by comparing plots treated with toxic references with untreated control plots. Additionally, a comparative literature review was included providing an overview of earthworm species composition and densities in agricultural crops from 14 European countries. The assessment of earthworm field studies from six different European countries revealed that common earthworm species of anecic and endogeic ecological groups are present at most field sites. Dominant species groups of endogeic and anecic earthworms can be defined that are abundant in all assessed countries. These are the endogeic species Aporrectodea caliginosa, Aporrectodea rosea and Allolobophora chlorotica, and the anecic species Lumbricus terrestris (Northern and Central Europe) and Lumbricus friendi (Southern Europe). Taking into account the high variability in total earthworm abundances, it can be concluded that the variability within regions was larger than the variability between regions. Analysis of the earthworm community and data of toxic references lead to the conclusion that testing in different zones is not considered necessary.

Metabolite fingerprinting is widely used to unravel the chemical characteristics of biological samples. Multivariate data analysis and other statistical tools are subsequently used to analyze and visualize the plasticity of the metabolome and/or the relationship between those samples. However, there are limitations to these approaches for example because of the multi-dimensionality of the data that makes interpretation of the data obtained from untargeted analysis almost impossible for an average human being. These limitations make the biological information that is of prime importance in untargeted studies be partially exploited. Even in the case of full exploitation, current methods for relationship elucidation focus mainly on between groups variation and differences. Therefore, a measure that is capable of exploiting both between- and within-group biological variation would be of great value. Here, we examined the natural variation in the metabolome of nine Arabidopsis thaliana accessions grown under various environmental conditions and established a measure for the metabolic distance between accessions and across environments. This data analysis approach shows that there is just a minor correlation between genetic and metabolic diversity of the nine accessions. On the other hand, it delivers so far in Arabidopsis unexplored chemical information and is shown to be biologically relevant for resistance studies. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11306-011-0375-3) contains supplementary material, which is available to authorized users.

1. Arthropod communities are structured by complex interactions between bottom-up (resource-based) and top-down (natural enemy-based) forces. Their relative importance in shaping arthropod communities, however, continues to be under debate. Bottom-up and top-down forces can be affected by intraspecific plant variation, for example by differences in concentrations of secondary metabolites that affect herbivore abundance through plant quality (bottom-up) or attract natural enemies of these herbivores (top-down). 2. Our objective was to investigate whether herbivore abundance is more strongly affected by plant-mediated bottom-up or top-down forces. 3. We used a model system of four cultivars of Brassica oleracea that show a high degree of variation in several plant traits, resistance to herbivores and attraction of natural enemies. During two field seasons, we recorded the abundance of several herbivorous and carnivorous insect species. To assess the relative importance of bottom-up and top-down forces, we quantified chemical and morphological traits of the cultivars (bottom-up) and assessed parasitization of herbivores and predator oviposition on plants inoculated with a controlled number of herbivores (top-down). 4. We show that intraspecific variation in plant chemistry and morphology consistently affects the abundance of insect herbivores and their natural enemies, resulting in cascading effects on tritrophic interactions in the associated insect community. Foliar profiles of glucosinolates and leaf toughness appeared most important for these effects. Brassica oleracea cultivars that harboured the largest numbers of herbivores also harboured the largest numbers of natural enemies. Differences in the fraction of herbivores parasitized and in predator oviposition on plants inoculated with a controlled number of herbivores could not explain the differences in natural abundance of herbivores. 5. Although abundance of herbivores is most likely influenced by a combination of bottom-up and top-down forces, it appears that in the tritrophic system investigated, bottom-up forces (plant chemistry and morphology) were more important for herbivore abundance than plant-mediated top-down forces (attraction and arrestment of natural enemies).

