Toxicity of Some Commonly Used Synthetic Insecticides Against Spodoptera exigua (Fab) (Lepidoptera: Noctuidae)

Spodoptera exigua (Lepidoptera: Noctuidae) is one of the major pests of many crops in Pakistan. Effectiveness of different insecticides was evaluated against field populations of 2 nd instar larvae of S. exigua under laboratory conditions because in lepidopterous pests resistance is developed in 3 rd instars. Bioassays were performed through leaf dip method to evaluate the dose- and time-mortality response for emamectin benzoate, lufenuron, chlorpyrifos and cypermethrin. Significant variation was revealed in lethal concentration and lethal time values. Among all the tested insecticides emamectin benzoate gave the lowest LC50 value i.e., 0.005 mg/l (95% FL: 0.0040.007 mg/l) followed by lufenuron i.e., LC50 value 0.65 mg/l (95% FL: 0.380.93 mg/l). While there was a non significant difference in the LC50 values of cypermethrin and chlorpyrifos i.e., 146 mg/l (95% FL: 108188 mg/l) and 175 mg/l (95% FL: 113256 mg/l), respectively. LT50 values showed that cypermethrin was more effective compared to chlorpyrifos; however, both required less than half the time required by emamectin to kill 50% population of 2 nd instar larvae of S. exigua. Lufenuron, however, required more time as compared to all tested insecticides. The order of effectiveness in terms of LT50 values was; cypermethrin > chlorpyriphos > emamectin benzoate > lufenuron. Responsiveness of S. exigua larvae provides important information with dose- and time-mortality for selection of insecticides in field for better pest management.