- - -
- - -
Dépôt Institutionnel de l’Université libre de Bruxelles / Université libre de Bruxelles Institutional Repository
Thèse de doctorat/ PhD Thesis Citation APA:
Meurisse, N. (2008). Chemical ecology of rhizophagus grandis (Coleoptera: Monotomidae) and its application to the biological control of dendroctonus micans (Coleoptera: Scolytinae) (Unpublished doctoral dissertation). Université libre de Bruxelles, Faculté des Sciences – Ecole Interfacultaire des Bioingénieurs, Bruxelles.
Disponible à / Available at permalink : https://dipot.ulb.ac.be/dspace/bitstream/2013/210567/4/bff1fb3c-bd4b-4a42-b511-c0435709a52c.txt
(English version below)
Cette thèse de doctorat a été numérisée par l’Université libre de Bruxelles. L’auteur qui s’opposerait à sa mise en ligne dans DI-fusion est invité à prendre contact avec l’Université (di-fusion@ulb.be).
Dans le cas où une version électronique native de la thèse existe, l’Université ne peut garantir que la présente version numérisée soit identique à la version électronique native, ni qu’elle soit la version officielle définitive de la thèse.
DI-fusion, le Dépôt Institutionnel de l’Université libre de Bruxelles, recueille la production scientifique de l’Université, mise à disposition en libre accès autant que possible. Les œuvres accessibles dans DI-fusion sont protégées par la législation belge relative aux droits d'auteur et aux droits voisins. Toute personne peut, sans avoir à demander l’autorisation de l’auteur ou de l’ayant-droit, à des fins d’usage privé ou à des fins d’illustration de l’enseignement ou de recherche scientifique, dans la mesure justifiée par le but non lucratif poursuivi, lire, télécharger ou reproduire sur papier ou sur tout autre support, les articles ou des fragments d’autres œuvres, disponibles dans DI-fusion, pour autant que :
Le nom des auteurs, le titre et la référence bibliographique complète soient cités;
L’identifiant unique attribué aux métadonnées dans DI-fusion (permalink) soit indiqué;
Le contenu ne soit pas modifié.
L’œuvre ne peut être stockée dans une autre base de données dans le but d’y donner accès ; l’identifiant unique (permalink) indiqué ci-dessus doit toujours être utilisé pour donner accès à l’œuvre. Toute autre utilisation non mentionnée ci-dessus nécessite l’autorisation de l’auteur de l’œuvre ou de l’ayant droit.
--- English Version ---
This Ph.D. thesis has been digitized by Université libre de Bruxelles. The author who would disagree on its online availability in DI-fusion is invited to contact the University (di-fusion@ulb.be).
If a native electronic version of the thesis exists, the University can guarantee neither that the present digitized version is identical to the native electronic version, nor that it is the definitive official version of the thesis.
DI-fusion is the Institutional Repository of Université libre de Bruxelles; it collects the research output of the University, available on open access as much as possible. The works included in DI-fusion are protected by the Belgian legislation relating to authors’ rights and neighbouring rights.
Any user may, without prior permission from the authors or copyright owners, for private usage or for educational or scientific research purposes, to the extent justified by the non-profit activity, read, download or reproduce on paper or on any other media, the articles or fragments of other works, available in DI-fusion, provided:
The authors, title and full bibliographic details are credited in any copy;
The unique identifier (permalink) for the original metadata page in DI-fusion is indicated;
The content is not changed in any way.
It is not permitted to store the work in another database in order to provide access to it; the unique identifier (permalink) indicated above must always be used to provide access to the work. Any other use not mentioned above requires the authors’ or copyright owners’ permission.
D 03548
UNIVERSITÉ LIBRE DE BRUXELLES
ÉCOLE DOCTORALE BIODIVERSITÉ, ÉCOLOGIE, ÉVOLUTION
Thèse présentée en vue de l'obtention du grade de Docteur en Sciences agronomiques et Ingénierie biologique
MEURISSE Nicolas
CHEMICAL ECOLOGY OF RHIZOPHAGUS GRANDIS (COLEOPTERA: MONOTOMIDAE)
And its application to the biological control of Dendroctomis micans (Coleoptera: Scolytinae)
Thèse dirigée par le Professeur Jean-Claude GRÉGOIRE
Directeur du Laboratoire de Lutte Biologique et Ecologie Spatiale (LUBIES)
Soutenue en février 2008 à l’Université Libre de Bruxelles
Membres du jury :
Prof. Jean-Christophe DE BISEAU Université Eibre de Bruxelles (Belgique) Prof. Charles DE CANNIÈRE Université Eibre de Bruxelles (Belgique)
Prof. Guy JOSENS Université Libre de Bruxelles (Belgique)
Dr. Marc KENIS CABI Europe (Switzerland)
Université Libre de Bruxelles
UNIVERSITÉ LIBRE DE BRUXELLES
ÉCOLE DOCTORALE BIODIVERSITÉ, ÉCOLOGIE, ÉVOLUTION
Thèse présentée en vue de l’obtention du grade de Docteur en Sciences agronomiques et Ingénierie biologique
MEURISSE Nicolas
CHEMICAL ECOLOGY OF RHIZOPHAGUS GRANDIS (COLEOPTERA: MONOTOMIDAE)
And its application to the biological control of Dendroctonus micans (Coleoptera: Scolytinae)
Thèse dirigée par le Professeur Jean-Claude GRÉGOIRE
Directeur du Laboratoire de Lutte Biologique et Ecologie Spatiale (LUBIES)
Soutenue en février 2008 à l’Université Libre de Bruxelles
Membres du jury :
Prof. Jean-Christophe DE BISEAU Prof. Charles DE CANNIÈRE Prof Guy JOSENS
Dr. Marc KENIS
Université Libre de Bruxelles (Belgique) Université Libre de Bruxelles (Belgique) Université Libre de Bruxelles (Belgique) CABI Europe (Switzerland)
Summary:
The Eurasian spruce bark beetle Dendroctonus micans is a major pest of spruce which is expanding its range in France, Turkey, England and Wales. Its monospecific predator Rhizophagus grandis has followed naturally the bark beetle into most areas and, since the 1960s, has also been mass-produced and successfully released within newly infested locations.
In this scope, the development of an effective trapping method would be very useful to assess the bark-beetle presence at previously uninfested sites, or predator establishment after release or natural spread. We demonstrated the efficiency of oxygenated monoterpenes-baited kairomone traps to monitor R. grandis in varions epidemiological conditions, including areas localized behind or at the limit of the pest’s distribution, or in areas where artificial releases were performed. Because the predator is strictly species-specific, another exciting possibility offered by the kairomone trapping is the indirect monitoring of the pest itself in areas of unknown status (e.g. areas under colonization, or considered as at risk at medium- term).
R. grandis is also considered as one of the most valuable natural enemies to strike aggressive North-American Dendroctonus species. In this respect, R. grandis has been recently applied in a neo-classical biological program against the red turpentine beetle D. valens, which invaded China from North America in the late 1990’s. In laboratory tests conducted on pine logs in the laboratory, or on living pine trees in the field, we demonstrated that R. grandis adults can successfully enter and reproduce into D. valens galleries.
