The pest kill rate of thirteen natural enemies as aggregate evaluation criterion of their biological control potential of Tuta absoluta.

Ecologists study how populations are regulated, while scientists studying biological pest control apply population regulation processes to reduce numbers of harmful organisms: an organism (a natural enemy) is used to reduce the population density of another organism (a pest). Finding an effective biological control agent among the tens to hundreds of natural enemies of a pest is a daunting task. Evaluation criteria help in a first selection to remove clearly ineffective or risky species from the list of candidates. Next, we propose to use an aggregate evaluation criterion, the pest kill rate, to compare the pest population reduction capacity of species not eliminated during the first selection. The pest kill rate is the average daily lifetime killing of the pest by the natural enemy under consideration. Pest kill rates of six species of predators and seven species of parasitoids of Tuta absoluta were calculated and compared. Several natural enemies had pest kill rates that were too low to be able to theoretically reduce the pest population below crop damaging densities. Other species showed a high pest reduction capacity and their potential for practical application can now be tested under commercial crop production conditions.

Shape and rate of movement of the invasion front of Xylella fastidiosa spp. pauca in Puglia.

In 2013, Xylella fastidiosa spp. pauca was first reported in Puglia, Italy, causing the olive quick decline syndrome (OQDS). Since then the disease has spread, prompting the initiation of management measures to contain the outbreak. Estimates of the shape of the disease front and the rate of area expansion are needed to inform management, e.g. the delineation of buffer zones. However, empirical estimates of the invasion front and the rate of spread of OQDS are not available. Here, we analysed the hundreds of thousands of records of monitoring data on disease occurrence in Puglia to estimate the shape of the invasion front and the rate of movement of the front. The robustness of estimation was checked using simulation. The shape of the front was best fitted by a logistic function while using a beta-binomial error distribution to model variability around the expected proportion of infected trees. The estimated rate of movement of the front was 10.0 km per year (95% confidence interval: 7.5-12.5 km per year). This rate of movement is at the upper limit of previous expert judgements. The shape of the front was flatter than expected. The fitted model indicates that the disease spread started approximately in 2008. This analysis underpins projections of further disease spread and the need for preparedness in areas that are still disease free.

Outbreak analysis with a logistic growth model shows COVID-19 suppression dynamics in China.

China reported a major outbreak of a novel coronavirus, SARS-CoV2, from mid-January till mid-March 2020. We review the epidemic virus growth and decline curves in China using a phenomenological logistic growth model to summarize the outbreak dynamics using three parameters that characterize the epidemic's timing, rate and peak. During the initial phase, the number of virus cases doubled every 2.7 days (range 2.2-4.4 across provinces). The rate of increase in the number of reported cases peaked approximately 10 days after suppression measures were started on 23-25 January 2020. The peak in the number of reported sick cases occurred on average 18 days after the start of suppression measures. From the time of starting measures till the peak, the number of cases increased by a factor 39 in the province Hubei, and by a factor 9.5 for all of China (range: 6.2-20.4 in the other provinces). Complete suppression took up to 2 months (range: 23-57d.), during which period severe restrictions, social distancing measures, testing and isolation of cases were in place. The suppression of the disease in China has been successful, demonstrating that suppression is a viable strategy to contain SARS-CoV2.

Organic matter reduces the amount of detectable environmental DNA in freshwater.

Environmental DNA (eDNA) is used for monitoring the occurrence of freshwater organisms. Various studies show a relation between the amount of eDNA detected and target organism abundance, thus providing a potential proxy for reconstructing population densities. However, environmental factors such as water temperature and microbial activity are known to affect the amount of eDNA present as well. In this study, we use controlled aquarium experiments using Gammarus pulex L. (Amphipoda) to investigate the relationship between the amount of detectable eDNA through time, pH, and levels of organic material. We found eDNA to degrade faster when organic material was added to the aquarium water, but that pH had no significant effect. We infer that eDNA contained inside cells and mitochondria is extra resilient against degradation, though this may not reflect actual presence of target species. These results indicate that, although estimation of population density might be possible using eDNA, measured eDNA concentration could, in the future, be corrected for local environmental conditions in order to ensure accurate comparisons.