Belowground communities can affect interactions between plants and aboveground insect communities. Such belowground–aboveground interactions are known to depend on the composition of belowground communities, as well as on the plant species that mediates these interactions. However, it is largely unknown whether the effect of belowground communities on aboveground plant–insect interactions also depends on genotypic variation within the plant species that mediates the interaction. To assess whether the outcome of belowground–aboveground interactions can be affected by plant genotype, we selected two white cabbage cultivars [Brassica oleracea L. var. capitata (Brassicaceae)]. From previous studies, it is known that these cultivars differ in their chemistry and belowground and aboveground multitrophic interactions. Belowground, we inoculated soils of the cultivars with either nematodes or microorganisms and included a sterilized soil as a control treatment. Aboveground, we quantified aphid [Brevicoryne brassicae (L.) (Hemiptera: Aphididae)] population development and parasitoid [Diaeretiella rapae (McIntosh) (Hymenoptera: Braconidae)] fitness parameters. The cultivar that sustained highest aphid numbers also had the best parasitoid performance. Soil treatment affected aphid population sizes: microorganisms increased aphid population growth. Soil treatments did not affect parasitoid performance. Cultivars differed in their amino acid concentration, leaf relative growth rate, and root, shoot, and phloem glucosinolate composition but showed similar responses of these traits to soil treatments. Consistent with this observation, no interactions were found between cultivar and soil treatment for aphid population growth or parasitoid performance. Overall, the aboveground community was more affected by cultivar, which was associated with glucosinolate profiles, than by soil community.

1. Plant resistance against herbivores can act directly (e.g. by producing toxins) and indirectly (e.g. by attracting natural enemies of herbivores). If plant secondary metabolites that cause direct resistance against herbivores, such as glucosinolates, negatively influence natural enemies, this may result in a conflict between direct and indirect plant resistance. 2. Our objectives were (i) to test herbivore-mediated effects of glucosinolates on the performance of two generalist predators, the marmalade hoverfly (Episyrphus balteatus) and the common green lacewing (Chrysoperla carnea) and (ii) to test whether intraspecific plant variation affects predator performance. 3. Predators were fed either Brevicoryne brassicae, a glucosinolate-sequestering specialist aphid that contains aphid-specific myrosinases, or Myzus persicae, a non-sequestering generalist aphid that excretes glucosinolates in the honeydew, reared on four different white cabbage cultivars. Predator performance and glucosinolate concentrations and profiles in B. brassicae and host-plant phloem were measured, a novel approach as previous studies often measured glucosinolate concentrations only in total leaf material. 4. Interestingly, the specialist aphid B. brassicae selectively sequestered glucosinolates from its host plant. The performance of predators fed this aphid species was lower than when fed M. persicae. When fed B. brassicae reared on different cultivars, differences in predator performance matched differences in glucosinolate profiles among the aphids. 5. We show that not only the prey species, but also the plant cultivar can have an effect on the performance of predators. Our results suggest that in the tritrophic system tested, there might be a conflict between direct and indirect plant resistance

Shoot glucosinolate profiles of Brassicaceae are known to vary within species, across environmental conditions, and between developmental stages. Here we study whether root profiles follow the intra-specific, environmental, and developmental variation observed for aerial parts in white cabbage cultivars. We also assess whether greenhouse studies can be used to predict shoot and root glucosinolate concentrations and profiles in the field. Root glucosinolate profiles showed significant intra-specific variation; however, this variation was unrelated to that in shoot profiles. One of the strongest determinants of the diversity in the root profiles was 2-phenylethyl glucosinolate (gluconasturtiin). Root profiles were generally comparable between greenhouse studies and field trials, whereas shoot profiles were highly plastic. We conclude that among white cabbage cultivars, shoot glucosinolate profiles are not indicative of root profiles. We further conclude that greenhouse assessments of root glucosinolates can be reliable predictors of root glucosinolate profiles in the field due to their low plasticity.

