Survivorship. developmental period, and adult longevity of the fruit fly, Drosophila melanogaster Meigen (Diptera: Drosophilidae), exposed to penicillin G, a beta-lactam antibiotic, was determined in laboratory testing. In the study, neonate larvae were placed and reared on dietary antibiotics at concentrations of 100. 200. 400, or 800 mg/L. All penicillin concentrations significantly decreased survivorship in an inverse relationship with third instars, pupae, and adults. Larvae fed on control diets of 0 mg/L of penicillin had a survival level of 91.00 +/- 327% to third instar and pupation, and 89.00 +/- 4.09% to adult emergence. Feeding on a diet containing the highest concentration of penicillin (800 mg/L) significantly decreased survivorship to third instar to 11.00 +/- 2.59% (chi(2) = 128.051; df =1; P= 0.0001) and to pupation (chi(2) -131.233; df =1; P= 0.0001) and adult emergence to approximately 10.00 +/- 1.00% (chi(2) = 124.832; df = 1; P= 0.0001). The highest concentration of dietary penicillin (800 mg/L) also significantly prolonged developmental time from neonate to third instars by 1.5 d (F = 17.229; df = 4; P= 0.0001) and from neonate to adult emergence by 3 d (F= 2.004; df = 4; P 0.032). Compared to the control group, adult longevity was significantly reduced by the antibiotic in a dose-related manner. The use of this antibiotic in insect artificial rearing enables an extensive search of possible insecticidal action of penicillin with high dietary levels for agricultural purposes.