Capturing variation in floral shape: a virtual3D based morphospace for Pelargonium.

BACKGROUND: Variation in floral shapes has long fascinated biologists and its modelling enables testing of evolutionary hypotheses. Recent comparative studies that explore floral shape have largely ignored 3D floral shape. We propose quantifying floral shape by using geometric morphometrics on a virtual3D model reconstructed from 2D photographical data and demonstrate its performance in capturing shape variation. METHODS: This approach offers unique benefits to complement established imaging techniques (i) by enabling adequate coverage of the potential morphospace of large and diverse flowering-plant clades; (ii) by circumventing asynchronicity in anthesis of different floral parts; and (iii) by incorporating variation in copy number of floral organs within structures. We demonstrate our approach by analysing 90 florally-diverse species of the Southern African genus Pelargonium (Geraniaceae). We quantify Pelargonium floral shapes using 117 landmarks and show similarities in reconstructed morphospaces for nectar tube, corolla (2D datasets), and a combined virtual3D dataset. RESULTS: Our results indicate that Pelargonium species differ in floral shape, which can also vary extensively within a species. PCA results of the reconstructed virtual3D floral models are highly congruent with the separate 2D morphospaces, indicating it is an accurate, virtual, representation of floral shape. Through our approach, we find that adding the third dimension to the data is crucial to accurately interpret the manner of, as well as levels of, shape variation in flowers.

Increased aridity drives post-fire recovery of Mediterranean forests towards open shrublands.

Recent observations suggest that repeated fires could drive Mediterranean forests to shrublands, hosting flammable vegetation that regrows quickly after fire. This feedback supposedly favours shrubland persistence and may be strengthened in the future by predicted increased aridity. An assessment was made of how fires and aridity in combination modulated the dynamics of Mediterranean ecosystems and whether the feedback could be strong enough to maintain shrubland as an alternative stable state to forest. A model was developed for vegetation dynamics, including stochastic fires and different plant fire-responses. Parameters were calibrated using observational data from a period up to 100 yr ago, from 77 sites with and without fires in Southeast Spain and Southern France. The forest state was resilient to the separate impact of fires and increased aridity. However, water stress could convert forests into open shrublands by hampering post-fire recovery, with a possible tipping point at intermediate aridity. Projected increases in aridity may reduce the resilience of Mediterranean forests against fires and drive post-fire ecosystem dynamics toward open shrubland. The main effect of increased aridity is the limitation of post-fire recovery. Including plant fire-responses is thus fundamental when modelling the fate of Mediterranean-type vegetation under climate-change scenarios.

Inbreeding, Allee effects and stochasticity might be sufficient to account for Neanderthal extinction.

The replacement of Neanderthals by Anatomically Modern Humans has typically been attributed to environmental pressure or a superiority of modern humans with respect to competition for resources. Here we present two independent models that suggest that no such heatedly debated factors might be needed to account for the demise of Neanderthals. Starting from the observation that Neanderthal populations already were small before the arrival of modern humans, the models implement three factors that conservation biology identifies as critical for a small population's persistence, namely inbreeding, Allee effects and stochasticity. Our results indicate that the disappearance of Neanderthals might have resided in the smallness of their population(s) alone: even if they had been identical to modern humans in their cognitive, social and cultural traits, and even in the absence of inter-specific competition, Neanderthals faced a considerable risk of extinction. Furthermore, we suggest that if modern humans contributed to the demise of Neanderthals, that contribution might have had nothing to do with resource competition, but rather with how the incoming populations geographically restructured the resident populations, in a way that reinforced Allee effects, and the effects of inbreeding and stochasticity.

