Fungal flora associated with Ips typographus: frequency, virulence, and ability to stimulate the host defence reaction in relation to insect population levels.

IPS typographus; BARK beetles; INSECTS; ARTHROPODA; FUNGI

This study was aimed at determining the composition of Ips typographus L. (Coleoptera: Scolytidae) associated fungal flora in France, its virulence, and its ability to stimulate host defence reactions. The relationship between these parameters and the beetle population levels was also considered. The study was conducted in 2001, 2002, and 2003 in Norway spruce (Picea abies (L.) Karst.) stands, with different bark beetle damage levels. In each stand, the frequency of association between fungi and I. typographus was determined. The virulence of the most frequent species was assessed through mass inoculations on living spruce trees. The ability to stimulate the host defence reactions was estimated with low-density inoculations. The most frequent species, Ophiostoma bicolor Davids. & Wells, Ophiostoma piceaperdum Rumbold, and Ophiostoma tetropii Mathiesen, were all pathogenic. Ophiostoma piceaperdum also induced intense defence reaction zones, suggesting that it could play a role in I. typographus population establishment on living trees. However, significant correlations between fungal frequencies and damage of the current year were observed only with O. tetropii or O. bicolor, and no relationships between damage of the previous year and fungal frequencies were found. The effects of some fungal species on beetle population dynamics was suggested, but selection of species during epidemic condition was not confirmed. [ABSTRACT FROM AUTHOR]

La composition de la flore fongique associée à Ips typographus L. (Coleoptera : Scolytidae), sa virulence et son aptitude à stimuler les défenses de l'hôte, ainsi que les relations entre ces paramètres et les niveaux de population de l'insecte, ont été étudiés en France. L'étude a été menée en 2001, 2002 et 2003 dans des peuplements d'épicéa (Picea abies (L.) Karst.) où les niveaux de dégâts dus aux insectes différaient. Les fréquences d'association entre les champignons et I. typographus y ont été estimées. La virulence des espèces majoritaires a été évaluée avec des inoculations massives sur des arbres vivants et leur aptitude à stimuler les réactions de défense, avec des inoculations ponctuelles. Les espèces majoritaires, Ophiostoma piceaperdum Rumbold, Ophiostoma bicolor Davids. & Wells et Ophiostoma tetropii Mathiesen, se sont toutes révélées pathogènes. Ophiostoma piceaperdum a aussi induit des réactions de défense importantes et pourrait ainsi participer à l'établissement des insectes sur les arbres vivants. Néanmoins, seules les fréquences d'O. tetropii et O. bicolor ont été corrélées avec les dommages de l'année en cours et aucune relation n'a été observée entre les fréquences d'association et les dommages antérieurs. Nos résultats suggèrent l'implication d'espèces fongiques dans la dynamique des populations d'insectes mais ne confirment pas la sélection d'espèces au cours d'une épidémie. [ABSTRACT FROM AUTHOR]

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