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The role of Pityophthorus spp. as vectors of pitch canker affecting Pinus radiata

Published online by Cambridge University Press:  02 April 2012

Joyce M. Sakamoto ,
Thomas R. Gordon ,
Andrew J. Storer  and
David L. Wood
Joyce M. Sakamoto*
Affiliation:
Department of Plant Pathology, University of California, Davis, California 95616, United States of America
Thomas R. Gordon
Affiliation:
Department of Plant Pathology, University of California, Davis, California 95616, United States of America
Andrew J. Storer
Affiliation:
School of Forest Resources and Environmental Science, Michigan Technological University, Houghton, Michigan 49931, United States of America
David L. Wood
Affiliation:
Division of Insect Biology, University of California, Berkeley, California 94720, United States of America
*
2 Corresponding author (e-mail: [email protected]).
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Abstract

The fungus Fusarium circinatum Nirenberg and O’Donnell (Hypocreaceae) causes pitch canker, a disease affecting pines worldwide. In California, many native insect species have been implicated in transmission of F. circinatum. This study showed that two twig beetle species, Pityophthorus setosus Blackman and Pityophthorus carmeli Swaine (Coleoptera: Curculionidae: Corthylini), can make wounds on healthy Monterey pine (Pinus radiata D. Don (Pinaceae)) branches that are suitable for infection by the pitch canker pathogen. Because these two species are not known to engage in maturation feeding and the observed wounds were not associated with tunneling, we hypothesize that the wounds reflect “exploratory tasting” to assess the suitability of the substrate for colonization. This behavior would help to explain how twig beetles can serve as wounding agents on healthy host branches, which are not amenable to colonization by these insects. We tested two specific hypotheses: (1) two native species of Pityophthorus can create wounds on F. circinatum-contaminated trees that are sufficient for development of disease; and (2) the efficiency with which F. circinatum infects beetle wounds is affected by relative humidity. Under growth-chamber conditions, both Pityophthorus species indulged in exploratory behavior that caused wounds suitable for development of pitch canker. Field experiments did not confirm a significant effect of beetle activity on infection frequency, perhaps because of an overall low infection rate due to low temperatures. Experiments conducted under controlled conditions documented a significant effect of relative humidity on the success rate of twig beetle-initiated infections.

Résumé

Le champignon Fusarium circinatum Nirenberg et O’Donnell (Hypocreaceae) est responsable du chancre poisseux, une maladie qui affecte les pins à l’échelle planétaire. En Californie, plusieurs espèces d’insectes indigènes ont été reliées à la transmission de F. circinatum. Notre étude montre que deux scolytes des brindilles, Pityophthorus setosus Blackman et Pityophthorus carmeli Swaine (Coleoptera: Curculionidae: Corthylini), peuvent causer sur les branches de pins de Monterey (Pinus radiata D. Don (Pinaceae)) saines des blessures propres à permettre l’infection par le pathogène du chancre poisseux. Parce que ces deux espèces ne sont pas connues pour faire de l’alimentation de maturation et que les blessures observées ne sont pas associées à des galeries, notre hypothèse veut que ces blessures représentent des évaluations gustatives exploratoires de la convenance du substrat pour la colonisation. Ce comportement permettrait d’expliquer comment les scolytes des brindilles peuvent servir d’agents vulnérants sur les branches saines de l’hôte qui ne sont pas convenables pour la colonisation par ces insectes. Nous testons deux hypothèses spécifiques: (1) les deux espèces indigènes de Pityophthorus peuvent causer sur des arbres contaminés par F. circinatum des blessures suffisantes pour le développement de la maladie et (2) l’efficacité de l’infection à F. circinatum reliée aux blessures faites par les coléoptères est affectée par l’humidité relative. Dans des conditions de chambre de croissance, les deux espèces de Pityophthorus ont un comportement exploratoire qui cause des blessures suffisantes pour le développement du chancre poisseux. Des expériences de terrain ne confirment cependant pas l’existence d’un effet significatif de l’activité des coléoptères sur la fréquence des infections, peut-être à cause d’un taux global d’infection bas dû aux basses températures. Des expériences menées en conditions contrôlées indiquent un effet significatif de l’humidité relative sur le taux de succès des infections reliées aux scolytes des brindilles.

[Traduit par la Rédaction]

Type
Articles
Information
The Canadian Entomologist , Volume 139 , Issue 6 , December 2007 , pp. 864 - 871
Copyright
Copyright © Entomological Society of Canada 2007

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