First-day pupae of the darkling beetle Tenebno molitor were exposed to CW microwaves in the far field of a horn-irradiated, temperature-controlled, anechoic chamber. They and controls were allowed to develop to the adult stage and were then examined for the presence of gross morphological abnormalities. Control pupae from an in-house colony developed significantly fewer developmental abnormalities than control pupae purchased from an outside supplier. The following experiments were performed at 5.95 GHz: (1) Pupae were held parallel to the electric-field vector for two hours at an E-field maximum (91 V m−1 RMS) of a standing-wave distribution; at a nominal dose rate of 130 W kg−1, no effect was observed in either sample of pupae. (2) Pupae were held parallel to the magnetic-field vector for two hours at an H-field maximum -1.53 A m−1 RMS) of a standing-wave distribution; at a nominal dose rate of 54 W kg−1, no effect was seen in colony pupae but significant effects were observed in cultures of the other pupae. (3) Pupae were held parallel to the electric-field vector in a traveling-wave distribution at 110 W m−2; only outside pupae were used, but no effect was detected for 13-hour exposures. Another experiment was performed at 10.025 GHz: Pupae were held antiparallel to Poynting's vector for four hours in a traveling-wave field at 50 W m−2; no effect was detected in colony pupae but a marginally significant effect was observed in the outside pupae. It was also demonstrated in samples of both pupal types that the condition under which they were maintained during development within the pupal stage could significantly affect the incidence of abnormalities in the adults.