Overt viral diseases induced from apparent latency following parasitization by the ichneumonid wasp, Hyposoter exiguae

Latent and/or asymptomatic viral infections are commonplace in insects, but factors inducing overt disease are poorly understood. Here we show that in Trichoplusia ni larvae parasitized by the ichneumonid wasp, Hyposoter exiguae, overt, lethal disease may on occasion be observed; however, disease has been consistently absent in control (non-parasitized) larvae. Thus far, we have detected two such diseases, one of which is caused by a granulosis virus affecting primarily fat body tissue. The other is associated with the presence of two viruses replicating together in larval midgut epithelial cells; of these, one has been identified as a non-occluded form of TnCPV. Since H. exiguae carries a polydnavirus, which is delivered to host larvae during oviposition, it is tempting to speculate that viral latency may in some cases be broken through immunosuppressive activity resulting from insect parasitism.