Prediction Of Pest Pressure on Corn Root Nodes – The POPP-Corn model

A model for the corn rootworm Diabrotica spp. (Coleoptera: Chrysomelidae) combined with a temporally-explicit model for development of corn roots across the soil profile was developed to link pest ecology, root damage and yield loss. Development of the POPP-Corn model focused on simulating root damage from rootworm feeding in accordance with empirical observations in the field to allow the virtual testing of efficacy from management interventions in the future. Here we present the model and demonstrate its applicability for simulating root damage by comparison between observed and simulated pest population development and root damage (assessed according to the node injury scale from 0 to 3) for field studies from the literature conducted in Urbana, Illinois (US) between 1991 and 2014. The model simulated the first appearance of larvae and adults to within a week of that observed in 88 and 71% of all years, respectively, and in all cases to within two weeks of the first sightings recorded for central Illinois. Furthermore, in 73% of all years simulated root damage differed by less than 0.5 node injury scale points compared to the observations made in the field between 2005 and 2014 even though accurate information for initial pest pressure (i.e., number of eggs in the soil) was not measured at the sites or available from nearby locations. This is, to our knowledge, the first time that pest ecology, root damage and yield loss have been successfully interlinked to produce a virtual field. There are potential applications in investigating efficacy of different pest control measures and strategies

A knowledge-based approach to designing control strategies for agricultural pests

Chemical control of insect pests remains vital to agricultural productivity, but limited mechanistic understanding of the interactions between crop, pest and chemical control agent have restricted our capacity to respond to challenges such as the emergence of resistance and demands for tighter environmental regulation. Formulating effective control strategies that integrate chemical and non-chemical management for soil-dwelling pests is particularly problematic owing to the complexity of the soil-root-pest system and the variability that occurs between sites and between seasons. Here, we present a new concept, termed COMPASS, that integrates ecological knowledge on pest development and behaviour together with crop physiology and mechanistic understanding of chemical distribution and toxic action within the rhizosphere. The concept is tested using a two-dimensional systems model (COMPASS-Rootworm) that simulates root damage in maize from the corn rootworm Diabrotica spp. We evaluate COMPASS-Rootworm using 119 field trials that investigated the efficacy of insecticidal products and placement strategies at four sites in the USA over a period of ten years. Simulated root damage is consistent with measurements for 109 field trials. Moreover, we disentangle factors influencing root damage and pest control, including pest pressure, weather, insecticide distribution, and temporality between the emergence of crop roots and pests. The model can inform integrated pest management, optimize pest control strategies to reduce environmental burdens from pesticides, and improve the efficiency of insecticide development

Novel Approach for Characterizing pH-Dependent Uptake of Ionizable Chemicals in Aquatic Organisms

Here, we present and evaluate a combined experimental and modeling approach for characterizing the uptake of ionizable chemicals from water and sediments into aquatic organisms under different pH conditions. We illustrate and evaluate the approach for two pharmaceuticals (diclofenac and fluoxetine) and one personal care product ingredient (triclosan) for the oligochaete Lumbriculus variegatus. Initially, experimental data on the uptake of the three chemicals at two pH values were fitted using a toxicokinetic model to derive uptake and depuration constants for the neutral and ionized species of each molecule. The derived constants were then used to predict uptake from water and sediment for other pH conditions. Evaluation of predictions against corresponding experimental data showed good predictions of uptake for all test chemicals from water for different pH conditions and reasonable predictions of uptake of fluoxetine and diclofenac from a sediment. Predictions demonstrated that the level of uptake of the study chemicals, across pH ranges in European streams, could differ by up to a factor of 3035. Overall, the approach could be extremely useful for assessing internal exposure of aquatic organisms across landscapes with differing pH. This could help support better characterization of the risks of ionizable chemicals in the aquatic environment

A STANDARDIZED TRI-TROPHIC SMALL-SCALE SYSTEM (TriCosm) FOR THE ASSESSMENT OF STRESSOR INDUCED EFFECTS ON AQUATIC COMMUNITY DYNAMICS

