Abstract:The relationships among the selectivity of Didesmococcus koreanus Borchs, branch physical structure and chemical substance in the eight host plants and D.koreanus were studied by using net covered means. It provide basis for to conducted ecological pest regulation and management by insect-resistant varieties. The results showed that the feeding-selectivity and oviposition-selectivity of D.koreanus to eight host plants all were significantly different, and orders of these selectivities were peach, plum, cherry plum, apricot, apple, pear, cherry and hawthorn. And these hosts were divided into three groups, the most favorite hosts were peach, plum, cherry plum and apricot, the favorite hosts were apple, pear and cherry, the inferior favorite host was hawthorn. Feeding-selectivity and oviposistion-selectivity of D.koreanus with the eight host plants of the hairs density, length, epidermis thickness, branch diameter, flavones and tannin, and all reached a very significant negative correlation, and their correlated coefficients r respectively were -0.9413 to-0.8816 and -0.9624 to-0.8943. The same reasoning, feeding-selectivity and oviposition-selectivity of D.koreanus with the eight host plants of branch’s soluble sugar, host plant’ssoluble protein, free amino acids, water content, CarE, AChE, GSTs and the insect’s soluble protein content, and all reached a very significant positive correlation, and their correlated coefficients r respectively were 0.9025 to 0.9413 and 0.8937 to 0.9201. Feeding-selectivity and oviposition-selectivity of D.koreanus are consistent on the eight host plants. Activity of CarE, AChE, GSTs and the soluble protein content of D.koreanus that feeding peach, plum, cherry plum and apricot which branches relatively smooth surface, low hair density, length short, thin epidermis, more content of host’s soluble proteins, free amino acids, water content, and low content flavones and tannins were relatively high. The D.koreanus of the host plant’s selectivity strong is serious harm to the eight hosts, these of apple, pear and cherry were inferior, and these of hawthorn are the worst.