Presence of polydnavirus transcripts in an egg-larval parasitoid and its lepidopterous host

The parasitoid Chelonus inanitus (Brasconidae, Hymenoptera) oviposits into eggs of Spodoptera littoralis (Noctuidae, Lepidoptera) and, along with the egg, also injects polydnaviruses and venom, which are prerequisites for suc cessful parasitoid development. The parasitoid larva develops within the em bryonic and larval stages of the host, which enters metamorphosis precociou sly and arrests development in the prepupal stage. Polydnaviruses are respo nsible for the developmental arrest and interfere with the host's endocrine system in the last larval instar. Polydnaviruses have a segmented genome a nd are transmitted as a provirus integrated in the wasp's genome. Virions a re only formed in female wasps and no virus replication is seen in the para sitized host. Here it is shown that very small amounts of viral transcripts were found in parasitized eggs and early larval instars of S. littoralis. Later on, transcript quantities increased and were highest in the late last larval instar for two of the three viral segments tested and in the penult imate to early last larval instar for the third segment. These are the firs t data on the occurrence of viral transcripts in the host of an egg-larval parasitoid and they are different from data reported for hosts of larval pa rasitoids, where transcript levels are already high shortly after parasitiz ation. The analysis of three open reading frames by RT-PCR revealed viral t ranscripts in parasitized S, littoralis and in female pupae of C. inanitus, indicating the absence of host specificity. For one open reading frame, tr anscripts were also seen in male pupae, suggesting transcription from integ rated viral DNA.