WIPFELKRANKHEIT - MODIFICATION OF HOST BEHAVIOR DURING BACULOVIRAL INFECTION

Infection with an endoparasite frequently alters host behaviour. This study provides the first quantification of larval behaviour in a bacul ovirus/ Lepidoptera system, and attempts to assess the ecological cons equences of behavioural modification during infection. Larvae of the m oth Mamestra brassicae (Lepidoptera: Noctuidae) exhibited higher rates of dispersal in the laboratory and field when infected with Mamestra brassicae nuclear polyhedrosis virus (MbNPV) than did uninfected larva e. They adopted positions at death which were not characteristic of he althy larvae, climbing higher on the foodplant and onto the top and ed ge of leaves. The horizontal and vertical distribution of virus follow ing larval lysis and the effects of rainfall on this distribution were assessed for comparison with the distributions of healthy and infecte d larvae. Exposure to rainfall increased the infectivity of vegetation in bioassays. Alternative explanations for the evolutionary origins o f behavioural modification are considered. I suggest that the behaviou ral changes observed are most likely to benefit the virus. In particul ar climbing prior to death is likely to result in contamination of mor e foliage with virus particles than would otherwise occur by increasin g exposure of cadavers to rainfall. Thus it may profoundly influence h orizontal transmission and the dynamics of the host-virus interaction.