In Europe, R. grandis is the only species regularly found in the brood Systems of D. micans, where adults and larvae attack the gregarious larvae of their prey. In such enclosed Systems, R.
grandis ’ functional response is therefore influenced by varions interrelated components, such as the prey density, the predator density, or the prey distribution. Measuring the predator’s success in tenus of larval survival and growth rates, we demonstrated the time spent by R.
grandis larvae to wound and kill their prey to be the main factor limiting their development.
This factor may be considerably influenced by the proportions of diseased, wounded or molting prey rise in the brood System, for instance as a resuit of an increase in prey density, or due to the presence of conspecific adults (which wound their prey but do not consume them entirely). Furthermore, our tests suggest that no cannibalism or noticeable intraspecific compétition occurred between R. grandis larvae, whereas some lighter mode of compétition probably took place.
R. grandis also exhibits a reproductive numerical response to prey density, which mainly relies on the perception of Chemical stimuli and inhibitors released in the bark beetle brood System.
In the current study, we developed a non-destructive approach to follow the dynamics of volatile compound production, using sequential sample collection on SPME fibers. Our tests demonstrated that the larval activity of D. micans or D. valens strongly influences the release of some oxygenated monoterpenes. However, our attempts to correlate the relative quantities of some Tdentffied Chemicals to offspring production were less^uccessfuî as îtToncemsThe identification of potential oviposition stimuli and inhibitors.
The problematic rose by the progression of D. micans, as well as detailed results of each of the described above studies are discussed in the two published papers and the three manuscripts forming this thesis. Bringing ail these studies together, several perspectives are also presented in the general discussion.
Keywords: Chemical ecology, forest entomology, predator-prey relationship, invasive pest monitoring, spruce bark beetle, spécifie predator, Dendroctonus valens, kairomone, oxygenated monoterpenes, semiochemical, insect trapping, integrated pest management, foraging strategy.
- 1 -
Résumé :
Ravageur des épicéas, Dendroctonus micans est toujours en voie d’extension en France, en Turquie, en Angleterre et au Pays de Galles. Dans la plupart de ces zones, le dendroctone est accompagné de manière naturelle par son prédateur monospécifique, Rhizophagus grandis.
Depuis les années 1960, le prédateur a également fait l’objet d’une production de masse et de programmes de lâchers dans les zones d’arrivée récente du scolyte.
Dans le cadre de la lutte biologique contre D. micans, les gestionnaires forestiers doivent donc estimer au plus tôt la présence du ravageur dans des zones jusque là indemnes, mais également vérifier l’établissement du prédateur par progression naturelle ou résultant d’introductions délibérées. Dans la présente étude, nous avons démontré l’efficacité de pièges d’interception appâtés à l’aide de monoterpènes oxygénés pour la capture de R. grandis. Celle-ci s’est faite dans différentes conditions épidémiologiques, incluant notamment des zones situées en arrière du front de progression du scolyte et des zones où des lâchers artificiels ont été réalisés.
Comme R. grandis est strictement inféodé au dendroctone, un autre avantage de la technique est la possibilité de réaliser un dépistage indirect du ravageur dans les zones où son statut est incertain (zones en cours de colonisation, ou considérées comme à risque à moyen terme).
Par ailleurs, R. grandis est également considéré comme un des meilleurs ennemis naturels potentiels pour lutter contre d’autres espèces de Dendroctonus aggressifs. Dans cette optique, R. grandis a été récemment utilisé dans un programme de lute biologique contre D. valens, ravageur invasif arrivé en Chine dans la fin des années 1990 en provenance d’Amérique du Nord. Nous avons démontré la capacité de R. grandis à s’introduire et à se reproduire dans les galeries de D. valens lors de tests de laboratoire, mais aussi sur des arbres vivants en pinèdes.
En Europe, R. grandis est strictement inféodé aux galeries de D. micans, où larves et adultes du prédateur s’attaquent aux larves grégaires du scolyte. Dans ce système clos, la réponse fonctionelle de R. grandis est influencée par plusieurs facteurs étroitement corrélés, la densité de proies, la densité de prédateurs, et la distribution des proies. En mesurant l’efficacité de prédation de R. grandis en termes de survie des larves et de taux de croissance, nous avons démontré l’influence sur leur développement du temps passé par les larves à blesser et à tuer leurs proies. Ce facteur est par ailleurs fortement dépendant de la proportion de larves malades, blessées ou en cours de mue au sein du système ; une proportion qui peut augmenter en réponse à une augmentation de la densité de proies, ou lorsque des adultes sont présents (ceux- ci blessent les proies mais ne les consomment pas entièrement). Enfin, nos tests suggèrent qu’il n’existe que peu de cannibalisme ou de compétition intraspécifique entre larves de R. grandis, tandis que des modes de compétition moins importants prennent vraisemblablement place.
R. grandis présente également une réponse numérique reproductive à la densité de proies disponibles, principalement basée sur la perception de stimuli et d’inhibiteurs présents dans les galeries du scolyte. Par la collecte de composés volatils présents dans ces systèmes à l’aide de fibres SPME, nous avons développé une méthode non-destructive pour suivre la dynamique de production des médiateurs chimiques. Nos tests ont démontré que l’activité des larves de D.
micans ou D. valens influence fortement la dynamique de production de certains monoterpènes oxygénés. En revanche, il n’a pas été été possible de corréler les différents composés identifiés au nombre de larves de R. grandis présentes dans le système.
La problématique soulevée par la progression de D. micans, de même que les résultats détaillés de chacune des études décrites ci-dessus sont discutés dans les deux papiers publiés et les trois manuscrits formant cette thèse. Les différentes perspectives apportées par ce travail sont également présentées dans la discussion générale.
- 2 -
Mots-clés : Ecologie chimique, entomologie forestière, relation prédateur-proie, surveillance de ravageur invasif, scolyte de l’épicéa, prédateur spécifique, Dendroctonus valens, kairomone, monoterpène oxygéné, médiateur chimique, capture d’insecte, lutte intégrée, stratégie d’exploitation.
French title:
Etude des médiateurs chimiques chez Rhizophagus grandis (Coleoptera : Monotomidae) et application à la lutte biologique contre Dendroctonus micans (Coleoptera : Scolytinae)
Current address :
Laboratoire de Lutte biologique et d’Ecologie spatiale Faculté des Sciences - Ecole Interfacultaire de Bioingénieurs CP 160-12, Université Libre de Bruxelles
50 Avenue F.D. Roosevelt B-1050 Bruxelles
Please refer to this work as follows:
Meurisse, N. 2008. Chemical ecology of Rhizophagus grandis (Coleoptera: Monotomidae) and its application to the biological control of Dendroctonus micans (Coleoptera : Scolytinae). PhD thesis.
Université Libre de Bruxelles, Brussels, Belgium.
- 3 -
A mon grand-père,
- 4
REMERCIEMENTS
Jean-Claude, je souhaite te remercier vivement pour ton aide tout au long de ma thèse. Merci pour ton enthousiasme communicatif, ta disponibilité et tes conseils avisés qui m’ont plus d’une fois revigoré dans mes efforts. Tout en m’initiant à acquérir un certain esprit critique et l’exigence de rigueur nécessaire à toute démarche scientifique, tu as également su m’accorder suffisamment de liberté individuelle quand c’était nécessaire.
