TableAdapter.Update() not deleting records from DB

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C#

table

I have created a dataset for my table tbl_Cust.In code created a tableadapter object adapter n a typed datatable custtb.then i have inserted 2 rows, updated 2 rows and deleted 2 rows in my datatable custdb thru code.
then i called adapter.Update(custtb) to update same in my DB.
Inserted&Updated records are reflecting in DB. But the deleted one are not actually removed from DB.

The code for DB update is like

this.dataSetDataTableFromDBBindingSource.EndEdit();
this.Validate();
this.adapter.Update(this.custtb);

my delete command of adapter is correct.I cant use delete method of adapter and delete each rows as i wanna do it in bulk.
Anyone idea on where it goes wrong?????
Thanks in advance