How including ecological realism impacts the assessment of the environmental effect of oil spills at the population level: The application of matrix models for Arctic Calanus species.

For oil spill responses, assessment of the potential environmental exposure and impacts of a spill is crucial. Due to a lack of chronic toxicity data, acute data is used together with precautionary assumptions. The effect on the Arctic keystone (copepod) species Calanus hyperboreus and Calanus glacialis populations is compared using two approaches: a precautionary approach where all exposed individuals die above a defined threshold concentration and a refined (full-dose-response) approach. For this purpose a matrix population model parameterised with data from the literature is used. Population effects of continuous exposures with varying durations were modelled on a range of concentrations. Just above the chronic No Observed Effect Concentration (which is field relevant) the estimated population recovery duration of the precautionary approach was more than 300 times that of the refined approach. With increasing exposure concentration and duration, the effect in the refined approach converges to the maximum effect assumed in the precautionary approach.

An experimental approach in revisiting the magnetic orientation of cattle.

In response to the increasing number of observational studies on an apparent south-north orientation in non-homing, non-migrating terrestrial mammals, we experimentally tested the alignment hypothesis using strong neodymium magnets on the resting orientation of individual cattle in Portugal. Contrary to the hypothesis, the 34 cows in the experiment showed no directional preference, neither with, nor without a strong neodymium magnet fixed to their collar. The concurrently performed 2,428 daytime observations-excluding the hottest part of the day-of 659 resting individual cattle did not show a south-north alignment when at rest either. The preferred compass orientation of these cows was on average 130 degrees from the magnetic north (i.e., south east). Cow compass orientation correlated significantly with sun direction, but not with wind direction. In as far as we can determine, this is the first experimental test on magnetic orientation in larger, non-homing, non-migrating mammals. These experimental and observational findings do not support previously published suggestions on the magnetic south-north alignment in these mammals.

Genotype assembly, biological activity and adaptation of spatially separated isolates of Spodoptera litura nucleopolyhedrovirus.

The cotton leafworm Spodoptera litura is a polyphagous insect. It has recently made a comeback as a primary insect pest of cotton in Pakistan due to reductions in pesticide use on the advent of genetically modified cotton, resistant to Helicoverpa armigera. Spodoptera litura nucleopolyhedrovirus (SpltNPV) infects S. litura and is recognized as a potential candidate to control this insect. Twenty-two NPV isolates were collected from S. litura from different agro-ecological zones (with collection sites up to 600 km apart) and cropping systems in Pakistan to see whether there is spatial dispersal and adaptation of the virus and/or adaptation to crops. Therefore, the genetic make-up and biological activity of these isolates was measured. Among the SpltNPV isolates tested for speed of kill in 3rd instar larvae of S. litura, TAX1, SFD1, SFD2 and GRW1 were significantly faster killing isolates than other Pakistani isolates. Restriction fragment length analysis of the DNA showed that the Pakistan SpltNPV isolates are all variants of a single SpltNPV biotype. The isolates could be grouped into three genogroups (A-C). The speed of kill of genogroup A viruses was higher than in group C according to a Cox' proportional hazards analysis. Sequence analysis showed that the Pakistan SpltNPV isolates are more closely related to each other than to the SpltNPV type species G2 (Pang et al., 2001). This suggests a single introduction of SpltNPV into Pakistan. The SpltNPV-PAK isolates are distinct from Spodoptera littoralis nucleopolyhedrovirus. There was a strong correlation between geographic spread and the genetic variation of SpltNPV, and a marginally significant correlation between the latter and the cropping system. The faster killing isolates may be good candidates for biological control of S. litura in Pakistan.

Functional Responses of Three Neotropical Mirid Predators to Eggs of Tuta absoluta on Tomato.

