Deconstructing the surrogate species concept: a life history approach to the protection of ecosystem services

How to bridge the gap between nature conservation and environmental risk assessment of contaminated ecosystems

When evaluating the risks of contamination in nature reserves, two issues play a role: nature protection and chemical risk assessment. The approaches adopted under these two schemes are not necessarily aligned. We argue that there is a fundamental difference in how the International Union for the Conservation of Nature (IUCN) and agencies like the US Environmental Protection Agency (EPA), the European Food Safety Authority (EFSA) and the European Chemicals Agency (ECHA) approach environmental assessments. The IUCN's Red List assessments focus on a species' survival potential, using population numbers, distribution areas, and broad threats without specifying these. It's a big-picture approach to identify species in need of conservation. On the other hand, EPA, EFSA and ECHA delve deeper into specific threats or hazards, specifically chemical pollutants. They assess how readily a chemical becomes available to organisms (bioavailability) and what its toxicity can be to individual species. These data are then used to predict the chemical's risk to a broader range of species through different approaches, e.g. species sensitivity distributions. In addition, arguments related to ecosystem functions, such as clean water and food production, may play a role. The current testing scheme is however, mainly focused on laboratory-cultured species and does not primarily consider specific ecological demands of red list species. We describe and analyse these two different systems, and develop a practical approach that combines their strengths. This could involve using IUCN Red List data to select species for further ecotoxicological assessment by EPA-like agencies. Integrating these results would underpin general conservation efforts and provide targeted protection for species with unique characteristics or high vulnerability to specific threats. This combined approach would move us closer to achieving the general protection of all species and the specific protection of those needing extra attention.

Using metabolomic profiling to inform use of surrogate species in ecological risk assessment practices

The U.S. EPA frequently uses avian or fish toxicity data to set protective standards for amphibians in ecological risk assessments. However, this approach does not always adequately represent aquatic-dwelling and terrestrial-phase amphibian exposure data. For instance, it is accepted that early life stage tests for fish are typically sensitive enough to protect larval amphibians, however, metamorphosis from tadpole to a terrestrial-phase adult relies on endocrine cues that are less prevalent in fish but essential for amphibian life stage transitions. These differences suggest that more robust approaches are needed to adequately elucidate the impacts of pesticide exposure in amphibians across critical life stages. Therefore, in the current study, methodology is presented that can be applied to link the perturbations in the metabolomic response of larval zebrafish (Danio rerio), a surrogate species frequently used in ecotoxicological studies, to those of African clawed frog (Xenopus laevis) tadpoles following exposure to three high-use pesticides, bifenthrin, chlorothalonil, or trifluralin. Generally, D. rerio exhibited greater metabolic perturbations in both number and magnitude across the pesticide exposures as opposed to X. laevis. This suggests that screening ecological risk assessment surrogate toxicity data would sufficiently protect amphibians at the single life stage studied but care needs to be taken to understand the suite of metabolic requirements of each developing species. Ultimately, methodology presented, and data gathered herein will help inform the applicability of metabolomic profiling in establishing the risk pesticide exposure poses to amphibians and potentially other non-target species.

Determining reliable parameter estimates for within-host and within-vector models of Zika virus

In this paper, we introduce three within-host and one within-vector models of Zika virus. The within-host models are the target cell limited model, the target cell limited model with natural killer (NK) cells class, and a within-host-within-fetus model of a pregnant individual. The within-vector model includes the Zika virus dynamics in the midgut and salivary glands. The within-host models are not structurally identifiable with respect to data on viral load and NK cell counts. After rescaling, the scaled within-host models are locally structurally identifiable. The within-vector model is structurally identifiable with respect to viremia data in the midgut and salivary glands. Using Monte Carlo Simulations, we find that target cell limited model is practically identifiable from data on viremia; the target cell limited model with NK cell class is practically identifiable, except for the rescaled half saturation constant. The within-host-within-fetus model has all fetus-related parameters not practically identifiable without data on the fetus, as well as the rescaled half saturation constant is also not practically identifiable. The remaining parameters are practically identifiable. Finally we find that none of the parameters of the within-vector model is practically identifiable.

