How load data items in Combobox condition on datetimepickers

Question

Hi all             I have a query like how to load dataitems in combobox from database checking condition between two datetime pickersvalues  in c# window forms

Select * from participant_details where Datefrm>='" + Datefrm1 + "' and DateTo<='" + DateTo1 + "' ", vCon);

                da.Fill(dt);

here Datefrm1 and DateTo1  are Datetimepickers values 

i didn't get correct result when I use the above code

please solve my problem


Reagards
NagaRaju