Tuta absoluta (Meyrick) has quickly developed into a significant tomato pest worldwide. While the recently found mirid predators Macrolophus basicornis (Stal), Engytatus varians (Distant) and Campyloneuropsis infumatus (Carvalho) of this pest are able to establish and reproduce on tomato, biological knowledge of these mirids is still limited. Here we describe the functional response of the three mirid predators of the tomato pest T. absoluta when offered a range of prey densities (four, eight, 16, 32, 64, 128 and 256 eggs) during a 24 h period inside cylindrical plastic cages in the laboratory. Engytatus varians and M. basicornis showed a type III functional response, whereas C. infumatus showed a type II functional response. At the highest prey densities, C. infumatus consumed an average of 51.0 eggs, E. varians 91.1 eggs, and M. basicornis 100.8 eggs. Taking all information into account that we have collected of these three Neotropical mirid species, we predict that M. basicornis might be the best candidate for control of the tomato borer in Brazil: it has the highest fecundity, the largest maximum predation capacity, and it reacts in a density-dependent way to the widest prey range.

Shifts in dynamic regime of an invasive lady beetle are linked to the invasion and insecticidal management of its prey.

The spread and impact of invasive species may vary over time in relation to changes in the species itself, the biological community of which it is part, or external controls on the system. We investigate whether there have been changes in dynamic regimes over the last 20 years of two invasive species in the midwestern United States, the multicolored Asian lady beetle Harmonia axyridis and the soybean aphid Aphis glycines. We show by model selection that after its 1993 invasion into the American Midwest, the year-to-year population dynamics of H. axyridis were initially governed by a logistic rule supporting gradual rise to a stable carrying capacity. After invasion of the soybean aphid in 2000, food resources at the landscape level became abundant, supporting a higher year-to-year growth rate and a higher but unstable carrying capacity, with two-year cycles in both aphid and lady beetle abundance as a consequence. During 2005-2007, farmers in the Midwest progressively increased their use of insecticides for managing A. glycines, combining prophylactic seed treatment with curative spraying based on thresholds. This human intervention dramatically reduced the soybean aphid as a major food resource for H. axyridis at landscape level and corresponded to a reverse shift towards the original logistic rule for year-to-year dynamics. Thus, we document a short episode of major predator-prey fluctuations in an important agricultural system resulting from two biological invasions that were apparently damped by widespread insecticide use. Recent advances in development of plant resistance to A. glycines in soybeans may mitigate the need for pesticidal control and achieve the same stabilization of pest and predator populations at lower cost and environmental burden.

Competition for resources: complicated dynamics in the simple Tilman model.

Graphical analysis and computer simulations have become the preferred tools to present Tilman's model of resource competition to new generations of ecologists. To really understand the full dynamic behaviour, a more rigorous mathematical analysis is required. We show that just a basic stability analysis is insufficient to describe the relevant dynamics of this deceptively simple model. To investigate realistic invasion and succession processes, not only the stable state is relevant, but also the time scales at which the system moves away from the unstable situation. We argue that the relative stability of saddle points is more important for the actual observed transient dynamics in realistic systems than the predicted asymptotic behaviour towards the stable equilibria. For the mathematical analysis this implies that not only the signs, but also the magnitudes of the eigenvalues of the Jacobi matrix at the stationary points, the rates at which the system evolves, must be considered. We present the underlying mathematics of the Tilman model in a way that should be accessible to any ecologist with a basic mathematical background.

Rapid Diversity Loss of Competing Animal Species in Well-Connected Landscapes.