A tale of two metrics: the EPA Risk Quotient Approach versus the delay in Population Growth Index for determination of pesticide risk to aquatic species

The potential risk that two closely related insecticides, spinetoram and spinosad, posed to three Cladoceran species, Ceriodaphnia dubia, Daphnia pulex, and D. magna was determined using two approaches, the USEPA Risk Quotient method and the Delay in Population Growth Index (DPGI). Results of the RQ method showed that spinetoram posed a risk to all three species, but spinosad posed a risk only to C. dubia. The DPGI analysis showed that exposure to spinetoram resulted in populations of all three species being delayed ≥ 3 generation times. Exposure to the LC₅₀ and the lower 95% CL resulted in delayed populations while exposure to the upper 95% CL concentration of spinetoram resulted in no recovery of any of the three species over the course of the modeling exercise (88 d). Exposure to the lower and upper 95% Cl and the LC₅₀ of spinosad resulted in C. dubia populations being delayed ≥ 3 generations. D. pulex populations were not negatively affected after exposure to spinosad. D. magna populations were delayed ≥ 3 generations, but only after exposure to the upper 95% Cl of spinosad. These results illustrate that although the EPA risk quotient method indicated that spinetoram posed a risk to all three species and that spinosad only posed a risk to C. dubia, the DPGI showed that D. magna would be negatively affected by spinosad and none of the three species would reach a predetermined number of individuals after exposure to the upper 95% CL of spinetoram. Because the DPGI uses the 95% Cl as well as the LC₅₀ in its calculation and produces a measure of population growth it provides more detailed information in terms of the potential risk of pesticides to populations than the RQ method.

Pop-guide: Population modeling guidance, use, interpretation, and development for ecological risk assessment

The assimilation of population models into ecological risk assessment (ERA) has been hindered by their range of complexity, uncertainty, resource investment, and data availability. Likewise, ensuring that the models address risk assessment objectives has been challenging. Recent research efforts have begun to tackle these challenges by creating an integrated modeling framework and decision guide to aid the development of population models with respect to ERA objectives and data availability. In the framework, the trade-offs associated with the generality, realism, and precision of an assessment are used to guide the development of a population model commensurate with the protection goal. The decision guide provides risk assessors with a stepwise process to assist them in developing a conceptual model that is appropriate for the assessment objective and available data. We have merged the decision guide and modeling framework into a comprehensive approach, Population modeling Guidance, Use, Interpretation, and Development for Ecological risk assessment (Pop-GUIDE), for the development of population models for ERA that is applicable across regulatory statutes and assessment objectives. In Phase 1 of Pop-GUIDE, assessors are guided through the trade-offs of ERA generality, realism, and precision, which are translated into model objectives. In Phase 2, available data are assimilated and characterized as general, realistic, and/or precise. Phase 3 provides a series of dichotomous questions to guide development of a conceptual model that matches the complexity and uncertainty appropriate for the assessment that is in concordance with the available data. This phase guides model developers and users to ensure consistency and transparency of the modeling process. We introduce Pop-GUIDE as the most comprehensive guidance for population model development provided to date and demonstrate its use through case studies using fish as an example taxon and the US Federal Insecticide Fungicide and Rodenticide Act and Endangered Species Act as example regulatory statutes. Integr Environ Assess Manag 2021;17:767-784. © 2020 SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Environmental risk assessment in agro-ecosystems: Revisiting the concept of receiving environment after the EFSA guidance document

