38th Annual Meeting of the Society for Invertebrate Pathology

Ascoviruses are transmitted to lepidopteran larvae by parasitoids mechanically during oviposition. There are four official ascovirus species accepted by ICTV. The Diadromus pulchellus ascovirus 4 (DpAV-4), which has a genome of 116 kb, replicates in the female genitalia. The Spodoptera frugiperda ascovirus 1 (SfAV-1) has a genome of 140 kb, infects only Spodoptera sp and replicates in the fat body tissue. The genomes of Heliothis virescens 3 (HvAV-3) and Trichoplusia ni ascovirus 2 (TnAV-2) are about 180 kb. The two have a similar wider host spectrum, with HvAV-3 replicating in the fat body and TnAV-2 replicating preferentially in the epidermis, tracheal matrix and connective tissues. It is hypothesized that the four ascoviruses evolved according to the genome size, host range, tissue tropism and degree of independence on replication in hymenopteran hosts from DpAV-4 to SfAV-1 to HvAV-3 to TnAV-2. Such evolution might have occurred by acquiring genes horizontally from hosts thereby increasing genome size, expanding host range and widening tissue tropism. In addition, iridoviruses, ascoviruses and poxviruses are all cytoplasmic viruses. Evolution might have occurred from a more nuclear replication dependent iridovirus to a complete nuclear replication independent entomopoxvirus in cytoplasm with ascovirus as a link.