Jamieson, Fausset and Brown on Isaiah 7:18

18. hiss--whistle, to bring bees to settle (see on Is 5:26).

fly--found in numbers about the arms of the Nile and the canals from it (Is 19:5-7; 23:3), here called "rivers." Hence arose the plague of flies (Ex 8:21). Figurative, for numerous and troublesome foes from the remotest parts of Egypt, for example, Pharaoh-nechoh.

bee--(De 1:44; Psa 118:12). As numerous in Assyria as the fly in marshy Egypt. Sennacherib, Esar-haddon, and Nebuchadnezzar fulfilled this prediction.