THE ECDYSTEROID UDP-GLUCOSYLTRANSFERASE GENE OF AUTOGRAPHA-CALIFORNICA NUCLEOPOLYHEDROVIRUS ALTERS THE MOLTING AND METAMORPHOSIS OF A NONTARGET INSECT, THE SILKWORM, BOMBYX-MORI (LEPIDOPTERA, BOMBYCIDAE)

The Autographa californica nucleopolyhedrovirus (AcMNPV) does not infe ct the silkworm and molecular studies on silkworm insusceptibility hav e not been performed. In cultured cells of the silkworm, the expressio n of viral genes has been reported. The, expression of AcMNPV genes an d their effect in vivo and in vitro was studied. In this study, the ea rly gene, the ecdysteroid UDP-glucosyltransferase (egt) gene of AcMNPV , which inactivates the insect moulting hormone by sugar conjugation, was examined to determine whether it would alter the growth of the sil kworm. Using wild-type (wt) AcMNPV, the egt gene deletion virus (vEGTD EL), anti the virus carrying the egt promoter-lacZ cassette in vEGTDEL (VEGTZ), the egt promoter-driven expression in cultured cells and in nonproductive infection of the silkworm was characterized. Infection o f cultured cells with vEGTZ at three different doses occurred in a sin gle cell manner. When budded wt AcMNPV was injected into the fourth an d fifth instar larvae, an increase in the amount of virus occurred and caused abnormal larval growth, which resulted in the prolongation or skipping of the larval instar, premature pupation, or death during the pupal stage. For infection of the fourth instar larvae, precocious me tamorphosis was observed. When the same amount of vEGTDEL was injected , the alteration of growth did not occur. These results suggest that t he egt gene was expressed in the primary infected cells of the silkwor m, and that the EGT was secreted into the haemocoel, which significant ly altered larval growth.