Their are 7 known chemicals in grapefruit seed . 5 of these have no known biological activities, Deacetyl-Nomilin, Deoxy-Limonol, Obacunol, Epi-iso obacunoic acid 17-0-beta-D-Glucoside, and Limonol. The other 2 are Nomilin(antifeedant) and Obacunone(anticataleptic and antifeedant) None of these would be of any use for your bees.
george