Laboratory applications of 4'-(3,3-dimethyl-l-triazeno) acetanilide (American Cyanamid CL-24055) to cotton plants limited leaf feeding and reduced the larval weights of the bollworm, Heliothis zea (Boddie); tobacco budworm, H. virescens (F.); cabbage looper, Trichoplusia ni (Hubner); yellow woollybear, Diacrisia virginica (F.); and cotton leafworm, Alabama argillacea (Hubner). Feeding damage by the cabbage looper was reduced 90% when larvae were placed on leaves 2 hr after 24 hours. Injection or topical applications of CL-24055 to bollworm larvae did not reduce larval feeding as much as foliage applications. In field-cage studies a 58% reduction occurred in populations of bollworm larvae after treatment with CL-24055. Also, in a field test with CL-24055, a 22% reduction occurred in squares and bolls damaged by Heliothis spp. Tobacco budworm larvae fed leaves treated with CL-24055 weighed less, whether or not the labial palpi were removed. The following materials caused no (A1%) reduction in tobacco budworm and cabbage looper larval feeding and weight: alpha- (3-phenylpropyl) piperonyl alcohol; phenacyl thiocyanate; N-sec- butyl- p -toluamide; p -(1,1,3,3-teracnetgyt-butyl) phenyl propionate; octyl m -toluate;4 (or5)-chloro- N-N -diethy 1-2-methylcyclohexanecarboxamide; N ,2,2-trimethy1-4',5'-(methylenedioxy)-3 (2-methylpropenyl)-2'-propylcyclopropanecarboxanilide; N -butylsuccinimide; 2-methyoxyethyl 4(or 5)-chloro-2-methylcyclohexanecarboxylate; calamus oil distillate fractions; imidazole; and the plant pigment quercetin (3,3', 4'5,7-pentahydroxyffavone).