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The concept of source-sink dynamics as a potentially important component of metapopulation dynamics was introduced in the 1980s. The objective of the present review was to review the considerable body of work that has been developed, to consider its theoretical implications as well as to understand how source-sink dynamics may manifest under field conditions in the specific case of nontarget arthropods in the agricultural environment. Our review concludes that metapopulation dynamics based on field observations are often far more complex than existing theoretical source-sink models would indicate, because they are dependent on numerous population processes and influencing factors. The difficulty in identifying and measuring these factors likely explains why empirical studies assessing source-sink dynamics are scarce. Furthermore, we highlight the importance of considering the spatial and temporal heterogeneity of agricultural landscapes when assessing the population dynamics of nontarget arthropods in the context of the risk from the use of plant protection products. A need is identified to further develop and thoroughly validate predictive population models, which can incorporate all factors relevant to a specific system. Once reliable predictive models for a number of representative nontarget arthropod species are available, they could provide a meaningful tool for refined risk evaluations (higher tier level risk assessment), addressing specific concerns identified at the initial evaluation stages (lower tier level risk assessment). Environ Toxicol Chem 2021;40:2667-2679. © 2021 ERM, FMC, Syngenta, Bayer AG, BASF SE, Corteva agriscience. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

The aim of the study was to investigate the potential impact of the insecticide chlorantraniliprole on queen-right bumblebee (Bombus terrestris) colonies under semi-field conditions in Phacelia tanacetifolia. The P. tanacetifolia crop was grown in soil treated with modelled worst-case 20-year plateau concentration of chlorantraniliprole in the top 20 cm of soil (equivalent to 0.088 mg a.s./kg). Additionally, two chlorantraniliprole spray applications at 60 g a.s./ha were made. In treatment T1 both spray applications took place before P. tanacetifolia flowering at growth stages BBCH 51–55 and BBCH 55–59. In T2 one spray application was conducted before P. tanacetifolia flowering at BBCH 55–59 and one application during P. tanacetifolia flowering and during daily bee flight at BBCH 61–62. The application in the control (C) and reference item treatment (R) (400 g dimethoate a.s./ha) was carried out during full P. tanacetifolia flowering and bumblebee flight. The bumblebee colonies were exposed to the treated flowering P. tanacetifolia crop for 20 days in the tunnels and afterwards the colonies were kept on a monitoring site. Results of this study indicate no significant differences between the chlorantraniliprole groups T1 and T2 and the control regarding all parameters assessed (i.e. adult and larval mortality, flight activity at the hive entrance, colony weight development, condition of the colonies and production of young queens and males). Overall, no effects of chlorantraniliprole on B. terrestris colonies including queen/male production, adult and larval survival, colony development and forager flight activity were found in this worst-case exposure set-up.

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.