Differences in Ecological Responses of Three Biotypes of Ostrinia nubilalis from the North Central United States1

Abstract

Development of corn borers from 3 geographic origins was studied at 3 localities: Waseca (south central Minnesota), Ankeny (central Iowa), and Portageville (southeast Missouri). The study was conducted on field corn, inbred WF9, and a sweet corn, Seneca Chief, in 1963 and 1964, and on field corn inbreds WF9 and Oh43 in 1965 and 1966. Identical procedures were used at all 3 localities in any given season, although procedures were modified and refined from year to year. Analyses of the 4 years' results show that the 3 populations differ in the following ecological characteristics: (a) percent of survival, (b) percent of larvae entering diapause, (c) number of tunnels made by each borer, (d) rate of development, and (e) sensitivity in survival to host-resistance factors. In all cases, the Minnesota population was distinctly different from the Missouri population, while the Iowa population was intermediate. It was shown also that the biology of each biotype was influenced by ecological conditions, such as the location of experimental plots and host variety. Two additional conclusions were reached regarding the relative sensitivity of the different biotypes to ecological conditions, (a) The Missouri biotype was curtailed in survival when grown in the north, and the Minnesota biotype was enhanced in survival when grown in the south. The results show that the curtailment was greater than the enhancement. This fact suggests that the biotype which is adapted to warmer conditions is more sensitive to temperature changes than the biotype which is adapted to cooler conditions, (b) The Missouri biotype, which is adapted to short days in Missouri, showed a higher rate of pupation when grown in the north, and the Minnesota biotype, which is adapted to long days in Minnesota, showed a higher rate of diapause when grown in the south. The increase in pupation of the Missouri biotype when grown in the north was greater than the increase in diapause of Minnesota biotype when grown in the south. This fact suggests that the biotype which is adapted to short days is more sensitive to changes in photoperiod than is the biotype which is adapted to long days. These conclusions regarding the sensitivity of different biotypes to habitats with different temperatures and photoperiods, if proved to be true generally, would have great ecological significance in the prediction of behavior of introduced pests in new territories.