Toxicity and biochemical effects of itol A on the brown planthopper, Nilaparvata lugens (Stål) (Hemiptera: Delphacidae)

Abstract

Itol A, a novel isoryanodane diterpene derived from Itoa orientalis Hemsl., has potent activities against insect pests. This study was conducted to determine the contact toxicity and biochemical effects of itol A on the Nilaparvata lugens. After macropterous females of N. lugens were exposed to itol A from 0.5 to 24 h, the mortality and poisoning symptoms were measured. Effects of itol A on the major enzymes activity and oxidative stress level were assessed in dose-response (with LD₁₀-LD₇₀ at 24 h) and time-course (with LD₅₀ at 0.5-24 h) experiments for the potential toxicity mechanisms. Based on the results, the mortality of N. lugens showed significant dose- and time-dependent effects, with the 24-h LD₅₀ value was 0.58 μg/insect. The symptoms of excitation, convulsion and paralysis were also observed. However, acetylcholinesterases (AChE) activity was not altered after itol A treatment compared to control. Na⁺/K⁺-ATPases, Ca²⁺-ATPases, Ca²⁺/Mg²⁺-ATPases, glutathione S-transferases (GSTs), cytochrome P450 monooxygenases (P450s), superoxide dismutases (SOD) and catalases (CAT) activities were significantly reduced in dose-response and time-course experiments. While acid phosphatases (ACP) and glutathione peroxidases (GPX) activities were significantly increased. We further revealed that itol A exposure resulted in the decrease of GSH/GSSG (reduced to oxidized glutathione) ratio and the increase of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) levels in both experiments. The results indicated that the inhibition of Na⁺/K⁺-ATPases, Ca²⁺-ATPases, Ca²⁺/Mg²⁺-ATPases, GSTs, P450s, SOD and CAT activities and the induction of oxidative stress was one of the potential biochemical mechanisms of itol A against N. lugens.

Keywords: Antioxidant system; Enzyme activity; Itol A; Nilaparvata lugens; Oxidative stress; Toxicity.