Abstract:

【Objective】 The research was to clarify the differentiation in the life-cycle of cotton aphid (Aphis gossypii Glover) on an overwintering host plant, Hibiscus syriacus L. in Nanjing, Jiangsu province, China. 【Method】 The cotton aphids on hibiscus trees were investigated by systematic observation method in a whole summer season. Survival and reproduction of cotton aphids from hibiscus tree and cotton were compared on different summer host-plants using host transplantation and life-table methods. 【Result】 There was a sedentary population of cotton aphid on the overwintering host-plant, hibiscus tree, in the whole summer of 2006 and 2007, and it was mainly apterous. The sedentary cotton aphids from hibiscus trees could not produce offspring and establish population when they were transferred directly to cucumber, muskmelon, zucchini, pumpkin, kidney bean and tomato. Although a minority of the sedentary aphid individuals from hibiscus could grow up into adults on cotton and cowpea, they produced fewer offspring and their net reproductive rate (R0) was less than one. However, the sedentary cotton aphids from hibiscus trees showed better fitness on cotton and zucchini after they were reared on the cotton for some generations. The sedentary aphids on summer hibiscus still kept the capacity to utilize some summer host-plants. 【Conclusion】 The diversity of life-cycle exists in the cotton aphid population on an overwintering host-plant, hibiscus in Nanjing, and the autoecious (host-specific) and heteroecious (host-alternating) coexist in the same population. The aphids, which life-cycle is host-specific on hibiscus, have lost or weakened the capacity to utilize some summer host-plants. The life-cycle of cotton aphid population on overwintering host-plant is flexible.

Key words: cotton aphid, life-cycle, population differentiation, host utilization, plasticity