Nychthemeral rhythm of sensitivity in fifth instar (L5) of Schistocerca gregaria to Fenitrothion, a synthetic organophosphorus insecticide

We evaluated the lethal doses (LD50 and LD80) of the organophosphorus insecticide fenitrothion on a wild strain of Schistocerca gregaria through topical application at different concentrations. Treatments were administered under extreme conditions, specifically between 8:00 and 9:00 a.m. and between 7:00 and 8:00 p.m. The results revealed nychthemeral variations in sensitivity to the insecticide, with differences in mortality between individuals treated in the morning and those treated in the evening. The data indicate that, at all tested doses, mortality was generally higher in L5 larvae treated in the morning compared to those treated in the evening, with observed mortality differences ranging from 2% to 7%.