Rearing of Heliothis virescens (F.) on diets containing 0.1–10.0 g rubidium chloride (RbCl)/liter had no adverse effects, and the resulting moths were labeled with elevated levels of Rb. However, lower levels of RbCl in males treated with 0.1 g approached the highest levels in insects from untreated diets. Some of the spermatophores transferred by labeled males were labeled.