Study on the sensitivity of Spodoptera litura (Fabricius) and Spodoptera exigua(Hübner)larvae to insecticides in tobacco fileds

Toxicity of 12 insecticides to the 3 rd -instar larvae and 9 insecticides to the 5 th -instar larvae of Spodoptera litura (Fabricius) was tested by topical application method respectively. Susceptibilities of different instar larvae to insecticide were compared. Toxicity of 9 insecticides to the 4 th -instar larvae of Spodoptera exigua (Hubner)was also evaluated. Results showed that toxicity of 12 insecticides to the 3 rd -instar larvae was declining in the order as following: emamectin benzoate, avatar, chlorfluazuron, chlorpyrifos, phoxim, flufenoxuron, tebufenozide, profenofos, endosulfan, spinosad, alpha-cypermethri, fiproni. Toxicity of 9 insecticides to the 5 th -instar larvae was declining in the order as following: emamectin benzoate, chlorfenapyr, avatar, methomyl, beta-cypermethrin, chlorpyrifos, profenofos , phoxim, endosulfan. The 5 th -instar larvae were more sensitive to high toxicity insecticides than the 3 rd -instar larvae, while the 3 rd -instar larvae were more sensitive to low toxicity insecticides than the 5 th -instar larvae. Chlorfenapyr and flufenoxuro exhibited the highest toxicity to the 4 th -instar larvae of Spodoptera exigua among the 9 insecticides, while phoxim, profenofos, chlorpyrifos and endosulfan exhibited low toxicity. Chlorfenapyr, avatar, and mamectin benzoate were all highly effective insecticides to control these two insect pests.