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COLD-HARDINESS IN THE EGGS OF THE RED TURNIP BEETLE, ENTOMOSCELIS AMERICANA (COLEOPTERA: CHRYSOMELIDAE)1

Published online by Cambridge University Press:  31 May 2012

G. H. Gerber
Affiliation:
Research Station, Agriculture Canada, Winnipeg, Manitoba R3T 2M9

Abstract

Eggs of the red turnip beetle, Entomoscelis americana Brown, were exposed to temperatures of 0°, −5°, −10°, −15°, and −20°C for 1–8 wk and for 200 days in the laboratory. At −5° and −10°C, there was no death attributable to the cold treatment. At −20°C, the cold treatment caused approximately 15% mortality in the 6- to 8-wk samples and 100% mortality in the 200-day samples. At 0° and −15°C, mortality in the 200-day samples was 39% and 23%, respectively. The data indicate that the embryos of E. americana are able to withstand cold temperatures for long periods and that the optimum temperature range for hibernation (between 0°C and −15°C) is similar to the one this beetle normally experiences in the subnivean air space once the hiemal threshold is established. For Canada, an evaluation of the snow cover and atmospheric air temperature data suggested that egg mortality due to exposure to temperatures of −20°C or lower in the subnivean air space should not occur in the various parts of the red turnip beetle’s range, except possibly the grassland region of the Prairie climatic zone.

Résumé

Des oeufs de la chrysomèle du navet, Entomoscelis americana Brown, ont été exposés à des températures de 0°, −5°, −10°, −15° et −20°C pendant 1 à 8 semaines et pendant 200 jours en laboratoire. À −5°, −10°C, on ne constate aucune mortalité attribuable au traitement par le froid. À −20°C, le traitement cause environ 15% de mortalité chez les échantillons de 6 à 8 semaines et 100% chez ceux de 200 jours. À 0° et −15°C, la mortalité chez les échantillons de 200 jours est de 39% et 23% respectivement. Les données révèlent que les embryons de E. americana sont capables de résister longtemps à des températures froides et que l’amplitude optimale de température pour l’hivernage (entre 0° et −15°C) se compare aux conditions que connaît normalement cet insecte dans l’espace aérien subnival une fois le seuil hiémal établi. Pour le Canada, une évaluation des données sur la couverture de neige et la température de l’air atmosphérique donne à penser que l’exposition à des températures de −20°C ou moins dans l’espace subnival ne devrait pas entraîner la mortalité des œufs dans les diverses parties de l’aire de distribution de la chrysomèle du navet, sauf peut-être dans la région herbagère de la zone climatique des Prairies.

Type
Articles
Copyright
Copyright © Entomological Society of Canada 1981

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