Korehelorus jinjuensis gen. et sp. nov., a new genus and species of the family Heloridae, is described and figured from a specimen preserved in the dark grey shales of the lower Albian Jinju Formation (Republic of Korea). This description further increases the diversity of the family Heloridae in the Mesozoic and provides additional evidence for a rapid decline of the latter in the Cretaceous. To date, no explanations nor hypotheses have been proposed to explain this particular pattern but we assume and hypothesize that the species and genus diversities of helorid wasps are linked with the diversity of their hypothetical hosts (i.e., Chrysopidae or closely related extinct lineages). We show that the Cretaceous chrysopoid diversity is dominated by the Mesochrysopidae and stem-chrysopid subfamily (Limaiinae), which declined and/or die out through the Cretaceous. We find a peak of diversity for the Heloridae, synchronous with that of the Mesochrysopidae and Limaiinae, leading us to suggest that the decline of these clades in the Cretaceous consequently triggered a decline in the Heloridae.