Procedures for declaring pest free status

Abstract

Procedures are presented for declaring an area to be pest free following an area-wide eradication programme against a population of an insect pest. These involve two probability models to deal with null trapping results, and a growth model to help verify that pests were no longer present when control actions were stopped. The two probability models are presented for a situation in which trapping for an insect pest is ongoing, and for which the trapping results are all negative. The models calculate the probability of such negative results if in fact insects were present. If this probability is sufficiently low, then the hypothesis that insects are present is rejected. The models depend on knowledge of the efficiency of the traps, and also the area of attractiveness of the traps. The possibility of a rebound of an incipient but non-detectable population, that remains after control measures are discontinued, is considered. Using a growth model, the rate of increase, of an insect population that starts from one or two insects, is examined. An example is given for tsetse flies - both means and confidence limits are calculated for a period of 24 reproductive periods after control has been terminated. If insects are disease vectors, it is also suggested that the progress of the disease be monitored to detect continuing transmission. This should be done in conjunction with a disease transmission model.