Technical Abstract: Genetically modified, mass reared insects present novel possibilities for the future of insect control. One concern about manipulation of insects is a possible loss of strain quality due to the introduction of a foreign gene of any sort into the insect genome. Eight transgenic strains of Cochliomyia hominivorax (Coquerel) (Diptera: Calliphoridae) were compared with the wild-type parental laboratory strain in laboratory culture. Measurements of average fertility, fecundity, and larval production were analyzed, and longevity studies were performed. Two transgenic strains had significantly lower larval productivity than control, one of which was explained by a homozygous lethal insertion of the transgene. Another strain produced significantly fewer eggs than control. Overall strain characteristics, including measurements from egg, larva, pupa, and adult stages, were compared. Transgenic colonies did not consistently show significantly lower individual or aggregate strain quality characteristics than the control parental colony; hence, the presence of the transgene used to produce the strains tested did not incur a discrete cost to the colonies of laboratory-reared C. hominivorax.