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EFFECTIVENESS OF GALL INDUCERS IN WEED BIOLOGICAL CONTROL1

Published online by Cambridge University Press:  31 May 2012

P. Harris  and
J.D. Shorthouse
P. Harris*
Affiliation:
Research Centre, Agriculture and Agri-Food Canada, PO Box 3000, Lethbridge, Alberta, Canada T1J 4B1
J.D. Shorthouse
Affiliation:
Department of Biology, Laurentian University, Sudbury, Ontario, Canada P3E 2C6
*
2 Author to whom correspondence and reprint requests should be addressed.
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Abstract

Gall inducers are favoured as biocontrol agents of weeds because they tend to have a narrow host range. Six insect and one nematode gall inducer used in Canada are described in terms of their biology, gall morphology, gall physiology, and effectiveness in weed control. The species differ in plant organ attacked, requirement for moisture, whether the galls are induced by secretions or by severing xylem, and effectiveness, which in part relates to the ability of the gall to import nutrients. The most powerful galls divert assimilates from other sinks via a gall’s vascular system joined to that of their host. One of our examples also has mechanisms to compensate for reduction of turgor during drought. Two of the gall inducers enhance their nutrient supply by severing xylem in a plant nutrient sink. One, in the short-term sink of a thistle capitulum, obtains about a quarter of its assimilates at the expense of other capitula. The other, in the long-term sink of a rosette root, approximately halves seed production. Hypotheses are presented to explain various aspects of gall development and function.

Résumé

Les organismes gallicoles sont des agents de contrôle des mauvaises herbes particulièrement appréciés, car ils ont tendance à être spécifiques à un petit nombre d’hôtes. Nous avons étudié la biologie et l’efficacité de contrôle de six insectes et d’un nématode gallicoles utilisés dans la lutte contre les mauvaises herbes au Canada, de même que la morphologie et la physiologie des galles qu’ils génèrent. Les espèces n’attaquent pas toutes les mêmes organes sur les plantes, elles ne nécessitent pas toutes les mêmes conditions d’humidité, certaines déclenchent la formation de galles par l’émission de sécrétions, d’autres par rupture du xylème, et elles n’ont pas toutes la même efficacité contre les mauvaises herbes selon que les galles qu’elles provoquent peuvent ou non importer des éléments nutritifs. Les galles les plus efficaces s’approprient les métabolites destinés à d’autres sites via leur propre système vasculaire relié à celui de l’hôte. L’un des cas étudiés possède également des mécanismes de compensation de la perte de turgescence au cours des périodes de dessication. Deux des espèces gallicoles augmentent leurs réserves nutritives en court-circuitant le xylème de la plante. L’une, dans la zone d’utilisation à court terme des métabolites d’un capitule de chardon, obtient environ un quart de ses éléments nutritifs aux dépens des autres capitules. L’autre, dans la zone d’utilisation à long terme des métabolites d’une racine en rosette, réduit la production de graines d’environ la moitié. Des hypothesès sont avancées pour expliquer divers aspects de la formation et du rôle des galles.

[Traduit par la Rédaction]

Type
Articles
Information
The Canadian Entomologist , Volume 128 , Issue 6 , December 1996 , pp. 1021 - 1055
Copyright
Copyright © Entomological Society of Canada 1996

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Footnotes

1

Lethbridge Research Centre contribution No. 3879499.

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