The Diachasmimorpha longicaudata entomopoxvirus (D1EPV), the first reported symbiotic entomopoxvirus, occurs in the venom apparatus of D. longicaudata female wasps and is introduced into Anastrepha suspensa larvae during parasitism. The D1EPV 250-300kb double stranded DNA genome encodes putative proteins having 30 to >60% amino acid identity with poxvirus homologs such as DNA helicase, DNA-dependent RNA polymerase, and the poxvirus-specific rifampicin resistance protein. Although the molecular characterization of D1EPV is progressing, little is known about its morphogenesis in and effects on host haemocytes. This paper describes (1) haemocytes of third instar A. suspensa, (2) D1EPV infection and morphogenesis, and (3) D1EPV-induced changes in haemocytes. A. suspensa third instars have 3-4 haemocyte morphotypes. Dot blots of DNA from infected haemocytes hybridized with a digoxigenin-labeled D1EPV genomic probe as early as 4h post-parasitism (hpp) and the intensity of the signal increased with time through 40 hpp. Immunofluorescence microscopy localized D1EPV proteins in cytoplasmic (but not nuclear) sites of infected haemocytes, within 24-36hpp. Electron microscopy confirmed the presence of viral envelopes, immature spheroids with centric nucleoids, budding virus, and extracellular enveloped virus in three haemocyte types, 24-84hpp and later. Infected haemocytes exhibited blebbing, DNA concatenation, and inability to encapsulate sephadex beads in vitro. These data indicate that D1EPV disrupts the normal function of host haemocytes, thereby insuring the successful development of D. longicaudata offspring and as such should be regarded as a symbiont of the wasp. [copyright] 2005 Elsevier Ltd. All rights reserved. Anastrepha suspensa (Tephritidae) : Host Diachasmimorpha longicaudata (Braconidae) : Parasite Circulatory system; Haemolymph; Associations; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts Anastrepha suspensa; Haemocytes; Hymenopteran parasites; Morphogenesis & cytopathic effects on haemocytes by parasite introduced entomopoxvirus; Diachasmimorpha longicaudata Diachasmimorpha longicaudata; Mutualism; Entomopoxvirus; Dipteran hosts; Morphogenesis & cytopathic effects of introduced entomopoxvirus; Anastrepha suspensa none