The susceptibility of eggs and different larval instars of the fall armyworm (Spodoptera frugiperda) to lufenuron, and the correlation between susceptibility to this pesticide and enzyme activity

Author of the article:WANG Qin-Qin** JIA Bo-Hai SHI Yan HE Lei-Ming WANG Mei-Zi ZHAO Te ZHOU Lin***

Author's Workplace：Henan Engineering Technology Research Center of Green-Pesticide Creation, Henan Key Laboratory for Creation and Application of Novel Pesticides, State Key Laboratory of High-Efficiency Production of Wheat-Maize Double Cropping, College of Plant Protection, Henan Agricultural University, Zhengzhou 450046, China

Key Words： Spodoptera frugiperda; lufenuron; bioassays; detoxifying enzyme; chitinase

Abstract：

 [Aim]  To determine the susceptibility of eggs and different larval instars of the fall armyworm (Spodoptera frugiperda) to lufenuron, and the correlation between susceptibility to this pesticide and the activity of detoxifying enzymes [mixed-function oxidase (MFO), carboxylesterase (CarEs), glutathione S-transferase (GSTs)], and chitinase (CH)]. [Methods]  Bioassays were conducted and the activity of MFO, CarEs, GSTs, and CH in eggs and different larval instars of S. frugiperda was measured in the laboratory. [Results]  The susceptibility of eggs and different larval instars to lufenuron gradually increased, then rapidly decreased. Eggs and 5th and 6th instar larvae were the least sensitive to lufenuron, with LC₅₀ values between 107.67 and 1 003.81 μg/mL. In contrast, the LC₅₀ values of 1st to 4th instar larvae were 11.90, 10.77, 1.38, and 2.26 μg/mL, respectively, and the corresponding toxicity indices were 84.35, 93.20, 727.40, and 444.16, respectively. Linear regression indicates that the relative toxicity indices of 1st to 4th instar larvae were negatively correlated with MFO and GSTs enzyme activity, but positively correlated with CH activity (P <0.01). [Conclusion]  The susceptibility of eggs and different larval instar of S. frugiperda to lufenuron were found to be significantly different. Increased CH activity in 1st- to 4th-instar larvae may exacerbate the toxicity of lufenuron. On the basis of these results, lufenuron is an ideal insecticide for controlling higher instar S. frugiperda larvae.