Matching commercial thrips predating phytoseids with the highly diversified climatic conditions of different strawberry production systems

Flower inhabiting thrips (Order: Thysanoptera) are a major threat to fruit quality in strawberry production around the world. As chemical control is often inefficient, alternative control measures are of broad and current interest. Their fast reproduction makes predatory mites highly suitable for thrips control in a crop with a relatively short cropping season like strawberry. However, climatic conditions of strawberry production can differ strongly depending on the production system (glasshouse, plastic tunnel, open field, etc.) and the time span of cultivation (depending mostly on planting date and the type of cultivar: summer-or everbearing). As predatory mites typically display a temperature-dependent life history and the current commercially available thrips predating phytoseids vary in geographic origin, one can assume that under certain climatic conditions some species will be more applicable than others. The goal of this study is to determine which species are suitable for which climatic conditions. Therefore all (Belgian) production systems and time spans are categorized into three climate types, simulated in the laboratory. The population build-up of seven predatory mite species (A. degenerans, A. montdorensis, A. andersoni, A. limonicus, A. swirskii, N. cucumeris and E. gallicus) were assessed for each of these climatic conditions. Under the coldest condition (A), the in West-Europe indigenous E. gallicus was the only species with a significant population build up. When moderate conditions (B) were simulated E. gallicus, N. cucumeris and A. limonicus were most successful. The warmest regime (C) was most adequate for E. gallicus and A. swirskii

Biosilicification Drives a Decline of Dissolved Si in the Oceans through Geologic Time

Biosilicification has driven variation in the global Si cycle over geologic time. The evolution of different eukaryotic lineages that convert dissolved Si (DSi) into mineralized structures (higher plants, siliceous sponges, radiolarians, and diatoms) has driven a secular decrease in DSi in the global ocean leading to the low DSi concentrations seen today. Recent studies, however, have questioned the timing previously proposed for the DSi decreases and the concentration changes through deep time, which would have major implications for the cycling of carbon and other key nutrients in the ocean. Here, we combine relevant genomic data with geological data and present new hypotheses regarding the impact of the evolution of biosilicifying organisms on the DSi inventory of the oceans throughout deep time. Although there is no fossil evidence for true silica biomineralization until the late Precambrian, the timing of the evolution of silica transporter genes suggests that bacterial silicon-related metabolism has been present in the oceans since the Archean with eukaryotic silicon metabolism already occurring in the Neoproterozoic. We hypothesize that biological processes have influenced oceanic DSi concentrations since the beginning of oxygenic photosynthesis

Thrips control with predatory mites A. limonicus and A. swirskii in different strawberry cultivation systems

Western flower thrips or Frankliniella occidentalis is the most common thrips present on strawberry plants and causes damage to strawberries worldwide. F. occidentalis feeds on the cell content of developing flowers and fruits which results in aberrant fruit characteristics: grooves, cat faces, bronzing and prominent seeds. To combat thrips, a wide range of chemical products are used. However, upcoming resistance of thrips to these chemicals causes loss of efficiency. Hence, a new solution to control thrips in strawberries is becoming a high priority. Both the risk for resistance when using chemicals and the urge to lower residues on fruit, increase the interest in natural enemies to control pests. At Research Centre Hoogstraten (PCH), we screened multiple predators for their suitability to control thrips in strawberry. Unique for strawberry cultivation in Belgium and The Netherlands is that it takes place in multiple systems year-round of which the season is relatively short and therefore it is important that predators can survive and establish a sufficient population in these different conditions. At PCH we screened compatible predators for their efficiency to control thrips in the different cultivation systems. This intense search payed off and two predatory mites proved their ability to combat thrips in both individual cages and multiple cultivation systems at PCH and private cultivators. Amblydromalus limonicus is able to control thrips in mild conditions, Amblyseius swirskii prefers warmer temperatures. The predatory mite is scattered over the crop and it will establish itself on the leaves whenever food is available. When thrips levels rise, the predatory mites increase in population and are able to keep thrips at non-damaging levels. A. limonicus and A. swirskii are therefore perfectly suitable to become an important aspect of integrated pest management (IPM) in strawberry so that high quality fruit can be maintained

The fate of buried organic carbon in colluvial soils: a long-term perspective

Colluvial soils are enriched in soil organic car- bon (SOC) in comparison to the soils of upslope areas due to the deposition and progressive burial of SOC. This burial of SOC has important implications for the global carbon cycle, but the long-term dynamics of buried SOC remain poorly constrained. We addressed this issue by determining the SOC burial efficiency (i.e. the fraction of originally de- posited SOC that is preserved in colluvial deposits) of buried SOC as well as the SOC stability in colluvial soils. We quan- tified the turnover rate of deposited SOC by establishing sed- iment and SOC burial chronologies. The SOC stability was derived from soil incubation experiments and the δ 13 C val- ues of SOC. The C burial efficiency was found to decrease with time, reaching a constant ratio of approximately 17 % by about 1000–1500 yr post-burial. This decrease is attributed to the increasing recalcitrance of the remaining buried SOC with time and a less favourable environment for SOC decom- position with increasing depth. Buried SOC in colluvial pro- files was found to be more stable and degraded in compari- son to SOC sampled at the same depth at a stable reference location. This is due to the preferential mineralisation of the labile fraction of the deposited SOC. Our study shows that SOC responds to burial over a centennial timescale; how- ever, more insight into the factors controlling this response is required to fully understand how this timescale may vary, depending on specific conditions such as climate and depo- sitional environment

Differential effects of water erosion and tillage erosion on carbon dynamics on Arable Land

Global agricultural soil erosion has been proved to be a carbon sink. Water erosion and tillage erosion are the two dominant forms of soil redistribution processes in agricultural catchments. However, there is still no research trying to evaluate whether they play different roles in perturbing the carbon dynamics of agricultural land. By calibrating a spatially distributed soil erosion model on a small agricultural catchment, the proportion of the deposits by water erosion and tillage erosion at different positions of the soil bank formed at the field border can be estimated: grain size analysis confirms that the relative contribution of tillage and water vary with landscape position. The results derived from the water erosion model are further processed with a model elucidating soil organic matter dynamics through the soil profile that is calibrated with detailed measured soil carbon profiles both on the slope and at the soil bank. Different decomposition rates for the carbon deposited by different erosion processes were derived from model simulations by matching observed and simulated profiles of total carbon as well as of delta 13C. Incubation of soil cores at both water erosion and tillage erosion dominated deposits was also conducted so that an attempt can be made to discriminate between the effects of burial and carbon quality on carbon decomposition rates. Different effects of water erosion and tillage erosion on the carbon dynamics in the catchment were assessed and possible mechanisms behind them are discussed using evidence from total carbon content, delta 13C and grain size profiles