Vanishing artifficial diffusion as a mechanism to accelerate convergence for multiphase porous media flow

Numerical solution of the equations governing multiphase porous media flow is challenging. A common approach to improve the performance of iterative non-linear solvers for these problems is to introduce artificial diffusion. Here, we present a mass conservative artificial diffusion that accelerates the non-linear solver but vanishes when the solution is converged. The vanishing artificial diffusion term is saturation dependent and is larger in regions of the solution domain where there are steep saturation gradients. The non-linear solver converges more slowly in these regions because of the highly non-linear nature of the solution. The new method provides accurate results while significantly reducing the number of iterations required by the non-linear solver. It is particularly valuable in reducing the computational cost of highly challenging numerical simulations, such as those where physical capillary pressure effects are dominant. Moreover, the method allows converged solutions to be obtained for Courant numbers that are at least two orders of magnitude larger than would otherwise be possible

Associative learning and memory retention of nectar yeast volatiles in a generalist parasitoid

Understanding how animals learn is crucial to interpreting animal behaviour. Flower-visiting insects, such as bees and parasitoids, are excellent animal models to study visual and olfactory learning, including memory phenomena. The diversity of resources flower-visiting insects exploit predisposes them to learn and remember the colours, shapes and odours associated with rewarding experiences (e.g. flowers), allowing them to focus on the most rewarding resources. Recent research has shown that nectar-living microbes release volatile organic compounds (VOCs) that contribute to overall flower scent. Nevertheless, little is known about the extent to which nectar microbiota mediate insect learning of floral preferences. In this study, we investigated whether VOCs produced by nectar microbes serve as a learning cue to parasitoids and how long any developed preference is maintained. Experiments were performed using the generalist aphid parasitoid Aphidius ervi and three nectar yeasts, including the nectar specialist Metschnikowia reukaufii and the generalist species Hanseniaspora uvarum and Sporobolomyces roseus. Results showed that naïve parasitoids had an innate preference for nectar fermented by the nectar specialist M. reukaufii, but not by the other two yeasts which had either a neutral (H. uvarum) or deterrent (S. roseus) effect. When parasitoids were conditioned with yeast-fermented nectar, they were strongly attracted to their odours 2 and 24h after conditioning, but not after 48h. Furthermore, when parasitoids were conditioned to one yeast-fermented nectar, they also showed increased attraction to other yeast-fermented nectars. This generalization suggests that their learning ability may have broader ecological consequences. However, this generalized response to other yeast VOCs lasted for only 2h. We conclude that parasitoids show conditioned responses to the scent of yeast-fermented nectar, and yeasts, therefore, may play an important but understudied role in shaping their foraging behaviour

Evolutie in actie. Behoud van de zeldzame Duinwespenorchis in de kustduinen-

Ecological speciation is the process by which one species diverges intotwo distinct phylogenetic lineages that gradually become reproductivelyisolated from each other after they have colonized a new habitat. Because ecological speciation typically occurs across a continuum of time and several intermediate stages, often called ecological races or ecotypes, can be discerned during the speciation process, it may result in a complex of taxa among which species limits are difficult to define. A typical example of a species group among which species limits are difficult to define is the genus Epipactis. It contains a complex of autogamous and non-autogamous taxa that may have arisen after the colonization of new habitats, followed by rapid adaptation and evolutionary changes in key traits that allow establishment and survival in these newly colonized habitats. However, the taxonomic status of these species is problematic and different authors have treated the taxonomy of Epipactis in different ways, some recognizing the different taxa as distinct species, others considering them only as minor intraspecific variants or ecological races. Here we present the results of genomic, meta-genomic and morphological analyses aimed at investigating the taxonomic status of coastal dune populations of the widespread terrestrial orchid Epipactis helleborine. Investigations of the mycorrhizal fungi associating with coastal dune populations and typical forest populations has shown that they associate with significantly different fungal communities. Crossing experiments show that both taxa easily cross and produce viable seeds. However, germination of seeds of dune populations in forest habitat andvice versa was always lower than that of seeds of coastal populations indune habitats or of forest populations in forest habitat, leading to strong reproductive isolation as a result of immigrant inviability. Genomic analyses using SNP markers further revealed that coastal dune populations diverged only about 50 generations ago from inland populations, went through a significant bottleneck and were most likely the result of a single colonization event. The sampled dune populations also showed very little genetic differentiation and no apparent spatial genetic structure was observed. Overall these results are consistent with a process of genetic divergence after a single very recent colonization event followed by extensive gene flow among populations. From a taxonomic point of view coastal dune populations of E. helleborine should not be treated as a separate species, but rather as an ecotype

