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PREDATION BY CALOSOMA SYCOPHANTA L. (COLEOPTERA: CARABIDAE): EVIDENCE FOR A LARGE IMPACT ON GYPSY MOTH, LYMANTRIA DISPAR L. (LEPIDOPTERA: LYMANTRIIDAE), PUPAE

Published online by Cambridge University Press:  31 May 2012

Ronald M. Weseloh
Affiliation:
Department of Entomology, Connecticut Agricultural Experiment Station, New Haven, Connecticut, USA 06504

Abstract

The impact of predation by Calosoma sycophanta L. on an increasing prey population was assessed by recapturing marked adult beetles, periodically observing tagged gypsy moth pupae, and examining gypsy moth pupal remains in different microhabitats. Adult beetles dispersed in random directions but many tended to remain near the trap at which they were originally caught, suggesting a low dispersal potential. About 75% of the adult beetles present in the plot on one day were still present the next day. Capture–recapture estimates suggested that there were at most about 250 male beetles and half as many females/ha in the plot. Calosoma larvae destroyed 70% of tagged gypsy moth pupae under burlap bands on tree trunks near ground level, which was much more than any other mortality factor. Although this percentage was the same when mortality was assessed by looking at pupal remains within 5 m of the ground on tree trunks, pupae higher in trees and on leaves were not attacked as frequently. On average, about 40% of the pupae present in the entire study area were destroyed by Calosoma larvae. Each female beetle in the site would have had to produce about 30 progeny to have this effect. These data suggest that a relatively low number of adult beetles can have a substantial impact on gypsy moth populations.

Résumé

On a évalué l'impact de la prédation par Calosoma sycophanta L. sur une population croissante de proie en recapturant des calosomes adultes marqués, en observant périodiquement des pupes marquées de la spongieuse, et en examinant les restes de pupes de la spongieuse dans différents microhabitats. Des calosomes adultes se sont dispersés en suivant des directions aléatoires mais plusieurs sont demeurés près du piège dans lequel ils avaient originellement été capturés, indiquant un faible pouvoir de dispersion. Environ 75% des calosomes adultes présents à un jour donné dans la parcelle, l'étaient toujours le lendemain. Les données de capture–recapture indiquent qu'il y avait environ 250 calosomes mâles et la moitié de femelles/ha dans la parcelle. Les larves de Calosoma ont éliminé environ 70% des pupes marquées de spongieuse placées près du sol sous des bandes de toile sur des troncs d'arbres, soit beaucoup plus que tout autre facteur de mortalité. Ce pourcentage était le même qu'estimé en examinant les restes de pupes situées à moins de 5 m du sol sur les troncs, mais les pupes situées plus haut sur les arbres et sur les feuilles n'étaient pas attaquées aussi fréquemment. En moyenne environ 40% des pupes présentes dans toute l'aire d'étude ont été détruites par les larves de Calosoma. Chaque femelle présente dans le site a dû produire environ 30 progénitures pour permettre une telle fréquence d'attaque. Ces données indiquent qu'un nombre relativement peu élevé de calosomes adultes peuvent avoir un impact substantiel sur les populations de spongieuse.

Type
Articles
Copyright
Copyright © Entomological Society of Canada 1985

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