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

The Impact of the north american waterburg Thrichocoria verticalis (Fieber) on aquatic macroinvertebrate comminities in southern Europe

The North American waterbug Trichocorixa verticalis (Heteroptera: Corixidae) has recently invaded brackish water systems on three continents. Despite its potential to be a keystone species in hypersaline waters in its home range, its effect on the communities it invades is yet unstudied. By doing a field survey in 29 ponds in Doñana, southern Europe some years after T. verticalis was first recorded there, we aimed to establish its prevalence and im- pact on the local invertebrate community, especially the local corixid community with which it is likely to compete. T. verticalis showed the highest prevalence among all seven Corixidae species found. It occasionally reached high local abundance, especially at high salinity. T. verticalis also appeared to be better than native Corixidae at coping with human disturbance. We could not identify significant effects of T. verticalis on the local corixid community nor on the invertebrate community at large. Further experimental research will be needed to confirm these results. Special attention should be paid to hypersaline systems where T. verticalis may act as a top predator.Peer reviewe

Prey colonization in freshwater landscapes can be stimulated or inhibited by the proximity of remote predators

1. Recent findings suggest that the colonization of habitat patches may be affected by the quality of surrounding patches. For instance, patches that lack predators may be avoided when located near others with predators, a pattern known as risk contagion. Alternatively, predator avoidance might also redirect dispersal towards nearby predator‐free patches resulting in so‐called habitat compression. However, it is largely unknown how predators continue to influence these habitat selection behaviours at increasing distances from outside of their own habitat patch. In addition, current information is derived from artificial mesocosm experiments, while support from natural ecosystems is lacking. 2. This study used bromeliad landscapes as a natural model system to study how oviposition habitat selection of Diptera responds to the cues of a distant predator, the carnivorous elephant mosquito larva. 3. We established landscapes containing predator‐free bromeliad habitat patches placed at increasing distances from a predator‐containing patch, along with replicate control landscapes. These patches were then left to be colonized by ovipositing bromeliad insects. 4. We found that distance to predators modulates habitat selection decisions. Moreover, different dipteran families had different responses suggesting different habitat selection strategies. In some families, predator‐free patches at certain distances from the predator patch were avoided, confirming risk contagion. In other families, these patches received higher numbers of colonists providing evidence of predator‐induced habitat compression. 5. We confirm that effects of predators in a natural ecosystem can extend beyond the patch in which the predator is present and that the presence or absence of remote predator effects on habitat selection depends on the distance to predators. The notion that perceived habitat quality can depend on conditions in neighbouring patches forces habitat selection studies to adopt a landscape perspective and account for the effects of both present and remote predators when explaining community assembly in metacommunities.</p

Is salinity tolerance the key to success for the invasive water bug Trichocorixa verticalis?

Trichocorixa verticalis is a North Amer- ican water bug (Heteroptera: Corixidae) that occurs in brackish and saline aquatic systems. Recently, it has been found invading three continents including Europe. Its invasive success has been attributed to the capacity of tolerating hypersalinity. We compared both the realized and standardized salinity niche of invasive T. verticalis and native Corixidae to verify if T. verticalis may fill in an unoccupied niche. We first established the field distribution of T. verticalis and native Corixidae along a salinity gradient. Second, we experimentally tested the salinity tolerance of T. verticalis and three common native Corixidae spe- cies. Of the seven Corixidae species found in the field study, three were positively related to the salinity gradient: S. selecta, S. stagnalis, and T. verticalis. T. verticalis showed the highest salinity optimum, however, after correcting for environmental back- ground variation, salinity optima differed little among the three halophilic species. In the salinity tolerance experiment, S. selecta outperformed T. verticalis, which performed as well as S. stagnalis. Based on our experimental results, we cannot support the hypoth- esis that T. verticalis’ invasion is mediated by a high salinity tolerance that allows this species to colonize habitats unoccupied by native Corixidae. Although these findings contrast with the field patterns in which T. verticalis showed the highest niche optimum and tolerance, these patterns may have been partly due to other environmental factors, particularly anthropo- genic disturbance. Our comparative results are for adults only, and it remains possible that relative salinity tolerance patterns for juveniles differ from that for adults, which may add to the observed field pattern.Peer reviewe

The presence of beneficial arthropods in organic versus IPM pear orchards and their ability to predate pear suckers (Cacopsylla pyri)

In Belgium, two cultivation methods of pear are widely applied, namely organic farming and integrated pest management (IPM). Organic pear orchards are characterized by the use of green techniques such as natural fertilizers and the restricted use of crop protection products, whereas integrated pest management combines a well-tuned integration of biological pest control and crop protection treatments. It is generally considered that these two cultivation methods have different effects on the density of beneficial arthropods in the orchard and the occurrence of common pests as well. Therefore, a large-scale monitoring study was executed comprising extensive samplings throughout the year in 14 pear orchards and comparing beneficial fauna population developments between organic and IPM pear orchards. Pear sucker (Cacopsylla sp. or pear psylla) which is considered the major pest of pear in Belgium, was monitored as well. Organic orchards clearly displayed a lower pear psylla pressure correlating with higher proportions of specific predator populations, particularly velvet mites (Trombidiidae) and spiders (Araneae). IPM orchards showed higher numbers of Anthocoris spp. in summer. In addition, predation of C. pyri was verified by PCR-based gut content analysis. Regarding the results of this prey-predator PCR, Anthocoridae had the highest chance for detection of psyllid DNA in their gut. Velvet mites also scored particularly well for the PCR detections, indicating that other arthropods besides Anthocoridae could have an impact on the psyllid pressure in a pear orchard

Interplay between lattice dynamics and superconductivity in Nb3Sn thin films

We investigate the link between superconductivity and atomic vibrations in Nb3Sn films with a thickness ranging from 10 to 50 nm. The challenge of measuring the phonon density of states (PDOS) of these films has been tackled by employing the technique of nuclear inelastic scattering by 119Sn isotopes to reveal the Sn-partial phonon density of states. With the support of ab initio calculations, we evaluate the effect of reduced film thickness on the PDOS. This approach allows us to estimate the changes in superconducting critical temperature Tc induced by phonon confinement, which turned out to be limited to a few tenths of K. The presented method is successful for the Nb3Sn system and paves the way for more systematic studies of the role of phonon confinement in Sn-containing superconductors.status: publishe