Predicting shifts in the distribution and abundance of pest organisms relies on an accurate forecasting of their response to climate change. The oak processionary moth (OPM)
Thaumetopoea processionea
...causes serious damages to oak trees in forest, urban and other landscapes as well as severe allergic reactions to humans and animals. In the 1990’s and 2000’s, the OPM extended its range from mainland Europe and the Middle East into northern Europe. In 2005, it was also accidentally introduced in the United Kingdom. Moreover, the intensity and the frequency of OPM outbreaks are thought to have recently increased in several countries of Europe including Belgium, the Netherlands, Germany and Austria. In the present study, we aimed at forecasting the potential distribution of the OPM in Europe under current and future climate conditions. We thoroughly compiled available records of established populations all across Europe and fitted MaxEnt and BIOCLIM models to infer bioclimatic requirements for this species. Both models showed good predictive performance under current climate conditions. In particular, the surroundings of London where the OPM recently got established were predicted as highly climatically suitable. Models also predicted that many parts of northern Europe where the OPM currently does not occur (e.g. central UK, Wales, Ireland, southern Scotland, Denmark, southern part of the Scandinavian Peninsula, etc.) might become climatically suitable by 2050. Our predictions warrant the need for proper communication and management planning around the risks associated with the potential expansion of the OPM in Europe.
Asexual lineages often exhibit broad distributions and can thrive in extreme habitats compared to their sexual counterparts. Several hypotheses can be proposed to explain this pattern. Asexual ...lineages could be versatile genotypes with wide environmental tolerance, enabling their dispersal and persistence across large geographic areas. Alternatively, asexual genotypes could be ecological specialists that thrive in specific environments and outcompete relative colonizing distantly related with similar conditions in the process. Several aphid species feature widespread obligate asexual lineages, commonly known as ‘superclones'. Yet it is often unknown whether these clones are widespread ecological generalists or successful specialists. To explore these hypotheses, we examined climatic niche differentiation among six globally distributed obligate asexual lineages of the cosmopolitan aphid pest, Brachycaudus helichrysi. To ensure that we were investigating the aphid genotype niche and not a by‐product of their association with endosymbionts mediating thermal tolerance, we first verified that clones hosted similar endosymbiont communities. Subsequently, we conducted multivariate analyses on clone occurrence data on a worldwide scale. Our results revealed that, despite their global distribution, B. helichrysi superclones occupy different climatic niches. This study represents the first evidence that aphid superclone distribution can be mediated by distinctive ranges of climatic tolerance.
We sampled ca 2500 specimens of Philaenus spumarius (Hemiptera: Aphrophoridae) throughout Corsica without a priori knowledge on the presence of symptoms on plants. We screened 448 specimens for the ...presence of Xylella fastidiosa (Xf) using qPCR and a custom nested PCR. qPCR appeared versatile and under-estimated the prevalence of Xf. Nested PCR showed that Xf was present in all populations. Molecular results were validated by prediction on the distribution of Xf made from tests conducted on plants, which shows the pertinence of using vectors in risk assessment studies. Xf was detected in tenerals and adults. Thus, P. spumarius could acquire Xf from its host plant, mostly Cistus monspeliensis in Corsica, which may act as reservoir for the next season. This contrasts with other observations and suggests that management strategies may have to be adapted on a case-by-case basis. At least two genetic entities and several variants of Xf not yet identified on plants were present in the insects, which suggests ancient introductions of Xf and a probable underestimation of the current diversity of the strains present in Corsica. Interestingly 6% of the specimens carried two subspecies of Xf. Studies are required to better characterize the strains present in Corsica and to determine how the disease was introduced, spread and why no sign of a potential epidemic was detected earlier. This study shows that, when sensitive enough methods are implemented, spittlebugs (and more specifically P. spumarius for which species distribution modelling shows it could be a good sentinel for Europe) can be used to predict and better assess the exact distribution of Xf. Furthermore, Xf multiply only in their foregut and does not become circulative, which facilitates its detection.
