In 2378, Icheb included this information, along with Kirk's encounters with the Baezians and the Chenari, in his final report to Captain Kathryn Janeway, as part of the Early Starfleet History course of his Academy training. (VOY: "Q2")
This species was only mentioned in dialogue.
The circumstances of Kirk's encounter with the Pelosians are revealed in the Department of Temporal Investigations novel Forgotten History — the Pelosian homeworld was experiencing a natural disaster, as a toxic gas-cloud enveloped the planet after a meteor strike.
With the reigning empress denying medical support to her people while proclaiming that it was a test of faith, ignorant of the fact that the surviving population would be too few and lack too many skills to survive for long if only her chosen few were saved, Kirk discreetly provided the population with medical supplies from the Enterprise.
When called to court-martial for his violation of the Prime Directive, Kirk defended his decision on the grounds that he could claim the medicines actually came from another city on the planet that had been destroyed in the catastrophe, rather than an alien world.