Population viability of a single species, when evaluated with metapopulation based landscape evaluation tools, always increases when the connectivity of the landscape increases. However, when interactions between species are taken into account, results can differ. We explore this issue using a stochastic spatially explicit meta-community model with 21 competing species in five different competitive settings: (1) weak, coexisting competition, (2) neutral competition, (3) strong, excluding competition, (4) hierarchical competition and (5) random species competition. The species compete in randomly generated landscapes with various fragmentation levels. With this model we study species loss over time. Simulation results show that overall diversity, the species richness in the entire landscape, decreases slowly in fragmented landscapes whereas in well-connected landscapes rapid species losses occur. These results are robust with respect to changing competitive settings, species parameters and spatial configurations. They indicate that optimal landscape configuration for species conservation differs between metapopulation approaches, modelling species separately and meta-community approaches allowing species interactions. The mechanism behind this is that species in well-connected landscapes rapidly outcompete each other. Species that become abundant, by chance or by their completive strength, send out large amounts of dispersers that colonize and take over other patches that are occupied by species that are less abundant. This mechanism causes rapid species loss. In fragmented landscapes the colonization rate is lower, and it is difficult for a new species to establish in an already occupied patch. So, here dominant species cannot easily take over patches occupied by other species and higher diversity is maintained for a longer time. These results suggest that fragmented landscapes have benefits for species conservation previously unrecognized by the landscape ecology and policy community. When species interactions are important, landscapes with a low fragmentation level can be better for species conservation than well-connected landscapes. Moreover, our results indicate that metapopulation based landscape evaluation tools may overestimate the value of connectivity and should be replaced by more realistic meta-community based tools.

Intensive agriculture reduces soil biodiversity across Europe.

Soil biodiversity plays a key role in regulating the processes that underpin the delivery of ecosystem goods and services in terrestrial ecosystems. Agricultural intensification is known to change the diversity of individual groups of soil biota, but less is known about how intensification affects biodiversity of the soil food web as a whole, and whether or not these effects may be generalized across regions. We examined biodiversity in soil food webs from grasslands, extensive, and intensive rotations in four agricultural regions across Europe: in Sweden, the UK, the Czech Republic and Greece. Effects of land-use intensity were quantified based on structure and diversity among functional groups in the soil food web, as well as on community-weighted mean body mass of soil fauna. We also elucidate land-use intensity effects on diversity of taxonomic units within taxonomic groups of soil fauna. We found that between regions soil food web diversity measures were variable, but that increasing land-use intensity caused highly consistent responses. In particular, land-use intensification reduced the complexity in the soil food webs, as well as the community-weighted mean body mass of soil fauna. In all regions across Europe, species richness of earthworms, Collembolans, and oribatid mites was negatively affected by increased land-use intensity. The taxonomic distinctness, which is a measure of taxonomic relatedness of species in a community that is independent of species richness, was also reduced by land-use intensification. We conclude that intensive agriculture reduces soil biodiversity, making soil food webs less diverse and composed of smaller bodied organisms. Land-use intensification results in fewer functional groups of soil biota with fewer and taxonomically more closely related species. We discuss how these changes in soil biodiversity due to land-use intensification may threaten the functioning of soil in agricultural production systems.

Baculovirus-induced tree-top disease: how extended is the role of egt as a gene for the extended phenotype?

Many parasites alter host behaviour to enhance their chance of transmission. Recently, the ecdysteroid UDP-glucosyl transferase (egt) gene from the baculovirus Lymantria dispar multiple nucleopolyhedrovirus (LdMNPV) was identified to induce tree-top disease in L. dispar larvae. Infected gypsy moth larvae died at elevated positions (hence the term tree-top disease), which is thought to promote dissemination of the virus to lower foliage. It is, however, unknown whether egt has a conserved role among baculoviruses in inducing tree-top disease. Here, we studied tree-top disease induced by the baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV) in two different host insects, Trichoplusia ni and Spodoptera exigua, and we investigated the role of the viral egt gene therein. AcMNPV induced tree-top disease in both T. ni and S. exigua larvae, although in S. exigua a moulting-dependent effect was seen. Those S. exigua larvae undergoing a larval moult during the infection process died at elevated positions, while larvae that did not moult after infection died at low positions. For both T. ni and S. exigua, infection with a mutant AcMNPV lacking egt did not change the position where the larvae died. We conclude that egt has no highly conserved role in inducing tree-top disease in lepidopteran larvae. The conclusion that egt is a 'gene for an extended phenotype' is therefore not generally applicable for all baculovirus-host interactions. We hypothesize that in some baculovirus-host systems (including LdMNPV in L. dispar), an effect of egt on tree-top disease can be observed through indirect effects of egt on moulting-related climbing behaviour.

