Virus-like particles have been found in the female reproductive tracts of allApantelesspp. thus far examined. Particles generally consist of putative baculovirus-like nucleocapsids which are enveloped singly or as groups within nuclei of calyx epithelial cells. Enveloped particles are injected into host caterpillars during oviposition. Subsequently, particle nucleocapsids appear in the cytoplasm of many host cells, and appear to be uncoated at nuclear pores.