Costus spicatus (Jacq.) Sw. and Costus spiralis (Jacq.) Roscoe var. spiralis (Costaceae) are economically important plants due to their pharmacological and medicinal properties and ornamental value. These plants are natives from the Brazilian Atlantic Rainforest and are fed upon by Agaraea minuta Schaus, 1892 (Lepidoptera: Arctiidae). This study describes the damage done by A. minuta on C. spicatus and C. spiralis and the biological and ecological aspects of parasitism of A. minuta by Diolcogaster sp. (Hymenoptera: Braconidae). Twenty stems of C. spicatus and C. spiralis with 100 last-instar caterpillars of A. minuta, were collected per plant in each of 2 years. The stem heights (F, P > 0.05), leaf lengths (F, P > 0.05), leaf widths (F, P > 0.05) and the number of leaves per stem (F, P > 0.05) of both plant species; number of pupae obtained from caterpillars of A. minuta (F, P > 0.05), adult emergence of this defoliator (F, P > 0.05) and of Diolcogaster sp. (F, P > 0.05) were similar during the 2 study periods. Agaraea minuta fed on C. spicatus and C. spiralis, and Diolcogaster sp. was shown to be a parasitoid suppressor of populations of this defoliator.