Replication of Anticarsia gemmatalis nuclear polyhedrosis virus in four lepidopteran cell lines

Anticarsia gemmatalis nuclear polyhedrosis virus (AgNPV; family Baculoviridae) is pathogenic for larvae of the velvetbean caterpillar, Anticarsia gemmatalis Hübner-an important pest of soybean. AgNPV is a viable alternative to chemical control of A. gemmatalis in Brazil, where its use as a pesticide has brought significant economic and environmental benefits. Although a significant amount of information is available on the ecological and biological control aspects of AgNPV, very little is known about the replication cycle and host specificity of this virus. We examined the susceptibility of four lepidopteran cell lines to AgNPV. Infections of the A. gemmatalis UFL-AG-286 cell line were highly productive. Ninety percent of infected cells had polyhedral inclusion bodies by 48 hr after infection, and the infectious virus titer was 10(8) IU/ml. Viral DNA replication was efficient, and the maximal rate of synthesis was between 6 and 12 hr after infection. Infections of the Spodoptera frugiperda IPLB-SF-21 cell line were productive but less efficient. Infections of Choristoneura fumiferana IPRI-CF-124T cells with this virus were poor, with only 5% of the cells forming polyhedra and an infectious virus titer of 10(6) IU/ml. The level of viral DNA replication was low, suggesting that this system was predominantly abortive. Infections of Bombyx mori BM-5 cell lines were abortive, and cells had apoptosis-like morphology. No polyhedra or increase in infectious levels were observed, and there was little or no replication of viral DNA. Our data suggest that restriction of AgNPV replication in abortive cell lines is due mainly to inability of viral DNA to replicate efficiently. The possible causes of low DNA replication are discussed. Our results suggest that the cell lines utilized in this study can provide an important model for studying mechanisms of AgNPV host specificity.