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WITHIN-CROWN DISTRIBUIONS OF MALE AND FEMALE BAGWORM (LEPIDOPTERA: PSYCHIDAE) PUPAE ON JUNIPER AS AFFECTED BY HOST DEFOLIATION1

Published online by Cambridge University Press:  31 May 2012

David L. Cox  and
Daniel A. Potter
David L. Cox
Affiliation:
Department of Entomology, University of Kentucky, Lexington, Kentucky, USA40546–0091
Daniel A. Potter
Affiliation:
Department of Entomology, University of Kentucky, Lexington, Kentucky, USA40546–0091
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Abstract

We examined the within-crown distributions of male and female bagworm, Thyridopteryx ephemeraeformis (Haworth), pupae on Juniperus virginiana L. as a function of prior defoliation. This was to evaluate the hypothesis that the differential movement of females to the upper crown before pupation would be strongest on heavily defoliated trees. Differential stratification of the sexes occurred irrespective of degree of defoliation, and despite the fact that competition, as evidenced by higher mortality of pupae and reduced weight of egg masses, was apparently greatest at the top of moderately and severely defoliated hosts. There was no relationship between height of pupation and risk of parasitism for either sex. Female larvae were ca. 4-fold more likely than males to abandon a low-lying host upon which they had fed and to ascend the trunks of nearby trees before pupating. Enhancement of larval dispersal by females is the most plausible explanation for the stratified distribution of bagworm pupae within trees.

Résumé

Nous avons examiné, la relation entre la distribution intra-cîme des pupes, maies et femelles des pschés, Thyridopteryx ephemeraeformis (Haworth) et la défoliation antérieure sur les Juniperus virginia L. Ceci avait pour but d’évaluer l’hypothèse que l’activité des femelles serait plus intense dans les cîmes les plus défoliées. Les stratifications différentielles des sexes avaient lieu sans tenir compte du degré de défoliation et en dépit du fait que la compétition, mise en évidence par une plus grande mortalité des pupes et par la réduction du poids des œufs, était apparemment plus importante dans les cîmes des hôtes modérements ou sévèrements défoliés. Il n’y avait pas de rapports entre la hauteur des pupes et le risque de parasitisme pour les maies ou les femelles. Il y avait environ quatre fois plus de larves femelles que de maies qui abondonnaient un hôte situé en bas, sur lequel elles s’étaient nourries, et qui montaient le long du tronc des arbres avoisinants avant de devenir pupes. Le besoin des femelles d’accroître la dispersion des larves est l’explication la plus plausible pour la distribution stratifiée des pupes de pschés dans les arbres.

Type
Articles
Information
The Canadian Entomologist , Volume 120 , Issue 6 , June 1988 , pp. 559 - 567
Copyright
Copyright © Entomological Society of Canada 1988

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