Contact toxicity was shown by diacylhydrazine insect growth regulators (IGRs) against strains of beet armyworm, bollworm and tobacco budworm when topically applied to different ages of their larvae. Methoxyfenozide (Intrepid) was the most toxic most of the time against strains of all three pests but 7 days were required for maximum toxicity. Of the five diphenyl benzoyl urea IGRs tested for contact toxicity only lufenuron showed an LD₅₀ against a reference strain of the beet armyworm. Great differences in toxicity between methoxyfenozide and tebufenozide (Confirm) were shown between five field collected strains of beet armyworm from the Lower Rio Grande Valley of Texas, U. S. A. and Tamaulipas, Mexico. There was an 891 fold difference in LD₅₀s for methoxyfenozide of the reference strain of beet armyworm and one of the field collected strains. LD₅₀'s for two of the field collected strains showed no significant differences. LD₅₀ ‘s of methoxyfenozide by the other three strains were significantly different from those shown for tebufenozide. A trend toward greater contact toxicity at all ages to bollworm than to tobacco budworm was shown for halofenozide, methoxyfenozide and tebufenozide.