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Effect of azadirachtin on parasitism rate of Gryon japonicum (Ashmead) and Ooencyrtus nezarae Ishii on pre-treated host eggs
As a broad-spectrum insecticide azadirachtin may cause acute toxicity and alter behavior of natural enemies. We evaluatedthe toxicity of azadirachtin on two egg parasitoids of Riptortus pedestris (Fabricius) (Hemiptera: Alydidae), Ooencyrtusnezarae Ishii (Hymenoptera: Encyrtidae) and Gryon japonicum (Ashmead) (Hymenoptera: Platygastridae), by pre-treatinghost eggs with five concentrations, i.e., 15, 10, 7.5, 5, and 2.5 mL/L. Azadirachtin significantly reduced parasitism byG. japonicum in 15 and 10 mL/L concentrations than other lower concentrations. Similar effect was also observed inO. nezarae. The parasitism reduction capacity (R) for G. japonicum was 40.8 and 33.1% in 15 and 10 mL/L concentrations,but it was 81.6 and 71.4% in O. nezarae, respectively. Based on the IOBC guideline, azadirachtin can be slightly ormoderately harmful to O. nezarae and slightly harmful or harmless to G. japonicum.
