Aphis Migration and the Efficiency of the Trapping Method

Abstract

Reproducible results were obtained when adhesive traps for aphides were placed at the same height in different parts of a potato field. The total catches in different localities in different seasons can therefore justifiably be compared. During the summer dispersal flights, different species flew at different heights, so traps at one height only are not suitable for comparing the relative abundance of different species. There was less variation in numbers caught on traps at 3–4 ft. above the ground than on traps at 5–6 ft. or at ground‐level.During the first fortnight of July an average of 200 aphides, 1.6% of which were Myzus persicae, was caught on traps in the position of potato plants. Most of these were not potato aphides, but it is suggested that some of them might act as vectors of potato viruses. The number of aphides caught was roughly proportional to the volume of free air space around the traps, and as the foliage increased in density the numbers caught on lower traps decreased in proportion.Wind‐speed records within and above the crop are discussed and it is shown that conditions are often suitable for voluntary aphis flight in and near the crop on relatively windy days. Records of catches on the half‐traps facing the wind and on the other halves showed that voluntary flight decreased with increasing height.Brilliant yellow traps, coated with adhesive grease, caught more aphides than white traps, which in turn caught more than black.