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EXPERIMENTAL MANIPULATION OF THE PHENOLOGY OF EGG HATCH IN CYCLIC POPULATIONS OF TENT CATERPILLARS

  • Judith H. Myers (a1)

Abstract

Eggs of western tent caterpillars hatch just as leaves of their food plants are developing. To determine the impact of asynchrony between leaf development and egg hatch during a year of peak density and the initiation of decline, egg masses were introduced to four study areas after the time of normal egg hatching. Survival of caterpillars was not significantly influenced by delays of 3–6 weeks in hatching. Populations composed primarily of introduced insects and control populations declined following the summer of the experiment. Although hatching of deployed eggs was delayed, caterpillar development during warmer temperatures later in the spring was sufficiently rapid that caterpillars from all groups reached the fifth instar by mid-June, and parasitization of caterpillars from control and experimental areas was similar. Tent caterpillar survival was apparently resilient to substantial delays in egg hatch which suggests that cyclic population declines are not likely to be associated with minor variation in the synchrony of leaf development and egg hatch.

Les oeufs de la Livrée de l’Ouest éclosent au moment où les feuilles de leurs plantes nourricières apparaissent. Pour déterminer l’impact d’un asynchronisme entre le développement des feuilles et l’éclosion des œufs au cours d’une année où la densité est à son zénith, et donc à l’approche du déclin, des masses d’oeufs ont été introduites en quatre points après le moment normal de l’éclosion. La survie des chenilles n’était pas significativement influencée par des retards de 3–6 semaines dans l’éclosion. Les populations composées surtout d’insectes introduits et les populations témoins se sont mises à décliner à la suite de l’été de l’expérience. Bien que l’éclosion des oeufs introduits ait été retardée, le développement des chenilles a été suffisamment rapide au cours des températures plus chaudes plus tard au printemps pour que les chenilles de tous les groupes atteignent le cinquième stade à la mi-juin, assurant un parasitisme aussi important dans les régions expérimentales que dans les régions témoins. La survie des chenilles ne semble pas avoir été affectée par les retards importants dans l’éclosion des oeufs, ce qui indique que les chutes de densité des populations cycliques ne sont probablement pas associées à des variations mineures du synchronisme entre le développement des feuilles et l’éclosion des oeufs.

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EXPERIMENTAL MANIPULATION OF THE PHENOLOGY OF EGG HATCH IN CYCLIC POPULATIONS OF TENT CATERPILLARS

  • Judith H. Myers (a1)

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