none Leiophron uniformis (Gahan), the braconid parasite of Lygus spp. nymphs, was successfully labeled with the element rubidium by the addition of RbCl to an artificial diet of its host Lygus hesperus Knight. A concentration of 200 ppm RbCl in the diet was sufficient to distinguish the labeled L. uniformis for 6-8 days from wasps collected from the field in July, but a higher concentration was required for wasps collected in September. The mean endogenous level of Rb in wasps collected in September was 2.3 times the level in the wasps collected in July.