The bacterium Xylella fastidiosa (Xf) is a harmful insect‐borne plant pathogen that causes severe diseases to major agricultural crops and many forest, ornamental and uncultivated plants. The ...pathogen, native to the Americas, has recently been detected in Europe, where it causes huge agricultural losses. The effect of landscape composition on the distribution of the vectors of the bacterium in Europe remains little explored. The present study aims at identifying how landscape composition impacts the distribution of the spittlebugs Philaenus spumarius and Neophilaenus campestris, which can carry and transmit the pathogen to plants and are considered to be the main vectors of Xf in the Mediterranean region. During the period 2015–2018, we thoroughly sampled the distribution of both species in the southwest of Iberian Peninsula. We characterized landscape composition in the sampling area by computing landscape metrics and fitted multivariate analyses and species distribution models (SDMs) to investigate spittlebugs’ response to climate and landscape structure. High densities of Mediterranean agro‐forestry systems (named “dehesas” in Spanish), sclerophyllous vegetation and broad‐leaved forests in the landscape, were positively associated with the presence of P. spumarius. Conversely, the high density of coniferous vegetation in the landscape was positively associated with the occurrence of N. campestris. For P. spumarius, SDMs accounting for ecologically relevant landscape descriptors yielded better predictive accuracy than models relying on climate only. These results highlight the importance of considering landscape information when modelling pests’ distributions and provide practical information to design landscape‐informed monitoring plans to prevent the spread of Xf in Europe.
Xylella fastidiosa (Xf) is a vector‐borne plant bacterium native to the Americas, which causes severe diseases to agricultural crops, ornamental plants and forest trees. The bacterium is becoming a ...source of worldwide health plant concern and disease outbreaks associated with Xf have occurred outside of its native range (in Europe, Asia and the Middle East). Several studies have estimated risks associated with Xf outbreaks in invaded regions under current climate conditions, but future climate change has been seldom addressed. In the present study, we calibrated correlative models of bioclimatic species distribution to forecast the potential range and severity of two economically important Xf‐related diseases (Pierce's disease and the bacterial leaf scorch of shade trees) by the period 2040–2060. Models predict that conditions could become highly favourable for Pierce's disease in economically important wine‐producing regions of the world, highlighting the need to design control strategies. Similarly, models suggest that risk of bacterial leaf scorch of shade trees might increase in temperate regions where it is still apparently absent. However, we note that substantial uncertainty in predictions arises from high levels of correlation among climatic variables in the calibration data set. The inherent lack of knowledge concerning whether the distribution of Xf‐related diseases is at climatic equilibrium or not in Europe may also influence our predictions. The models provide valuable information to identify regions where increased surveillance efforts should be made and where control strategies are required.
The study predicts a worldwide increase of the range of two Xylella fastidiosa‐related plant diseases (Pierce's disease of grapevine and bacterial leaf scorch of trees) caused by global change by 2050.
Trypanosomes are protozoan parasites found worldwide, infecting humans and animals. In the past decade, the number of reports on atypical human cases due to Trypanosoma lewisi or T. lewisi-like has ...increased urging to investigate the multiple factors driving the disease dynamics, particularly in cities where rodents and humans co-exist at high densities. In the present survey, we used a species distribution model, Maxent, to assess the spatial pattern of Trypanosoma-positive rodents in the city of Niamey. The explanatory variables were landscape metrics describing urban landscape composition and physiognomy computed from 8 land-cover classes. We computed the metrics around each data location using a set of circular buffers of increasing radii (20m, 40m, 60m, 80m and 100m). For each spatial resolution, we determined the optimal combination of feature class and regularization multipliers by fitting Maxent with the full dataset. Since our dataset was small (114 occurrences) we expected an important uncertainty associated to data partitioning into calibration and evaluation datasets. We thus performed 350 independent model runs with a training dataset representing a random subset of 80% of the occurrences and the optimal Maxent parameters. Each model yielded a map of habitat suitability over Niamey, which was transformed into a binary map implementing a threshold maximizing the sensitivity and the specificity. The resulting binary maps were combined to display the proportion of models that indicated a good environmental suitability for Trypanosoma-positive rodents. Maxent performed better with landscape metrics derived from buffers of 80m. Habitat suitability for Trypanosoma-positive rodents exhibited large patches linked to urban features such as patch richness and the proportion of landscape covered by concrete or tarred areas. Such inferences could be helpful in assessing areas at risk, setting of monitoring programs, public and medical staff awareness or even vaccination campaigns.
•A model linking landscape to the presence of Trypanosoma-positive rodents is proposed.•It allows to predict the potential distribution of the pathogen from urban landscape.•Such inferences can help assessing risk areas and anticipate health hazards.
