Parece ser que el parasitoide entro casualmente a California antes de 1913 por
ecesis con sus hospederos (ver material estudiado) aunque no se pueden excluir la posibilidad de aclimatacion de algunas poblaciones introducidas deliberadamente.
However, Borns and Goldthwait (1966) suggested, on the basis of ages of living trees on the outermost moraine and estimates of
ecesis, that ice retreat and moraine stabilization did not occur until the early or middle 19th century.
The tree ages need to be adjusted to account for the time between moraine stabilization and seedling germination ("
ecesis"; McCarthy and Luckman, 1993; Winchester and Harrison, 2000).