Population Ecology of Wiseana cervinata, a Pasture Pest in New Zealand

Abstract

SUMMARY (2) However, large yearly variations in densities of damaging subterranean larvae are caused by variations in survival of surface-dwelling eggs and young larvae. Because of this variation and the strong density dependence which precedes it, densities of damaging larvae in one year are unrelated to those of larvae or moths in the previous year. (3) In summer-dry areas, the variations in damaging larval densities are correlated with variations in summer temperatures. Pasture cover during summer may affect the distribution of larvae but has no effect on overall survival or population density. (4) Subterranean larvae are highly aggregated in the soil and increase linearly in weight over the 8 month period during which damage occurs. Mortality over this period averages 50% but varies widely depending partly on the incidence of the fungus Metarhizium anisopliae (Met.) Sor. and a nucleopolyhedrosis virus. (5) The virus can cause up to 90% mortality but does not appear to regulate populations from year to year.