The environmental risk assessment (ERA) for genetically modified plants (GMPs) is a prerequisite for commercial approval of these new varieties according to regulatory systems worldwide. The first country to regulate GM crops was the USA and the issue of possible environmental impacts was based on the principles used in risk assessment of pesticides. Two main pillars of this approach are the use of surrogate species for testing effects on non-target organisms using a tiered assessment with clear thresholds to indicate the need to move between tiers. The latest EFSA guidance document on ERA of Genetically Modified Organisms considers specifically the receiving environment in preparation of ERA for commercial cultivation of GMPs. According to existing guidelines in the EU, the receiving environment is defined by three mutually interacting components: the characteristics of the environmental stressor (i.e. the GM plant), the bio-geographical regions where the commercial release of the crop is expected and the agricultural systems therein. Difference in agronomic and ecological conditions (e.g. use of different varieties, vegetation of adjacent areas, non-target species assemblages, sensitivity of local species to the stressors) suggests that explicit considerations of the receiving environments are necessary. Results from field experiments indicate that differences in cultivation practices, e.g. the herbicide regime used on herbicide-tolerant GM crops, may induce direct and indirect effects on wild plant distribution and abundance, with consequent repercussions on food webs based on these plants. Moreover, ecological literature indicates that the concept of surrogate species has clear limitations if applied broadly to any ERA. Starting from case studies regarding GMPs, this paper discusses some ecological and agronomic characteristics of agro-ecosystems, which have implications in the elaboration of both hazard and exposure analyses during ERA. The species selection approach indicated in the EFSA Guidance Document and the consideration of the area(s) of the expected release of the new variety may provide the basis to an ecologically sound ERA for a range of environmental stressors. The quality of the data that become available for risk managers with this approach may support a more transparent and dependable ERA and risk management for GMPs as well as for other potential environmental stressors in agro-ecosystems.

Population viability in a host-parasitoid system is mediated by interactions between population stage structure and life stage differential susceptibility to toxicants

The effects of toxicants, such as pesticides, may be more severe for some life stages of an organism than others. However, in most toxicity studies, data is developed for only one life stage, which may lead to misleading interpretations. Furthermore, population stage-structure may interact with differential susceptibility, especially when populations consist of higher proportions of individuals in more susceptible stages at the time of toxicant exposure. We explore the interaction of differential stage susceptibility and stage distribution using a stage-structured Lefkovitch matrix model. We incorporate lab-derived toxicity data for a common parasitoid, the braconid Diaeretiella rapae (M’Intosh), a common natural enemy of the cabbage aphid (Brevicoryne brassicae L.), exposed to the pesticide imidacloprid. We compare population outcomes of simulations in which we vary both the population stage structure along with the susceptibility of each stage to toxicants. Our results illustrate an interaction between differential susceptibility and initial stage distribution, highlighting the fact that both of these demographic features should be considered in interpreting toxicity data and the development of ecological risk assessments.

Cross-Taxa Distinctions in Mechanisms of Developmental Effects for Aquatic Species Exposed to Trifluralin

Standard ecological risk assessment practices often rely on larval and juvenile fish toxicity data as representative of the amphibian aquatic phase. Empirical evidence suggests that endpoints measured in fish early life stage tests are often sufficient to protect larval amphibians. However, the process of amphibian metamorphosis relies on endocrine cues that affect development and morphological restructuring and are not represented by these test endpoints. The present study compares developmental endpoints for zebrafish (Danio rerio) and the African clawed frog (Xenopus laevis), 2 standard test species, exposed to the herbicide trifluralin throughout the larval period. Danio rerio were more sensitive and demonstrated a reduction in growth measurements with increasing trifluralin exposure. Size of X. laevis at metamorphosis was not correlated with exposure concentration; however, time to metamorphosis was delayed relative to trifluralin concentration. Gene expression patterns indicate discrepancies in response by D. rerio and X. laevis, and dose-dependent metabolic activity suggests that trifluralin exposure perturbed biological pathways differently within the 2 species. Although many metabolites were correlated with exposure concentration in D. rerio, nontargeted hepatic metabolomics identified a subset of metabolites that exhibited a nonmonotonic response to trifluralin exposure in X. laevis. Linking taxonomic distinctions in cellular-level response with ecologically relevant endpoints will refine assumptions used in interspecies extrapolation of standard test effects and improve assessment of sublethal impacts on amphibian populations. Environ Toxicol Chem 2020;39:1797-1812. Published 2020. This article is a US government work and is in the public domain in the USA.

