Two alfalfa varieties (Gannong No.3 and Gannong No.9) were used to investigate the effect of phosphorus application on oviposition selection,growth and development of Odontothrips loti,and the resistance of alfalfa to thrips.The egg laying amount of adults,growth and development of nymphs under different phosphorus levels were observed.The soluble sugar content,nitrogen content and phosphorus content were determined as well.The result showed that the egg laying amount of thrips on the leaf of same alfalfa variety increased significantly with the increase of phosphorus level.The survival ratio of 1-2 instar nymph increased significantly after phosphorus application,but the developmental period did not change significantly.There was no significant changes in 3-4 instar nymph survival ratio and developmental period.The soluble sugar content,phosphorus content and sugar to nitrogen ratio of alfalfa were significantly increased after phosphorus application and there was no significant correlation with egg laying amount,there was a significant positive correlation between phosphorus content and 1-2 instar nymphs survival rate of Gannong No.9.Two alfalfa varieties did not show significant antixenosis and antibiosis to thrips after phosphorus application.