Insect growth regulators (IGRs) Ro 20–3600 and MV‐678 were found to be ineffective to adults of the rice weevil,Sitophilus oryzae(L.), via wheat treatment. On the other hand, the two IGRs and another IGR, R‐20458 were very effective by direct contact, e.g., the IGR MV‐678 caused 100% mortality at 20 ppm (v/v) dosage applied topically to pupae of the rice weevil. The mode of action was apparently similar for all the IGRs tested, however, they differed in relative potency.