Lethal and sublethal effects of toxicants on bumble bee populations: a modelling approach

Pollinator decline worldwide is well-documented; globally, chemical pesticides (especially the class of pesticides known as neonicotinoids) have been implicated in hymenopteran decline, but the mechanics and drivers of population trends and dynamics of wild bees is poorly understood. Declines and shifts in community composition of bumble bees (Bombus spp.) have been documented in North America and Europe, with a suite of lethal and sub-lethal effects of pesticides on bumble bee populations documented. We employ a mathematical model parameterized with values taken from the literature that uses differential equations to track bumble bee populations through time in order to attain a better understanding of toxicant effects on a developing colony of bumble bees. We use a delay differential equation (DDE) model, which requires fewer parameter estimations than agent-based models while affording us the ability to explicitly describe the effect of larval incubation and colony history on population outcomes. We explore how both lethal and sublethal effects such as reduced foraging ability may combine to affect population outcomes, and discuss the implications for the protection and conservation of ecosystem services.

Are honeybees suitable surrogates for use in pesticide risk assessment for non-Apis bees?

Historically, bee regulatory risk assessment for pesticides has centred on the European honeybee (Apis mellifera), primarily due to its availability and adaptability to laboratory conditions. Recently, there have been efforts to develop a battery of laboratory toxicity tests for a range of non-Apis bee species to directly assess the risk to them. However, it is not clear whether the substantial investment associated with the development and implementation of such routine screening will actually improve the level of protection of non-Apis bees. We argue, using published acute toxicity data from a range of bee species and standard regulatory exposure scenarios, that current first-tier honeybee acute risk assessment schemes utilised by regulatory authorities are protective of other bee species and further tests should be conducted only in cases of concern. We propose similar analysis of alternative exposure scenarios (chronic and developmental) once reliable data for non-Apis bees are available to expand our approach to these scenarios. In addition, we propose that in silico (simulation) approaches can then be used to address population-level effects in more field-realistic scenarios. Such an approach could lead to a protective, but also workable, risk assessment for non-Apis species while contributing to pollination security in agricultural landscapes around the globe. © 2019 Society of Chemical Industry.

A Hybrid Individual-Based and Food Web-Ecosystem Modeling Approach for Assessing Ecological Risks to the Topeka Shiner (Notropis topeka): A Case Study with Atrazine

A hybrid model was used to characterize potential ecological risks posed by atrazine to the endangered Topeka shiner. The model linked a Topeka shiner individual-based bioenergetics population model (TS-IBM) to a comprehensive aquatic system model (CASM_TS ) to simulate Topeka shiner population and food web dynamics for an Iowa (USA) headwater pool. Risks were estimated for monitored concentrations in Iowa, Missouri, and Nebraska (USA), and for monitored concentrations multiplied by 2, 4, and 5. Constant daily atrazine concentrations of 10, 50, 100, and 250 µg/L were assessed. Exposure-response functions were developed from published atrazine toxicity data (median effect concentrations [EC50s] and no-observed-effect concentrations). Two toxicity scenarios were developed: the first included sensitive and insensitive species of algae, and the second reduced algal EC50 values to increase atrazine sensitivity. Direct and indirect effects of atrazine on Topeka shiner prey were modeled; direct effects on Topeka shiner were not assessed. Risks were characterized as differences between population biomass values of 365-d baseline and exposure simulations. The results indicated no discernable food web effects for monitored atrazine concentrations or constant exposures of 10 µg/L on Topeka shiner populations for either toxicity scenario. Magnified monitored concentrations and higher constant concentrations produced greater modeled indirect effects on Topeka shiners. The hybrid model transparently combines species-specific and surrogate species data to estimate food web responses to environmental stressors. The model is readily updated by new data and is adaptable to other species and ecosystems. Environ Toxicol Chem 2019;38:2243-2258. © 2019 SETAC.

