Population ecology of Wiseana cervinata, a pasture pest in New Zealand.
Abstract
Populations of the hepialid Wiseana cervinata on 0.8-ha plots in pastures in New Zealand appeared to be regulated by density-dependent recruitment, possibly due to moth dispersal and immigration. However, large yearly variations in densities of damaging subterranean larvae were caused by variations in survival of surface-dwelling eggs and young larvae. Because of this variation and the strong density dependence which preceded it, densities of damaging larvae in one year were unrelated to those of larvae or moths in the previous year. In summer-dry areas, the variations in damaging larval densities were correlated with variations in summer temperatures. Pasture cover during summer may have affected the distribution of larvae but had no effect on overall survival or population density. The subterranean larvae were highly aggregated in the soil and increased linearly in weight over the 8-month period during which damage occurred. Mortality over this period averaged 50% but varied widely, depending partly on the incidence of the fungus Metarhizium anisopliae and a nucleopolyhedrosis virus. The virus caused up to 90% mortality but did not appear to regulate populations from year to year.