عنوان مقاله [English]
نویسندگان [English]چکیده [English]
The cabbage aphid, Brevicoryne brassicae (L.), is one of the major pests of the plant family Brassicaceae that causes serious damages to cabbage and oilseed rape. The cabbage aphid is also able to build up populations on ornamental cabbage during the winter months. To determine the level of cold tolerance in its overwintering populations, adult aphids were collected on cabbages planted in the field of Faculty of Agriculture, Tarbiat Modares University in autumn 2008 and winter 2009. The supercooling points and survivorship of the adults were studied at sub-zero temperatures for 24 h. The mean supercoolig point varied from -23.9 Â± 0.46ÂºC in November to -19.8 Â± 0.34ÂºC in May. About 70-95% of the cabbage aphid adults could tolerate -5Â°C/24 h in all months. The survival rate for the treated adults at -10ÂºC/24 was about 55% from October through November and 87% in December. The LT80 (the temperature at which 80% of population die after 24 h exposure to cold temperatures) was at its highest
(-11.32Â°C) in May, showing the lowest level of cold tolerance in the population. The LT80 ranged from
-13.81 to -14.79 Â°C from December to February, showing the highest level of cold tolerance. Findings indicated that cabbage aphid populations hold a high capacity to tolerate cold temperatures in the course of winter while being active and sexually reproductive at the same time that leads to their quick grow and emergence as an economic severe pest early in the next season.