European Corn Borer Populations in Relation to the Estimation of Crop Loss1

Abstract

Studies were conducted at Ankeny, Iowa; Waseca, Minnesota; and Wooster, Ohio, during 1953, 1954, and 1955 to analyze the relationship between midsummer and fall European corn borer ( Pyrausta nubilalis (Hbn.)) populations and their effect on corn yield. These relationships are affected by the interactions of a number of factors: (1) the proportion of the first brood that pupate in the summer, (2) the selection of fields and plants for egg deposition by the moths, and (3) the survival of the different developmental stages of the second brood individuals. A summer population of a given size many give rise to fall populations manyfold larger, or may end up with fall populations a fraction of the original size. Furthermore, fall populations of the same size may consist of very different proportions of the residual first-brood population and the second-brood population. The quantitative relationships between midsummer and fall populations are further complicated by the following factors: (1) Differential egg deposition owing to plant development; the plants that were more attractive to moths for egg deposition during the first brood will be less so during the second brood, and vice versa. (2) Nonattractiveness to the second-brood moths for egg deposition of the plants that are heavily infested with first brood borer. (3) Decreased survival of the second-brood larvae on plants with heavy first-brood injury. This fact may have been the result of a lack of suitable feeding sites on such plants. The paradoxical relationship between borer population and yield as shown in some cases, e.g., the fewer borers on the plants the less the yield, or the more borers the greater the yield, is clarified on the basis of the foregoing analyses of the borer population dynamics. Based upon these analyses the conclusion is reached that while the fall population may be a reliable basis for estimating the borer population entering hibernation, the summer population is probably a more realistic index for estimating the loss in yield of corn caused by borer infestation in the current year.