Observations on the Control of Insects by Hand-collection

Abstract

The paper deals with the control of insects by hand-collection. An experimental study of the method as used against Antestia on coffee in Kenya is described. The rate of increase of the yield of insects collected falls off in a definite and measurable manner as the time spent on the work increases. The formula for the curve fitting the results is P = 100(1 − (V.e.)^−t) where “ P ” is the percentage collected of the total Antestia present, “ t ” is the time spent collecting, and “ V ” is a coefficient which has different values according to the conditions prevailing. In practice one careful experimental picking provides data for the calculation of the formula which may be used to determine the cost of hand-picking any percentage.The results show that in theory 100 per cent. of the insects can never be obtained by hand-picking, and that in practice the cost of picking an adequate percentage is almost invariably prohibitive.It is probable that the experimental results obtained will prove valid in other cases of hand-picking. Much of the expenditure on this method is unproductive.Details of a thorough long-continued attempt to control Antestia on thirty-five acres of coffee by hand-picking are given. The attempt proved unsuccessful, and it is suggested that it may actually have been responsible for the maintenance of the severe attack.The kind co-operation and assistance of a number of coffee planters are acknowledged. Except for the first experiments in 1933 Mr. H. Naismith Jones assisted me throughout, and the investigation owes a great deal to his careful supervision of much of the field work.