In vivo enhancement of baculovirus infection by the viral enhancing factor of a granulosis virus of the cabbage looper, Trichoplusia ni (Lepidoptera: Noctuidae)

The ability of the viral enhancing factor (VEF) from Trichoplusia ni granulosis virus to enhance the infectivity of Autographa californica multiply enveloped nuclear polyhedrosis virus (AcMNPV) was measured in mid-fourth instar T. ni bioassays. In dose-response bioassays with a constant AcMNPV dose and VEF concentrations varying from 1 to 40 ng/larva, mortality increased linearly with the log dose of VEF from 20.8 to 93.1%. Reciprocal bioassays in which the dose of VEF was constant while that of the virus was varied yielded parallel dose response lines with a calculated potency ratio (LD50 for virus alone/LD50 for virus + VEF) of 3. In addition to increasing mortality, 40 ng of VEF significantly reduced median survival times of LD20 and LD90 doses of AcMNPV by 9.5 and 10.7 hr, respectively. VEF also enhanced AcMNPV in neonates of T. ni. Increased susceptibility of T. ni larvae to T. ni singly enveloped nuclear polyhedrosis virus (a potency ratio of 16 with 40 ng of VEF), and Anticarsia gemmatalis multiply enveloped nuclear polyhedrosis virus (a potency ratio of ca. 10.0 with 40 ng of VEF) was also demonstrated.