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STRUCTURAL DAMAGE AND GALL INDUCTION BY PEGOMYA CURTICORNIS AND PEGOMYA EUPHORBIAE (DIPTERA: ANTHOMYIIDAE) WITHIN THE STEMS OF LEAFY SPURGE (EUPHORBIA × PSEUDOVIRGATA) (EUPHORBIACEAE)

Published online by Cambridge University Press:  31 May 2012

Andre Gassmann
Affiliation:
CAB International Institute of Biological Control, European Station, CH-2800, Delémont, Switzerland
Joseph D. Shorthouse
Affiliation:
Department of Biology, Laurentian University, Sudbury, Ontario, Canada P3E 2C6

Abstract

Leafy spurge (Euphorbia × pseudovirgata [Schur]) is an herbaceous perennial and serious weed of European origin that has been accidently introduced into North America. The European anthomyiid flies Pegomya curticornis (Stein) and Pegomya euphorbiae (Kieffer) are found on several spurge species in Europe and also attack leafy spurge. The two flies induce identical galls on the subterranean stems of their host plants, and the shoots wilt and die. Eggs are laid on the shoot tip, and the larvae bore into the stem by eating pith which is later replaced by callus. This is a rare example of an insect with both boring and gall-inducing feeding strategies. Galls are induced when larvae feed on the ring of vascular tissue. There is no proliferation of nutritive cells but instead thick layers of gall parenchyma are produced. The vascular connections are broken at the gall level and concentric vascular bundles appear in the cortical and gall parenchyma. After pupation an inner periderm differentiates around the chamber surface.

Résumé

Accidentellement introduite d’Europe, l’euphorbe feuillue (Euphorbia × pseudovirgata [Schur]), est en Amérique du Nord, une importante mauvaise herbe vivace. En Europe, plusieurs espèces d’euphorbes, en l’occurrence l’euphorbe feuillue, sont attaquées par les mouches anthomyiides indigènes, Pegomya curticornis (Stein) et Pegomya euphorbiae (Kieffer). Ces deux espèces entraînent la formation de galles identiques sur les tiges souterraines de leur plantes hôtes, causant ainsi la flétrissure et la mort des pousses. Les oeufs sont placés à l’extrémité de la pousse et la larve creuse dans la tige dévorant la moelle qui sera remplacée par une callosité. Ceci constitue un rare cas de comportement alimentaire où un insecte creuse une tige et entraine la formation d’une callosité. Les galles se forment lorsque les larves se nourrissent dans la zone de tissus vasculaires. Dans la galle, il n’y a pas de prolifération de cellules nutritives mais plutôt production de couches épaisses de parenchyme. Des liens vasculaires sont brisés au niveau de la galle et des bourlets vasculaires concentriques apparaîssent dans le parenchyme cortical et celui de la galle. Après la nymphose, un périderme interne se différencie autour de la surface de la chambre.

Type
Articles
Copyright
Copyright © Entomological Society of Canada 1990

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