•Pacific Herring biomass off the WCVI increased during 2006–2014.•High Herring biomass was repeatedly found on the continental shelf (depths < 185 m).•Low densities of Herring along the shelf break ...could reflect predation avoidance.•Covariation in spatio-temporal densities between Herring and its prey was positive.•Spatio-temporal covariation between Herring and both Hake and Sardine was negative.
Determining how fish respond to variation in biotic and abiotic conditions is a crucial prerequisite to forecasting changes in productivity and spatial distribution of fish stocks and designing sustainable marine resource management strategies. In the present study, we investigated the physical and biological drivers of the spatio-temporal dynamics of Pacific Herring (Clupea pallasi), which is a marine forage fish species important for commercial fisheries and First Nations in the northeastern Pacific. We fit multivariate spatio-temporal models to fisheries-independent trawl- and acoustics-based data collected off the West Coast of Vancouver Island (WCVI), Canada, during summers over the period 2006–2014. We evaluated the effects of the main ocean environmental drivers of WCVI lower trophic level productivity, including sea surface temperature (SST), chlorophyll a, fluorescence, salinity, oxygen, transmissivity and zooplankton density on variation in Pacific Herring biomass. Models were also used to measure spatio-temporal covariation with other pelagic, semi-pelagic, and bottom-associated fish species occurring off the WCVI to address potential competitive and predation interactions. Through application of these spatio-temporal models we found: (i) Pacific Herring biomass off the WCVI increased during 2006–2014; the highest Pacific Herring biomass was repeatedly found on the continental shelf (depths < 185 m) while low densities were usually observed along the shelf break (depths > 185 m), where Euphausiids, Pacific Hake, Sablefish and Arrowtooth Flounder were more abundant, which could reflect predation avoidance behaviour; (ii), the local biomass of Pacific Herring was related quadratically to the average SST in May; (iii) a positive covariation in spatio-temporal densities between Pacific Herring and its common zooplankton prey, supporting a potential bottom-up control hypothesis; (iv) a negative covariation in spatio-temporal densities between Pacific Herring and both Pacific Hake and Pacific Sardine, which could reflect predation and competitive interactions, respectively; and (v) a positive covariation in spatio-temporal densities between Pacific Herring and several groundfish species (i.e., Arrowtooth Flounder, Sablefish, Pacific Halibut, Pacific Cod), which highlights the need for an accurate assessment of the relative contribution of those species to the total summer predation pressure experienced by Pacific Herring off the WCVI. The findings of this study contribute to a better understanding of the WCVI marine ecosystem.
•We performed a nematological survey in plantain agrosystems in the Caribbean.•P. coffeae was the most prominent plant-feeding nematode in plantain fields.•Nematode abundances were apparently ...affected by the previous crops and soil type.•This study will be useful for the design of control methods.
Understanding the influence of soil properties and cultural practices on the communities of plant-feeding nematodes (PFNs) in agrosystems is a prerequisite for cost-efficient and environment-friendly pest control. Although plantain is a staple food crop in the Caribbean, the relationships between PFN communities and environmental factors are poorly understood in plantain agrosystems. In this study, which was conducted in Martinique (French West Indies), we quantified the PFNs in 301 root samples taken from 53 plantain fields that differed in climate, edaphic conditions, and cultural practices. The physico-chemical properties were also determined for the soil in each field. Coinertia analysis (CI) and General Linear Mixed Models (GLMMS) were used to investigate the relationships between the PFN communities, soil properties, and cultural practices. Four nematode taxa were found in plantain roots: Radopholus similis, Pratylenchus coffeae, Helicotylenchus multicinctus, and Meloidogyne spp. The lesion nematode P. coffeae was the most prominent PFN species, followed by the burrowing nematode R. similis, root-knot nematodes Meloidogyne spp., and the spiral nematode H. multicinctus. P. coffeae was significantly more abundant in ferralsols and nitisols (which have a low organic matter content and a high exchangeable cation content) than in andosols (which have a high organic matter content). Nematode abundances were apparently affected by the previous crops e.g., P. coffeae was slightly more abundant in fields where tuber plants such as sweet potato, yam, or dasheen were the previous crop; R. similis was particularly abundant in fields where banana or plantain was the previous crop; and Meloidogyne spp. were abundant in fields where a market garden was the previous crop. The results of this study will be useful for the design of PFN control methods in plantain.
