Pupae of Tenebrio molitor were individually irradiated for two hours by CW 9.0-GHz microwaves in X-band waveguide (TE-10 mode) at fixed power levels of incident radiation; the power levels ranged from 10 to 320 mW and resulted in estimated dose rates approximating 25 to 800 mW g−1. Subsequent examination of adults for gross structural abnormalities revealed that the occurrence of defects was a complex function of power level of incident radiation: as the level was increased from 10 to 80 mW, incidence of defects first increased and then decreased; above 80 mW, the incidence of defects increased once more. The probability of pupal mortality increased only in the region above 80 mW. Neither intact (“ideal”) nor structurally defective (“nonideal”) pupae exhibited much evidence of teratogenesis at 80 mW; other-wise, as observed earlier in our laboratory, ideal pupae were more resistant to insult at levels of irradiation in the range 20 to 320 mW. Data are also presented which indicate that susceptibility to microwave irradiation might be positively correlated with culturing and exposure of Tenebrio under conditions of low relative humidity.