Un grand merci également à tous les lecteurs de cette thèse ainsi qu’à plusieurs correcteurs anonymes pour certains de ses chapitres. Ma plus sincère gratitude se porte encore vers l’ensemble de l’équipe LUBIES. Un merci tout particulier à Marius, Frédéric, Jean-Marc, Aiko et Olivier. J’ai toujours pu compter sur votre soutien, et ce fut un réel plaisir de partager mon quotidien avec vous durant ces quelques années. Anne-Catherine, David, Nathalie, Thibaut, Rachid, Laurent, Pauline, Jeanne, Sylvie, Julie, Anaï, Tamara, Pierre, Roberta, Natalia et les autres, nous avons partagé des périodes plus ou moins longues au Labo. Merci pour tous ces moments de partage. Merci aussi pour ces discussions passionnées, quoique toujours trop courtes, qui surgissaient le plus souvent à l’improviste. Un grand merci à Laurent Grumiau, pour m’avoir appris à dompter ce capricieux appareillage qu’est le GC-MS. Je souhaiterais également remercier le Professeur R. Wegensteiner (Universitât fur Bodenkultur, Wien) pour son initiation à l’étude des pathogènes chez les coléoptères, ainsi que le Professeur B.
Wermelinger (Swiss Fédéral Institute for Forest, Birsmendorf) pour ses magnifiques
photographies de Rhizophagus grandis. Zhao, o &tl^
HÈo
Cette page de remerciements ne serait pas complète si je manquais d’y mentionner le FRIA.
Cet organisme m’a offert l’opportunité de mener à bien ce projet de recherches durant plusieurs années, mais également de prendre part à un colloque international. Le Département Santé des Forêts français a également offert son soutien financier dans le cadre de ce travail.
Ma gratitude se porte encore vers tous nos collaborateurs de terrain, belges ou étrangers, sans lesquels la pose et le relevé des pièges à kairomones n’aurait jamais pu être réalisés.
Enfin, je tiens à exprimer mes plus sincères remerciements à ma famille. Jean, ton hospitalité et ton aide m’ont été particulièrement précieuses en Bretagne. Anne-Hélène, même dans mes plus forts moments de doute, tu m’as toujours montré ton soutien inconditionnel. Cette thèse
n’aurait jamais pu aboutir ^ns toi^ _____________
Nicolas
-
5 -
TABLE OF CONTENTS
CHAPTER 1: General introduction... 7
1.1 Bark beetles and conifer related pests... 8
1.2 The conifer-beetle-fungi complex... 9
1.3 Management tactics in forest ecosystems...13
1.4 The study System: D. micans and R. grandis... 16
1.5 Aim of the thesis... 21
Article I. Le dendroctone de l’épicéa en France... 23
CHAPTER 2: Early D. micans and R. grandis monitoring... 37
Article II. Kairomone traps for bark-beetle management... 41
CHAPTER 3: Biological control of north-american Dendroctonus species ...55
Manuscript I. R. grandis as a biocontrol agent against D. valens...59
CHAPTER 4: Predatory behaviour of R. grandis... 67
Manuscript II. Prédation success in R. grandis ... 71
CHAPTER 5: The rôle of semiochemichals in thei?. grandis numerical response... 79
Manuscript III. Sequential volatiles sampling in bark beetle brood chambers ... 85
CHAPTER 6: General discussion... 109
6.1. Functional and numerical response in the predator R. grandis... 110
6.2. Rôle of semiochemicals in R. grandis reproductive response...113
6.3. Use of semiochemicals in D. micans management... 114
6.4 Other perspectives ... 116
REFERENCES... 121
SUPPLEMENTARY MATERIAL... 131
Appendix I. Techniques of bark-beetle semiochemicals identification... 132
Appendix II. The functional response of predators... 135
Appendix III. The aggregative response of predators... 137
Appendix IX. Comparison of the volatiles identified... 138
GLOSSARY... 142
- 6 -
CHAPTER 1
GENERAL INTRODUCTION
“Theory without practice is fantasy, practice without theory is chaos. ” Anonymous
This general introduction is intended to provide the reader with some conceptual, historical and methodological insights within the scope of forest entomology. The first sections address how bark beetles may hâve a significant impact on forest ecosystems and how they interact with host trees, associated microorganisms or natural enemies. The way scientists may provide some useful tools to forest managers in the scope of Integrated Pest Management (IPM) is explored in the next section. Particular focuses will be made on semiochemicals-based management tactics and the use of natural enemies in the context of biological control. A spécial highlight will also be given on the spécifie relationship between the coleopteran predator R. grandis and its barkbeetle prey D. micans. An outline of the thesis will be presented at the end of the chapter.
1.1. Bark beetles and conifer related pests
Insects may damage woody plants in a variety of different ways (Berryman 1986), either reducing their carbohydrate metabolism due to the loss of photosynthetic tissues (defoliators), reducing the flow of carbohydrates and nutritions material (sap feeders, vascular tissues consumers), or killing the trees in a direct or indirect manner (woody tissues consumers, diseases vectors). However, phytophagous insects that are considered as forest pests - i.e. those that may become abundant enough to hâve a serions économie impact - are restricted to a relatively small number of species (Berryman 1986). Some examples include bark beetle and weevils (Coleoptera: Curculionidae), longhoms (Coleoptera: Cerambyeidae); aphids (Homoptera: Aphidoidea), or moths (Lepidoptera). Their damage can cause the death of the trees, affect timber products in a variety of ways, such as growth réduction, reduced grade of wood, stem deformity, reduced seed crops, or hâve more subtle effects on récréation, wildlife, esthetic and fire hazard ( Berryman 1986).
Insects that attack already weakened trees are called secondary pests. Most of these species exclusively feed on dead or decaying materials, and may only become problematic when insects bore their galleries in timber used for fumiture or veneer, or if they transport pathogenic fungi to living trees during a period of feeding by young adults (Knizek & Beaver 2004). On another hand, insects that are aggressive in their behaviour and attack healthy trees are called primary pests. A shift from secondary to primary pest status may also sometimes occur according to the local pest density (Borden 1984, Hedgren et al. 2003a,b).
Among phytophagous insects, scolytines are the most economically important forest pests worldwide, and the single most destructive pests in the boréal and temperate régions of
Chapter 1 __________________________________________________________
- 8 -
General introduction
the Northern hemisphere (Berryman 1986, Wood & Bright 1992). Most aggressive représentatives belong to the Dendroctonus and Ips généra. In British Columbia, for instance, an historical outbreak of the mountain pine beetle D. ponderosae Hopkins is currently covering almost 9 million hectares (Aukema et al. 2006). In Central and Northern Europe, the spruce bark beetle I. typographus (Linné) is considered by far as the main forest pest problem. Data collected in ten European countries showed that at least 2 800 000 hectares were attacked by this species between 1990 et 2001, resulting in the death of more than 31 billion m^ of spruce (Grégoire & Evans 2004).
1.2. The conifer-beetle-fungi complex
The population dynamics of forest pests, as a fonction of individual rates of birth, death, and migration, is mainly determined by the resources requirements of the species, together with environmental favorability. This is particularly true as it concems bark beetles, whose environment is composed of varions physical and biological components that closely interact with each other (Berrymann 1986, Fig. 1). These include host tree abondance and suitability, particular colonization strategies exhibited by bark beetles, as well as complex multitrophic interactions with associated microorganisms or natural enemies.
