The molting hormonal activity of methoxyfenozide (RH-2485), tebufenozide (RH-5992), five analogs with various alkyl groups, and 18 acyl analogs was measured by using cultured integument of rice stem borers, Chile suppressalis Walker. The hormonal activity of methoxyfenozide was remarkably high (EC50 = 1.1 x 10(-9) M), being equivalent to that of tebufenozide (RH-5992). The hormonal activity of several tebufenozide analogs with varying alkyl groups such as CH3, n-C3H7, i-H-3(7), n-C4H9 and n-C5H11 at the para-position of the benzene ring furthest from the tert-butyl group was lower than that of tebufenozide (alkyl group is C2H5). The activity decreased to varying degrees as a result of replacement of the 3,5-dimethylphenyl moiety of tebufenozide with either a phenyl, naphthyl, or cyclohexyl group. Both 1- and 2-naphthyl derivatives were very active (EC50 = 4.3 X 10(-8) M and 3.2 x 10(-8) M, respectively) without any significant difference between them. The activity of the 1-cyclohexenyl analog (EC50 1.0 x 10(-7) M) was about 40x that of the corresponding 3-cyclohexenyl analog (EC50 = 4.4 x 10(-6) M), but 1/100 that of tebufenozide. The activity varied parabolically with respect to the molecular hydrophobicity, and decreased with longer acyl moieties. (C) 2000 Elsevier Science Inc. All rights reserved.