Spiroplasma symbiont of the pea aphid, Acyrthosiphon pisum (Insecta : Homoptera)

From a laboratory strain of the pea aphid, Acyrthosiphon pisum, we discover ed a previously unknown facultative endosymbiotic bacterium. Molecular phyl ogenetic analysis based on 16S ribosomal DNA revealed that the bacterium is a member of the genus Spiroplasma. The Spiroplasma organism showed stable vertical transmission through successive generations of the host. Injection of hemolymph from infected insects into uninfected insects established a s table infection in the recipients. The Spiroplasma symbiont exhibited negat ive elects on growth, reproduction, and longevity of the host, particularly in older adults. Of 58 clonal strains of A. pisum established from natural populations in central Japan, 4 strains possessed the Spiroplasma organism .