Figure 1. Conceptual view of the déterminants of density changes in insect populations. The basic environment, which is subdivided into biotic, physical and disturbance factors, together with the density of the insect population, détermine the favorability of the environment for the average individual (interactions e and c). Individual rates of birth, death, and migration are determined by the resource requirements of the species together with environmental favorability (interaction a); these rates govem the growth rates of the population (interaction b). Finally, population density may affect the basic properties of the environment (interaction d) and through this the favorability of the environment for future générations (delayed feedback).
(Berrymann 1986).
BASIC
BIOTIC
Ho«t abundanoe Hast gHSlity
O* «wemce of COfqp»lttpr»
ENVI R O N M E N T
PHYSICAL OISTUHBAWCE
Ge«9reiklty Woatfw
CaiasUophes So^
Cfonate
Hmrwn activHies
- 9 -
Chapter 1
Trees defences
In coniferous trees, resin production may be largely constitutive (preformed, primary resin) composed of material produced and stored in specialized secretory structures, or induced (inducible, secondary resin) as the resuit of injury. Resin production relies on a complex assemblage of isoprene (C5H10) units as building block to produce a mixture of a turpentine (monoterpenes, Cio and sesquiterpenes, C15) and rosin (diterpenes, C20) fraction (Phillips &
Croteau 1999). Ail terpenes and terpenoids precursors are formed in the cytosol through the mevalonate/acetate pathway, or in the plastids through the mevalonate-independent pathway (Trapp & Croteau 2001).
Oleoresin production, accumulation and mobilization structures may though greatly differ among conifer species (Lewinshon et al. 1991). The simplest organizational structure is exhibited by cedar species {Thuja spp.), where isolated oleoresin-containing cells are scattered throughout the stems. Other conifers largely rely on primary oleoresin production, or “pitching out”, and therefore exhibit higher degrees of anatomical organization in their secretory structures (Fig. 2). These range from oleoresin accumulation in cyst-like resin blisters in firs (Abies spp.), to elaborate network of interconnected resin ducts located throughout the wood and the bark in pines {Pinus spp.). Most conifers lie between these two extremes, as are Douglas firs {Pseudotsuga spp.), larches (Larix spp.) and spruces {Picea spp.). In general, the more complex is the specialized resin secretory structure, the more reliant is the conifer species on constitutive defenses (Phillips & Croteau 1999).
Figure 2. Anatomical structure of coniferous trees.
I : cross section
2: radial-longitudinal section 3: tangential-longitudinal section 4: growth ring
5: earlywood 6: latewood 7: earlywood ray 8: fusiform ray
9: longitudinal resin canal 10: transversal resin canal
II : small tangential pits in earlywood 12: thin-walled tracheid with pits
Picture source: http://web gci.ulaval.ca/cours/gci64214/partie9.pdf
10 -
The turpentine fraction contains a range of insect and microbial toxins, such as a-pinene, P- pinene, 3-carene, limonene and other biologically active agents that often act synergistically to discourage insect prédation because of their toxicity and deterrency (Raffa & Berryman 1983).
Turpentine also acts as a solvent for transporting the higher molecular weights diterpenoids (rosin fraction) to the wounded tissue. Upon exposure to the atmosphère, the volatile fraction evaporates, leaving a semi-cristalline mass of resin acids that oxidatively polymerize to form a hardener barrier that seals the wound, often trapping insect invaders and microbial pathogens in the matrix (Gijzen et al. 1993). The évolutive success of the Pinaceae, which are largely distributed throughout the Northern hemisphere, would probably be largely determined by their efficiency in repelling initial invasion of foreign organisms (Trapp & Croteau 2001).
However, and despite the great toxicity of oleoresin', most species of aggressive bark beetles and their associated taxa hâve shown a great ability to resist copions and toxic resin flow or vapours (Byers 1995). The mode of actions and target sites of oleoresin terpenoids are poorly known. Previously reported mechanisms include inhibition of the nervous System of insects (Ryan & Byrne 1988), or may concems inhibition of cytochrome P-450 dépendent monooxygenase (De Oliveira et al. 1997).
Moreover, the volatile monoterpenes constituents of conifer oleoresin serve diverse fonctions in bark beetle Chemical ecology (Raffa & Berryman 1983, Byers 2004); (1) long- and short-range récognition of suitable host, as bark beetles direct towards a species-specific air plume issuing from stressed or wounded trees; (2) feeding stimulation and deterrence, as the final host sélection criteria through gustatory sélection of the bark; (3) plant résistance, as beetle-fungi complexes induce a qualitative and quantitative alteration of the preformed constitutive resin; (4) pheromone/allomone biosynthesis, as many bark beetles synthesize sex and aggregation pheromones from turpentine components of host oleoresin; (5) interspecific interactions, as many predators, parasites and competitors are attracted towards bark beetles attacked trees.
_________________________________________________ General introduction
'Terpenoids are known to aid varions plants’ defence mechanisms against natural enemies. Monoterpenes and oxygenated monoterpenes hâve thus been suggested and tested as fumigants to strike varions insect pests. These incinde honseflies, rice weevils, german cockroaches or mnshrooms sciarids (Shaaya et al. 1997, Lee et al. 2001, Choi et al. 2006). For the mnshroom sciarid for instance, Choi et al. (2006) demonstrated an a-pinene LD50 of 9.85pl/L air afler 24 honrs exposure.
- 11 -
Bark beetles and their associated microorganisms
Bark beetles may attack a variety of host plant material. Some species breed and feed into the phloem (phloephagous species of the subfamily Scolytinae, the true bark beetles). Others bore into the wood and feed primarily on symbiotic ambrosia fungi living in the galleries (xylomycetophagous species of the subfamilies Scolytinae and Platypodinae, the ambrosia beetles). Other scolytines also develop in seeds and fruits (speimophagous species) in twigs and small stems, or in the pétioles of fallen leaves (myelophagous species) (Knizek & Beaver 2004). Overall, many bark beetle species are associated with microorganisms (fungi, yeasts, bacteria and protozoans), borne in specialized anatomical structures called mycangia or on other external, invaginated body parts (Levieux & Cassier 1994, Lewinson et al. 1994, Six &
Paine 1999, Klepzig et al. 2004). Their most common représentatives are known to cause discoloration in the sapwood and are at the origin of important losses to forestry and wood industry worldwide (the blue-stain fungi belonging to the ascomycete généra Ophiostoma and Ceratocystis) (Wegensteiner 2004). The rôle of some of these vectored fungi is clearly mutualistic, as they assist the beetles in the host killing or provide food sources for their brood.
Conversely, the benefits provided to the insect by some other extemally transported pathogenic fungi spores are less clear (Francke-Grossmann 1967, Paine et al. 1997, Klepzig et al. 2001, Kirisits 2004).
The rôle of symbiotic and non-symbiotic microorganisms is also of particular importance in the Chemical ecology of bark beetles. Basidiomycete fungi, yeasts and bacteria were shown to play a rôle in host tree monoterpenes conversion to oxygenated dérivatives, such as a-terpineol, bomeol, myrtenol, pinocamphone, terpinen-4-ol, ?ra«5-pinocarveol, verbenols and verbenone (Brand et al. 1975, Chararas et al. 1980, Busmann & Berger 1994, Van Dyk et al. 1998, Byers 2004). Oxygenated monoterpenes are used as deterrent or antiaggregant to reduce intra and interspecific compétition (Byers 1983, Schlyter et al. 1989, Lindgren & Miller 2002a,b). They may also act as components of aggregation pheromones of many aggressive bark beetle species (Byers 2004, Luxova et al. 2007).