From diverse origins to specific targets: Role of microorganisms in indirect pest biological control

Integrated pest management (IPM) is today a widely accepted pest management strategy to select and use the most efficient control tactics and at the same time reduce over-dependence on chemical insecticides and their potentially negative environmental effects. One of the main pillars of IPM is biological control. While biological control programs of pest insects commonly rely on natural enemies such as predatory insects, parasitoids and microbial pathogens, there is increasing evidence that plant, soil and insect microbiomes can also be exploited to enhance plant defense against herbivores. In this mini-review, we illustrate how microorganisms from diverse origins can contribute to plant fitness, functional traits and indirect defense responses against pest insects, and therefore be indirectly used to improve biological pest control practices. Microorganisms in the rhizosphere, phyllosphere and endosphere have not only been shown to enhance plant growth and plant strength, but also promote plant defense against herbivores both above-and belowground by providing feeding deterrence or antibiosis. Also, herbivore associated molecular patterns may be induced by microorganisms that come from oral phytophagous insect secretions and elicit plant-specific responses to herbivore attacks. Furthermore, microorganisms that inhabit floral nectar and insect honeydew produce volatile organic compounds that attract beneficial insects like natural enemies, thereby providing indirect pest control. Given the multiple benefits of microorganisms to plants, we argue that future IPMs should consider and exploit the whole range of possibilities that microorganisms offer to enhance plant defense and increase attraction, fecundity and performance of natural enemies. © 2020 by the authors. Licensee MDPI, Basel, Switzerland

Identification and application of bacterial volatiles to attract a generalist aphid parasitoid from laboratory to greenhouse assays

BACKGROUND: Recent studies have shown that microorganisms emit volatile compounds that affect insect behaviour. However, it remains largely unclear whether microbes can be exploited as a source of attractants to improve biological control of insect pests. In this study, we used a combination of coupled gas chromatography electroantennography (GC-EAG) and Y-tube olfactometer bioassays to identify attractive compounds in the volatile extracts of three bacterial strains that are associated with the habitat of the generalist aphid parasitoid Aphidius colemani, and to create mixtures of synthetic compounds to find attractive blends for A. colemani. Subsequently, the most promising blend was evaluated in two-choice cage experiments under greenhouse conditions. RESULTS: GC-EAG analysis revealed 20 compounds that were linked to behaviourally attractive bacterial strains. A mixture of two EAG-active compounds, styrene and benzaldehyde applied at a respective dose of 1 μg and 10 ng, was more attractive than the single compounds or the culture medium of the bacteria in Y-tube olfactometer bioassays. Application of this synthetic mixture under greenhouse conditions resulted in significant attraction of the parasitoids, and outperformed application of the bacterial culture medium. CONCLUSION: Compounds isolated from bacterial blends were capable of attracting parasitoids both in laboratory and greenhouse assays, indicating that microbial culture are an effective source of insect attractants. This opens new opportunities to attract and retain natural enemies of pest species and to enhance biological pest control

Is cell-to-cell scale variability necessary in reservoir models?

