Type of Damage dealt by belt rats:

Amarr Navy - EM / Thermal
Angel Cartel - Kinetic / Explosive / Thermal
Blood Raider - Thermal / EM
Caldari - Kinetic / EM
Gallente - Kinetic / Thermal
Guristas - Kinetic / Thermal
Khanid - EM / Thermal
Mercenaries - EM / Kinetic / Thermal / Explosive
Minmatar Fleet - Thermal / Explosive
Mordu's Legion - EM / Kinetic / Thermal
Rogue Drones - ALL Damage Types
Sansha's Nation - EM / Thermal
Serpentis - Kinetic / Thermal
Thukker Tribe - Explosive / Thermal

Main Damage type to shoot at the enemy:
Angel - Explosive
Blood Raiders - Thermal / EM (weak against EM)
Caldari - Kinetic
Guristas - Kinetic
Mercenary - Thermal
Mordus - Thermal & Kinetic
Rogue Drones - EM
Sansha - Thermal / EM (weak against EM)
Serpentis - Thermal / Kinetic