Claoxylon and Micrococca are the only Euphorbiaceae genera that have rough dried leaves (fresh ones are smooth) because of protruding styloid (needle-like) crystals more or less perpendicular to the leaf surface, which perforate the epidermis and cuticle. A broad leaf anatomical study of the subtribes Claoxylinae, the monogeneric Lobaniliinae, and Mercurialis of the Mercurialinae (95 of a possible 235 species in all six genera) showed that styloids are present in Claoxylon, Discoclaoxylon, Erythrococca, Lobanilia, and Micrococca, and lacking in Claoxylopsis and Mercurialis. Contrary to Claoxylon, the dried leaves of Discoclaoxylon, Erythrococca, Lobanilia, and Micrococca are not rough, because the styloids do not perforate the epidermis during drying and therefore herbarium leaves generally remain smooth. The presence of styloids supports a clade in a recent molecular phylogenetic study that unites subtribes Claoxylinae and Lobaniliinae as Claoxylinae s.l. Mercurialis (no styloids) is sister to all other taxa (with styloids) in the monophyletic Claoxylinae s.l. The styloids form a synapomorphy for a monophyletic part of the Claoxylinae (Claoxylon, Discoclaoxylon, Erythrococca, Lobanilia, and Micrococca). Other leaf anatomical notes are provided, together with an overview of the occurrence of styloids, stomata, and druse crystals for most species in the Claoxylinae. The indumentum ranges from (virtually) absent to a sparse or dense tomentum of straight and thick- or thin-walled unicellular hairs (most common), curly hairs, or two-armed hairs (‘Malpighiaceous hairs’). The last two hair types probably form diagnostic characters for species groups within the genus Claoxylon

Collembola are soil dwelling organisms that provide important ecosystem services within soils. To increase realism in evaluating potential effects of plant protection products a Collembola two-generation study was developed. This test assesses the potential for recovery of Collembola when exposed to plant protection products. Juvenile individuals of Folsomia candida (Willem, Ann Soc Entomol Belg 46:275-283, 1902) which hatched under conditions of exposure to a test substance in a modified OECD 232 bioassay were introduced into a second consecutive bioassay containing the same test substance aged in soil. This test system determines whether a population which was initially impacted by a substance in a 1st bioassay shows normal reproduction or survival in a 2nd bioassay after aging of the test substance in soil. An intermediate period for juvenile growth is included between the 1st and 2nd bioassay in order to reduce the control treatment variability in reproduction and mortality to fulfill the validity criteria according to the OECD 232 guideline. The Collembola two-generation study is able to differentiate between substances showing either a potential long-term risk or comprising a low risk. Comparing the results of this two generation study with data from semi-field or field studies indicates a high degree of conservatism when this test is considered within a tiered risk assessment scheme. This approach represents a valuable tool which makes the risk assessment more efficient by providing an alternative refinement option for highly conservative tier 1 Collembola risk assessment.

In the first step of earthworm risk assessment for plant protection products (PPPs), the risk is assessed by comparing the no-observed effect levels (NOELs) from laboratory reproduction tests with the predicted exposure of the PPP in soil, while applying a trigger value (assessment factor [AF]) to cover uncertainties. If this step indicates a potential risk, field studies are conducted. However, the predicted environmental concentration in soil, which can be calculated, for example, for different soil layers (ranging from 0-1 cm to 0-20 cm), and the AF determine the conservatism that is applied in this first step. In this review paper, the tier 1 earthworm risk assessment for PPPs is calibrated by comparing the NOEL in earthworm reproduction tests with effect levels on earthworm populations under realistic field conditions. A data set of 54 pairs of studies conducted in the laboratory and in the field with the same PPP was compiled, allowing a direct comparison of relevant endpoints. The results indicate that a tier 1 AF of 5 combined with a regulatory relevant soil layer of 0 to 5 cm provides a conservative tier 1 risk assessment. A risk was identified by the tier 1 risk assessment in the majority of the cases at application rates that were of low risk for natural earthworm populations under field conditions. Increasing the conservatism in the tier 1 risk assessment by reducing the depth of the regulatory relevant soil layer or by increasing the tier 1 AF would increase the number of false positives and trigger a large number of additional field studies. This increased conservatism, however, would not increase the margin of safety for earthworm populations. The analysis revealed that the risk assessment is conservative if an AF of 5 and a regulatory relevant soil layer of 0 to 5 cm is used. Integr Environ Assess Manag 2016;12:643-650. © 2015 SETAC.

