The effectiveness of a granulosis virus applied to field populations of Pieris rapae (Lepidoptera)

Abstract

A granulosis virus (apparently Bergoldia virulenta Tanada) which causes a highly virulent disease of the larvae of Pieris rapae, is recorded from Australia. External symptoms of the disease and the period of survival after infection vary according to larval age at infection. In four field experiments, aqueous suspensions of disease particles applied as sprays to natural infestations of P. rapae induced epizootics which persisted until the experiments ceased 3–7 weeks later. Larval populations on the disease plots were markedly lower than on the controls although the disease usually spread to the controls within a few weeks; the proportion of larvae reaching the later and more damaging instars was much lower on the disease plots, few larvae reaching the fifth instar and very few reaching the pupal stage. In one experiment in which the effects of disease and DDT sprays were compared, the levels of control were similar, although fewer larvae reached the later instars on the disease plots.