Ecotypes of the European Corn Borer 1 in North America 234

Survival of 10 populations of Ostrinia nubilalis (Hubner) was progressive from north (Morris, Minn.) to south (Portageville, Mo.) except that survival decreased again at Tifton, Ga., because of the stunted condition of the corn and the density of the test insect populations. In the south, increasing temperature overrode photoperiod (shorter photophase, longer scotophase) and reduced the number of borers that diapaused. Conversely, in the north, photoperiod (longer photophase, shorter scotophase) overrode decreasing temperature, but again the result was a reduction in diapause. The highest percentage diapause occurred at the latitude where the photoperiod-temperature interaction was most severe. From the diapause response, populations of European corn borers in North America fit 3 ecotypes: a northern one represented by the Minnesota and Quebec populations; a central one represented by the Iowa, Nebraska, Ohio, and Frederick Co., Md., populations; and a southern one represented by the Alabama, Georgia, Missouri, and Somerset Co., Md., populations.