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THE CHALCID SEED WASP, MEGASTIGMUS NIGROVARIEGATUS HYMENOPTERA: TORYMIDAE, ON ROSA RUGOSA THUNB. IN NOVA SCOTIA

Published online by Cambridge University Press:  31 May 2012

Tanya L. Gillan
Affiliation:
Department of Biology, Saint Mary's University, Halifax, Nova Scotia, Canada B3H 3C3
David H.S. Richardson
Affiliation:
Department of Biology, Saint Mary's University, Halifax, Nova Scotia, Canada B3H 3C3

Abstract

Two naturalized populations and two planted populations of Rosa rugosa Thunb. were studied with respect to chalcid seed wasp infestation. Megastigmus nigrovariegatus Ashmead was found in hips from planted R. rugosa in Halifax and Dartmouth, Nova Scotia, but not from bushes at naturalized sites. The percentage of infested hips at the Halifax and Dartmouth locations was 26 and 31%, respectively. The percentage of infested achenes within a single hip varied widely from 3 to 79% at the Halifax site and 7 to 60% at the Dartmouth site.Adult emergence was over 75% successful when achenes were over 2 mm in diameter but less than 15% for smaller achenes. The exit hole on the achene faced the outer wall of the hip. Adults emerged later in Nova Scotia than in the United States and between 59 and 72% were female. More than one adult wasp was observed ovipositing on a single hip.

Résumé

La sensibilité aux infestations du chalcis granivore Megastigmus nigrovariegatus Ashmead a été étudiée chez deux populations naturalisées et deux populations plantées de rosiers Rosa rugosa Thunb. Le chalcis a été trouvé dans les fructifications des rosiers plantés à Halifax et à Dartmouth, Nouvelle-Écosse, mais pas dans les rosiers naturalisés. Le pourcentage de fructifications infestées a été évalué à 26% à Halifax et à 31% à Dartmouth. Le pourcentage d’akènes infestés dans chaque fructification variait de 3 à 79% à Halifax et de 7 à 60% à Dartmouth. Soixante-quinze pourcent des akènes de plus de 2 mm de diamètre ont produit des adultes, comparativement à seulement 15% dans le cas des akènes plus petits. Le trou laissé par les adultes émergés dans les akènes donnait sur la paroi extérieure de la fructification.

Les adultes émergeaient plus tard en Nouvelle-Écosse qu’ aux États-Unis et 59–72% des adultes étaient des femelles. Plusieurs femelles pondeuses ont été observées sur une même fructification.

[Traduit par la Rédaction]

Type
Articles
Copyright
Copyright © Entomological Society of Canada 1997

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