Bark beetle natural enemies
Bark beetles are threatened by a variety of predators, parasites and pathogens. These include birds, spiders, mites, other insects, nematodes, fungi, bacteria and viruses, which hâve a négative impact on the prey population by causing their death or lowering their reproduction.
However, to maintain pest populations at low levels or suppress incipient outbreaks, such
Chapter 1 __________________________________________________________
- 12 -
General introduction
organisms hâve also to attack a number of prey that is in direct relationship to the density of the prey population (Berrymann 1986). Because scolytines population levels are much strongly influenced by the availability of susceptible breeding material, or by processes of pheromone- mediated mass-attacks, this last condition is though rarely met (Wainhouse 2004).
Overall, only parasitoid complexes of some economically important bark beetle species hâve been extensively studied (e.g. Ips typographus, Scolytus spp., Dendroctonus micans), and other records are often restricted to parasitoid-hosts lists and catalogues (performed from general parasitoid collection on bark beetle infested logs, Kenis et al. 2004). Bark beetle associated predators usually hâve a broad range of prey, and most of them prey on occasion on fungal cultures or behave as scavengers. Only a few species are defmitely known to feed on living eggs, larvae, pupae, or adults of bark beetles. Among the most extensively investigated species are Thanasimus spp. (Coleoptera: Cleridae), Rhizophagus spp. (Coleoptera:
Monotomidae), Medetera spp. (Diptera: Dolichopodidaa) and Lonchaea spp. (Diptera:
Lonchaeidae) (Kenis et al. 2004). Some extensive reviews of the natural enemies of conifer- feeding bark beetles in Europe are provided by Herting (1973), Mills (1983) and Kenis et al.
(2004).
1.3. Management tactics in forest ecosystems
During the last décades, an increasing interest for sustainable and environmentally-safe agricultural practices has greatly enhanced scientist’s attention in the development of integrated pest management (IPM) methods. In the particular case of forestry, most IPM attempts are made on manipulating the plant, the natural enemy or the pest populations in such a way that outbreaks are avoided. It primarily relies on good sylvicultural practices such as the choice of appropriate varieties according to settling conditions or mixed stands plantations. On susceptible mature stands, fertilization or thinning may also help to reduce the stress of the trees, and-so 4mprove their defénses againstdnsect attaeks. Other management techmt}ues are^
targeting the pest population dynamics itself, from a direct (use of pesticides or semiochemicals) or more indirect manner (use of natural enemies).
Semiochemicals-based management
Historically, the first unattended use of a semiochemicals-based suppression tactic in forest was performed by European foresters in employing trap trees against bark beetles (Borden
1995). Felled trees volatiles associated with pheromones from the pioneer beetles resulted in a
- 13 -
Chapter 1
semiochemicals-mediated mass attack localized on trap trees, thus diverting bark beetles populations from adjacent standing timber.
More recently, sophisticated identification techniques allowed scientists to identify and reproduce a variety of bark beetle semiochemicals (Appendix I). As a conséquence, synthetic pheromone components are nowadays widely applied in bark-beetle management attempts using trapping apparatus, either for mass-trapping or monitoring purposes (Borden 1995, Byers 2004). Sticky screen or wire traps are cheaper and easily transported, but offer a poor visual/physical stimulus and do not allow an easy removal of captured beetles. Cylinder with holes/barrier types traps are more expensive, heavier and require frequent maintenance, but offer a strong visual/physical stimulus and permit capture of attracted beetle in a separate réceptacle. A good review of the improvement of devices involved in bark beetle trapping is provided by Borden (1993). Other, but promising aspects of semiochemicals application for bark beetle management are the repellent properties of verbenone (Lindgren & Miller 2002a,b, Gillette et al. 2006), or the sélective attraction of natural enemies within attacked settlements (Erbilgin & raffa 2001, Aukema & Raffa 2005).
Biological control
There are basically two types of biological control strategies. Augmentation and conservation methods consist to enhance the effectiveness of natural enemies already présent in the environment and that hâve a significant impact on the population dynamics of pests (Hawkins & Comell 1999), whereas classical biological control relies on the importation and artificial establishment of non-native natural enemies (Wainhouse 2004). In contrast to the more local effects of augmentation, classical biological control is intended to be often self- sustaining over large areas.
In augmentation and conservation programme, one proposed approach to strike forest pests such as bark beetles is to manipulate polyphagous predators movements through sélective semiochemicals application (Aukema & Raffa, 2005). A strong attraction to Dendroctonus sp.
pheromones and plant signais had been shown for some opportunist bark beetle predators such as Temnochila chlorodia (Fettig et al, 2004), Tenebroides collaris (Erbilgin & Raffa, 2001), or Thanasimus sp. (Aukema & Raffa, 2005, Miller et al., 1987). However, the main problem encountered with this technique is to attract the predator alone without its target pest, which is not conceivable when both species respond to the same semiochemicals blends.
Rates of success of classical biocontrol programmes performed in forests are similar to most cropping Systems; only about a quarter of natural enemies’ introductions are successfull.
- 14 -
General introduction
and less than half of them will give some level of control (Waage and Mills 1992). Forest ecosystems may though dérivé greater benefit from programmes that are only partially successful (Wainhouse 2004), as they provide relatively “stable” habitats compared to high value agricultural Systems, and can sustain higher levels of pest damage without significant loss. As a conséquence, and despite their relatively low value per unit area, forests are often assumed to be favorable habitats for classical biological control. In this respect, predators and parasitoids that are species-specific or whose host range is limited are usually regarded as the most suitable candidates. Pathogenic organisms can also be considered, although their application as microbial insecticides is relatively distinct from the use of other natural enemies.
Notable successes hâve been obtained using the bacterium Bacillus thuringiensis (Bt), nucleopolyhedroviruses (NPVs), enthomopathogenic fungi and nematodes (Cane et al. 1995, Wainhouse 2004, Lachance et al. 2007). A detailed review of principles and application in biological control in forest can be found in Dahlsten and Mills (1999).
At ail, relatively few biological control attempts hâve been performed aiming at coleopteran pests, and in particularly as it concerns bark beetles (Mills 1983, Miller et al. 1987, Fig. 3). The invasive bark beetle Ips grandicollis had been targeted in Australia using seven North American natural enemies - two beetle predators and five wasp parasitoids (Berisford &
Dahlsten 1989, Waterhouse & Sands 2001). Only two of the parasitoids hâve become established, but one of them, Roptrocerus xylophagorum, is now widespread and causes up to 70% parasitisation (Samson & Smibert 1986). Partially successful introduction of two African bethylid parastoid wasps has also been performed in Mexico against the coffee borer Hypothenemus hampei (Damon & Valle 2002, Batchelor et al. 2006). In North America, Thanasimus formicarius had been released at least two times to control the Southern pine beetle Dendroctonus frontalis Zimmermann, but no recovery attempts hâve been made (Miller et al. 1987). More recently, promising results hâve been obtained conceming the sélective attraction of polyphagous predator species without their target pests using appropriate semiochemical blends (Erbilgin 8c Raffa 2001, Aukema & Raffa 2005). At last, the successful use of the coleopteran predator Rhizophagus grandis against Dendroctonus micans is, as we know, the only classical biological control programme that has ever been carried out against a bark beetle in Europe. It is also probably the first performed with a monospecific predator to control a forest pest. The case of R. grandis will be largely developed in the last sections of this chapter.