Wild Bee Toxicity Data for Pesticide Risk Assessments

Pollination services are vital for agriculture, food security and biodiversity. Although many insect species provide pollination services, honeybees are thought to be the major provider of this service to agriculture. However, the importance of wild bees in this respect should not be overlooked. Whilst regulatory risk assessment processes have, for a long time, included that for pollinators, using honeybees (Apis mellifera) as a protective surrogate, there are concerns that this approach may not be sufficiently adequate particularly because of global declines in pollinating insects. Consequently, risk assessments are now being expanded to include wild bee species such as bumblebees (Bombus spp.) and solitary bees (Osmia spp.). However, toxicity data for these species is scarce and are absent from the main pesticide reference resources. The aim of the study described here was to collate data relating to the acute toxicity of pesticides to wild bee species (both topical and dietary exposure) from published regulatory documents and peer reviewed literature, and to incorporate this into one of the main online resources for pesticide risk assessment data: The Pesticide Properties Database, thus ensuring that the data is maintained and continuously kept up to date. The outcome of this study is a dataset collated from 316 regulatory and peer reviewed articles that contains 178 records covering 120 different pesticides and their variants which includes 142 records for bumblebees and a further 115 records for other wild bee species.

The trouble with surrogates in environmental risk assessment: a daphniid case study

The use of indicator species to test for environmental stability and functioning is a widespread practice. In aquatic systems, several daphniids (Cladocera: Daphniidae) are commonly used as indicator species; registration of new pesticides are mandated by the Environmental Protection Agency to be accompanied by daphniid toxicity data. This reliance upon a few species to infer ecosystem health and function assumes similar responses to toxicants across species with potentially very different life histories and susceptibility. Incorporating lab-derived life-history data into a simple mathematical model, we explore the reliability of three different daphniid species as surrogates for each other by comparing their responses to reductions in survivorship and fecundity after simulated exposure to toxicants. Our results demonstrate that daphniid species' responses to toxicant exposure render them poor surrogates for one another, highlighting that caution should be exercised in using a surrogate approach to the use of indicator species in risk assessment.

Adapting population models for application in pesticide risk assessment: A case study with Mead's milkweed

Population models can facilitate assessment of potential impacts of pesticides on populations or species rather than individuals and have been identified as important tools for pesticide risk assessment of nontarget species including those listed under the Endangered Species Act. Few examples of population models developed for this specific purpose are available; however, population models are commonly used in conservation science as a tool to project the viability of populations and the long-term outcomes of management actions. We present a population model for Mead's milkweed (Asclepias meadii), a species listed as threatened under the Endangered Species Act throughout its range across the Midwestern United States. We adapted a published population model based on demographic field data for application in pesticide risk assessment. Exposure and effects were modeled as reductions of sets of vital rates in the transition matrices, simulating both lethal and sublethal effects of herbicides. Two herbicides, atrazine and mesotrione, were used as case study examples to evaluate a range of assumptions about potential exposure-effects relationships. In addition, we assessed buffers (i.e., setback distances of herbicide spray applications from the simulated habitat) as hypothetical mitigation scenarios and evaluated their influence on population-level effects in the model. The model results suggest that buffers can be effective at reducing risk from herbicide drift to plant populations. These case studies demonstrate that existing population models can be adopted and integrated with exposure and effects information for use in pesticide risk assessment. Environ Toxicol Chem 2018;37:2235-2245. © 2018 SETAC.

