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TRANSMISSION OF THE PITCH CANKER FUNGUS, FUSARIUM SUBGLUTINANS F. SP. PINI, TO MONTEREY PINE, PINUS RADIATA, BY CONE- AND TWIG-INFESTING BEETLES

Published online by Cambridge University Press:  31 May 2012

Kelli Hoover ,
David L. Wood ,
Andrew J. Storer ,
Joseph W. Fox  and
William E. Bros
Kelli Hoover
Affiliation:
Department of Entomology, University of California, Davis, California, USA 95616
David L. Wood*
Affiliation:
Division of Insect Biology, University of California, Berkeley, California, USA 94720
Andrew J. Storer
Affiliation:
Division of Insect Biology, University of California, Berkeley, California, USA 94720
Joseph W. Fox
Affiliation:
Division of Insect Biology, University of California, Berkeley, California, USA 94720
William E. Bros
Affiliation:
Department of Biological Sciences, San Jose State University, San Jose, California, USA 95192
*
1 Address for reprint requests.
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Abstract

Conophthorus radiatae Hopkins, Ernobius punctulatus Fall, and Pityophthorus spp. infest cones and twigs of Monterey pines (Pinus radiata D. Don) and thus may be important vectors of the pitch canker fungus Fusarium subglutinans f. sp. pini in the central coast of California. Fifteen percent of 1st-year Monterey pine conelets infested with C. radiatae prior to August 1990 developed pitch canker by May 1991. Conophthorus radiatae, E. punctulatus, and Pityophthorus spp. were dissected from some of these conelets and found carrying F. s. pini. Between June 1990 and May 1991, 16% of 695 randomly selected uninfested 1st-year conelets from a total of 329 separate cone whorls were infested by at least one of the above beetle species, and F. s. pini was isolated from 42% of the attacked conelets. Average percentage contamination of beetles per conelet was highest for adults of Pityophthorus spp. (38%), followed by adults of C. radiatae (33%), larvae of E. punctulatus (24%), and larvae of Pityophthorus spp. (5%). There were significant associations between conelets that contained contaminated C. radiatae, Pityophthorus spp., and/or E. punctulatus and conelets with F. s. pini.

Under experimental conditions, C. radiatae and E. punctulatus transmitted the fungus to healthy cones. Ernobius punctulatus required an entrance tunnel by C. radiatae to enter and infect the cone. Artificially wounded cones did not develop pitch canker. Intra- and interspecific transmission of F. s. pini was demonstrated among these beetle species. In infested branch tips without cones, interspecific transmission of F. s. pini between E. punctulatus and Pityophthorus spp. was also demonstrated.

The roles of C. radiatae and E. punctulatus as vectors of F. s. pini and of Pityophthorus spp. as potential vectors are discussed in relation to the epidemiology of pitch canker disease. The spread of pitch canker to California’s native pines as well as other conifers may be enhanced by interspecific transmission of F. s. pini between E. punctulatus and C. radiatae in cones and between E. punctulatus and Pityophthorus spp. in branch tips. Ernobius punctulatus provides a pathway for the fungus to potential insect vectors that attack several hosts and a variety of plant parts.

Résumé

Conophthorus radiatae Hopkins, Ernobius punctulatus Fall, et Pityophthorus spp. infestent les cônes et les rameaux du pin de Monterey (Pinus radiata D. Don) au centre de la côte californienne et peuvent donc être d’importants vecteurs de la nécrose causée par Fusarium subglutinans f. sp. pini. Quinze pour-cent des cônes de première année infestés par C. radiatae avant août 1990 étaient porteurs de la maladie en mai 1991. Des coléoptères, C. radiatae, E. punctulatus, et Pityophthorus spp., prélevés dans certains de ces jeunes cônes étaient porteurs du champignon. Entre juin 1990 et mai 1991, 16% de 695 jeunes cônes sains de première année choisis au hasard parmi 329 groupes de cônes ont été infestés par au moins une des espèces de coléoptères et la maladie a été décelée chez 42% des jeunes cônes attaqués. Ce sont les adults de Pityophthorus spp. qui causent le pourcentage moyen de contamination par jeune cône le plus élevé (38%), suivis des adults de C. radiatae (33%), puis des larves d’E. punctulatus (24%), et des larves de Pityophthorus spp. (5%). Des relations significatives ont été constatées entre la fréquence des jeunes cônes infestés par des C. radiatae, Pityophthorus spp., et (ou) E. punctulatus et la fréquence des jeunes cônes porteurs de la maladie.

Dans des conditions expérimentales, C. radiatae et E. punctulatus ont réussi à propager le champignon à des cônes sains. Ernobius punctulatus nécessite l’existence d’un tunnel creusé par C. radiatae pour pénétrer à l’intérieur du cône et l’infecter. Des cônes ont été meurtris artificiellement et ils n’ont pas été affectés par la maladie. Les coléoptères se transmettent le vecteur de maladie entre individus d’une même espèce et d’une espèce à l’autre. La propagation interspécifique de F. s. pini entre E. punctulatus et Pityophthorus spp. a été observée aux extrémités de rameaux sans cônes infectés.

Le rôle de C. radiatae et E. punctulatus comme vecteurs de F. s. pini et des espèces de Pityophthorus comme vecteurs potentiels de la maladie est examiné en fonction de ce que l’on connaît de l’épidémiologie de la nécrose. La propagation de la maladie aux pins californiens indigènes de même qu’à d’autres conifères peut être facilitée par la transmission interspécifique du vecteur entre E. punctulatus et Pityophthorus spp. aux extrémités des rameaux. Ernobius punctulatus constitue une voie de transmission du champignon à des insectes vecteurs potentiels qui s’attaquent à une variété d’hôtes et à diverses parties de plantes.

[Traduit par la Rédaction]

Type
Articles
Information
The Canadian Entomologist , Volume 128 , Issue 6 , December 1996 , pp. 981 - 994
Copyright
Copyright © Entomological Society of Canada 1996

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