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Climate impacts vector-borne disease transmission through a complex interplay of influences on all the actors involved: the vector, the host and the pathogen. Climate change can lead to shifts in disease distribution, exposing naive host populations and potentially leading to sanitary crisis. Assessing the effects of climate change on diseases is necessary in order to better prepare and mitigate such impacts. The basic reproduction ratio (R0) measures the number of secondary cases arising from the introduction of one infected host in a susceptible population. It reflects the risk of transmission if the pathogen is introduced. Some of its parameters such as the vector biting rate, the vector mortality rate, the extrinsic incubation period and, the vector to host ratio exhibit a strong climatic dependence. Linking these parameters with climate observations or simulations allows mapping of past and future R0. We illustrate this approach by applying it to two diseases caused by Orbiviruses transmitted by Culicoides biting midges: bluetongue and African horse sickness. We map R0 anomalies for Europe for past (1961 to 2010) and future (2011 to 2050) periods and assess the uncertainty of the results presented. This approach also enables a better understanding of the underlying mechanisms involved in transmission risk increase or decrease. We discuss (i) the conditions necessary to apply this approach to other diseases, (ii) its strengths and limits, and (iii) propose entomological, epidemiological and climatic studies to further improve the approach. (Texte intégral)

International audience; The parasitism of the horse chestnut leafminer remains at a low level in Europe since many years. As a consequence, horse chestnuts in regions with more than 20 years of C. ohridella infestation still suffer from heavy leafminer attack.However, results of our investigations show changes in the parasitoid complex over the years, reflecting three different strategies exemplified by three parasitoidspecies. (1) The abundance of the most common parasitoid, Minotetrastichus frontalis, seems to remain at the same low level, indicating that the parasitoid does not actively search for special leafminer hosts but rather encounter them by chance. The relative impact of these species decreases as other parasitoids gain importance. (2) Other species, like Pediobius saulius, seem to undergo a slow adaptation process. Their relative importance in the parasitoid complex increases at many locations infested for a long time. In the long run, parasitism of these species may reach levels exhibiting a controlling effect on the leafminer's populations. (3) A third group of species seems to follow the spread of its new host and invade new regions. Starting in the year 2000, the originally eastern European species Cirrospilus talitzkii was recorded from C. ohridella in countries where it has never been found before on any other leafminer. Meanwhile, the species can be found as a regular element of the parasitoid complex of the horse chestnut leafminer in many south and central European countries. To the present, these changes in the parasitoid complex have no significant impact on overall parasitism of C. ohridella. However, there are measurable effects, like an increasing rate of pupal parasitism due to the action of P. saulius. In the long run, changes in the parasitoid spectrum of the horse chestnut leafminer may increase the impact of parasitism and contribute substantially to the control of the invasive species in future.

International audience; 1. Biological invasions have an anthropogenic origin, and although many species are able to spread on their own within the newly invaded area, long-distance dispersal events shown to accelerate rates of spread are frequently associated with human activities. In a previous study, the performances of several invasion models of the spread of the horse chestnut leafminer Cameraria ohridella in Germany were compared, demonstrating that the best model in qualitative and quantitative terms was a stratified dispersal model taking into account the effect of human population density on the probability of long-distance dispersal events. 2. Similar data were collected in France over 4 years (2000-2004, 5274 observation points). These data were used to assess the performance of the best-fit models from Germany using the original parameters and to model the spread of the leafminer in France. 3. The stratified dispersal model accounting for variations in human population density developed in Germany, predicted the invasion of France with a similar level of predictive power as in the area where it was developed. This suggests that an equivalent level of predictability can be expected in a newly invaded country with similar environmental conditions. 4. We applied the model to forecast the future invasion dynamics in the UK from 2005 to 2008, based on the first observations of Cameraria in the country in 2002-2004. Predictions are discussed in the light of different prevailing environmental conditions. 5. Synthesis and application. The model and predictions developed in this study provide one of the few examples of an a priori model of invasion in a newly invaded country, and provide a simple modelling framework that can be used to explore the spread of other invading organisms. In the case of Cameraria, little can be done to prevent or slow its spread but our model, by predicting changes in distribution and rates of spread, provides fore-warning of where and when damaging pest populations are likely to appear.

La mineuse du marronnier Cameraria ohridella est une espèce invasive en Europe dont l’origine est inconnue. Sa dispersion est très rapide et cinq ans après son premier signalement aux frontières françaises, elle était présente en automne 2003 dans la plupart des départements. Son potentiel de développement est très important, et deux ou trois ans après son installation, elle peut, dès le début de mois de juillet, provoquer la chute des feuilles de son hôte préféré Aesculus hippocastanum. Les principaux résultats sur les recherches réalisées en Europe dans le cadre du contrat européen Controcam sont présentés., Origin, dispersion, host plants, control : principal findings of research carried out within the framework of a European Controcam project Horse-chestnut leaf-miner Cameraria ohridella, the origins of which are somewhat unclear, is an invasive species in Europe. It is capable of extremely rapid dispersion and five years after first being reported on the French mainland it had already spread to most parts of the country by Autumn 2003. The pest presents an extremely large development potential, and just two or three years after establishing on its preferred host, Aesculus hippocastanum, can cause the latter to lose its leaves. The article presents the main findings of research into the pest carried out under the terms of a European Controcam contract.

International audience; Although it is likely that the horse chestnut leaf miner Cameraria ohridella (Lepidoptera: Gracillaridae)entered France in the course of 1998, its first observation was recorded near Paris in 2000. The rapid spread of the leafminer throughout Europe suggested that the country would be quickly invaded, and surveys were carried out in 2001, 2002 and 2003 to follow its nationwide spread. Surveys aiming at detecting the presence of the pest by visual observation of leaf damages were carried out in late summer/early autumn in the centre and East of the country in 2001, whereas they were extended to the West in 2002 and 2003. The pattern of spread derived from the spatial analysis of these data is compared to the pattern of spread already described for Germany in term of spread rate and possible relationship with human population density.

International audience; The leafminer Cameraria ohridella Deschka & Dimic is an invasive pest of horse chestnut, Aesculus hippocastanum L., trees that has spread rapidly across Europe over the past 19 yr. It was recently reported in the United Kingdom, Denmark, and the Ukraine, and this spread is expected to continue through the Scandinavian countries until the northern limit of the host tree distribution is reached. The presence of the species is generally reported first in the cities, either as consequence of human-related transportation or because of the higher number of host trees in these areas. As a consequence, detailed studies of the spread of this pest through rural areas have not yet been carried out. We have monitored the spread of the moth at the fringe of its known distribution in eastern France during the period 2001-2003. The population was estimated by observing the damage caused by the pest and by establishing a network of pheromone traps. Pheromone traps were set up to measure two generations in 2001 and 2002, whereas the spatial pattern of the spread of the species measured by damage assessment was followed for each generation between 2001 and 2003 (nine generations). Spatial and temporal patterns in the population estimates made using these two methods were compared. We found that estimates made from damage assessment correlated with log-transformed estimates from pheromone trap catches, suggesting that both techniques can be used to monitor the spread of this pest. Over the period 2001-2003, the spread rate ranged from 17.0 to 37.9 km/yr, depending on the population threshold and method used.