Abstract: An investigation was conducted on the mortality and detoxification enzyme activities of Spodoptera litura (Fabricius) larvae under the toxic stress of three pesticides: Emamectin benzoate · chlorfenapyr (EBC), Spodoptera litura nucleopolyhedrovirus (SpltNPV), and Bacillus thuringiensis (BT). The immersion method was used to study the toxic effects of EBC, SpltNPV, and BT on the 4th instar larvae of Spodoptera litura. Meanwhile, a microplate reader was employed to determine the effects of these three insecticides on the activities of carboxylesterase (CarE), multifunctional oxidase (MFO), and glutathione S-transferase (GSTs). The results showed that after 12 h of treatment with EBC, SpltNPV, and BT, the 4th instar larvae of Spodoptera litura displayed symptoms including sluggish movement, darkened body color, wrinkled body walls, and a reduction in both body length and width. When EBC was diluted within the range of 2 500 to 7 500 times, the corrected mortality rate of the 4th instar larvae of Spodoptera litura ranged from 60.71% to 100.00%, with the median lethal time (LT₅₀) spanning from 76.70 to 111.50 h. When SpltNPV was diluted between 375 and 1 500 times, the corrected mortality rate ranged from 67.86% to 100.00%, and the LT₅₀ was between 74.17 and 116.6 h. When BT was diluted from 750 to 3 000 times, the corrected mortality rate ranged from 78.57% to 100.00%, and the LT₅₀ ranged from 83.00 to 120.00 h. When the 4th instar larvae of Spodoptera litura were treated with EBC diluted 5 000 times, SpltNPV diluted 750 times, and BT diluted 1 500 times, an increase in CarE activity and a decrease in MFO activity were observed in each treatment group within the range between 12 h and 48 h, whereas GSTs activity exhibited fluctuating changes.

Key words: Spodoptera litura (Fabricius), pesticide, toxicity, detoxification enzyme, activity