Most parasitoid wasps parasitize herbivorous insects, so nectar from flowers is readily available. However, parasitoid wasps are also an important component of the rich invertebrate communities at livestock facilities in large accumulations of manure, where flowers are largely absent. Little is known about adult parasitoid diet and nutrition in these communities. The present study examined this in Spalangia cameroni Perkins, a pupal parasitoid of filth flies. Like many parasitoid wasps, S. cameroni feed on host fluids, and in the laboratory readily feed on honey or a sucrose solution, which increases their longevity. Here adult longevity in the presence of six potential food sources, bovine manure, sorghum silage, bovine milk, buckwheat inflorescence (Polygonaceae), sweet alyssum inflorescence (Brassicaceae), or dandelion inflorescence (Asteraceae), was compared to that with water or honey. Only parasitoids given buckwheat lived as long as parasitoids given honey, and parasitoids given honey or buckwheat lived longer than parasitoids given water. Parasitoids readily ate buckwheat nectar, avoiding pollen grains. Diet affected the amount of free sugars, glycogen, and lipids in complex ways. Compared to parasitoids that were given just water, parasitoids with access to honey or sucrose had higher sugar and glycogen levels, but not detectably higher lipid levels. Access to buckwheat had no detectable effect on a parasitoid's free sugar, glycogen, or lipid levels; however, then after 4 d with just water, sugar levels were lower and glycogen levels were higher compared to parasitoids that had been given access to only water the entire time.