Being the most invasive and destructive pests in maize fields, the promising insect; is the fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae). The first onset of fall armyworm in Egypt started in 2019 in the south of Egypt among maize plants in Aswan Governorate. Heading north, the pest spread quickly to Luxor, Qena, Sohag and Assuit governorates in the south. Many synthetic insecticides were recommended to control this insect pest. For this purpose, this research was to evaluate the potential effectiveness and toxicity of the following insecticides, Methomyl (Lannate^® 90%), Chlorpyrifos (Dofos 48%) and Spinosad (Tracer 24%) on the biological aspects of S. frugiperda in the laboratory. Bioassays were conducted on the newly molted 4^th instar of S.  frugiperda larvae under 25 ± 2 °C room temperature, 70 ± 10% relative humidity. The LC₅₀ values were 105.5, 470, and 2.5 ppm for the compounds methomyl, chlorphyrifos, and spinosad, respectively. Distilled water was served to the control group. Accumulative larval mortality percentages were 42, 55 and 44 for methomyl, chlorpyrifos, and spinosad, respectively. A significant increase in the total duration of the consecutive larval instars and pupae was recorded post-treatment at the 4^th instar larvae with the LC₅₀ concentrations of tested insecticides. Accordingly, the differences were significant in the toxicity to S. frugiperda; hence, the variation in LC₅₀ is a reference to the varying actions of the tested insecticides. These data indicate that these recommended synthetic insecticides are effective in controlling fall armyworm instars.