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ACTIVITY PATTERNS OF PARASITOIDS ON THE SWAINE JACK PINE SAWFLY, NEODIPRION SWAINEI (HYMENOPTERA: DIPRIONIDAE), AND PARASITOID IMPACT ON THE HOST

Published online by Cambridge University Press:  31 May 2012

Peter W. Price  and
Howard A. Tripp
Peter W. Price
Affiliation:
Laurentian Forest Research Centre, Canadian Forestry Service, Quebec, Quebec
Howard A. Tripp
Affiliation:
Laurentian Forest Research Centre, Canadian Forestry Service, Quebec, Quebec
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Abstract

Field studies enabled the identification of some limiting factors to which parasitoids were exposed in exploiting the sawfly host, Neodiprion swainei Middleton, and aspects of their quantitative and qualitative impact on the host population. Emergence patterns and flight activity of parasitoids in the spring indicated that larval parasitoids were vulnerable to hyperparasitism by cocoon parasitoids. Although cocoon parasitoids were limited by a shortage of time in which to exploit the host in the spring they still reduced the overwintered host population by 66% in 1969. All forms of predation caused less than 10% sawfly mortality so parasitoids formed the major mortality factor in the spring. Sawfly in prolonged diapause appeared to be immune from cocoon parasitoid attack and thereby efficiency of these parasitoids was limited. However, cocoon parasitoid activity was selective on sawfly that would normally have emerged early in the season and thus delayed the average development of the host population. The complex food web based on the sawfly host provided a sensitive buffering mechanism to produce a degree of stability in the host–parasitoid interaction. The composition of the parasitoid faunae before and after establishment in N. swainei populations of the introduced Pleolophus basizonus (Gravenhorst) indicates the rapidity with which the parasitoid became influential in the complex.

Résumé

Des études conduites en forêt ont permis d’identifier quelques uns des facteurs de régulation confrontés par les parasitoïdes en colonisant la Tenthrède de Swaine, Neodiprion swainei Middleton, et d’élucider certains aspects de leur impact quantitatif et qualitatif sur la population de l’hôte. D’après les modes d’émergence et l’activité aérienne de ces parasitoïdes au printemps, leurs larves étaient sujettes à l’hyperparasitisme par les parasitoïdes du cocon. Encore que leur colonisation de l’hôte fût de courte durée au printemps, les parasitoïdes du cocon en 1969 n’en réduisaient pas moins de 66% la population de l’hôte après l’hiver. Toutes les formes de prédation n’ayant détruit que moins de 10% des Tenthrèdes, les parasitoïdes constituaient donc le principal facteur de mortalité au printemps. En état de diapause prolongée, la Tenthrède semblait immunisée contre l’attaque des parasitoïdes du cocon, d’où limitation de l’efficacité de ceux-ci. Toutefois, l’activité des parasitoïdes du cocon s’avérait sélective sur la Tenthrède qui, normalement, aurait émergé plus tôt dans la saison et par ainsi retardé le développement moyen de la population de l’hôte. Le tissu nutriciel complexe fixé sur la Tenthrède-hôte constituait un mécanisme tampon conférant un certain degré de stabilité à l’interaction de l’hôte et des parasitoïdes.

Type
Articles
Information
The Canadian Entomologist , Volume 104 , Issue 7 , July 1972 , pp. 1003 - 1016
Copyright
Copyright © Entomological Society of Canada 1972

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