- 15 -
Chapter 1
1.4. The study System: D. micans and R. grandis
OverView of D. micans natural enemies
Although they are relatively well documented, there are relatively few natural enemies associated with the great spruce bark beetle, Dendroctonus micans (Kugelann) (Gaprindashvili et al. 1967, Herting 1973, Grégoire 1987, Sanguignol 1981, Mills 1983, Kenis et al. 2004).
Unlike many aggressive bark beetles colonizing living trees, D. micans does not need to mass- attack and kill its host, and is characterized by the ability of single females to start a new colony on apparently healthy trees (Grégoire 1988).
Figure 3. The use of parasitoids and predators in classical biological control against forest insect pests. Introductions were classified as successful if some degree of control was achieved (Wainhouse 2004, after Dahlsten & Mills 1999).
Among hymenopteran parasitoids, the ectoparasitic ichneumonid Dolichomitus terebrans (Ratzeburg) is the most common D. micans associate (Brichet & Severin 1902, Francke- Grossmann & Ruhm 1954). The impact of the parasitoid on D. micans was recognized at the beginning of the 20th century, as belgian foresters were asked to collect and conserve D.
-
16 -
General introduction
terebrans pupae till emergence, for further releases in D. micans attacked spruce stands (Brichet & Severin 1902). However, this monovoltine species is more often found associated to Pissodes sp. (Curculionidae), and its ovipositor cannot traverse the thickest spruce barks (Bevan & King 1983, Grégoire 1988). With regards to D. micans, ovipositor length seems to be the limiting factor for most hymenopterans, such as the braconid Dendroster middendorfi Ratzeburg or the peromalid Rhopalicus tutela (Walker).
Beside parasitoids, many polyphagous predatory insects hâve also been described as D.
micans associâtes, within orders Diptera (e.g. in families Dolichopodidae, Lonchaeidae Muscidae, Phoridae Sciaridae, Stratiomyidae, Syrphidae) and Coleoptera (e.g. in families Carabidae, Cleridae, Histeridae, Monotomidae, Nitidulidae, Staphylinidae, Tenebrionidae).
Although they usually behave as secondary pests, other bark beetles such as Ips typographus (Linné) and Pityogenes chalcographus (Linné) are also potential competitors for D. micans.At last, some phoretic and parasitic mites and nematodes, as well as entomopathogenic fungi, are possibily detrimental to D. micans eggs and larvae in the laboratory (Baisier 1990).
R. grandis, monospecific predator of D. micans
Of ail organisms susceptible to significantly regulate D. micans populations, the monospecific predator Rhizophagus grandis Gyllenhal (Coleoptera: Monotomidae) is considered, by far, as the most efficient (Bergmiller 1903, Francke-Grossmann & Ruhm 1954, Grégoire 1988). The genus Rhizophagus Herbst encompasses 14 species in Europe, most of which live under the bark of conifers or broadleaves and are supposedly at least partiy predacious, mycetophagous or saprophagous (Weber 1902, Vogt 1966, Bouget & Moncoutier 2003). Rhizophagus grandis, on the contrary, feeds exclusively within Dendroctonus micans brood galleries, where it efficiently devours eggs, larvae, pupae and callow adults of the prey (Weber 1902, Vogt 1966).
The close association between R. grandis and D. micans has first been described in Germany at the beginning of the 20* century, (Weber 1902, Bergmiller 1903). Foremost studies were mainly considered from a taxonomie and faunistic point of view (Mequignon 1909, Horion 1960), but a new lease of interest arouse when the beetle was for the first time used in the Georgian SSR as a biocontrol agent against D. micans (Tvaradze 1977). Most recent studies emphasized the rôle of semiochemicals in R. grandis strict specificity, a rare feature among predatory insects. First, adults use spécifie long- and short-range attractants to locate their prey. Grégoire et al. (1992b) and Wyatt et al. (1993) showed from flight windtunnel experiments that R. grandis orientation and landing behaviour dépend on the simultaneous perception of the prey-host-tree visual, physical and Chemical eues. Some of
- 17 -
these attractive compounds were identified from frass analysis as a mixture of simple oxygenated monoterpenes (Grégoire et al. 1991, Grégoire et al. 1992a,b). Frass-issuing volatiles are also involved in R. grandis short-range orientation to locate D. micans entrance hole on the tree surface, as well as in prey récognition within the brood gallery (Merlin et al.
1984). Secondly, Chemicals play also an active rôle in R. grandis oviposition régulation.
Stimuli were shown in D. micans frass (Grégoire et al. 1991, Grégoire et al. 1992b, Baisier 1990), while still unclearly identified inhibitors are supposedly présent in feces, ecdysis or due to glandular sécrétions of R. grandis larvae (Baisier 1990). This interplay between stimuli and inhibitors détermine, inter alia, an optimal density of predator larvae into the bark beetle gallery, thus preventing extreme cases of intra-specific compétition (Baisier 1990). At the end of their development, mature larvae become photopositive, leave the brood chambers and pupate in the ground or at the stem base of the tree (Grégoire 1988).
Such chemically-mediated specificity mechanisms, associated to an uncommon résistance to the host tree monoterpenes (Everaerts et al. 1988), allow R. grandis to occupy a relatively preserved ecological niche. In Belgium, and even though D. micans is there quite sparse, about 90% of the prey’s mature brood chambers (i.e. Systems containing at least some fourth instar larvae) are successfully colonized by R. grandis (Grégoire 1984).
R. grandis releases in biocontrol programmes
Supposedly native to Siberia (Schedl 1932), D. micans had been increasing its range through Western Europe during the 20*^ Century, most of the time followed by R. grandis. In some areas, however, spruce habitat heterogeneity induces a faster géographie expansion of the pest compared to its predator. It results in a temporal gap between the bark beetle arrivai and the subséquent predator establishment. Outbreak situation may therefore last for many years, offering D. micans a sufficient time window to kill a significant amount of trees. In such situations, R. grandis artificial releases are required to shorten the uncertain delay between pest and predator arrivai.
Récognition of the value of R. grandis as a potential biological control agent for Dendroctonus micans came during the early 1960s when the first releases of laboratory-bred beetles were performed in the Georgian SSR from Tchecoslovaquian strings (Kobakhidze et al.
1970, Table 1). Accidentally introduced in the région during the 1950’s, the pest was there occasioning large outbreaks on 130 000 ha of Picea orientalis. By 1970, 54 000 predators had been released from a production performed on previously infested logs (Tvaradze 1977). After about 15 years, the pest level in the area was stabilized well below the économie threshold to
Chapter 1 __________________________________________________________
- 18 -
General introduction
about 2-3% attacked tree. From Georgia, D. micans recently extended its range to Turkey, where a biocontrol programme bas also been implemented (Yüksel 1996). In France, D. micans regularly progressed from the end of the 19*’’ century, but was not followed by its predator in ail areas (Grégoire et al. 1985, Van averbeke & Grégoire 1995, article 1). First biocontrol attempts were performed with success in 1978 in the Massif Central, although low amounts of beetles had been released. The programme developed on a much larger scale from 1983.
