Defoliating caterpillars are the second most impor tant group of pests in eucalyptus plantations in Brazil, only behind leaf-cutting ants. In the past decade new species of eucalyptus defoliating lepidopterans have appeared in the countr y. Eupseudosoma involuta (Seep 1852) (Lepidoptera: Arctiidae) is considered a primary pest of eucalyptus in several regions of Brazil. Upon pupation, they were placed individually in glass tubes (2.5 cm diameter, 8.5 cm length); then, 20 pupae were offered to T. diatraeae females in a 28:1 (parasitoid:host) ratio for 72 h.Thereafter, the females were removed and containers with E. involuta pupae were maintained in a climatic chamber. The parameters determined were: level of parasitism, number of emerged and not emerged parasitoids and duration of the egg–adult cycle. The experimental level of parasitism reached 80 %, with an emergence rate of 80 %. Under these conditions the T. diatraeae egg-adult cycle was 19.4 ± 0.8 (SE) days in E. involuta pupae. These results demonstrate for the first time the ability of T. diatraeae to parasitize the pupae of E. involuta.