POLYDNAVIRUS INFECTION INHIBITS SYNTHESIS OF AN INSECT PLASMA-PROTEIN, ARYLPHORIN

The wasp Campoletis sonorensis injects a segmented, double-stranded DN A polydnavirus (CsPDV) along with its egg during parasitization of Hel iothis virescens larvae. After parasitization, CsPDV protects the wasp egg and larva by selectively disabling the host's cellular immune res ponse. Other host physiological systems including growth and developme nt are affected to the apparent benefit of the parasite. To begin the characterization of the biochemical effects and mode of action of CsPD V on host growth, the titre of a developmentally regulated insect stor age protein, arylphorin, was studied. Parasitized or virus-infected in sects had substantially less circulating arylphorin than control insec ts. Fat bodies from parasitized larvae also synthesized less arylphori n in vitro. However, Northern blots of total RNA from parasitized and non-parasitized, control insects showed that the arylphorin transcript level was unaffected by parasitization suggesting a biochemical block at the translational level. In vitro translation followed by immunopr ecipitation of arylphorin indicated that the mRNA was present and tran slatable at equal levels in both parasitized and control insects. Inje ction of purified virus elicited the response observed in naturally pa rasitized larvae, demonstrating that the effect on arylphorin synthesi s is mediated, either directly or indirectly, by polydnavirus gene pro duct(s).