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ANALYSIS OF LIFE TABLES FOR THE LARCH CASEBEARER (LEPIDOPTERA: COLEOPHORIDAE) IN OREGON

Published online by Cambridge University Press:  31 May 2012

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

Abstract

Life tables for Coleophora laricella (Hübner) at three locations in Oregon were completed for six generations from overwintering larvae in 1978–1979 through overwintering larvae in 1984–1985. Egg densities (per 100 buds) were high (range 279–1038) at Catherine Creek, moderate (49–705) at Tollgate, and low (14–200) at Emigrant Springs. Mortality of early stages was in the order CC>T>ES and tended to equalize overwintering densities. Ten within-generation mortalities (k-values) were calculated. Adult mortality (or reduced fecundity) was always highest. The key factor at Tollgate was mortality of needleminers along with winter-to-spring disappearance. At Catherine Creek, the key factor was mortality of fall casebearers. At Emigrant Springs, the expanding population of an introduced parasite, Agathis pumila (Ratz.), indicated a change in the key factor from mortality of needleminers to parasitism. Mortality of fall casebearers at Emigrant Springs was density dependent. Parasitism caused by A. pumila and another introduced species, Chrysocharis laricinellae (Ratz.), showed characteristics of delayed density dependence.

Résumé

On a élaboré des tables de survie dans quatre localités de l’Oregon, pour six générations de Coleophora laricella (Hübner), débutant avec les larves hivernantes de 1978–1979 et se terminant avec celles de 1984–1985. Les densités d’oeufs (par 100 bourgeons) étaient élevées (limites de 279–1038) à Catherine Creek, modérées (49–705) à Tollgate, et basses (14–200) à Emigrant Springs. La mortalité des premiers stades suivait l’ordre CC>T>ES, tendant à égaliser les densités d’hivernement. On a estimé 10 valeurs de mortalilté intra-génération (valeurs de k). La mortalité adulte (ou baisse de fécondité) était toujours la plus élevée. Le facteur-clé à Tollgate était la mortalité des mineuses d’aiguilles et la disparition au cours de l’hiver–printemps. A Catherine Creek, le facteur-clé était la mortalité des porte-cases de l’automne. A Emigrant Springs, les populations croissantes d’un parasite introduit, Agathis pumila (Ratz.), ont marqué le remplacement de la mortalité des mineuses d’aiguilles par le parasitisme comme facteur-clé. La mortalité des porte-cases d’automne était dépendante de la densité à Emigrant Springs. Le parasitisme par A. pumila et par une autre espèce introduite, Chrysocharis laricinellae (Ratz.), montrait des caractéristiques de dépendance de la densité avec délai.

Type
Articles
Copyright
Copyright © Entomological Society of Canada 1986

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