Sublethal Effects of Baculovirus in the Cabbage Moth, Mamestra brassicae

Abstract

Sublethal effects of pathogens such as baculoviruses, in particular vertical transmission to subsequent host generations, may play an important role in their ecology and population dynamics and could also be of relevance in their use as pest control agents. The effects of a range of sublethal concentrations of a nuclear polyhedrosis virus (NPV) were investigated in fourth and fifth instar larvae of the cabbage moth, Mamestra brassicae. Survivors of the NPV inoculation exhibited an extended developmental time in both the larval and the pupal phase compared with control larvae. There was a general trend toward increasing developmental time with increasing viral concentration. Pupal weight, sex ratio, fecundity, and egg viability were not significantly different between insects subjected to viral challenge and control groups. A low level of NPV mortality (0.55%) was recorded in the progeny of adults which had developed from larvae subject to viral challenge. Viral death in progeny larvae occurred predominantly during the second instar. Vertical transmission, although occurring at low levels, may be vital for the long-term persistence of the virus, particularly in a mobile pest species such as M. brassicae, which occupies ephemeral habitats.