Simulated developmental and reproductive impacts on amphibian populations and implications for assessing long-term effects

Fish endpoints measured in early life stage toxicity tests are often used as representative of larval amphibian sensitivity in Ecological Risk Assessment (ERA). This application potentially overlooks the impact of developmental delays on amphibian metamorphosis, and thereby reduced survival, in amphibian populations constrained by habitat availability. Likewise, the effects of reduced productivity or altered sexual development as a result of chemical exposure are not presented in terms of lower population fecundity in these surrogate tests. Translating endpoints measured in toxicity tests to those that are more representative of amphibian ecology and population dynamics provides a means of identifying how developmental effects result in long-term impacts. Here we compare effects of developmental delay on metamorphosis success in six anuran species and simulate population-level impacts of subsequent reductions in larval survival as well as potential reductions in fecundity as a result of developmental impacts. We use deterministic matrix models to compare realistic combinations of amphibian demographic rates and relative impacts of reduced growth on larval survival and subsequently on population growth. Developmental delays are less detrimental in species with longer and less synchronous larval periods. All six species were most sensitive to changes in first-year survival, and damping ratios were generally a good indicator of resilience to perturbations in both larval survival and fecundity. Further identification of species and population-level vulnerabilities can improve the evaluation of sublethal effects in relevant context for ERA.

The evolution of toxicant resistance in daphniids and its role on surrogate species

Prolonged exposure to a disturbance such as a toxicant has the potential to result in rapid evolution to toxicant resistance in many short-lived species such as daphniids. This evolution may allow a population to persist at higher levels of the toxicant than is possible without evolution. Here we apply evolutionary game theory to a Leslie matrix model for a daphniid population to obtain a Darwinian model that couples population dynamics with the dynamics of an evolving trait. We use the Darwinian model to consider how the evolution of resistance to the lethal or sublethal effects of a disturbance may change the population dynamics. In particular, we determine the conditions under which a daphniid population can persist by evolving toxicant resistance. We then consider the implications of this evolution in terms of the use of daphniids as surrogate species. We show for three species of daphniids that evolution of toxicant resistance means that one species may persist while another does not. These results suggest that toxicant studies that do not consider the potential of a species (or its surrogate) to develop toxicant resistance may not accurately predict the long term persistence of the species.

Analysis of lethal and sublethal impacts of environmental disasters on sperm whales using stochastic modeling

Mathematical models are essential for combining data from multiple sources to quantify population endpoints. This is especially true for species, such as marine mammals, for which data on vital rates are difficult to obtain. Since the effects of an environmental disaster are not fixed, we develop time-varying (nonautonomous) matrix population models that account for the eventual recovery of the environment to the pre-disaster state. We use these models to investigate how lethal and sublethal impacts (in the form of reductions in the survival and fecundity, respectively) affect the population's recovery process. We explore two scenarios of the environmental recovery process and include the effect of demographic stochasticity. Our results provide insights into the relationship between the magnitude of the disaster, the duration of the disaster, and the probability that the population recovers to pre-disaster levels or a biologically relevant threshold level. To illustrate this modeling methodology, we provide an application to a sperm whale population. This application was motivated by the 2010 Deepwater Horizon oil rig explosion in the Gulf of Mexico that has impacted a wide variety of species populations including oysters, fish, corals, and whales.

Population modeling for pesticide risk assessment of threatened species-A case study of a terrestrial plant, Boltonia decurrens

Although population models are recognized as necessary tools in the ecological risk assessment of pesticides, particularly for species listed under the Endangered Species Act, their application in this context is currently limited to very few cases. The authors developed a detailed, individual-based population model for a threatened plant species, the decurrent false aster (Boltonia decurrens), for application in pesticide risk assessment. Floods and competition with other plant species are known factors that drive the species' population dynamics and were included in the model approach. The authors use the model to compare the population-level effects of 5 toxicity surrogates applied to B. decurrens under varying environmental conditions. The model results suggest that the environmental conditions under which herbicide applications occur may have a higher impact on populations than organism-level sensitivities to an herbicide within a realistic range. Indirect effects may be as important as the direct effects of herbicide applications by shifting competition strength if competing species have different sensitivities to the herbicide. The model approach provides a case study for population-level risk assessments of listed species. Population-level effects of herbicides can be assessed in a realistic and species-specific context, and uncertainties can be addressed explicitly. The authors discuss how their approach can inform the future development and application of modeling for population-level risk assessments of listed species, and ecological risk assessment in general. Environ Toxicol Chem 2017;36:480-491. © 2016 SETAC.

