Although the resemblance of the polydnavirus virions to those of conventional insect viruses suggests that the former evolved from the latter, to date no molecular evidence supports this hypothesis. In the case of ascoviruses and ichnoviruses, well-conserved genes found among the three ascoviruses sequenced so far (SfAV1a [23] , TnAV2c [24] , and HvAV3e [25] ) are not found in ichnovirus genomes. As noted above, the principal reason for this is that the genomes of the latter viruses appear to contain mainly wasp genes, not viral genes. This highlights the need for new and alternative types of sequence data obtained from pertinent biological systems. In this regard, DpAV4 has features that could provide important insights. Indeed, it is the only ascovirus known to replicate in both its wasp and caterpillar hosts. It is transmitted vertically from wasp to caterpillars to suppress the defence response of the latter host, thereby enabling parasite development [26, 27] . Moreover, in males and females of D. pulchellus, the DpAV4 genome resides in the nuclei of all hosts cells, providing a possible example of what may have been an intermediate stage in the symbiogenesis that led to the evolutionary origin of ichnoviruses.