Bracon mellitor Say, the most important hymenopteran ectoparasite of the cotton boll weevil, Anthonomus grandis Boheman, in the southern United States and northern Mexico, was reared for the first time in vitro on semi-artificial diets devoid of insect parts. The comparative duration of the biological cycles from egg to adult, when this parasitoid was reared in vivo on boll weevil larvae, and on semi-artificial diets with and without insect hemolymph, were ca. 10, 12 and 14 days, respectively. Adult yields obtained with diets devoid of hemolymph were low (15 - 20%), but adults appeared normal, had normal sex ratios and reproduced.