Age-dependent regulation of protein synthesis in an aphid endosymbiont by the host insect

In an old (45–50 days) aphid, the endosymbionts synthesize protein species which are not produced in the young (13–20 days) ones. Symbionin, the only protein synthesized in vivo by the endosymbionts of pea aphids, was not produced to any great extent in old hosts. It seems that control of the host over the endosymbiont is weakened in old insects, and that some of the symbiont's own genes begin to be expressed.