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Knowing the phylogeographic structure of invasive species is important for understanding the underlying processes of invasion. The micromoth Phyllonorycter issikii, whose larvae damage leaves of lime trees Tilia spp., was only known from East Asia. In the last three decades, it has been recorded in most of Europe, Western Russia and Siberia. We used the mitochondrial cytochrome c oxidase subunit I (COI) gene region to compare the genetic variability of P. issikii populations between these different regions. Additionally, we sequenced two nuclear genes (28S rRNA and Histone 3) and run morphometric analysis of male genitalia to probe for the existence of cryptic species. The analysis of COI data of 377 insect specimens collected in 16 countries across the Palearctic revealed the presence of two different lineages: P. issikii and a putative new cryptic Phyllonorycter species distributed in the Russian Far East and Japan. In P. issikii, we identified 31 haplotypes among which 23 were detected in the invaded area (Europe) and 10 were found in its putative native range in East Asia (Russian Far East, Japan, South Korea and China), with only two common haplotypes. The high number of haplotypes found in the invaded area suggest a possible scenario of multiple introductions. One haplotype H1 was dominant (119 individuals, 67.2%), not only throughout its expanding range in Europe and Siberia but, intriguingly, also in 96% of individuals originating from Japan. We detected eight unique haplotypes of P. issikii in East Asia. Five of them were exclusively found in the Russian Far East representing 95% of individuals from that area. The putative new cryptic Phyllonorycter species showed differences from P. issikii for the three studied genes. However, both species are morphologically undistinguishable. They occur in sympatry on the same host plants in Japan (Sendai) and the Russian Far East (Primorsky krai) without evidence of admixture.

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Classical biological control is often advocated as a tool for managing invasive species. However, accurate evaluations of parasitoid species complexes and assessment of host specificity are impeded by the lack of morphological variation. Here, we study the possibility of host races/species within the eulophid wasp Pediobius saulius, a pupal generalist parasitoid that parasitize the highly invasive horse-chestnut leaf-mining moth Cameraria ohridella. We analysed the population genetic structure, host associations and phylogeographic patterns of P. saulius in Europe using the COI mitochondrial gene. This marker strongly supports a division into at least five highly differentiated parasitoid complexes, within two of which clades with differing degrees of host specialization were found: a Balkan clade that mainly (but not only) attacks C. ohridella and a more generalist European group that attacks many hosts, including C. ohridella. The divergence in COI (up to 7.6%) suggests the existence of cryptic species, although this is neither confirmed by nuclear divergence nor morphology. We do not find evidence of host tracking. The higher parasitism rates observed in the Balkans and the scarcity of the Balkan–Cameraria haplotypes out of the Balkans open the possibility of using these Balkan haplotypes as biological control agents of C. ohridella elsewhere in Europe.

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National audience

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National audience

International audience

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La mineuse du marronnier Cameraria ohridella Deschka and Dimic est un lépidoptère dont l'origine est inconnue. Cette espèce, découverte en macédoine il y a plus de 20 ans, a ensuite colonisé progressivement toute l'Europe. Elle provoque d'importants dégâts sur le marronnier d'inde Aesculus hippocastanum L., mais d'autres espèces de marronniers et d'érables peuvent être attaquées. Les dégâts n'entraînent pas de risques immédiats de déclin des arbres mais posent des problèmes esthétiques et économiques pour les arbres urbains. L'accroissement rapide des populations de la mineuse, la grande disponibilité de la plante hôte dans les villes, l'absence de prédateurs, et de parasites spécifiques ne facilitent pas la lutte contre cet insecte. Les possibilités et les limites de l'application des différentes stratégies de lutte sont discutées., The horse-chestnut leaf miner, Cameraria ohridella Deschka and Dimic is a lepidopteran of unknown origin. This species was first obseгved in Macedonia more than 20 years ago and since then, it had spread over almost al Europe. It causes outbreaks on the European horse-chestnut Aesculus hippocastanum L., but other horse chestnut and maple species may be attacked. The damages do not lead to immediate plant health problem but pose aesthetical and economical problem on urban trees. The rapid growth of moth populations, the great host plant availability in urban environnement, and the lack of predators and specific parasitoides make the control of this insect difficult. The possibilities and limits of the use of the different control methods аге discussed.

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.

National audience

International audience; The very fast spread of the horse-chestnut leafminer Cameraria ohridella throughout Europe has been mainly attributed to a very high dispersal ability combined with wind or human passive transportationover long distances.However, the species effective dispersal characteristics remain to be better understood. Here we present data of experiments aiming to describe the decrease in population estimate as a function of distance to a population source. Firstly, we analysed the decrease in infestation level on horse-chestnut trees along three transect avenues departing from population source located in green areas in Brussels. Secondly, we describe the decrease in catches of pheromone traps disposed along two transects departing from an isolated group of infested chestnut trees. Results of these two experiments suggest that the active dispersal ability might be very short (approx. 100m), and that the largest part of the dispersal could be the result of infested leaves (or fragments) blown from population source during the winter.The evolutionary perspective of this hypothesis (i.e. do leafminers benefit from being dispersed with their leaves) and applied consequences for pest management at the scale of cities is discussed.

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.