THE RELATION BETWEEN INFESTATION BY THE STALK BORER, BUSSEOLA FUSCA, AND YIELD OF MAIZE IN EAST AFRICA

The relation between yield and infestation by the maize stalk borer, Busseola fusca Fuller, is expressed as a series of regression lines for crops of different potential yields. The reasons are given for assuming that the regression is rectilinear, and that the regression coefficient b, or rate of fall in yield, is proportional to the maximum expected yield of the crop, that is that b proportional to (y) over bar. For the crops examined, the formula for a general regression line of yield, as hundreds of pounds of dry grain per acre, on infestation, as the percentage of plants attacked transformed to angles, is y = 45.1 - 0.55x for a high-yielding area, and y = 14.55 - 0.23x for a lower yielding crop. This is equivalent to a 35 Ib./acre increase in grain yield for every 1% decrease in infestation for the higher yielding group, and 17 Ib. increase per 1% decrease for the lower. The applications of the relationship are discussed, in particular to studies of the economics of control by insecticides, and of the accuracy of methods of sampling infestations.