A NEW INSECT-CELL LINE FROM TRICHOPLUSIA NI (BTI-TN-5B1-4) SUSCEPTIBLE TO TRICHOPLUSIA NI SINGLE ENVELOPED NUCLEAR POLYHEDROSIS-VIRUS

The replication of Trichoplusia ni SNPV (TnSNPV) in a new Lepidopteran cell line, BTI-Tn-5B1-4 (Tn-5B1-4), is presented. This cell line was highly susceptible to TnSNPV with infection rates exceeding 90% by 48 hr postinfection (pi). Budded virus (BV) was present in the culture me dium 14 hr pi and reached a maximum titer of 3.2 x 10(6) TCID50/ml 48 hr pi. Cell-associated virus was produced 12 hr pi and reached a maxim um titer of 2.4 x 10(6) TCID50/ml 36 hr pi. Serial passage of TnSNPV w as initiated in Tn-5B1-4 cells with infectious hemolymph obtained from T. ni larvae infected with TnSNPV occlusion bodies (OBs). TnSNPV was subsequently grown in this cell line for 60 serial passages. Levels of BV infectivity were maintained at approximately 3.2 x 10(5) TCID50/ml through passage 60. Early passage virus (i.e., 1-7 passages) resulted in approximately 500 to 700 OB/cell, whereas later passages (i.e., 7- 60) showed an average decrease from 450 to 100 OB/cell. Bioassay resul ts showed high infectivity (approximately 95%) with early passage viru s; however, infectivity dropped off rapidly in later passages with no larval infectivity seen after passage 20. In addition, the effects of cryopreservation on virulence and yield of TnSNPV-BV, produced in the Tn-5B1-4 parental cell line, BTI-Tn-5B1, at 4 and -100 degrees C, were investigated. By 6 weeks, BV titers for samples stored at both temper atures had decreased by as much as one order of magnitude. Although gr adual decreases in titer were observed under both storage conditions, -100 degrees C appeared to be more suitable for long term cryopreserva tion. (C) 1994 Academic Press, Inc.