Limitations in dose-response and surrogate species methodologies for risk assessment of Cry toxins on arthropod natural enemies

Dose-response assays and surrogate species are standard methods for risk analysis for environmental chemicals. These assume that individuals within a species have unimodal responses and that a surrogate species can predict responses of other related taxa. We exposed immature individuals of closely related aphidophagous coccinellid predators, Cycloneda sanguinea and Harmonia axyridis, to Cry1Ac and Cry1F toxins through uniform and constant artificial tritrophic exposure through Myzus persicae aphids. Both toxins were detected in coccinellid pupae, with individual and interspecific variation. Uptake was significantly higher in H. axyridis than in C. sanguinea, both in the proportion of individuals and the concentrations per individual. We also observed bimodal uptake of the Cry toxins by H. axyridis, which indicated that some individuals had low bioaccumulation and some had high bioaccumulation. This suggests that standard dose-response assays need to be interpreted with caution and future assays should examine the modality of the responses. In addition, the similarity in the biological effects of the Cry toxins in the two predators was due to different biological exposure mechanisms. The majority of H. axyridis were exposed both internally and in the gut, while C. sanguinea was exposed primarily in the gut. Thus, despite their close phylogenetic relatedness, these species would not be good surrogates for each other and the surrogate species methodology should be tested more rigorously.

Pesticide-Induced Stress in Arthropod Pests for Optimized Integrated Pest Management Programs

More than six decades after the onset of wide-scale commercial use of synthetic pesticides and more than fifty years after Rachel Carson's Silent Spring, pesticides, particularly insecticides, arguably remain the most influential pest management tool around the globe. Nevertheless, pesticide use is still a controversial issue and is at the regulatory forefront in most countries. The older generation of insecticide groups has been largely replaced by a plethora of novel molecules that exhibit improved human and environmental safety profiles. However, the use of such compounds is guided by their short-term efficacy; the indirect and subtler effects on their target species, namely arthropod pest species, have been neglected. Curiously, comprehensive risk assessments have increasingly explored effects on nontarget species, contrasting with the majority of efforts focused on the target arthropod pest species. The present review mitigates this shortcoming by hierarchically exploring within an ecotoxicology framework applied to integrated pest management the myriad effects of insecticide use on arthropod pest species.

Life history differences influence the impacts of drought on two pond-breeding salamanders

Drought is a strong density-independent environmental filter that contributes to population regulation and other ecological processes. Not all species respond similarly to drought, and the overall impacts can vary depending on life histories. Such differences can necessitate management strategies that incorporate information on individual species to maximize conservation success. We report the effects of a short-term drought on occupancy and reproductive success of two pond-breeding salamanders that differ in breeding phenology (fall vs. spring breeder) across an active military base landscape in Missouri, USA: We surveyed ~200 ponds for the presence of eggs, larvae, and metamorphs from 2011 to 2013. This period coincided with before, during, and after a severe drought that occurred in 2012. The two species showed contrasting responses to drought, where high reproductive failure (34% of ponds) was observed for the spring breeder during a single drought year. Alternatively, the fall breeder only showed a cumulative 8% failure over two years. The number of breeding ponds available for use in the fall decreased during the drought due to pond drying and/or a lack of re-filling. Estimates of occupancy probability declined for the fall-breeding salamander between 2012 and 2013, whereas occupancy probability estimates of the spring breeder increased post-drought. The presence of fish, hydroperiod, the amount of forest cover surrounding ponds, and canopy cover were all found to affect estimates of occupancy probabilities of each species. Pond clustering (distance to nearest pond and the number of ponds within close proximity), hydroperiod, forest cover, and canopy cover influenced both estimates of colonization and extinction probabilities. Our results show life history variation can be important in determining the relative susceptibility of a species to drought conditions, and that sympatric species experiencing the same environmental conditions can respond differently. Consideration of the spatial network and configuration of habitat patches that act as refuges under extreme environmental conditions will improve conservation efforts, such as the placement of permanent ponds for aquatic organisms. A better awareness of species-specific tolerances to environmental filters such as drought can lead to improved management recommendations to conserve and promote habitat for a greater diversity of species across landscapes of spatially connected populations.

