Development and survival of stalk borer,Papaipema nebris(Guenée), larvae under natural conditions were investigated by intensively sampling noncrop, grassy areas and bordering corn rows. The logistic function was used to derive developmental curves based on centigrade degree-day accumulations. The curves predicted the proportion of larvae in each stadium. Comparison of developmental curves for 1984 and 1985 indicated that other factors, in addition to temperature, played a role in regulating population development. In particular, synchronization between Julian date and phenology of late instars was noted. Partial life tables were constructed to describe stage-specific mortality. Effect of parasitoids on larval populations seemed to be limited, with parasitism rates of all stages<5%. Information on larval survival has suggested the following working hypothesis on stalk borer population dynamics: weather conditions during egg hatch, as well as predation and environmental factors during larval movement to new host plants, are important factors determining stalk borer population numbers in agroecosystems.