During the 1983-1999 period, a Belgian-French coopération contributed to the production and release of 530 000 insects (Kenis et al 2004). Predator establishment was also investigated in a sériés of permanent plots and in some temporary surveys. It showed the predator establishment in 75% of the bark beetle galleries within 3-4 years after releases (Grégoire et al. 1989, Van averbeke & Grégoire 1994, Gilbert & Grégoire 2003).
In France, the First release criteria (500-1000 pairs/site) were asset to ascertain the efficiency of the technique. They were then lowered to allow the treatment of larger surfaces located on the borders of the infested areas (10-50 pairs/site) (Grégoire 2001, Dupin de Saint- Cyr Personal communication). Rearing techniques were also improved, with the use an artificial diet and oviposition stimulants (Dekerck 1980, Baisier et al. 1988, Grégoire et al.
1992a). In the présent days, the Université Libre de Bruxelles (ULB) is still involved in cooperative biocontrol projects with the French forest managers operating at the Office National des Forêts (ONF), the Centre Régional de la Propriété Forestière (CRPF) and the Département Santé des Forêts (DSF). In this context, the main activities provided by ULB include R. grandis production, assistance in field releases, as well as the development of kairomone-based monitoring programmes (article I).
In the United Kingdom, D. micans was First discovered in 1982, in the north-west of England and in Wales (Bevan & King 1983). A rearing and release programme was started-up by the Forestry Commission one year later, combined with a reinforcement of internai quarantine procedures and the establishment of a pest-free zone around the mfested areas (Fielding et al. 1991a, Evans & Fielding 1994, Fielding & Evans 1997). Between 1984 and 1995, 156 400 insects were produced from Belgian strains and released in the British public and private forests (10-50 pairs/site) (Kenis et al. 2004). The successfui predator establishment was observed in 34% of the pest brood Systems after two years, a proportion that rose to 68%
of the galleries after 3 years and 88% after 4 years (Fielding & Evans 1997). As D. micans is still extending its range in Great-Britain, the biocontrol programme is still continuing.
- 19 -
Chapter 1
More recently, R. grandis has been applied in a neo-classical biological programme against the red turpentine beetle Dendroctonus valens LeConte, which invaded China from North America in the late 1990’s. First laboratory suitability assessments, as well as part of First field introduction trials, are reported in the third chapter of this thesis.
Table 1. The overall framework for the implémentation of classical biocontrol, application to R. grandis use against D. micans (adapted from Wainhouse 2004).
Activit)’ Key information and sélection criteria
Pest Taxonomie identity Dendroctonus micans (Kugelann)
évaluation Likely area of origin Siberia
Ecology in origin area Primary pest of spruce
Natural enemies in origin area Some unspecific predators and parasitoids One monospecific predator, R. grandis
Area of invasion Western Europe. Turkey
Ecology in target area Primary pest of spruce
Natural enemies in target area Few unspecific predators and parasitoids R. grandis usually follows after 6-10 years Biocontrol Taxonomie identity Rhizophagus grandis Gyllenhal
agent Degree of specialization Monospecific
Impact on pest in origin area Important, more than 90% of colonized broods
Past releases Successful in Georgia, Turkey, France and UK
Searching efficiency High, kairomones-mediated prey location during flight (adults), after landing (adults) and in brood chambers (adults and larvae)
Seasonal synchrony High, R. grandis fly from march to novermber Numerical response Reproductive (at the prey gallery level)
Aggregative (at the stand level)
Functional response At low density of prey, then reach a plateau Development time Relatively short compared to the one of the prey Rearing Methodology Initiated on spécifie prey, then alternative prey
Synthetic oviposition stimuli available
Main difficulties Beauveria bassiana Balsamo
Adverse effects from other fiingi. nematods and mites Release Release procedure At the stem of attacked trees (10-50 adult pairs /ha)
Genetic variation Never tested. supposedly not problematic (continuons distribution with endemic area) Evaluation, Pest population monitoring Visual surveys, (baited traps)
monitoring Natural enemy monitoring Visual surveys, baited traps Natural enemy establishment AIways observed after release
Impact on pest Significant réduction 6-10 years after releases Impact on non-target organisms R. grandis never observed out of D. micans galleries
- 20 -
General introduction
1.5. Aim of the thesis
The main goal of this thesis is a better understanding of the various mechanisms playing a rôle in the response of R. grandis to its spécifie prey D. micans. This study is multidisciplinary in the sense that it includes interrelated aspects in both behavioural and Chemical ecology.
Furthermore, these two aspects strongly influence the population dynamics of both the predator and its barkbeetle prey, which may hâve numerous wider implications in the scope of biological control.
The problematic rose by the progression of D. micans in Europe, and more especially in France, is reviewed in the current chapter (article I). The biological particularities of the beetle are described, as well as the question of its population dynamics and its régulation by R. grandis.
Moreover, recommendations are made conceming the most appropriate striking method with a spécial discussion on the use of R. grandis in biocontrol programmes. The second chapter reviews the principles of the biological control of D. micans using the predator R. grandis. It more particularly reports on the importance of an early assessment of the pest, and on the first application of kairomone traps for R. grandis détection (article II). The opportunity to use R.
grandis as a biocontrol agent for other Dendroctonus species, such as the invasive species D.
valens (manuscript I), is discussed in the third chapter. The functional response of R. grandis, and more especially the way the density of prey and other environmental conditions influence the predator’s fitness, are discussed in the fourth chapter (manuscript II). At last, the chapter five (manuscript III) concems the R. grandis’ numerical response, and in particular the way semiochemicals released in the bark beetle brood System affect the predator oviposition process.
- 21 -
ARTICLE I /
1 *2
Hubert Pauly , Nicolas Meurisse
Le dendroctone de l’épicéa en France ; situation et mesures de lutte en cours
In press in Revue forestière française (to be published in February 2008, volume 6-2007)
Résumé
Ravageur des épicéas, le dendroctone est arrivé dans le nord-est de la France à la fin du dix- neuvième siècle. La progression inexorable de son aire de répartition l’a amené à coloniser progressivement la quasi-totalité des pessières françaises. Pourvu d’une résistance exceptionnelle aux défenses constitutives de l’épicéa, le dendroctone est une des rares espèces de scolytes capable de s’attaquer à des arbres parfaitement sains. Ces dégâts sont particulièrement importants dans les zones situées en limites de distribution du dendroctone, où celui-ci y s’installe le plus souvent sans être accompagné par son prédateur spécifique, Rhizophagus grandis. Après cette phase de pullulation, qui peut durer plusieurs années, le ravageur est généralement rejoint par le prédateur, et ces niveaux de population rapidement ramenés à un état endémique. Les dégâts occasionnés aux peuplements deviennent alors presque imperceptibles. Espèce au fonctionnement biologique original, le dendroctone a fait l’objet de programmes de recherche spécifiques qui ont conduit à la mise au point d’une méthode de lutte biologique inédite dans le secteur forestier. Afin de réduire au minimum le délai entre l’arrivée du dendroctone et celle de son prédateur, des lâchers artificiels de R.
grandis sont réalisés en France depuis une vingtaine d’années. De même, des techniques prometteuses de suivi de la progression géographique de l’espèce et de son prédateur sont en cours d’élaboration.
' Département Santé des Forêts, Echelon du Sud-Ouest. 50 Chemin d'Artigues, F-33150 Cenon.
^ Laboratoire de Lutte biologique et Ecologie spatiale. CP 160-12 Université Libre de Bruxelles. 50 Avenue F.D.
