Apollyon (Left Behind #5) by Tim LaHaye and Jerry B. Jenkins

Apollyon: The Destroyer Is Unleashed
As the world’s thousands of believers gather in Jerusalem for a stadium rally, the Tribulation Force struggles with their own personal crises. Nicolae Carpathia continues his rise to power, forcing believers underground. But Nicolae isn’t prepared for a plague of scorpion-like locusts tormenting his followers―with a pain so horrible that men try to kill themselves but aren’t allowed to die.