Neonicotinoid Insecticides and Their Impacts on Bees: A Systematic Review of Research Approaches and Identification of Knowledge Gaps

It has been suggested that the widespread use of neonicotinoid insecticides threatens bees, but research on this topic has been surrounded by controversy. In order to synthesize which research approaches have been used to examine the effect of neonicotinoids on bees and to identify knowledge gaps, we systematically reviewed research on this subject that was available on the Web of Science and PubMed in June 2015. Most of the 216 primary research studies were conducted in Europe or North America (82%), involved the neonicotinoid imidacloprid (78%), and concerned the western honey bee Apis mellifera (75%). Thus, little seems to be known about neonicotinoids and bees in areas outside Europe and North America. Furthermore, because there is considerable variation in ecological traits among bee taxa, studies on honey bees are not likely to fully predict impacts of neonicotinoids on other species. Studies on crops were dominated by seed-treated maize, oilseed rape (canola) and sunflower, whereas less is known about potential side effects on bees from the use of other application methods on insect pollinated fruit and vegetable crops, or on lawns and ornamental plants. Laboratory approaches were most common, and we suggest that their capability to infer real-world consequences are improved when combined with information from field studies about realistic exposures to neonicotinoids. Studies using field approaches often examined only bee exposure to neonicotinoids and more field studies are needed that measure impacts of exposure. Most studies measured effects on individual bees. We suggest that effects on the individual bee should be linked to both mechanisms at the sub-individual level and also to the consequences for the colony and wider bee populations. As bees are increasingly facing multiple interacting pressures future research needs to clarify the role of neonicotinoids in relative to other drivers of bee declines.

Incorporating variability in point estimates in risk assessment: Bridging the gap between LC50 and population endpoints

Historically, point estimates such as the median lethal concentration (LC50) have been instrumental in assessing risks associated with toxicants to rare or economically important species. In recent years, growing awareness of the shortcomings of this approach has led to an increased focus on analyses using population endpoints. However, risk assessment of pesticides still relies heavily on large amounts of LC50 data amassed over decades in the laboratory. Despite the fact that these data are generally well replicated, little or no attention has been given to the sometime high levels of variability associated with the generation of point estimates. This is especially important in agroecosystems where arthropod predator-prey interactions are often disrupted by the use of pesticides. Using laboratory derived data of 4 economically important species (2 fruit fly pest species and 2 braconid parasitoid species) and matrix based population models, the authors demonstrate in the present study a method for bridging traditional point estimate risk assessments with population outcomes. The results illustrate that even closely related species can show strikingly divergent responses to the same exposures to pesticides. Furthermore, the authors show that using different values within the 95% confidence intervals of LC50 values can result in very different population outcomes, ranging from quick recovery to extinction for both pest and parasitoid species. The authors discuss the implications of these results and emphasize the need to incorporate variability and uncertainty in point estimates for use in risk assessment.

Time will tell: resource continuity bolsters ecosystem services

A common suggestion to support ecosystem services to agriculture provided by mobile organisms is to increase the amount of natural and seminatural habitat in the landscape. This might, however, be inefficient, and demands for agricultural products limit the feasibility of converting arable land into natural habitat. To develop more targeted means to promote ecosystem services, we need a solid understanding of the limitations to population growth for service-providing organisms. We propose a research agenda that identifies resource bottlenecks and interruptions over time to key beneficial organisms, emphasising their resulting population dynamics. Targeted measures that secure the continuity of resources throughout the life cycle of service-providing organisms are likely to effectively increase the stock, flow, and stability of ecosystem services.