Aphids of the genus Stomaphis, which have a very long stylet, are parasitic on tree trunks and feed on phloem through thick xylem. Stomaphis japonica on Quercus acutissima, Q. serrata and Q. variabilis; S. yanonis on Celtis sinensis and Zelkova serrata; and S. malloti on Mallotus japonicus were surveyed every season from 1981 to 1998 at six sites situated in natural forests in Kyoto, Japan. From fragmentary observations, their life cycles were inferred and possible host alternation of S. japonica is discussed. Stomaphis yanonis and S. malloti are monoecious and holocyclic in Kyoto, as has also been observed near Tokyo and at Ise city, Mie Prefecture, respectively. Stomaphis japonica was found throughout the year on Q. serrata passing through a holocycle, but was found only from late May to mid-November on Q. acutissima and Q. variabilis, where neither oviparae nor males occurred. Alatae flew to Q. acutissima and Q. variabilis in late May to mid-June and settled there. However, all virginoparae emerged as alatae from October and left these trees in mid-October to early November. These observations suggest that Stomaphis japonica in this area comprise two sympatric populations: a monoecious population living on Q. serrata all year round and a heteroecious population alternating between Q. serrata as a primary host and Q. acutissima and Q. variabilis as secondary hosts.