Distribution of the First-Generation Egg Masses of the European Corn Borer in Corn Fields1

Abstract

Observations on the distribution of the first-generation egg masses in 20 fields of field corn in waseca Minnesota, during 10 seasons, 1948 to 1957, show the following points: 1. The egg populations varied from negligibly low levels of less than 10 egg musses per 100 plants to a high of 380 per 100 plants. 2 The distribution of the egg masses is essentially random, hut shows a tendency towards contagiosity. 3. This particular pattern of distribution is followed throughout the entire period of egg deposition in a given field. 4. The frequency index, i.e. , the per cent of plants with one or more egg masses, is to an extent directly proportional to the highest. egg mass count, i.e. , the highest number of egg masses found alive on anyone day. On the basis of these observations, it is suggested that the frequency index may be used as an index for estimation of the density of egg populations. Sixty per cent. of plants receiving egg masses will be equivalent to the critical egg mass count of 50. It is believed that the use of the frequency index method involves less work than making an egg mass count.