and complete development of the immature wasp in the caterpillar. Additionally, genes expressed from the polydnavirus in the parasitised host alter host development and metabolism to be beneficial for the growth and survival of the parasitoid larva. Potential carrier subfamilies Ichneumonoidea Braconidae Microgastrinae Miracinae Cheloninae Cardiochilinae Mendeselinae Khoikhoiinae Ichneumonidae Campopleginae Banchinae Characteristics Both genera of PDV share certain characteristics: the virus particles of each contain multiple segments of dsDNA (double-strand, or "normal" DNA, as contrasted with positive- or negative-sense single-strand DNA or RNA, as found in some other viruses) with each segment containing only part of the full genome (much like chromosomes in eukaryotic organisms) the genome of the virus has eukaryotic characteristics such as the presence of introns (common for insect genes but rare for viruses) and a low coding density the genome of each virus is integrated into the host wasp genome the genome is organized in several multiple-member genes families (which differ between Bracoviruses and Ichnoviruses) the virus particles are only produced in specific cell types in the female wasp's reproductive organs The morphologies of the two genera are different when observed by electron microscopy. Ichnoviruses tend to be ovoid while bracoviruses are short rods. The virions of Bracoviruses are released by cell lysis; the virions of Ichnoviruses are released by budding. Evolution Nucleic acid analysis suggests a very long association of the viruses with the wasps (estimated 73.7 million years ± 10 million). Older wasp-derived theory Two proposals have been advanced for how the wasp/virus association developed. The first suggests that the virus is derived from wasp genes. Many parasitoids that do not use PDVs inject proteins that provide many of the same functions, that is, a suppression of the immune response to the parasite egg. In this model, the braconid and ichneumonid wasps packaged genes for these functions into the viruses—essentially creating a gene-transfer system that results in the caterpillar producing the immune-suppressing factors. In this scenario, the PDV structural proteins (capsids) were probably "borrowed" from existing viruses. Current endogenous virus theory The alternative proposal suggests that ancestral wasps developed a beneficial association with an existing virus that eventually led to the integration of the virus into the wasp's genome. Following integration, the genes responsible for virus replication and the capsids were (eventually) no longer included in the PDV genome. This hypothesis is supported by the distinct morphology differences between IV and BV, suggesting different