The Crickets Chirp.

No one knows where the sound comes from or where the the cricket is but they hear it. But when they realize it's a curse. Multiple targets must succeed wisdom save against the spellcasters spellsave DC.

Or

The spellcaster summons a medium sized uncontrollable swarm of insects for the area that are unaligned for (1 d10 turns) if more than two people believe in it and hear it within 120 ft.

At higher spell levels. From level 1 to level 3.(level 1 large swarm, level 2 huge, or level 3 gargantuan size swarms of insects.)