Abstract:  The dynamics of corn aphid （Rhopalosiphum maidis Fitch） and predator ladybirds in 26 corn varieties （lines） were systematically investigated in Zhaotong， Yunnan Province， to compare their resistance to aphid among varieties in corn field by using the methods of aphid number ratio， and to study the relationship between resistance and the population ratio of ladybirds to aphid in different corn varieties. The results indicated that there were 9 highly resistant varieties （Ludan 15， Shengyu 6， Yunrui 62， Jingdan 11， Yunrui 339， Yunrui 407， Yunrui 668， Yunrui 89， Yunrui 7）， 6 resistant varieties （Yunrui 392， Yunrui 222， Linyu 9， Yunrui 999， Yunrui 10， Yunrui 505）， 1 moderately resistant varieties （Zhenhe 99）， 4 susceptible varieties （Yunrui 666， Zudan 808， Xuanhuangdan 5， Linyu 8）， and 6 highly susceptible varieties ［Linyu 10 （white）， Datian 1， Haiyu 92， Xuanhuangdan 2， Yunrui 108， Shidan 4］. Among the above 26 varieties， the variety with high resistance tended to have high ratio of ladybirds to corn aphid， and a power function was regressed between the ratio value of aphid and the ratio value of ratio of ladybirds to corn aphid， implying an association of resistance of corn with predator ladybirds in controlling aphid population in field.

Key words: corn, corn aphid, ladybirds, resistance to aphid, ratio of ladybirds to corn aphid