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DIFFERENCES IN POST-DIAPAUSE THERMAL REQUIREMENTS FOR EGGS OF TWO RANGELAND GRASSHOPPERS

Published online by Cambridge University Press:  31 May 2012

William P. Kemp
Affiliation:
Rangeland Insect Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Bozeman, Montana, USA59717–0001
Norma E. Sánchez
Affiliation:
Rangeland Insect Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Bozeman, Montana, USA59717–0001

Abstract

A study was conducted to examine the springtime hatching characteristics of Melanoplus sanguinipes (F.) and Aulocara elliotti (Thomas) eggs on rangeland. Laboratory experiments showed that eggs of M. sanguinipes required fewer accumulated degree days (DD) to complete post-diapause development than those of A. elliotti at a constant temperature of 23.3°C. Springtime field observations revealed that A. elliotti nymphs emerged prior to or concurrent with M. sanguinipes. Additionally, results suggest that A. elliotti nymphs emerge over a shorter interval than M. sanguinipes. Much of the variation in springtime emergence could be attributed to species-specific oviposition sites, pod depth, and pod orientation that resulted in A. elliotti eggs accumulating heat more rapidly than M. sanguinipes eggs. Results help explain some of the variation found in egg hatching of these two grasshopper species on rangeland.

Résumé

On a conduit une étude visant à préciser les caractéristiques de l’éclosion printannière des oeufs de Melanoplus sanguinipes (F.) et Aulocara elliotti (Thomas) dans les pâturages. Des expériences en laboratoire ont montré que les oeufs de M. sanguinipes requièrent moins de degrés-jours (DJ) pour compléter leur développement post-diapause que ceux de A. elliotti à la température constante de 23,3°C. Des observations de terrain au printemps ont révélé que les nymphes de A. elliotti émergent avant ou en même temps que celles de M. sanguinipes. De plus, les résultats suggèrent que les nymphes de A. elliotti émergent durant un intervalle plus court que celles de M. sanguinipes. On a pu attribuer une bonne partie de la variation du moment d’émegence à l’utilisation de sites de ponte spécifiques de l’espèce, la profondeur des sacs d’oeufs et leur orientation. Ces facteurs agissent de sorte qu’il s’ensuit une accumulation plus rapide de chaleur par les oeufs de A. elliotti que ceux de M. sanguinipes. Ces résultats expliquent en partie la variation observée de l’éclosion des oeufs chez ces deux espèces de criquets des pâturages.

Type
Articles
Copyright
Copyright © Entomological Society of Canada 1987

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