Plant size is a major predictor of ecological functioning. We tested the hypothesis that feeding damage to plants increases with plant size, as the conspicuousness of large plants makes resource finding and colonisation easier. Further, large plants can be attractive to herbivores, as they offer greater amounts and ranges of resources and niches, but direct evidence from experiments testing size effects on feeding damage and consequently on plant fitness is so far missing. We established a common garden experiment with a plant size gradient (10-130 cm height) using 21 annual Brassicaceae species, and quantified plant size, biomass and number of all aboveground components (flowers, fruits, leaves, stems) and their proportional feeding damage. Plant reproductive fitness was measured using seed number, 1000 seed weight and total seed weight. Feeding damage to the different plant components increased with plant size or component biomass, with mean damage levels being approximately 30 % for flowers, 5 % for fruits and 1 % for leaves and stems. Feeding damage affected plant reproductive fitness depending on feeding damage type, with flower damage having the strongest effect, shown by greatly reduced seed number, 1000 seed weight and total seed weight. Finally, we found an overall negative effect of plant size on 1000 seed weight, but not on seed number and total seed weight. In conclusion, being conspicuous and attractive to herbivores causes greater flower damage leading to higher fitness costs for large plants, which might be partly counterbalanced by benefits such as enhanced competitive/compensatory abilities or more mutualistic pollinator visits.

The cabbage aphid Brevicoryne brassicae is a specialist herbivore that sequesters glucosinolates from its host plant as a defense against its predators. It is unknown to what extent parasitoids are affected by this sequestration. We investigated herbivore-mediated effects of glucosinolates on the parasitoid wasp Diaeretiella rapae and the predator Episyrphus balteatus. We reared B. brassicae on three ecotypes of Arabidopsis thaliana that differ in glucosinolate content and on one genetically transformed line with modified concentrations of aliphatic glucosinolates. We tested aphid performance and the performance and behavior of both natural enemies. We correlated this with phloem and aphid glucosinolate concentrations and emission of volatiles. Brevicoryne brassicae performance correlated positively with concentrations of both aliphatic and indole glucosinolates in the phloem. Aphids selectively sequestered glucosinolates. Glucosinolate concentration in B. brassicae correlated negatively with performance of the predator, but positively with performance of the parasitoid, possibly because the aphids with the highest glucosinolate concentrations had a higher body weight. Both natural enemies showed a positive performance-preference correlation. The predator preferred the ecotype with the lowest emission of volatile glucosinolate breakdown products in each test combination, whereas the parasitoid wasp preferred the A. thaliana ecotype with the highest emission of these volatiles. The study shows that there are differential herbivore-mediated effects of glucosinolates on a predator and a parasitoid of a specialist aphid that selectively sequesters glucosinolates from its host plant. Electronic supplementary material The online version of this article (doi:10.1007/s10886-012-0065-2) contains supplementary material, which is available to authorized users.

Intraspecific variation in plants can affect soil organisms. However, little is known about whether the magnitude of the effect depends on the degree of interaction with the roots. We analyzed effects of plant intraspecific variation on root herbivores and other soil organisms that interact directly with living plant roots, as well as on decomposer organisms that interact more indirectly with roots. We used four different white cabbage (Brassica oleracea var. capitata) cultivars exhibiting a high degree of intraspecific variation in root glucosinolate profiles. Intraspecific variation affected root-feeding nematodes, whereas decomposer organisms such as earthworms and Collembola were not affected. Root-feeding nematodes were most abundant in one of the cultivars, Badger Shipper, which lacked the glucosinolate gluconasturtiin. The effect of the intraspecific variation in glucosinolate composition may have been restricted to root-feeding nematodes due to the rapid degradation of glucosinolates and their breakdown products in the soil. Additionally, the low biomass of root-feeding nematodes, relative to other soil organisms, limits the possibility to affect higher trophic level organisms. Our results show that variation in root chemistry predominantly affects belowground herbivores and that these effects do not extend into the soil food web.