Abstract: Insecticidal compositions comprising a synthetic surfactant and capsaicin or other capsaicinoid exhibit synergistic effects against numerous insects, not only as to activity-enhancement effect but more importantly as to activity-extending effect, especially against Fall Army Worms, Alfalfa Weevils, Corn Ear Worms, Corn Leaf Aphids, True Army Worms, Grasshoppers, Potato Leaf Hoppers, Beanleaf Beetles, and Soybean Thrips, when applied to the insect or its habitat, especially as an aqueous solution, suspension, or emulsion. Effective kill levels are observed as long as fourteen days after application whereas, using the individual components, effective kill levels do not ordinarily extend beyond 24 hours after application.