From Halopedia, the Halo wiki
In 2462, as a revenge for Kig-Yar nest relocations on High Charity caused by the rapidly increasing Unggoy numbers, some radical Kig-Yar shipmasters poisoned Unggoy infusion supplies, making several thousand affected Unggoy males sterile. The Covenant leadership's lack of response to this event, which became known as the "Infusion Incident", eventually caused the Unggoy to revolt, beginning the Unggoy Rebellion.
List of appearances
- Halo: Contact Harvest (First appearance)
- Halo: The Thursday War
- Halo: Mortal Dictata
- Halo 2: Anniversary
- Halo 5: Guardians (Mentioned only)