Evaluation of different concentrations antibiotics on gut bacteria and growth of Ectropis obliqua Prout (Lepidoptera: Geometridae)

The use of antibiotics to remove gut bacteria is a commonly used method to study gut function of insects. We assessed the impact of the artificial diet made from tea powder with different concentrations of antibiotics mixture (containing tetracycline, gentamicin, penicillin, and rifampicin) on Ectropis obliqua Prout (Lepidoptera: Geometridae) survival, growth, and reproduction. Antibiotic-induced bacterial clearance was monitored by Polymerase Chain Reaction (PCR) and by Colony-counting Methods. The results indicated that administration of the antibiotic mixture at a concentration of 200μg/ml caused the increase of gut bacteria, while a concentration of 300μg/ml was more effective in clearing gut bacteria but the concentration of 400μg/ml caused a large number of larval deaths. The concentration of 300μg/ml had no significant effect on the growth and development of E. obliqua , but had impact on fecundity. Therefore, we could use 300μg/ml concentrations of the antibiotic mixture to obtain sterile E. obliqua to study the function of intestinal microbes.