Toxoneuron (=Cardiochiles) nigriceps polydnavirus encodes a putative aspartyl protease and is highly expressed in parasitised host larvae.

Toxoneuron (=Cardiochiles) nigriceps (Viereck) (Hymenoptera: Braconidae) is an endophagous parasitoid of larval stages of the tobacco budworm, Heliothis virescens (F.) (Lepidoptera: Noctuidae). This parasitoid is associated with a polydnavirus (TnBV), injected at oviposition along with the egg, and involved in the disruption of host immune reaction and endocrine balance. This paper reports the molecular characterisation of TnBV2, one of the most abundant genes in TnBV genome. TnBV2 expression produces a mature 0.6 kb transcript in fat body, prothoracic glands and haemocytes, as early as 6 h after parasitoid oviposition. Only in haemocytes a specific longer transcript of 2.5 kb is found 24 h after parasitisation. The putative translation product of TnBV2 contains a retroviral type aspartyl protease domain. The possible origin and functional role of this TnBV gene are discussed.