Abstract: 【Aim】 To explore the effects of potassium application on the oviposition selection, growth and development, adult longevity and fecundity of Odontothrips loti on alfalfa, and to illustrate the relationship between the nutrient content in alfalfa leaves applied with potassium and the life parameters of O. loti. 【Methods】 The number of eggs, duration and survival rates of various immature developmental stages, and the longevity and fecundity of the second generation adults of O. loti fed with leaves of Medicago sativa cv. Gannong No. 3 applied with different amounts of potassium (40, 60, 80 and 100 mg/kg) (without potassium application as the control) were investigated. Meanwhile the soluble sugar, free amino acid and potassium contents in alfalfa leaves were measured. 【Results】 The number of eggs laid by O. loti eggs in per compound leaf of alfalfa decreased first and then increased with increasing amount of potassium application, and was the lowest at 60 mg/kg potassium treatment, 45.58% lower than the control. The egg hatching rate and the survival rate of the 1st-2nd instar nymphs on alfalfa leaves applied with potassium did not change significantly, but the survival rate of the 3rd-4th instar nymphs and the total immature survival rate of O. loti went down significantly, with the largest decrease at 100 mg/kg and 80 mg/kg potassium treatment, which decreased by 54.36% and 48.48% compared with the control, respectively. There was no significant change in the egg and the 1st-2nd instar nymphal duration of O. loti on alfalfa leaves applied with different amounts of potassium, while the 3rd-4th instar nymphal duration and the total immature developmental duration were prolonged. The fecundity of the second generation adults of O. loti on alfalfa leaves applied with different amounts of potassium was reduced significantly, and the adult longevity was shortened significantly than the control (except 40 mg/kg potassium treatment). After potassium application, both the soluble sugar and potassium contents in alfalfa leaves increased, the free amino acid content decreased, and the sugar to nitrogen ratio increased. The correlation analysis showed that there was no significant correlation between the potassium content in alfalfa leaves and the total immature survival rate and the fecundity of O. loti adults, while the soluble sugar content and the sugar to nitrogen ratio were extremely negatively correlated with the survival rate of the 3rd-4th instar nymphs and the fecundity of adults and significantly negatively correlated with the total immature survival rate of O. loti. 【Conclusion】 Potassium-applied alfalfa has significant antixenosis to the oviposition of O. loti adults. The application of potassium increases the soluble sugar content and the sugar to nitrogen ratio in alfalfa leaves, exerting significant antibiosis to O. loti by affecting the growth and development of nymphs, shortening adult longevity and reducing the fecundity of adults.

Key words: Odontothrips loti, potassium, alfalfa, oviposition selection, growth and development, adult longevity, fecundity