Aerial dispersal using silk ('ballooning') has evolved in spiders (Araneae), spider mites (Acari) and in the larvae of moths (Lepidoptera). Since the 17th century, over 500 observations of ballooning behaviours have been published, yet there is an absence of any evolutionary synthesis of these data. In this paper the literature is reviewed, extensively documenting the known world fauna that balloon and the principal behaviours involved. This knowledge is then incorporated into the current evolutionary phylogenies to examine how ballooning might have arisen. Whilst it is possible that ballooning co-evolved with silk and emerged as early as the Devonian (410-355 mya), it is arguably more likely that ballooning evolved in parallel with deciduous trees, herbaceous annuals and grasses in the Cretaceous (135-65 mya). During this period, temporal (e.g. bud burst, chlorophyll thresholds) and spatial (e.g. herbivory, trampling) heterogeneities in habitat structuring predominated and intensified into the Cenozoic (65 mya to the present). It is hypothesized that from the ancestral launch mechanism known as 'suspended ballooning', widely used by individuals in plant canopies, 'tip-toe' and 'rearing' take-off behaviours were strongly selected for as habitats changed. It is contended that ballooning behaviour in all three orders can be described as a mixed Evolutionary Stable Strategy. This comprises individual bet-hedging due to habitat unpredictability, giving an underlying randomness to individual ballooning, with adjustments to the individual ballooning probability being conferred by more predictable habitat changes or colonization strategies. Finally, current methods used to study ballooning, including modelling and genetic research, are illustrated and an indication of future prospects given.

No abstract

No abstract

Recent guidance identified toxicokinetic-toxicodynamic (TK-TD) modeling as a relevant approach for risk assessment refinement. Yet, its added value compared to other refinement options is not detailed, and how to conduct the modeling appropriately is not explained. This case study addresses these issues through 2 examples of individual-level risk assessment for 2 hypothetical plant protection products: 1) evaluating the risk for small granivorous birds and small omnivorous mammals of a single application, as a seed treatment in winter cereals, and 2) evaluating the risk for fish after a pulsed treatment in the edge-of-field zone. Using acute test data, we conducted the first tier risk assessment as defined in the European Food Safety Authority (EFSA) guidance. When first tier risk assessment highlighted a concern, refinement options were discussed. Cases where the use of models should be preferred over other existing refinement approaches were highlighted. We then practically conducted the risk assessment refinement by using 2 different models as examples. In example 1, a TK model accounting for toxicokinetics and relevant feeding patterns in the skylark and in the wood mouse was used to predict internal doses of the hypothetical active ingredient in individuals, based on relevant feeding patterns in an in-crop situation, and identify the residue levels leading to mortality. In example 2, a TK-TD model accounting for toxicokinetics, toxicodynamics, and relevant exposure patterns in the fathead minnow was used to predict the time-course of fish survival for relevant FOCUS SW exposure scenarios and identify which scenarios might lead to mortality. Models were calibrated using available standard data and implemented to simulate the time-course of internal dose of active ingredient or survival for different exposure scenarios. Simulation results were discussed and used to derive the risk assessment refinement endpoints used for decision. Finally, we compared the "classical" risk assessment approach with the model-based approach. These comparisons showed that TK and TK-TD models can bring more realism to the risk assessment through the possibility to study realistic exposure scenarios and to simulate relevant mechanisms of effects (including delayed toxicity and recovery). Noticeably, using TK-TD models is currently the most relevant way to directly connect realistic exposure patterns to effects. We conclude with recommendations on how to properly use TK and TK-TD model in acute risk assessment for vertebrates.