Reservoir models typically contain hundreds-of-thousands to millions of grid cells in which petrophysical properties such as porosity and permeability vary on a cell-to-cell basis. However, although the petrophysical properties of rocks do vary on a point-to-point basis, this variability is not equivalent to the cell-to-cell variations in models. We investigate the impact of removing cell-to-cell variability on predictions of fluid flow in reservoir models. We remove cell-to-cell variability from models containing hundreds of thousands of unique porosity and permeability values to yield models containing just a few tens of unique porosity and permeability values grouped into a few internally homogeneous domains. The flow behavior of the original model is used as a reference. We find that the impact of cell-to-cell variability on predicted flow is small. Cell-to-cell variability is not necessary to capture flow in reservoir models; rather, it is the spatially correlated variability in petrophysical properties that is important. Reservoir modelling effort should focus on capturing correlated geologic domains in the most realistic and computationally efficient manner

Bacterial phylogeny predicts volatile organic compound composition and olfactory response of an aphid parasitoid

There is increasing evidence that microorganisms emit a wide range of volatile compounds (mVOCs, microbial volatile organic compounds) that act as insect semiochemicals, and therefore play an important role in insect behaviour. Although it is generally believed that phylogenetically closely related microbes tend to have similar phenotypic characteristics and therefore may elicit similar responses in insects, currently little is known about whether the evolutionary history and phylogenetic relationships among microorganisms have an impact on insect‐microbe interactions. In this study, we tested the hypothesis that phylogenetic relationships among 40 Bacillus strains isolated from diverse environmental sources predicted mVOC composition and the olfactory response of the generalist aphid parasitoid Aphidius colemani . Results revealed that phylogenetically closely related Bacillus strains emitted similar blends of mVOCs and elicited a comparable olfactory response of A. colemani in Y‐tube olfactometer bioassays, varying between attraction and repellence. Analysis of the chemical composition of the mVOC blends showed that all Bacillus strains produced a highly similar set of volatiles, but often in different concentrations and ratios. Benzaldehyde was produced in relatively high concentrations by strains that repel A. colemani , while attractive mVOC blends contained relatively higher amounts of acetoin, 2,3‐butanediol, 2,3‐butanedione, eucalyptol and isoamylamine. Overall, these results indicate that bacterial phylogeny had a strong impact on mVOC compositions and as a result on the olfactory responses of insects

Invasion speeds for structured populations in fluctuating environments

We live in a time where climate models predict future increases in environmental variability and biological invasions are becoming increasingly frequent. A key to developing effective responses to biological invasions in increasingly variable environments will be estimates of their rates of spatial spread and the associated uncertainty of these estimates. Using stochastic, stage-structured, integro-difference equation models, we show analytically that invasion speeds are asymptotically normally distributed with a variance that decreases in time. We apply our methods to a simple juvenile-adult model with stochastic variation in reproduction and an illustrative example with published data for the perennial herb, \emph{Calathea ovandensis}. These examples buttressed by additional analysis reveal that increased variability in vital rates simultaneously slow down invasions yet generate greater uncertainty about rates of spatial spread. Moreover, while temporal autocorrelations in vital rates inflate variability in invasion speeds, the effect of these autocorrelations on the average invasion speed can be positive or negative depending on life history traits and how well vital rates ``remember'' the past

Identification and application of bacterial volatiles to attract a generalist aphid parasitoid: from laboratory to greenhouse assays

BACKGROUND Recent studies have shown that microorganisms emit volatile compounds that affect insect behaviour. However, it remains largely unclear whether microbes can be exploited as a source of attractants to improve biological control of insect pests. In this study, we used a combination of coupled gas chromatography‐electroantennography (GC–EAG) and Y‐tube olfactometer bioassays to identify attractive compounds in the volatile extracts of three bacterial strains that are associated with the habitat of the generalist aphid parasitoid Aphidius colemani, and to create mixtures of synthetic compounds to find attractive blends for A. colemani. Subsequently, the most attractive blend was evaluated in two‐choice cage experiments under greenhouse conditions. RESULTS GC–EAG analysis revealed 20 compounds that were linked to behaviourally attractive bacterial strains. A mixture of two EAG‐active compounds, styrene and benzaldehyde applied at a respective dose of 1 μg and 10 ng, was more attractive than the single compounds or the culture medium of the bacteria in Y‐tube olfactometer bioassays. Application of this synthetic mixture under greenhouse conditions resulted in significant attraction of the parasitoids, and outperformed application of the bacterial culture medium. CONCLUSION Compounds isolated from bacterial blends were capable of attracting parasitoids both in laboratory and greenhouse assays, indicating that microbial cultures are an effective source of insect attractants. This opens new opportunities to attract and retain natural enemies of pest species and to enhance biological pest control