Comparative low lethal effects of three insecticides on demographical traits and enzyme activity of the Spodoptera exigua (Hubner)

Many species of devastating insect pests have acquired a high degree of resistance to insecticides in the field during the last few decades. Spodoptera exigua, for example, is the most damaging pests of economic crops with a worldwide spread. In a present study, the comparative growth, reproduction, and detoxification enzyme activity were evaluated along with exposure to three insecticides at low lethal doses of lufenuron, indoxacarb, and spinosad as compared to the control. Results indicate that the larval developmental time was significantly extended on lufenuron (21.5 +/- 29 days) followed by indoxacarb (20.28 +/- 0.24 days) and spinosad (19.74 +/- 0.23 days) as compared to that on the control (18.13 +/- 0.13 days). Similarly, the lowest number of eggs of S. exigua females were recorded on lufenuron (328.75 +/- 50.81 eggs) followed by spinosad (367 +/- 36.4 eggs) and indoxacarb (411.58 +/- 42.38 eggs) as compared to that on the control (560.2 +/- 13.47). Interestingly, the lowest intrinsic rate of increase (r) (0.121 +/- 0.009) and highest mean generation time (T) (36.2 +/- 0.35 days) were observed when larvae were treated to a low lethal concentration (LC20) of lufenuron as compared to that of indoxacarb, spinosad, and control. In addition, considerably lower activity of all detoxification enzymes in larvae was recorded on lufenuron after control as compared to that on indoxacarb and spinosad. Our study serves as a reference and basis for the toxicity and low lethal evaluation of lufenuron, indoxacarb, and spinosad on life table parameters and enzymatic properties in S. exigua, which may contribute to identifying targets for effective control of S. exigua.