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RELATIONSHIP BETWEEN PARASITISM OF LARCH CASEBEARER (LEPIDOPTERA: COLEOPHORIDAE) AND DEAD HOSTS IN THE BLUE MOUNTAINS, 1973–1983

Published online by Cambridge University Press:  31 May 2012

Roger B. Ryan
Roger B. Ryan
Affiliation:
U.S Department of Agriculture, Pacific Northwest Forest and Range Experiment Station, Forestry and Range Sciences Laboratory, La Grande, Oregon, USA 97850
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Abstract

Between 1973 and 1983 two newly introduced parasites, Agathis pumila (Ratz.) and Chrysocharis laricinellae (Ratz.), caused an increasing impact on populations of the larch casebearer, Coleophora laricella (Hbn.), as measured by percentage parasitism based on adult emergence and the associated mortality of hosts that did not produce parasites. Total impact of the parasites cannot be measured by adult emergence alone but must include parasite-killed hosts from which no parasites emerged. Nevertheless, trends in parasite effectiveness are represented by percentages based solely on adult emergence. Only 53.1% of the adult A. pumila successfully emerged in 1983 samples. Furthermore, the number of emerged plus non-emerged A. pumila was only 53.3% of the number expected based on previous samples of that same generation. This mortality of A. pumila took place even in the absence of significant populations of C. laricinellae, indicating that although C. laricinellae may cause some reduction in parasitism by A. pumila, other factors are also responsible.

Résumé

Durant la période 1973 à 1983, les parasites nouvellement introduits, Agathis pumila (Ratz.) et Chrysocharis laricinellae (Ratz.), ont causé un impact croissant sur les populations du porte-case du mélèze, Coleophora laricella (Hbn.), mesuré par le pourcentage du parasitisme basé sur l'émergence des adultes et la mortalité associée. L'effet total des parasites ne peut pas être mesuré par l'émergence des adultes seulement, mais doit comprendre les hôtes tués par les parasites et de qui pas de parasites sont émergés. Cependant, la tendance de l'efficacité des parasites est représentée suffisamment par le pourcentage du parasitisme basé seulement sur l'émergence des adultes. Seulement 53,1% des adultes de A. pumila dans les prises de 1983 sont émergées. De plus, le nombre d'adultes de A. pumila émergé et pas émergé était seulement 53,3% du nombre anticipé, basé sur les prises de ces générations auparavant. Cette mortalité de A. pumila est arrivée malgré l'absence des populations importantes de C. laricinellae, indiquant que quoique C. laricinellae cause peut-être quelque réduction du parasitisme par A. pumila, il y a d'autres facteurs aussi responsables.

Type
Articles
Information
The Canadian Entomologist , Volume 117 , Issue 8 , August 1985 , pp. 935 - 939
Copyright
Copyright © Entomological Society of Canada 1985

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