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ASSOCIATION BETWEEN A NATIVE SPITTLEBUG (HOMOPTERA: CERCOPIDAE) ON MONTEREY PINE AND AN INTRODUCED TREE PATHOGEN WHICH CAUSES PITCH CANKER DISEASE

Published online by Cambridge University Press:  31 May 2012

Andrew J. Storer*
Affiliation:
Division of Insect Biology, University of California, Berkeley, California, USA 94720
David L. Wood
Affiliation:
Division of Insect Biology, University of California, Berkeley, California, USA 94720
Karen R. Wikler
Affiliation:
Department of Plant Pathology, University of California, Davis, California, USA 95616
Thomas R. Gordon
Affiliation:
Department of Plant Pathology, University of California, Davis, California, USA 95616
*
1Author to whom reprint requests should be addressed.

Abstract

Juvenile Monterey pines, Pinus radiata D. Don (Pinaceae), in a native stand on the Monterey Peninsula, California, exhibited wilted green shoots in the spring of 1996. The pitch canker fungus, Fusarium subglutinans (Wollenweb. & Reinking) P.E. Nelson, Toussoun & Marasas f.sp. pini, was subsequently isolated from 95% of these shoots. Spittle masses produced by Aphrophora canadensis Walley were observed on the symptomless shoots of many of these trees. The pitch canker fungus was isolated from the feeding sites of this insect on 55% of symptomless shoots, and from shoot sections adjacent to these feeding sites on 29% of the shoots. Shoots with spittlebugs feeding on them in May 1996 were more likely to develop pitch canker disease by September 1996 and March 1997 than shoots without spittlebugs. Shoots with spittle masses in March 1997 were as likely to develop pitch canker disease by May and August 1997 as shoots without spittle masses, but the origin of the infection was most likely where A. canadensis feeding had taken place. In a controlled test, the incidence of pitch canker on shoots of potted Monterey pines was dependent on the presence of a spittlebug and a spore suspension of the pathogen. Thus, both field observations and controlled studies show an association between native A. canadensis and the introduced pitch canker pathogen. The role of A. canadensis in the epidemiology of pitch canker disease remains to be determined.

Résumé

Au printemps de 1996, les nouvelles pousses de jeunes pins de Monterey, Pinus radiata D. Don (Pinaceae) d’une forêt indigène de la péninsule de Monterey, Californie, montraient des signes de flétrissure. Le champignon Fusarium subglutinans (Wollenweb. et Reinking) P.E. Nelson, Toussoun et Marasas f.sp. pini, qui cause le chancre fusarien du pin, a par la suite été isolé dans 95% de ces pousses. Des masses de sécrétions produites par Aphrophora canadensis Walley ont été observées sur les pousses saines de plusieurs des arbres malades. Le champignon a été isolé aux sites d’alimentation du cercope sur 55% des pousses saines et dans les sections des pousses adjacentes aux sites d’alimentation sur 29% des pousses. Les pousses porteuses de cercopes en mai 1996 se sont avérées plus susceptibles d’être affectées par la maladie en septembre 1996 et mars 1997 que les pousses sans cercopes. Les pousses portant des masses de sécrétions en mars 1997 sont devenues aussi susceptibles de porter la maladie en mai et août 1997 que les pousses sans sécrétions en mars 1997, mais l’infection a sans doute commencé aux endroits où des cercopes s’étaient nourris. Dans une expérience en conditions contrôlées, l’incidence du champignon sur les pousses de pins de Monterey en pots s’est avérée fonction de la présence d’un cercope et de la présence d’une suspension de spores du pathogène. Les observations en nature et les expériences en laboratoire mettent donc en lumière une association entre le cercope indigène A. canadensis et le pathogène introduit responsable du chancre fusarien du pin. Le rôle d’A. canadensis dans l’épidemiologie du chancre fusarien du pin reste à déterminer.

[Traduit par la Rédaction]

Type
Articles
Copyright
Copyright © Entomological Society of Canada 1998

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