During oviposition, the parasitic wasp Diachasmimorpha longicaudata introduces an entomopoxvirus (D1EPV) and a rhabdovirus (D1RhV) into larvae of its tephritid fruit fly host Anastrepha suspensa. D1EPV and D1RhV replicate, respectively, in host hemocytes and epidermal cells. Both viruses, like many beneficial viruses of parasitic wasps, are retained in all wasp generations but their avenue(s) of transmission are unknown. This study tests the hypothesis that D1RhV is transmitted transovarially or through larval feeding on infected host hemolymph. Transmission electron microscopy (TEM) revealed no virions in pre-vitellogenic or vitellogenic ova, or in the lateral oviduct of D. longicaudata females. However, numerous virions occurred in subchorionic regions of 33-36-h-old oviposited eggs. This suggests that D1RhV is introduced into the egg either as (a) intact virions after chorionogenesis but prior to oviposition and/or as (b) unencapsidated RNA molecules, undetectable by TEM in pre-vitellogenic ova, that subsequently replicate and assemble into mature virions. D1RhV particles also occurred in the midgut lumen of 20-24-h-old wasp first instars, suggesting that they were ingested. These virions may have been released from the egg into the hemolymph during hatching or may have come from virions introduced by the female wasp directly into the host, separate from the egg. D1RhV particles were also evident in the intracellular vesicles and intercellular spaces of the larval midgut. Taken together, these data support the hypothesis that D1RhV is transovarially transmitted as virions and/or as unencapsidated RNA. Further studies are needed to determine whether the D1RhV that ultimately resides within the female wasp's accessory gland filaments is the progeny of the virus from the egg and/or larval midgut cells. [copyright] 2005 Elsevier Ltd. All rights reserved. Anastrepha suspensa (Tephritidae) : Host Diachasmimorpha longicaudata (Braconidae) : Parasite Associations; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts Anastrepha suspensa; Hymenopteran parasites; Rhabdovirus transovarial transmission to parasite progeny; Diachasmimorpha longicaudata Diachasmimorpha longicaudata; Mutualism; Transovarial transmission to progeny; parasitized dipteran host; Rhabdovirus; Dipteran hosts; Anastrepha suspensa none