Natural mortality of European corn borer (Lepidoptera: Pyralidae) larvae : Field study and modeling

Natural mortality of Ostrinia nubilalis (Huebner) larvae on corn was studied under 30 field-infestation conditions at 3 sites. High mortality occurred during the days immediately after egg hatching when >50% of hatched larvae died, followed by a lower and more stable mortality rate. Two models, one with constant mortality rate and the other with variable mortality rate, were proposed and tested to describe this pattern. These models described the time course of larval survival rate well. The 2nd model was used to compute the European corn borer survival rate at various dates in relation to larval development. The mean mortality rate was 74% during the 1st instar, then remained similar, then decreased by 13% during the 2nd and 3rd instars and 16% during the 4th instar. A high variability in survival rate between infestations was observed as early as the 1st instar. Multiple regressions were used to model relationships between larval survival rate and environmental factors (climatic factors and infestation conditions). Phenological stage of corn at the date of infestation was the primary factor influencing the larval survival rate. The relationship explained >45% of the variability.