Abstract: 【Aim】 This study aims to explore the effects of four adjuvants, namely orange peel essential oil (OPEO), γ-aminobutyric acid (GABA), lecithin and diethyl maleate (DEM), on the toxicity of the botanical pesticide 1% azadirachtin (AZ) water dispersible granule (WG), and to screen adjuvants with synergistic effect as tank-mix adjuvants of 1% AZ WG to control the brown planthopper, Nilaparvata lugens. 【Methods】 The toxicity of AZ and AZ with adjuvants OPEO, GABA, lecithin or DEM to the 3rd instar nymphs of N. lugens was evaluated by the rice seedling dipping method and continuous immersion method, and the activities of glutathione S-transferase (GST), carboxylesterase (CarE) and acetylcholinesterase (AChE) in the 3rd instar nymphs of N. lugens after treatment with 20 mg a.i./L AZ or 20 mg a.i./L AZ with adjuvants were determined. The effect of adding adjuvants on the contact angle of AZ solution (40 mg a.i./L) on the leaf of rice was evaluated. 【Results】At 96 h after the rice seedling dipping treatment, the addition of DEM had a significant synergistic effect on the gastric toxicity of AZ, with the synergistic ratio of 1.512, while at 72 h after the continuous immersion treatment, the addition of OPEO or DEM significantly increased the systemic activity of AZ, with the synergistic ratios of 1.486 and 1.560, respectively. The GST activities in the 3rd instar nymphs of N. lugens in treatments with AZ plus OPEO and AZ plus DEM were decreased by 69.4% and 65.5%, respectively, and the CarE activity in treatment with AZ plus DEM was decreased by 88.2% as compared to those in just AZ treatment. After adding OPEO or DEM, the initial contact angles of liquid droplets of AZ solution on the adaxial leaf of rice was reduced from 110° to 64.5° and 67.9°, respectively. 【Conclusion】 Adding OPEO or DEM can significantly improve the toxicity of AZ to N. lugens, and improve the wetting ability of AZ solution on the leaf of rice. So, the two substances have some potential value as tank-mix adjuvants of 1% AZ WG to control N. lugens.

Key words: Nilaparvata lugens, tank-mix adjuvant, botanical pesticide, toxicity, synergistic effect, detoxification enzymes, contact angle