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

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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.