Spodoptera exigua, beet armyworm is an agricultural insect pest in tropical and subtropical areas of the world. Long-lasting contact with heavy metals could change sensitivity of insects to other stressor, such as insecticide. Spinosad is a nerve poison and it kills pests that it contacts and/or ones that consume it. Spinosad overstimulates nerve cells by prolonging electrical impulses by acting like acetylcholine. The aim of our study was to compare activity of larvae of S. exigua and sensitivity of them before and after bioinsecticide (spinosad) application. We used two strains of S. exigua: exposed over 100 generations to sub-lethal concentration of cadmium (44 mg Cd/kg dry weight of larval diet) and kept in standardised conditions. Stimulated locomotor activity was recorded during open-field test. Five insects, placed in separate holes in transparent lucite plate, were simultaneously observed. The analysis was made with freely available SwisTrack software that allows simultaneous tracking of more than one insect. For measurement of acetylcholinesterase activity we used acetylthiocholine iodide as a substrate. We found no differences in insect activity between control group and groups treated with spinosad in both breeding strains of S. exigua. We found differences in the changes of the acetylcholinesterase activity between the treated and no treatment groups in control strain of S. exigua, but not in the cadmium strain.