The combined effects of insect viruses and insecticides have been investigated both in the field (McEwen and Hervey 1958, Genung 1960, Getsin 1962, Wolfenbarger 1965, and Dempster 1968) and in the laboratory (Benz 1971). This paper reports quantitative studies of interactions of insect nuclear-polyhedrosis virus (NPV) and the insecticides DDT and rotenone suspended in peanut oil. These insecticides were chosen because one (DDT) stimulates insect respiration and thus is believed to enhance the effect of virus on larvae, while the other (rotenone) has the opposite effect (O'Brien 1967).