Géraldine Roux-Morabito

Phylogeographic structure and past history of the circum-Mediterranean species Tomicus destruens Woll. (Coleoptera: Scolytinae).

Phylogeographic studies are often focused on temperate European species with relict footholds in the Mediterranean region. Past climatic oscillations usually induced range contractions and expansions from refugial areas located in southern Europe, and spatial distribution of genetic diversity show that northward expansions were usually pioneer‐like. Actually, few studies have focused on circum‐Mediterranean species, which probably were not influenced in the same way by climatic oscillations. We present the phylogeography of the bark beetle Tomicus destruens, which is restricted to the whole Mediterranean basin and the Atlantic coasts of North Africa and Portugal. We systematically sequenced 617 bp of the mitochondrial genes COI and COII for 42 populations (N = 219). Analysis revealed 53 haplotypes geographically structured in two clades, namely eastern and western clades, that diverged during the Pleistocene. A contact zone was identified along the Adriatic coast of Italy. Interestingly, we found contrasting levels of genetic structure within each clade. The eastern group was characterized by a significant phylogeographic pattern and low levels of gene flow, whereas the western group barely showed a spatial structure in haplotype distribution. Moreover, the main pine hosts were different between groups, with the Aleppo‐brutia complex in the east and the maritime pine in the west. Potential roles of host species, climatic parameters and geographical barriers are discussed and the phylogeographic patterns are compared to classical models of postglacial recolonization in Europe.

Population genetic structure of Tomicus piniperda L. (Curculionidae: Scolytinae) on different pine species and validation of T. destruens (Woll.)

Genetic diversity and population structure of Tomicus piniperda was assessed using mitochondrial sequences on 16 populations sampled on 6 pine species in France. Amplifications of Internal transcribed space 1 (ITS1) were also performed. Our goals were to determine the taxonomic status of the Mediterranean ecotype T. piniperda destruens, and to test for host plant or geographical isolation effect on population genetic structure. We showed that T. piniperda clusters in two mtDNA haplotypic groups. Clade A corresponds to insects sampled in continental France on Pinus sylvestris, P. pinaster and P. uncinata, whereas clade B gathers the individuals sampled in Corsica on P. pinaster and P. radiata and in continental France on P. pinea and P. halepensis. Insects belonging to clade A and clade B also consistently differ in the length of ITS1. Individuals belonging to both clades were found once in sympatry on P. pinaster. Genetic distances between clades are similar to those measured between distinct species of Tomicus. We concluded that clade B actually corresponds to the destruens ecotype and forms a good species, T. destruens. Analyses of molecular variance (amova) were conducted separately on T. destruens and T. piniperda to test for an effect of either geographical isolation or host species. Interestingly, the effect of host plant was significant for T. piniperda only, while the effect of geographical isolation was not. Pine species therefore seems to act as a significant barrier to gene flow, even if host race formation is not observed. These results still need to be confirmed by nuclear markers.

Novel insect-tree associations resulting from accidental and intentional biological 'invasions': a meta-analysis of effects on insect fitness.

The translocation of species beyond their native range is a major threat to biodiversity. Invasions by tree-feeding insects attacking native trees and the colonization of introduced trees by native insects result in new insect-tree relationships. To date there is uncertainty about the key factors that influence the outcome of these novel interactions. We report the results of a meta-analysis of 346 pairwise comparisons of forest insect fitness on novel and ancient host tree species from 31 publications. Host specificity of insects and phylogenetic relatedness between ancient and novel host trees emerged as key factors influencing insect fitness. Overall, fitness was significantly lower on novel host species than on ancient hosts. However, in some cases, fitness increased on novel hosts, mainly in polyphagous insects or when close relatives of ancient host trees were colonized. Our synthesis enables greatly improved impact prediction and risk assessment of biological invasions.

Preference-performance relationship and influence of plant relatedness on host use by Pityogenes chalcographus L.

1 Pityogenes chalcographus L. (Coleoptera: Scolytinae) causes damage in European coniferous forests, primarily on Picea abies L. Karst., but is also recorded on other native and exotic Pinaceae species. Estimating the adequacy between adult preference and larval performance of this beetle among its host‐range, as well as the influence of plant taxonomic relatedness on these parameters, would provide useful information on the beetles ability to shift onto novel hosts. 2 Choice and no‐choice assays were conducted under laboratory conditions. Adult preference and larval performance parameters among two native (Pinus sylvestris L. and Picea abies) and three exotic north American [Pinus contorta Dougl., Picea sitchensis (Bong.) Carr. and Pseudotsuga menziesii Mirbel (Franco)] conifer species were measured. 3 Pityogenes chalcographus exhibited a significant positive relationship between preference and performance. Picea abies was both the preferred and the most suitable host species for larval development. The closest relative, P. sitchensis, was the second best choice in terms of preference and performance. Pseudotsuga menziesii occupied an intermediate position for both beetle preference and performance, and Pinus spp. were the least suitable hosts for beetle development. 4 Adult preference and larval performance ranking among hosts provides little support to the plant taxonomic relatedness hypothesis. Taxonomic relatedness could play a role on the diet breadth, although only at a limited scale, within the genus Picea. At higher taxonomic levels, other factors such as bark thickness might be decisive.