Chemical impacts on the environment are routinely assessed in single-species tests. They are employed to measure direct effects on non-target organisms but indirect effects on ecological interactions can only be detected in multi-species tests. Micro- and mesocosms are more complex and environmentally realistic, yet, they are less frequently used for environmental risk assessment because resource demand is high while repeatability and statistical power are often low. Test systems fulfilling regulatory needs (i.e. standardization, repeatability and replication) and the assessment of impacts on species interactions and indirect effects are lacking. Here we describe the development of the TriCosm, a repeatable aquatic multi-species test with three trophic levels and increased statistical power. High repeatability of community dynamics of three interacting aquatic populations (algae, Ceriodaphnia, Hydra) was found with an average coefficient of variation of 19.5% and the ability to determine small effect sizes. The TriCosm combines benefits of both single-species tests (fulfillment of regulatory requirements) and complex multi-species tests (ecological relevance) and can be used, for instance at an intermediate tier in environmental risk assessment. Furthermore, comparatively quickly generated population and community toxicity data can be useful for the development and testing of mechanistic effect models. This article is protected by copyright. All rights reserved

Introducing the 2-DROPS model for two-dimensional simulation of crop roots and pesticide within the soil-root zone

Mathematical models of pesticide fate and behaviour in soils have been developed over the last 30 years. Most models simulate fate of pesticides in a 1-dimensional system successfully, supporting a range of applications where the prediction target is either bulk residues in soil or receiving compartments outside of the soil zone. Nevertheless, it has been argued that the 1-dimensional approach is limiting the application of knowledge on pesticide fate under specific pesticide placement strategies, such as seed, furrow and band applications to control pests and weeds. We report a new model (2-DROPS; 2-Dimensional ROots and Pesticide Simulation) parameterised for maize and we present simulations investigating the impact of pesticide properties (thiamethoxam, chlorpyrifos, clothianidin and tefluthrin), pesticide placement strategies (seed treatment, furrow, band and broadcast applications), and soil properties (two silty clay loam and two loam top soils with either silty clay loam, silt loam, sandy loam or unconsolidated bedrock in the lower horizons) on microscale pesticide distribution in the soil profile. 2-DROPS is to our knowledge the first model that simulates temporally- and spatially-explicit water and pesticide transport in the soil profile under the influence of explicit and stochastic development of root segments. This allows the model to describe microscale movement of pesticide in relation to root segments, and constitutes an important addition relative to existing models. The example runs demonstrate that the pesticide moves locally towards root segments due to water extraction for plant transpiration, that the water holding capacity of the top soil determines pesticide transport towards the soil surface in response to soil evaporation, and that the soil type influences the pesticide distribution zone in all directions. 2-DROPS offers more detailed information on microscale root and pesticide appearance compared to existing models and provides the possibility to investigate strategies targeting control of pests at the root/soil interface

Mechanistic effect modeling of earthworms in the context of pesticide risk assessment: Synthesis of the FORESEE Workshop.

Earthworms are important ecosystem engineers, and assessment of the risk of plant protection products towards them is part of the European environmental risk assessment (ERA). In the current ERA scheme, exposure and effects are represented simplistically and are not well integrated, resulting in uncertainty when applying the results to ecosystems. Modeling offers a powerful tool to integrate the effects observed in lower tier laboratory studies with the environmental conditions under which exposure is expected in the field. This paper provides a summary of the FORESEE Workshop ((In)Field Organism Risk modEling by coupling Soil Exposure and Effect) held January 28‐30, 2020 in Düsseldorf, Germany. This workshop focussed on toxicokinetic‐toxicodynamic (TKTD) and population modeling of earthworms in the context of environmental risk assessment. The goal was to bring together scientists from different stakeholder groups to discuss the current state of soil invertebrate modeling, explore how earthworm modeling could be applied to risk assessments, and in particular how the different model outputs can be used in the tiered ERA approach. In support of these goals, the workshop aimed at addressing the requirements and concerns of the different stakeholder groups to support further model development. The modeling approach included four submodules to cover the most relevant processes for earthworm risk assessment: Environment, Behavior (feeding, vertical movement), TKTD, and Population. Four workgroups examined different aspects of the model with relevance for: Risk assessment, earthworm ecology, uptake routes, and cross‐species extrapolation and model testing. Here, we present the perspectives of each workgroup and highlight how the collaborative effort of participants from multidisciplinary backgrounds helped to establish common ground. In addition, we provide a list of recommendations for how earthworm TKTD modeling could address some of the uncertainties in current risk assessments for plant protection products

