The electrode was inserted in the hypopharynx of the tobacco cutworm larva and the antifeeding compounds were topically applied at the various mouth parts by means of the microsyringe. The larval hypopharyn and maxillary palps were the most sensitive targets to chlordimeform and clerodin, respectively. The results led to the conclusion that the proposed primary sites of action of clerodin are the maxillary palps. On the other hand, primary site of action of chlordimeform is the hypopharynx.