The green peach aphid, Myzus persicae Sülzer, is an important sap-sucking pest of many plants, including Chinese cabbage. The objective of the present study was to determine the effects of sublethal concentrations of two insecticides (flonicamid and thiamethoxam) and the action mechanisms on the feeding behavior of M. persicae. The median lethal concentrations (LC 50 ) of flonicamid and thiamethoxam for adult M. persicae were 2.56 and 4.02 mg/L, respectively. The sublethal concentrations of flonicamid were 0.44 mg/L (LC 10 ) and 1.25 mg/L (LC 30 ), and those of thiamethoxam were 1.19 mg/L (LC 10 ) and 2.45 mg/L (LC 30 ). The developmental period of M. persicae nymphs was 5.9 days at LC 10 and 6.1 days at LC 30 for both insecticides compared to 5.7 days for the control. Adult longevities at LC 10 and LC 30 of flonicamid were 13.2 and 13.7 days, respectively. Adult longevity at LC 10 of thiamethoxam was 14.7 days. Control adult longevity was 11.6 days. Total fecundity was higher at LC 10 (41.8 offspring/female) and LC 30 (43.0 offspring/ female) of flonicamid, and at LC 10 (42.1 offspring/female) of thiamethoxam than that of the control (29.5 offspring/female). Feeding behavior analysis using an electrical penetration graph showed that sublethal doses of flonicamid and thiamethoxam had significant effects on the duration of phloem ingestion. However, higher doses of flonicamid induced starvation by inhibition of phloem ingestion and higher doses of thiamethoxam induced contact toxicity rather than inhibition of feeding behavior. This study provides the basis for a more efficient use of these pesticides in Korea.

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