Abstract: 【Aim】 To clarify the effects of antibiotics on the obligate symbiont in the pea aphid, Acyrthosiphon pisum and investigate the impacts of the symbiont Serratia symbiotica on the growth, development and reproduction of A. pisum. 【Methods】 The type of facultative symbionts in adults of the green morph of A. pisum used in this study was detected by diagnostic PCR. The facultative symbionts were removed by injecting and feeding antibiotics to establish A. pisum line without facultative symbionts. The copy numbers of specific gene fragment of the obligate symbiont Buchnera aphidicola in A. pisum adults with and without S. symbiotica were determined by quantitative PCR. The body weight, rates of ecdysis, mortality rates and fecundity of A. pisum with and without S. symbiotica were recorded. 【Results】The A. pisum adults used in this study harbored only one facultative symbiont, S. symbiotica. The facultative S. symbiotica in A. pisum adults could be removed by injecting antibiotics, while the injection of antibiotics had no effect on the content of the obligate symbiont B. aphidicola. Compared with S. symbiotica-harboring A. pisum adults, S. symbiotica-removed A. pisum adults gained weight very slowly, and had less than one-third of the weight of S. symbiotica-harboring A. pisum adults at 9 d after birth. S. symbiotica-removed A. pisum adults had longer 1st instar nymphal duration, higher mortality rate and fewer offspring produced by per adult. 【Conclusion】The laboratory green A. pisum line carries the symbiont S. symbiotica. The removal of the symbiont S. symbiotica from A. pisum does not affect the content of the obligate symbiont B. aphidicola but has a negative effect on the growth, development and reproduction of A. pisum.

Key words: Acyrthosiphon pisum, symbiont, life history parameters, injection of antibiotics