Consequences of short-term feeding inhibition from exposure to pesticides for individuals and populations of aquatic invertebrates

Recently, several scientific committees of the European Commission have identified research needs to enhance the risk assessment of plant protection products (PPPs). This PhD explicitly focuses on contributing to the research needs of assessing effects under highly time-variable exposure, increasing the ecological realism in effect assessment approaches, considering effect assessment of combined stressors (natural and anthropogenic) and improving ecological modelling. The presented work focuses on the observation of potential impacts of PPPs (imidacloprid and carbaryl) on feeding of aquatic invertebrates (Gammarus pulex and Daphnia magna) under more environmentally-realistic exposures. Isolated feeding depression and its combination with additional stress is explored. Investigations include the determination of consequences of alterations in feeding for further behavioural traits of individuals and its transposition to the population level. An ecological model is used as a virtual laboratory to allow the interpretation of complex impacts observed which in turn helps to evaluate the model used. A key finding is that feeding assays with G. pulex are able to reveal impacts of PPPs at environmentally-relevant concentrations and that the measurement of recovery potential is important. However, the method used requires further improvement in order to extrapolate impacts to the population and ecosystem level. The possibility of short-term impacts on feeding causing severe impacts at the individual and population level is shown for D. magna. Direct extrapolation from the feeding assay with imidacloprid to other individual traits is not possible. Impacts are found to depend on food availability and the individual’s reproductive strategy, which is found to be more flexible under multiple stresses than has been reported in the literature. Further research is required in order to generalise these findings

Evidence for Links between Feeding Inhibition, Population Characteristics, and Sensitivity to Acute Toxicity for <i>Daphnia magna</i>

A population experiment with <i>Daphnia magna</i> tested the hypothesis that short-term feeding inhibition provokes a shift in population structure that will vary with conspecific pressure (e.g., pressure occurring from individuals of the same species due to competition for food and space) and increases population sensitivity to a xenobiotic exposure due to size-dependent toxicity (e.g., decreasing sensitivity with increasing body length). Populations were exposed for one week to a feeding inhibitor (imidacloprid, 0.15 or 12.0 mg/L) followed by one week of recovery and one day of exposure to an acute toxin (carbaryl, 0.0098 mg/L). Identical exposure under low and high conspecific pressure was studied by delaying the start of exposure for half of the populations by two weeks; thus populations were in a different stage of population development when exposure occurred. Feeding inhibition of 97% (12.0 mg/L imidacloprid) caused a shift in population structure toward smaller individuals but also reduced population abundance by up to 56 ± 7% with a strong influence of conspecific pressure. Increased population sensitivity to carbaryl was observed after feeding inhibition of 97% as hypothesized. Carbaryl exposure for one day resulted in population decline of up to 23 ± 6% when populations were not previously exposed to imidacloprid. Identical carbaryl exposure provoked a four times stronger decline in population abundance when exposure occurred following feeding inhibition of 97%. In conflict with the hypothesis, this was at least in part due to changes in the reproductive strategy of daphnids following exposure to imidacloprid rather than driven by the shift in population structure. The differences in population sensitivity to additional stress (carbaryl) occurring one week after feeding inhibition caused by exposure to imidacloprid adds a further challenge to understanding potential impacts from multiple stressors as occurring in the field at the population level