Diapause, embryo growth and supercooling capacity of Epirrita autumnata eggs from northern Fennoscandia

• Published in: Entomologia Experimentalis et Applicata
• Main Authors: Nilssen, Arne, Tenow, Olle
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1990
• Subjects: Midwinter; Fennoscandia
• Online Access: http://dx.doi.org/10.1111/j.1570-7458.1990.tb01414.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1570-7458.1990.tb01414.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1570-7458.1990.tb01414.x

Abstract The supercooling point (SCP) of individual Epirrita autumnata eggs (approx. 60 eggs batch −1 ) was tested each month from September (eggs newly laid) to April under laboratory conditions simulating winter temperatures in the field (from + 4 to −30 °C). Parallel to each test, one batch of eggs was transferred from the acclimation treatment to room temperature (∼22 °C) and the incubation duration to the first 50% hatch was recorded, giving a measure of embryo growth at the time of the SCP test. Data also give information on egg mortality, which generally was low. The SCP was found to be equivalent to the lower lethal temperatures for this species. Already in autumn, the SCP was in a low range of −34.9 to −36.5 °C and either rose (at a storage temperature of ≥ −3 °C) to a range between −28.3 and −29.8 °C in February, due to reduced cold hardiness during embryogenesis, or remained unchanged because the eggs were in quiescence (at ≤ −10 °C). The time to 50% hatch at ∼22 °C decreased from 60 days to 10–14 days in January when it either continued to decrease up to hatch (at ≥ −3 °C), or remained unchanged, indicating end of diapause in January. In December, 260 degree‐days (DD) above a threshold of + 5.8 °C was required for 50% hatch; in February the corresponding figures were 362 DD and −2 °C. When the supercooling point moved from the low to the high SCP range, the frequency distribution of the individual SCPs changed from positively to negatively skewed. The transition was rapid, intermediary distributions being flat and covering both ranges. Thus, in the field the eggs run the risk of freezing mainly at two temperature levels: below about −36 °C during diapause and post‐diapause quiescence (in midwinter) and below about −29 °C during embryogenesis (in late winter spring). Résumé Diapause, développement embryonnaire et résistance au froid des œufs d' Epirrita autumnata du nord de la Scandinavie La température de congélation (supercooling point: SCP) de chaque œuf de E. (Oporinia) autumnata (Lépido, ...