How to call CascadingDropDown ServiceMethod at on click

Is it possible to load the content of CascadingDropDown ServiceMethod when the client user click the drop down?

I have this CascadingDropDown with ServiceMethod="GetCarMakes". GetCarMakes is called when the control is loaded. but I want it to only load when user click the down arrow.. is this possible?

thank you

my environment is ASP.net with VB.net code behind