How to filter your data source depends on what type of datasource you use...
For DataTable, you can use BindingSource.Filter or DataView or in some cases SqlDataSourceView.FilterExpression.
From your code above, it looks like the datasource you use (datasourceaccountnature) is a collection (of EntityCollection<T>) type.
Typically for collections as datasource in gridview, the filtering can be done as shown in the code below:
See if this helps.