Roosevelt, B-1050 Bruxelles.
- 23 -
Chapter 1
Introduction
Dendroctonus micans Kugelann, également appelé dendroctone ou hylésine géant de l’épicéa, est le plus grand des scolytes européens (Figure 1). Cette espèce, quasi exclusivement inféodée au genre Picea, est vraisemblablement originaire de l’est sibérien. Son arrivée en Europe est renseignée par les naturalistes depuis la fin du dix-huitième siècle (Grégoire, 1988).
Actuellement, le dendroctone est toujours en progression dans l’Ouest de l’Europe, en France, en Angleterre et au Pays de Galles (Fielding et Evans, 1997); de même que dans certaines régions à l’Est de la Mer Noire, comme en Turquie (Akinci et al.
2003) (Figure 2). En France, le front de colonisation du ravageur traverse le pays depuis la Basse-Normandie et le Pays de Loire jusqu’au sud-ouest du Massif central.
Dans ses zones d’origine, les populations de dendroctone sont essentiellement régulées par la présence d’un petit coléoptère prédateur de la famille des Monotomidae, Rhizophagus grandis Gyllenhal. Ce dernier est en revanche absent dans les zones récemment colonisées par D. micans, où des proliférations importantes du scolyte sont régulièrement observées. Pour cette raison, des introductions artificielles de prédateurs sont effectués lors de programmes de lutte biologique, réalisés notamment en France et au Royaume-Uni (Fielding & Evans, 1997 ; Grégoire, 2001). Ces lâchers sont totalement inoffensifs pour la biodiversité locale du fait de la spécificité de R. grandis (Bergmiller, 1903 ; Grégoire et al, 1989).
Ils constituent actuellement le moyen de lutte le plus efficace, tant sur le plan économique que de l’efficacité technique, pour enrayer la prolifération du dendroctone.
Cet article propose de réaliser la synthèse actuelle de la problématique du dendroctone en France. 11 y sera tout d’abord fait état de la progression récente du ravageur dans les forêts françaises. Nous y discuterons ensuite de la dynamique des populations du dendroctone, de l’influence
de différents facteurs sur les dégâts occasionnés aux peuplements, mais également de certaines particularités biologiques de l’insecte. Nous aborderons également les différentes méthodes de contrôle et de lutte préconisées contre ce ravageur. La lutte biologique à l’aide de R.
grandis sera plus particulièrement détaillée.
Nous nous attarderons enfin sur les nouvelles possibilités de surveillance en pessière offertes par la technique des pièges à kairomones.
Figure 1. Le dendroctone de l’épicéa, anciennement hylésine géant (Grégoire J.-C., Université Libre de Bruxelles).
Distribution géographique
Arrivé dans le Nord-Est de la France à la fin du dix-neuvième siècle (Carie et ai, 1979), le dendroctone s’est dans un premier temps propagé naturellement dans les pessières autochtones les plus proches (Vosges, Jura, Alpes). Dès 1959, la présence du ravageur a été constatée dans le Morvan (Carie et al, 1979), région d’où il a pu progresser pour envahir graduellement la majorité des pessières du Massif Central (Figure 3). Les importants travaux d’enrésinement effectués à travers le pays après la dernière guerre mondiale ont ensuite favorisé l’extension de son aire de distribution. Dès 1972, d’importantes attaques sont recensées en Haute-Loire et en Lozère (Carie et al, 1979). Plus à l’ouest, le Limousin est également atteint en 1977 et de fortes infestations y sont signalées à partir de 1986 (Lemperière, 1994). L’insecte progresse tout aussi rapidement vers le sud-est, le sud des
- 24 -
A.I. Le dendroctone de l'épicéa en France
Cévennes est colonisé en 1984 (Lemperière, 1994). La progression du dendroctone vers le Sud-ouest est plus régulière : en 2001 il atteint le sud de l’Aveyron et le Tarn, en 2003 la frange ouest de l’Hérault. Plus anecdotique, l’apparition du ravageur dans les Pyrénées (Ariège) en 1989, est certainement la conséquence de transports de bois contaminés.
Une progression similaire du scolyte est également observée dans le Nord-ouest de la France avec l’arrivée de l’insecte en
Haute-Normandie via la Picardie, elle- même probablement atteinte de proche en proche par les populations venant de Belgique. La Basse-Normandie est à son tour colonisée (exception faite de la Manche), et en 2005 le dendroctone fait son apparition dans la Sarthe. Les départements du centre de la France, pourvus de boisements épars d’épicéas, semblent faire l’objet d’une colonisation plus aléatoire.
L’éloignement des peuplements les uns des autres rend la progression du ravageur moins systématique.
1^51 («il? art«
11
m
Figure 2. Aire de répartition de D. micans(Organisation Européenne et Méditerranéenne pour la Protection des Plantes, 2006).
Depuis cette introduction, l’insecte s’est légèrement propagé vers l’ouest. Un échange commercial de bois soutenu entre la Normandie et la Bretagne semble également responsable de la récente arrivée du dendroctone dans le Finistère (observation réalisée en 2004 par un
propriétaire forestier et confirmée en 2006 par le Département de la santé des forêts).
En 2007, parmi les régions et départements relativement boisés en épicéa, seuls les suivants sont indemnes de ce scolyte : le centre de la Bretagne, la Manche et l’ouest du piémont pyrénéen.
- 25 -
Figure 3. Progression du dendroctone dans les pessières françaises. Dates de premières observations du ravageur et voies de colonisation hypothétiques. En arrière-fond, l’intensité de la coloration traduit la densité des boisements en épicéa.
Dynamique des populations
L’importance des attaques du dendroctone est principalement liée à la taille de ses populations, elle-même dépendante de l’ancienneté de la colonisation du site par le ravageur. En effet, si les populations invasives de D. micans croissent dans un premier temps de façon importante, elles sont généralement rejointes puis régulées après un certain nombre d’années par R.
grandis. Ce dernier, considéré comme le principal agent de contrôle naturel des populations du dendroctone, en est un prédateur exclusif. Les larves et les adultes de K grandis (Figure 4) se nourrissent essentiellement des œufs et des stades immatures (Baisier, 1990). Aussi, la présence de R. grandis dans un peuplement donné est-elle strictement inféodée à celle de D. micans. Si cette spécificité se traduit chez ce prédateur par une remarquable capacité de localisation des galeries du dendroctone à courte distance (Meurisse et al, sous presse), sa capacité de
dissémination à plus longue distance n’a en revanche jamais été mise en évidence.
Ainsi, la fragmentation de l’habitat peut engendrer une discontinuité temporelle entre l’arrivée du scolyte et celle de son prédateur, donnant lieu à une expansion de l’aire de présence du dendroctone parfois bien plus rapide que celle de R. grandis.
Cette situation engendre des dégâts importants sur les zones où le ravageur est invasif et peut perdurer pendant une dizaine d’années, laps de temps parfois nécessaire au prédateur pour rejoindre sa proie. Dans certaines régions séparées de l'aire d'extension principale par une barrière géographique, comme au Royaume-Uni, cette jonction peut également ne jamais se produire, nécessitant l’introduction artificielle du prédateur (Fielding et al.
1997).
De tels cas de dynamique explosive des populations, avec de fortes conséquences pour les peuplements d’épicéas, jalonnent l’histoire de cet insecte au cours de
