On Shabbat 10a, the Tosafot indicate (based on the Mahzor Vitri) that since people wear a belt in their slacks they do not need an additional belt, but that in Talmudic times when people did not wear slacks they did need a belt for davening. What about a man who wears slacks held up by suspenders. Does he require a belt for davening?

Tosefos understand that a belt is necessary to avoid the problem of Libo Roeh Ervaso and therefore a tight or elasticised waistband would take care of the need for separation.

The Shulchan Aruch O.C. 91:2 does not rule like Tosefos, rather he follows the opinion of Ba'al haTerumos and others who learn that the requirement of wearing a belt is in order to be presentable before Hash-m and even if the problem of Libo Roeh Ervaso is obviated one should still wear a belt. The Magen Avraham writes that if one does not usually wear a belt at other times then it is not necessary to wear one for Davening. A regular pair of trousers worn with suspenders would be fine since this is a respectable form of dress.

All the best

Ilan Segal