Aquatic toxicity tests with substances that are poorly soluble in water have been conducted using different methods, and estimates of toxicity have varied accordingly. The present study illustrates differences in toxicity values resulting from variation in test designs and solution preparation methods, and offers guidance on the best way to conduct these tests. Consequences for environmental risk assessment and classification are also discussed. The present study mainly considers active ingredients of plant protection products, but is also considered relevant to other chemicals. It is recommended that toxicity tests be conducted only up to the saturation limit, dispersants avoided, and solvents used only if necessary to support handling and speed of dissolution. Analytical measurements of exposure concentrations should reflect what organisms are exposed to. If acute toxicity testing at the saturation limit yields no adverse effects, further testing should not normally be required; the toxicity value of the endpoints should be considered as the saturation limit and adverse classification should not be required. Chronic testing, if required, should then be conducted at the practical saturation limit as this is the most realistic worst-case exposure scenario. If no adverse effects occur, the risk should be acceptable because higher aqueous exposure cannot occur. This could be substantiated by testing additional species. Assessment factors on no observed effect concentration (NOEC) values at the saturation limit require careful consideration in the risk assessment to avoid unnecessarily low regulatory acceptable concentrations.

Groups of linyphiid spiders (Erigone spp.) (Araneae, Linyphiidae), collected at intervals from arable land, were tested in laboratory bioassays to determine the proportion of individuals that exhibited ballooning behaviour on each field sampling occasion. There was no significant variation in the proportions of spiders in each test group ballooning in the laboratory over a year. Investigations of ground density and aerial dispersal, in a grass field and a winter-wheat field, confirmed that peaks in numbers of spiders observed ballooning in the field generally coincided with population peaks in the summer and autumn. Significant correlations between ground populations and aerial catches were found for total spiders, immature spiders, and Bathyphantes gracilis (Blackwall) in both fields, adult spiders in the grass field, Erigone spp. in the grass, and Meioneta rurestris (C.L. Koch) in the wheat. The other groups analysed, Lepthyphantes tenuis (Blackwall) in both fields, Erigone spp. in wheat, and M. rurestris in grass, showed similar but non-significant trends. No significant difference was found between overall ground-to-air ratios for males compared to females, but adult spiders were more likely to balloon than immatures.

A field experiment was carried out to determine whether different levels of food availability affected the retention rate of ballooning spiders landing in trays of seedling barley plants, half of which were infested with aphids from laboratory cultures. The trays were placed within bases in the field, then collected sequentially and spider numbers assessed in each tray. Deposition trays, containing trapping fluid only, were used to measure ballooning activity throughout the experimental period. The experiment was repeated four times. Overall, ballooning spiders were more likely to be retained in trays where aphid prey were present, with a total of 340 spiders found in the infested trays and 251 in the aphid-free trays, over the four experiments. Most of the spiders found were of the family Linyphiidae. In the second and fourth experiments the increased retention of spiders in the aphid-infested trays was statistically significant. Immature linyphiids alone also showed significantly higher retention in the infested trays in those two experiments and in the fourth experiment were largely responsible for the higher numbers found in the infested trays. There was also a statistically significant trend for a higher retention rate of female spiders, compared to males, in the barley trays than would have been expected from the ratios of females to males caught in the deposition trapping trays alone.

An algae population model was applied to describe measured effects of pulsed exposure to chlorotoluron on populations of Pseudokirchneriella subcapitata in 2 laboratory flow‐through chemostat tests with different exposure regimes. Both tests enabled evaluation of adverse effects on algae during the exposure and population recovery afterward. Impacts on population densities after chlorotoluron exposure were directly visible as biomass loss in the chemostats. Recovery was observed after each exposure peak. The test results indicate that P. subcapitata is unlikely to show an increased sensitivity to chlorotoluron after pulsed exposure. No altered response or adaptation of the algae to chlorotoluron was observed, with the exception of the last high peak in flow‐through test 2. Therefore, an adaptation to the test substance cannot be excluded after long‐term exposure. However, recovery to the steady‐state level after this peak indicates that the growth rate (fitness) was not significantly reduced in the population with higher tolerance. No differences in chlorotoluron impact on the populations over time in terms of growth were detected. Model predictions agreed well with the measured data. The tests and modeling results validate the model to simulate population dynamics of P. subcapitata after pulsed exposure to chlorotoluron. Model predictions and extrapolations with different exposure patterns are considered reliable for chlorotoluron. The good reproducibility of the population behavior in the test systems supports this conclusion. An example modeled extrapolation of the experimental results to other (untested) exposure scenarios shows a potential approach to using the validated model as a supportive tool in risk assessment. Environ Toxicol Chem 2019;38:2520–2534. © 2019 SETAC