Abstract
A DIFFICULTY frequently met in insecticide field trials is that although the insecticide application may kill the insects on the treated plots at the time, these plots may be re-invaded very quickly by insects from the control plots and surrounding untreated areas. This is particularly marked in the case of trials on the control of cotton Lygus (Lygus vosseleri, Popp.), where the greater part of the damage is done by an immigration of highly mobile adults into the crop. One method of avoiding this difficulty is to use large plots of several acres in extent; but the very size of the plots seriously reduces the precision of an experimental comparison, besides being very expensive in time, materials and labour. Recent work has shown that where the principal purpose of the experiments is to study the effect of Lygus upon the yield of cotton, the result may be obtained very much more simply by using the repellent effect of certain insecticides.
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