Understanding the spatial stability of the plant-feeding nematode (PFN) community in agrosystems represents a fundamental step in the integrated control of some damaging species because modifications ...of soil properties in intensively managed agrosystems may allow growers to manipulate the balance between pathogenic and non-pathogenic species.
In the present study, we tested the hypothesis that a community of four PFN species (Criconemella onoensis, Helicotylenchus erythrinae, Hemicriconemoides cocophillus, and Pratylenchus zeae) in a sugarcane agrosystem is spatially structured according to macro-scale soil properties. This hypothesis was studied by using a sugarcane field in Martinique in which soil properties had been heavily modified by hillock-leveling in the 1970s, resulting in a great variation in soil properties over a small area (20.8 × 16.0 m). The goal of the study was to measure the temporal stability of the PFN community spatial structure and to identify the soil parameters associated with differences in nematode abundance. A systematic sampling design was used to collect data in the field that were analyzed using co-inertia and STATIS-Coa. The field study was complemented by a greenhouse experiment.
The field study documented the existence of a stable spatial pattern of the PFN community, a pattern that was structured in relation to macro-scale soil factors such as soil carbon, nitrogen, and phosphorus content and soil texture. The constant spatial pattern of the PFN community results from the differences in distributions among C. onoensis and the three other PFN species. C. onoensis was consistently more abundant in the deeply-leveled areas of the field, while the other PFN species were more abundant in the non-leveled areas. H. erythrinae was consistently more abundant in those parts of the field with higher soil pH and sodium content. These results suggested that soil properties can affect permanently the competitive balance among PFN species.
The observed relationships between PFN and these macro-scale factors were validated in a greenhouse experiment with different ratios of soil from the leveled and non-leveled areas of the field site.
Modification of some major soil properties (pH, Na+ content, soil organic content) by cultural practices such as hillock-leveling, fertilization, and liming, could greatly affect the balance among PFN species in agricultural fields.
► Statis-Coa and co-inertia analysis were used to study the spatial pattern of PFNs. ► Results show that PFN community is structured by macro-scale soil properties. ► Soil texture and organic matter affect mainly the spatial pattern of Criconomella. ► Abundance of Helicotylenchus erythrinae is linked to higher pH and Na+ content. ► We suggest that the competitive balance among species is affected by soil factors.
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•Using RADseq we inferred the first fully-resolved phylogeny of Dendroctonus genus.•Dendroctonus presumably originated during the early Miocene.•The mrca of all extant Dendroctonus ...was distributed across Palearctic and Nearctic.•The mrca presumably bored individual galleries and mass attacked pines.•The gregarious larval behavior has independently evolved twice.
The bark beetle genus Dendroctonus contains some of the most economically important pests of conifers worldwide. Despite many attempts, there is no agreement today on the phylogenetic relationships within the genus, which limits our understanding of its evolutionary history. Here, using restriction-site associated DNA (RAD) markers from 70 specimens representing 17 species (85% of the known diversity) we inferred the phylogeny of the genus, its time of origin and biogeographic history, as well as the evolution of key ecological traits (host plants, larval behavior and adults’ attack strategies). For all combinations of tested parameters (from 6444 to 23,570 RAD tags analyzed), the same, fully resolved topology was inferred. Our analyses suggest that the most recent common ancestor (mrca) of all extant Dendroctonus species was widely distributed across eastern Palearctic and western Nearctic during the early Miocene, from where species dispersed to other Holarctic regions. A first main inter-continental vicariance event occurred during early Miocene isolating the ancestors of D. armandi in the Palearctic, which was followed by the radiation of the main Dendroctonus lineages in North America. During the Late Miocene, the ancestor of the ‘rufipennis’ species group colonized north-east Palearctic regions from western North America, which was followed by a second main inter-continental vicariance event isolating Pleistocene populations in Asia (D. micans) and western North America (D. murrayanae and D. punctatus). The present study supports previous hypotheses explaining intercontinental range disjunctions across the Northern Hemisphere by the fragmentation of a continuous distribution due to climatic cooling, host range fragmentation and geological changes during the late Cenozoic. The reconstruction of ancestral ecological traits indicates that the mrca bored individual galleries and mass attacked the boles of pines. The gregarious feeding behavior of the larvae as well as the individual attack of the base of trees have apparently independently evolved twice in North America (in the ‘rufipennis’ and the ‘valens’ species groups), which suggests a higher adaptive potential than previously thought and may be of interest for plant protection and biodiversity conservation in a rapidly changing world.
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