Movement behaviour of the carabid beetle Pterostichus melanarius in crops and at a habitat interface explains patterns of population redistribution in the field.

Animals may respond to habitat quality and habitat edges and these responses may affect their distribution between habitats. We studied the movement behaviour of a ground-dwelling generalist predator, the carabid beetle Pterostichus melanarius (Illiger). We performed a mark-recapture experiment in two adjacent habitats; a large plot with oilseed radish (Raphanus sativus) and a plot with rye (Secale cereale). We used model selection to identify a minimal model representing the mark-recapture data, and determine whether habitat-specific motility and boundary behaviour affected population redistribution. We determined movement characteristics of P. melanarius in laboratory arenas with the same plant species using video recording. Both the field and arena results showed preference behaviour of P. melanarius at the habitat interface. In the field, significantly more beetles moved from rye to oilseed radish than from radish to rye. In the arena, habitat entry was more frequent into oilseed radish than into rye. In the field, movement was best described by a Fokker-Planck diffusion model that contained preference behaviour at the interface and did not account for habitat specific motility. Likewise, motility calculated from movement data using the Patlak model was not different between habitats in the arena studies. Motility (m2 d-1) calculated from behavioural data resulted in estimates that were similar to those determined in the field. Thus individual behaviour explained population redistribution in the field qualitatively as well as quantitatively. The findings provide a basis for evaluating movement within and across habitats in complex agricultural landscapes with multiple habitats and habitat interfaces.

Soil food web properties explain ecosystem services across European land use systems.

Intensive land use reduces the diversity and abundance of many soil biota, with consequences for the processes that they govern and the ecosystem services that these processes underpin. Relationships between soil biota and ecosystem processes have mostly been found in laboratory experiments and rarely are found in the field. Here, we quantified, across four countries of contrasting climatic and soil conditions in Europe, how differences in soil food web composition resulting from land use systems (intensive wheat rotation, extensive rotation, and permanent grassland) influence the functioning of soils and the ecosystem services that they deliver. Intensive wheat rotation consistently reduced the biomass of all components of the soil food web across all countries. Soil food web properties strongly and consistently predicted processes of C and N cycling across land use systems and geographic locations, and they were a better predictor of these processes than land use. Processes of carbon loss increased with soil food web properties that correlated with soil C content, such as earthworm biomass and fungal/bacterial energy channel ratio, and were greatest in permanent grassland. In contrast, processes of N cycling were explained by soil food web properties independent of land use, such as arbuscular mycorrhizal fungi and bacterial channel biomass. Our quantification of the contribution of soil organisms to processes of C and N cycling across land use systems and geographic locations shows that soil biota need to be included in C and N cycling models and highlights the need to map and conserve soil biodiversity across the world.

Exploitation of chemical signaling by parasitoids: impact on host population dynamics.

Chemical information mediates species interactions in a wide range of organisms. Yet, the effect of chemical information on population dynamics is rarely addressed. We designed a spatio-temporal parasitoid--host model to investigate the population dynamics when both the insect host and the parasitic wasp that attacks it can respond to chemical information. The host species, Drosophila melanogaster, uses food odors and aggregation pheromone to find a suitable resource for reproduction. The larval parasitoid, Leptopilina heterotoma, uses these same odors to find its hosts. We show that when parasitoids can respond to food odors, this negatively affects fruit fly population growth. However, extra parasitoid responsiveness to aggregation pheromone does not affect fruit fly population growth. Our results indicate that the use of the aggregation pheromone by D. melanogaster does not lead to an increased risk of parasitism. Moreover, the use of aggregation pheromone by the host enhances its population growth and enables it to persist at higher parasitoid densities.