NATURAL MORTALITY OF EUROPEAN CORN-BORER (LEPIDOPTERA, PYRALIDAE) LARVAE - FIELD-STUDY AND MODELING

Natural mortality of Ostrinia nubilalis (Hubner) larvae on corn was st udied 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 ra te. Two models, one with constant mortality rate and the other with va riable mortality rate, were proposed and tested to describe this patte rn. These models described the time course of larval survival rate wel l. The 2nd model was used to compute the European corn borer survival rate at various dates in relation to larval development. The mean mort ality rate was 74% during the Ist 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 Ist instar. Multiple regressions were used to model relationships between larval survival rate and environmental fa ctors (climatic factors and infestation conditions). Phenological stag e of corn at the date of infestation was the primary factor influencin g the larval sun;val rate. The relationship explained >45% of the vari ability.