Fecundity and larval development of Monochamus galloprovincialis (Coleoptera Cerambycidae) in experimental breeding

Abstract•The study aimed at clarifying basic life traits (fecundity, mortality and development) of Monochamus galloprovincialis, the vector of Bursaphelenchus xylophilus, the causative agent of the Pine Wilt Disease, in Portugal.• Mating and oviposition experiments were conducted on P. sylvestris logs under laboratory conditions during two years. Larval development was followed outdoors.• Fecundity was high, with 138.2 eggs per female.• For the first time, the number of larval instars (4) in M. galloprovincialis was recognized and instars were described.• Informations are provided on the shape and size of the larval galleries. Boring of galleries in sapwood and heartwood started at the third instar. All instars could overwinter but adults emerged simultaneously resulting in a univoltine life cycle for the majority of the individuals.• An obligatory diapause in the forth instar was assumed. However, 8.1% of the insects had a two year development.• Important differences in mortality were noted between the two experimental years, which could be explained by differences on the size of the breeding logs.• There is a high biological proximity between M. galloprovincialis populations in France and those in Portugal and Northern Europe. However, a higher fecundity and longevity was observed in France, as well as a higher percentage of insects with a two year development, compared with portuguese populations.Résumé• L’objectif de l’étude était de clarifier certaines caractéristique de base —fécondité, mortalité, développement) de Monochamus galloprovincialis, le vecteur de Bursaphelenchus xylophilus, agent du dépérissement des pins au Portugal.• Durant deux ans, des expériences d’accouplement et de ponte ont été conduites sur rondins de P. sylvestris au laboratoire. Le développement larvaire a été suivi en extérieur.• La fécondité a été élevée, avec 138.2 œufs par femelle.• Pour la première fois chez M. galloprovincialis, le nombre de stades larvaires (4) de M. galloprovincialis a été défini et ceux-ci ont été décrits.• Des informations sont fournies sur la forme et la taille des galleries larvaires. Le forage des galeries dans l’aubier et le bois de cœur commence au troisième stade. Tous les stades peuvent hiverner mais les adultes émergent simultanément, ce qui conduit à un cycle annuel pour la plupart des individus.• Une diapause obligatoire intervient au quatrième stade. Cependant, 8.1 % des insectes ont un développement sur deux ans.• Des différences importantes ont été notes entre les deux années d’étude. Elles pourraient s’expliquer par la taille différente des rondins d’élevage.• Il existe une proximité biologique élevée entre les populations françaises de M. galloprovincialis et celles du Portugal et d’Europe de Nord. Cependant, une fécondité et une longévité plus élevées, ainsi qu’une proportion plus haute d’insectes ayant un développement sur deux ans, ont été observées en France par rapport aux populations portugaises.

Occurrence of Bursaphelenchus mucronatus (Nematoda; Aphelenchoididae) in France and association with Monochamus galloprovincialis (Coleoptera: Cerambycidae)

As a consequence of the recent introduction of the pine wood nematode Bursaphelenchus xylophilus in Portugal, nematodes of the genus Bursaphelenchus were looked for in various French pine forests, in trees attacked by Monochamus galloprovincialis, the vector insect of B. xylophilus, and in the insects themselves. Trap trees were felled in 12 localities distributed all over the country. Nematodes were extracted from transversal stem discs; insects emerging from the trap trees were studied. B. hellenicus, B. leoni, B. mucronatus and B. sexdentati were isolated, but not B. xylophilus. The presence of B. mucronatus and the absence of B. xylophilus were confirmed by molecular markers. B. mucronatus was isolated from several regions with an average prevalence of 19%. The infestation of M. galloprovincialis by B. mucronatus reached 26.7%. The wide distribution of B. mucronatus in France could have an effect on the extension of B. xylophilus in a case of an introduction.RésuméSuite à la récente introduction du nématode du pin Bursaphelenchus xylophilus, au Portugal, les nématodes du genre Bursaphelenchus ont été recherchés dans diverses forêts de pins françaises, sur les arbres attaqués par Monochamus galloprovincialis, le vecteur de B. xylophilus, et sur les insectes eux-mêmes. Des arbres pièges ont été abattus dans 12 localités réparties sur le territoire national. Les nématodes ont été extraits de sections transversales de tronc, et les insectes émergeant des arbres pièges ont été étudié. B. hellenicus, B. leoni, B. mucronatus et B. sexdentati ont été isolés, mais pas B. xylophilus. La présence de B. mucronatus et l’absence de B. xylophilus ont été confirmées par des marqueurs moléculaires. B. mucronatus a été isolé de plusieurs régions avec une fréquence moyenne de 19 %. Le taux de contamination de M. galloprovincialis par B. mucronatus atteignait 26,7 %. La vaste distribution de B. mucronatus en France pourrait avoir un effet sur la propagation de B. xylophilus dans le cas d’une introduction accidentelle.

Lack of genetic differentiation after host range extension argues for the generalist nature of Pityogenes chalcographus (Curculionidae: Scolytinae)

ContextThe bark beetle, Pityogenes chalcographus, is one of the main pests in Picea abies stands, and it has also been found on other European Pinaceae species. With massive introductions of North American conifer species into European forests, this insect has extended its host range to exotic Pinaceae species.AimThis study assessed whether a wider host range has influenced the genetic structure of P. chalcographus and has led to host specialization.MethodsInsects were collected from two different regions of France, where eight native and exotic conifer species coexist and were analyzed using mitochondrial and nuclear genetic markers.ResultsConsiderable haplotypic diversity was observed within the regions and within host species from where P. chalcographus populations were collected. No genetic differentiation, especially with respect to host species associations, could be detected. Moreover, no relationship could be established between closely related P. chalcographus haplotypes and taxonomically related conifer species.ConclusionThe capacity of P. chalcographus for host shifting and dispersal may have played a key role in the rapid extension of its host range. These findings are important for pest management in forests and health and phytosanitary measures in the timber trade, especially for risk assessment in mixed coniferous forests including tree species of major economic importance.