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INTERACTIONS BETWEEN THE DOUGLAS-FIR SEED CHALCID, MEGASTIGMUS SPERMOTROPHUS (HYMENOPTERA: TORYMIDAE), AND THE WESTERN CONIFER SEED BUG, LEPTOGLOSSUS OCCIDENTALIS (HEMIPTERA: COREIDAE)

Published online by Cambridge University Press:  31 May 2012

S.E. Blatt  and
J.H. Borden
S.E. Blatt
Affiliation:
Centre for Pest Management, Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6
J.H. Borden
Affiliation:
Centre for Pest Management, Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6
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Abstract

In two laboratory experiments, adult western conifer seed bugs, Leptoglossus occidentalis Heidemann, did not feed on seed infested by the Douglas-fir seed chalcid, Megastigmus spermotrophus Wachtl. When presented with seed lots containing 0, 20, 40, 60, 80, or 100% chalcid-infested seed, seed bugs fed on uninfested seed only when the percent chalcid infestation was ≤ 40% (Exp. 1), ≤ 20% (Exp. 2, females), or ≤ 60% (Exp. 2, males). In a third experiment, nymphs exposed to similar seed lots did not feed on M. spermotrophus when sound seeds were present. However, when exposed to 100% chalcid-infested seed, nymphs in two of 10 replicates fed on M. spermotrophus. Feeding by seed bugs caused seeds to lose 51% of their weight on average, but 18% of 43 test seeds on which seed bugs had fed germinated. In three Douglas-fir orchards surveyed, both species exhibited a clonal preference, but the ranking of clones preferred by each species was not the same. These results suggest that the impacts of L. occidentalis and M. spermotrophus are segregated and additive.

Résumé

Au cours de deux expériences en laboratoire, des punaises des graines de résineux Leptoglossus occidentalis Heidemann ont refusé de se nourrir de graines infestées par le Chalcis du Douglas, Megastigmus spermotrophus Wachtl. En présence de lots de graines contenant 0, 20, 40, 60, 80 et 100% de graines infestées, les punaises se sont nourries de graines saines seulement dans les lots infestés à ≤ 40% (exp. 1) ou à ≤ 20% (exp. 2, femelles), ou à ≤ 60% (exp. 2, mâles). Au cours d’une troisième expérience, des larves exposées aux mêmes conditions ont refusé de se nourrir de graines infestées lorsque des graines saines étaient présentes. Cependant, en présence de lots de graines infestés à 100%, les larves de deux des 10 groupes expérimentaux se sont nourries de graines infestées. L’alimentation des punaises sur les graines a réduit la masse des graines de 51% en moyenne, mais, parmi les graines expérimentales à même lesquelles les punaises s’étaient nourries, seulement 18% ont germé. Dans quatre plantations de sapins de Douglas, les deux espèces ont montré des préférences pour certains clones, mais l’ordre de préférence des clones différait chez les deux espèces. Ces résultats semblent indiquer que les impacts respectifs de L. occidentalis et M. spermotrophus sont distincts et cumulatifs.

[Traduit par la Rédaction]

Type
Articles
Information
The Canadian Entomologist , Volume 130 , Issue 6 , December 1998 , pp. 775 - 782
Copyright
Copyright © Entomological Society of Canada 1998

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