Enhancement in Activity of Homologous and Heterologous Baculoviruses Infectious to Fall Armyworm (Lepidoptera: Noctuidae) by Selected Optical Brighteners

The nuclear polyhedrosis virus (NPV) from Spodoptera frugiperda (J. E. Smith) (SfMNPV) was the most active virus tested against fall armyworm, larvae (LC50 = 8.1 PIB per mm2). No LC 50s could be obtained for the alfalfa looper, Autographa californica (Speyer), NPV (AcMNPV), the celery looper, Anagrapha falcifera (Kirby), NPV (AfMNPV), the wax moth, Galleria mellonella (L.), NPV (GmMNPV), or the bollworm, Helicoverpa armigera (Hübner), NPV (HaMNPV). The addition of an optical brightener, Tinopal LPW® (1%), (Sigma Co., St. Louis, MO) significantly enhanced the activities of all NPVs. The most activie NPV/Tinopal LPW combination was SfMNPV, followed by AcMNPVm HaMNPV, AfMNPV, and GmMNPV. In terms of speed of kill, SfMNPV was the most active virus tested. When Tinopal LPW was added, the LT50 was reduced by more than 35%. The addition of Tinopal LPW to the heterologous NPVs resulted in LC50 and LT50 values that were comparable to SfMNPV alone. Five of eight brighteners acted as activity enhancers for SfMNPV (i.e., Blankophor BBH, Blankophor HRS, Blankophor P167, Blankophor RKH, and Tinopal LPW), whereas Blankophor BSU, Blankophor DML, and Blankophor LPG did not enhance virus activity.

Infection of Spodoptera frugiperda and Choristoneura fumiferana cell lines with the baculovirus Choristoneura fumiferana nuclear polyhedrosis virus

The growth properties of cell lines derived from Spodoptera frugiperda (alfalfa looper) and Choristoneura fumiferana (spruce budworm) were investigated. The data demonstrated that the spruce bud worm cell line grew more slowly than the alfalfa looper cell line, and this reduced growth rate appeared to affect the rate of baculovirus replication in infected cells. Trypsinizing the spruce budworm cells or varying the multiplicity of infection did not greatly influence the rate of viral replication. Autographa californica nuclear polyhedrosis virus was able to replicate its DNA and synthesize late and very late proteins in both cell lines but did not produce infectious extracellular virus in the spruce budworm cell line. The replication cycle of C. fumiferana nuclear polyhedrosis virus did not produce late proteins or infectious extracellular virus in the alfalfa looper cells. The results indicate that S. frugiperda cells are nonpermissive for the C. fumiferana nuclear polyhedrosis virus but C. fumiferana cells are semipermissive for the A. californica nuclear polyhedrosis virus, resulting in an abortive infection.Key words: baculovirus, host specificity, AcMNPV, CfMNPV, spruce budworm.

PATHOGENICITY OF TWO NUCLEAR POLYHEDROSIS VIRUSES IN THE BLACK CUTWORM, AGROTIS IPSILON (LEPIDOPTERA: NOCTUIDAE),

LC50 and LT50 values for two multicapsid nuclear polyhedrosis viruses isolated from the alfalfa looper, Autographa californica (Speyer), and a mint looper, Rachiplusia ou (Guenée), were determined against black cutworm, Agrotis ipsilon (Hufnagel), neonate larvae, 1-day-old larvae reared at 15 °C before testing, and 1-day-old larvae reared at 27 °C before testing. The results showed that black cutworm larvae have low to moderate susceptibility to these viruses. As the larvae developed, their susceptibility to the viruses rapidly declined. Initial growth of larvae surviving sublethal dosages of these viruses was reduced, but pupal weights of these larvae were not significantly different from untreated controls.