Abstract: Many years observations on the patterns of population fluctuation of aphids on crucifer vegetables in Hangzhou suburbs show that only two species of aphids, Myzus persicae and Lipaphis erysimi occurred on crucifer vegetables. The mixed populations of the two aphids showed two peaks each year, with the first one from May to June and the second one around November. The average population density in the two peaks usually reached over 500 aphids per plant, and the second peak usually exceeded the first one in both density and duration. However , in years with low temperature in late summer and early autumn, the aphid population density r apidly increased from August to September and reached over 1000 aphids per plant in peak period, and was very low in both midsummer and midwinter . M . persicae was pr edominant from December to May of t he following year , L . erysimi was predominant from July to October, and their relative predominance was alternat ed each year from May to July and from October to December,respectively. Temper ature is a key factor affecting the seasonal fluctuation pattern of the mix ed population of the two aphids and their interspecific difference in seasonal fluctuation. The influence of other factors such as plant nut rition and natural enemies w as also discussed.

Key words: Myzus persicae, Lipaphis erysimi, Seasonal population fluctuation, Crucifer vegetables, Pinus thunbergii, intrinsic water use efficiency, climate change, stable carbon isotope ratio, tree ring