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SEX RATIOS OF THE WESTERN SPRUCE BUDWORM (LEPIDOPTERA: TORTRICIDAE)

Published online by Cambridge University Press:  31 May 2012

Robert W. Campbell ,
Torolf R. Torgersen ,
Kevin P. Hosman  and
Nilima Srivastava
Robert W. Campbell
Affiliation:
Research Entomologist, Pacific Northwest Forest and Range Experiment Station, Forestry Sciences Laboratory, Corvallis, Oregon 97331U.S.A.
Torolf R. Torgersen
Affiliation:
Research Entomologist, Pacific Northwest Forest and Range Experiment Station, Forestry Sciences Laboratory, La Grande, Oregon 97850U.S.A.
Kevin P. Hosman
Affiliation:
Research Associate, College of Forestry, Wildlife and Range Sciences, University of Idaho, Moscow, Idaho 83843U.S.A.
Nilima Srivastava
Affiliation:
Research Associate, College of Forestry, Wildlife and Range Sciences, University of Idaho, Moscow, Idaho 83843U.S.A.
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Abstract

Populations of the western spruce budworm, Choristoneura occidentalis, were sampled in western Montana, central Idaho, and eastern Oregon. In 22 of 24 populations, the proportion of females among pupae did not differ from 0.5. Similarly, in 21 of 24 populations, the proportion of females among adults was not different from 0.5. In all populations, differences between survival rates of male and female pupae were attributed to chance. The proportion of females among pupae (a) did not differ between insects on Douglas-fir and those on grand fir, (b) was slightly but significantly higher among insects in the mid-crown than among those in the lower crown, and (c) was significantly higher among the insects in the one site studied where average defoliation of current-year shoots was greater than 50%. Variation in the proportion of females among adults should have a negligible effect on the dynamics of these populations.

Résumé

Des populations de tordeuse occidentale de l'épinette, Choristoneura occidentalis, ont été échantillonnées dans l'ouest du Montana, le centre de l'Idaho et l'est de l'Oregon. La proportion de pupes femelles n'était pas différente de 0.5 pour 22 populations sur 24. De même, la proportion d'adultes femelles ne différait pas de 0.5. Les différences entre les incidences de survie des pupes mâles et femelles ont été attribuées au hasard. La proportion de pupes femelles (a) ne montrait pas de différence entre les insectes provenant du sapin de Douglas et ceux provenant du sapin de Vancouver, (b) était significativement, bien que légèrement, plus élevée chez les insectes provenant du milieu plutôt que du bas de la couronne et (c) était significativement plus élevée chez les insectes du site d'étude où la défoliation des pousses de l'année courante dépassait 50%. La variation de la proportion d'adultes femelles devrait avoir un effet négligeable sur la dynamique des populations.

Type
Articles
Information
The Canadian Entomologist , Volume 115 , Issue 9 , September 1983 , pp. 1059 - 1063
Copyright
Copyright © Entomological Society of Canada 1983

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References

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