Diuraphis noxia is a newly established alien pest in the Czech Republic. There were two population explosions during the period 1993–2012. A successful overwintering of the anholocyclic populations of D. noxia was the cause of a population explosion in the oncoming growth season. Viviparous parthenogenetic females of the anholocyclic populations and diapausing eggs of holocyclic populations could overwinter at the same time. Analysis of the course of winter temperatures showed that a complete winter mortality of anholocyclic populations depended mainly on the duration of the freezing period, when temperature dropped below −5°C, and on the intensity of the frost. We proposed the cumulative effective freeze (in minus degree days) as a key parameter for the aphid anholocyclic population's mortality during overwintering. This parameter equalled −10.1 degree days for relatively warm winter period 2006–2007, whereas in the relatively cold winter period of 2009–2010, this parameter reached −87.1 DD, which caused complete mortality of anholocyclic populations. A cumulative effective freeze could be used for short-time prognosis of D. noxia population explosion.