Three insecticides, recommended by the Ministry of Agriculture, Egypt, for use against cotton and vegetable pests were tested . These insecticides were methomyl, methamidophos and chlorpyrifos. These insecticides were tested against the third instar of Spodoptera littoralis(Boisd.)larvae parasitized by Microplitis rufiventris (kok.) and non-parasitized S.littoralis larvae of the same age.In the first part which larvae fed oncastor oil leaves contaminated with insecticides.The insecticides can be arranged in the following descending order according to their LC₅₀ 's and statisticaly analysis. In larvae, chlorpyrifos,methomyl and methamidophos. In the second part which larvae fed on poisoned semi-artificial died. The tested insecticides can be arranged in the following descending order according to their  LC₅₀ 's and statistical analysis. In both parasitized and non-parasitized larvae, methomyl, methamidophos, chlorpyrifos.