INFLUENCE OF LARVAL AGE ON THE LETHAL AND SUBLETHAL EFFECTS OF THE NUCLEOPOLYHEDROVIRUS OF TRICHOPLUSIA NI IN THE CABBAGE-LOOPER

The nucleopolyhedrovirus of Trichoplusia ni (TnSNPV) shows promise as a bioinsecticide against cabbage loopers (T. ni). We examined the effe cts of larval age at time of treatment and of the dose of virus ingest ed on the lethal and sublethal effects of TnSNPV on T. ni. The surviva l and LD50 Of cabbage loopers increased with the age of larvae at the time of treatment. The sublethal effects of TnSNPV included prolonged development and reduced pupal weight, egg production, and hatching suc cess of eggs. The sublethal effects of TnSNPV did not vary among the t hree doses of virus used but were a function of larval age. The sublet hal effects of TnSNPV mere greatest when caterpillars were treated wit h virus at 92 and 144 h of age (third and fourth instar, respectively) . Individuals that were treated at 192 h (fifth instar) and survived t o adulthood did not appear to be impaired. These findings suggest that TnSNPV should be applied when cabbage loopers are in the early stages of development to maximize the bioinsecticidal activity of the virus. (C) 1998 Academic Press.