* Legally: No. They can make their own choices about their life, including where they live, who they associate with, and what they do.
* Socially/Familially: This is complex. Many 18-year-olds maintain close relationships with their parents and choose to communicate and consider their parents' opinions. Others may have more distant relationships and choose to be less communicative. The level of expectation and obligation varies greatly from family to family. While there's no legal requirement to answer, ignoring parents completely could strain or damage the relationship.
In short, there's no legal obligation, but the social and familial expectations are highly variable and dependent on the specific family dynamic.